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Zhang B, Radder J, Giannakopoulos I, Grant A, Lagore R, Waks M, Tavaf N, van de Moortele PF, Adriany G, Sadeghi-Tarakameh A, Eryaman Y, Lattanzi R, Ugurbil K. Performance of receive head arrays versus ultimate intrinsic SNR at 7 T and 10.5 T. Magn Reson Med 2024; 92:1219-1231. [PMID: 38649922 PMCID: PMC11209800 DOI: 10.1002/mrm.30108] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 02/26/2024] [Accepted: 03/21/2024] [Indexed: 04/25/2024]
Abstract
PURPOSE We examined magnetic field dependent SNR gains and ability to capture them with multichannel receive arrays for human head imaging in going from 7 T, the most commonly used ultrahigh magnetic field (UHF) platform at the present, to 10.5 T, which represents the emerging new frontier of >10 T in UHFs. METHODS Electromagnetic (EM) models of 31-channel and 63-channel multichannel arrays built for 10.5 T were developed for 10.5 T and 7 T simulations. A 7 T version of the 63-channel array with an identical coil layout was also built. Array performance was evaluated in the EM model using a phantom mimicking the size and electrical properties of the human head and a digital human head model. Experimental data was obtained at 7 T and 10.5 T with the 63-channel array. Ultimate intrinsic SNR (uiSNR) was calculated for the two field strengths using a voxelized cloud of dipoles enclosing the phantom or the digital human head model as a reference to assess the performance of the two arrays and field depended SNR gains. RESULTS uiSNR calculations in both the phantom and the digital human head model demonstrated SNR gains at 10.5 T relative to 7 T of 2.6 centrally, ˜2 at the location corresponding to the edge of the brain, ˜1.4 at the periphery. The EM models demonstrated that, centrally, both arrays captured ˜90% of the uiSNR at 7 T, but only ˜65% at 10.5 T, leading only to ˜2-fold gain in array SNR in going from 7 to 10.5 T. This trend was also observed experimentally with the 63-channel array capturing a larger fraction of the uiSNR at 7 T compared to 10.5 T, although the percentage of uiSNR captured were slightly lower at both field strengths compared to EM simulation results. CONCLUSIONS Major uiSNR gains are predicted for human head imaging in going from 7 T to 10.5 T, ranging from ˜2-fold at locations corresponding to the edge of the brain to 2.6-fold at the center, corresponding to approximately quadratic increase with the magnetic field. Realistic 31- and 63-channel receive arrays, however, approach the central uiSNR at 7 T, but fail to do so at 10.5 T, suggesting that more coils and/or different type of coils will be needed at 10.5 T and higher magnetic fields.
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Affiliation(s)
- Bei Zhang
- Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, USA
| | - Jerahmie Radder
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN 55455
| | - Ilias Giannakopoulos
- Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
| | - Andrea Grant
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN 55455
| | - Russell Lagore
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN 55455
| | - Matt Waks
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN 55455
| | - Nader Tavaf
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN 55455
| | | | - Gregor Adriany
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN 55455
| | | | - Yigitcan Eryaman
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN 55455
| | - Riccardo Lattanzi
- Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
| | - Kamil Ugurbil
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN 55455
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Šiurytė P, Tourais J, Zhang Y, Coletti C, van de Steeg-Henzen C, Mandija S, Tao Q, Henningsson M, Weingärtner S. Preparation-based B 1 + mapping in the heart using Bloch-Siegert shifts. Magn Reson Med 2024. [PMID: 39044620 DOI: 10.1002/mrm.30232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Revised: 06/11/2024] [Accepted: 07/10/2024] [Indexed: 07/25/2024]
Abstract
PURPOSE To develop and evaluate a robust cardiacB 1 + $$ {\mathrm{B}}_1^{+} $$ mapping sequence at 3 T, using Bloch-Siegert shift (BSS)-based preparations. METHODS A longitudinal magnetization preparation module was designed to encode| B 1 + | $$ \mid {\mathrm{B}}_1^{+}\mid $$ . After magnetization tip-down, off-resonant Fermi pulses, placed symmetrically around two refocusing pulses, induced BSS, followed by tipping back of the magnetization. Bloch simulations were used to optimize refocusing pulse parameters and to assess the mapping sensitivity. Relaxation-inducedB 1 + $$ {\mathrm{B}}_1^{+} $$ error was simulated for variousT 1 $$ {\mathrm{T}}_1 $$ /T 2 $$ {\mathrm{T}}_2 $$ times. The effective mapping range was determined in phantom experiments, and| B 1 + | $$ \mid {\mathrm{B}}_1^{+}\mid $$ maps were compared to the conventional BSS method and subadiabatic hyperbolic-secant 8 (HS8) pulse-sensitized method. CardiacB 1 + $$ {\mathrm{B}}_1^{+} $$ maps were acquired in healthy subjects, and evaluated for repeatability and imaging plane intersection consistency. The technique was modified for three-dimensional (3D) acquisition of the whole heart in a single breath-hold, and compared to two-dimensional (2D) acquisition. RESULTS Simulations indicate that the proposed preparation can be tailored to achieve high mapping sensitivity across variousB 1 + $$ {\mathrm{B}}_1^{+} $$ ranges, with maximum sensitivity at the upperB 1 + $$ {\mathrm{B}}_1^{+} $$ range.T 1 $$ {\mathrm{T}}_1 $$ /T 2 $$ {\mathrm{T}}_2 $$ -induced bias did not exceed 5.2% $$ \% $$ . Experimentally reproducedB 1 + $$ {\mathrm{B}}_1^{+} $$ sensitization closely matched simulations forB 1 + ≥ 0 . 3 B 1 , max + $$ {\mathrm{B}}_1^{+}\ge 0.3{\mathrm{B}}_{1,\max}^{+} $$ (mean difference 0.031± $$ \pm $$ 0.022, compared to 0.018± $$ \pm $$ 0.025 in the HS8-sensitized method), and showed 20-fold reduction in the standard deviation of repeated scans, compared with conventional BSSB 1 + $$ {\mathrm{B}}_1^{+} $$ mapping, and an equivalent 2-fold reduction compared with HS8-sensitization. Robust cardiacB 1 + $$ {\mathrm{B}}_1^{+} $$ map quality was obtained, with an average test-retest variability of 0.027± $$ \pm $$ 0.043 relative to normalizedB 1 + $$ {\mathrm{B}}_1^{+} $$ magnitude, and plane intersection bias of 0.052± $$ \pm $$ 0.031. 3D acquisitions showed good agreement with 2D scans (mean absolute deviation 0.055± $$ \pm $$ 0.061). CONCLUSION BSS-based preparations enable robust and tailorable 2D/3D cardiacB 1 + $$ {\mathrm{B}}_1^{+} $$ mapping at 3 T in a single breath-hold.
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Affiliation(s)
- Paulina Šiurytė
- Department of Imaging Physics, Delft University of Technology, Delft, The Netherlands
| | - Joao Tourais
- Department of Imaging Physics, Delft University of Technology, Delft, The Netherlands
| | - Yi Zhang
- Department of Imaging Physics, Delft University of Technology, Delft, The Netherlands
| | - Chiara Coletti
- Department of Imaging Physics, Delft University of Technology, Delft, The Netherlands
| | | | - Stefano Mandija
- Department of Radiotherapy, Division of Imaging & Oncology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Qian Tao
- Department of Imaging Physics, Delft University of Technology, Delft, The Netherlands
| | - Markus Henningsson
- Department of Health, Medicine and Caring Sciences, Linköping University, Linköping, Sweden
| | - Sebastian Weingärtner
- Department of Imaging Physics, Delft University of Technology, Delft, The Netherlands
- HollandPTC, Delft, The Netherlands
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Payne K, Zhao Y, Bhosale AA, Zhang X. Dual-Tuned Coaxial-Transmission-Line RF Coils for Hyperpolarized 13C and Deuterium 2H Metabolic MRS Imaging at Ultrahigh Fields. IEEE Trans Biomed Eng 2024; 71:1521-1530. [PMID: 38090865 PMCID: PMC11095995 DOI: 10.1109/tbme.2023.3341760] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2023]
Abstract
OBJECTIVE Information on the metabolism of tissues in healthy and diseased states plays a significant role in the detection and understanding of tumors, neurodegenerative diseases, diabetes, and other metabolic disorders. Hyperpolarized carbon-13 magnetic resonance imaging (13C-HPMRI) and deuterium metabolic imaging (2H-DMI) are two emerging X-nuclei used as practical imaging tools to investigate tissue metabolism. However due to their low gyromagnetic ratios (ɣ13C = 10.7 MHz/T; ɣ2H = 6.5 MHz/T) and natural abundance, such method required a sophisticated dual-tuned radiofrequency (RF) coil. METHODS Here, we report a dual-tuned coaxial transmission line (CTL) RF coil agile for metabolite information operating at 7T with independent tuning capability. The design analysis has demonstrated how both resonant frequencies can be individually controlled by simply varying the constituent of the design parameters. RESULTS Numerical results have demonstrated a broadband tuning range capability, covering most of the X-nucleus signal, especially the 13C and 2H spectra at 7T. Furthermore, in order to validate the feasibility of the proposed design, both dual-tuned 1H/13C and 1H/2H CTLs RF coils are fabricated using a semi-flexible RG-405 .086" coaxial cable and bench test results (scattering parameters and magnetic field efficiency/distribution) are successfully obtained. CONCLUSION The proposed dual-tuned RF coils reveal highly effective magnetic field obtained from both proton and heteronuclear signal which is crucial for accurate and detailed imaging. SIGNIFICANCE The successful development of this new dual-tuned RF coil technique would provide a tangible and efficient tool for ultrahigh field metabolic MR imaging.
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Runderkamp BA, Roos T, van der Zwaag W, Strijkers GJ, Caan MWA, Nederveen AJ. Whole-liver flip-angle shimming at 7 T using parallel-transmit k T -point pulses and Fourier phase-encoded DREAM B 1 + mapping. Magn Reson Med 2024; 91:75-90. [PMID: 37799015 DOI: 10.1002/mrm.29819] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Revised: 06/18/2023] [Accepted: 07/13/2023] [Indexed: 10/07/2023]
Abstract
PURPOSE To obtain homogeneous signal throughout the human liver at 7 T. Flip angle (FA) shimming in 7T whole-liver imaging was performed through parallel-transmit kT -point pulses based on subject-specific multichannel absoluteB 1 + $$ {\mathrm{B}}_1^{+} $$ maps from Fourier phase-encoded dual refocusing echo acquisition mode (PE-DREAM). METHODS The optimal number of Fourier phase-encoding steps for PE-DREAMB 1 + $$ {\mathrm{B}}_1^{+} $$ mapping was determined for a 7T eight-channel parallel-transmission system. FA shimming experiments were performed in the liver of 7 healthy subjects with varying body mass index. In these subjects, firstB 0 $$ {\mathrm{B}}_0 $$ shimming and Fourier PE-DREAMB 1 + $$ {\mathrm{B}}_1^{+} $$ mapping were performed. Subsequently, three small-flip-angle 3D gradient-echo scans were acquired, comparing a circularly polarized (CP) mode, a phase shim, and a kT -point pulse. Resulting homogeneity was assessed and compared with estimated FA maps and distributions. RESULTS Fourier PE-DREAM with 13 phase-encoding steps resulted in a good tradeoff betweenB 1 + $$ {\mathrm{B}}_1^{+} $$ accuracy and scan time. Lower coefficient of variation values (average [min-max] across subjects) of the estimated FA in the volume of interest were observed using kT -points (7.4 [6.6%-8.0%]), compared with phase shimming (18.8 [12.9%-23.4%], p < 0.001) and CP (43.2 [39.4%-47.1%], p < 0.001). kT -points delivered whole-liver images with the nominal FA and the highest degree of homogeneity. CP and phase shimming resulted in either inaccurate or imprecise FA distributions. Here, locations having suboptimal FA in the estimated FA maps corresponded to liver areas suffering from inconsistent signal intensity and T1 -weighting in the gradient-echo scans. CONCLUSION Homogeneous whole-liver 3D gradient-echo acquisitions at 7 T can be obtained with eight-channel kT -point pulses calculated based on subject-specific multichannel absolute Fourier PE-DREAMB 1 + $$ {\mathrm{B}}_1^{+} $$ maps.
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Affiliation(s)
- Bobby A Runderkamp
- Department of Radiology and Nuclear Medicine, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam, the Netherlands
| | - Thomas Roos
- Spinoza Centre for Neuroimaging, Royal Netherlands Academy for Arts and Sciences (KNAW), Amsterdam, the Netherlands
- High-Field Research Group, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Wietske van der Zwaag
- Spinoza Centre for Neuroimaging, Royal Netherlands Academy for Arts and Sciences (KNAW), Amsterdam, the Netherlands
- Computational and Cognitive Neuroscience and Neuroimaging, Netherlands Institute for Neuroscience, KNAW, Amsterdam, the Netherlands
| | - Gustav J Strijkers
- Department of Biomedical Engineering and Physics, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands
| | - Matthan W A Caan
- Department of Biomedical Engineering and Physics, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands
| | - Aart J Nederveen
- Department of Radiology and Nuclear Medicine, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam, the Netherlands
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Matsuda T, Iwadate Y, Mori F, Takeda K, Sasaki M. Using Phase Difference Information to Detect Errors in the Flip Angle Measured with Actual Flip Angle Imaging at 7T. Magn Reson Med Sci 2024; 23:102-109. [PMID: 36450525 PMCID: PMC10838719 DOI: 10.2463/mrms.tn.2022-0053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Accepted: 09/25/2022] [Indexed: 01/05/2024] Open
Abstract
Flip angle (FA) measurements using the actual flip angle imaging (AFI) method may induce significant errors in ultrahigh fields. We aimed to develop a method for detecting errors in FA measurements using phase information at 7 tesla. We performed computer simulations to elucidate the relationship between the FA calculation errors and the phase difference between the two AFI source images. We then examined whether a method based on the phase difference could detect FA calculation errors and determine the prescribed nominal FA of the scanner for accurate measurements in phantoms and healthy volunteers. The simulations confirmed that the calculated FA values erroneously decreased when the longitudinal magnetization and phase in one of the source images were inverted. Tests on phantoms and human subjects demonstrated that the phase difference information between the source images with a cut-off of 90° could readily detect FA calculation errors in the AFI method.
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Affiliation(s)
- Tsuyoshi Matsuda
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Shiwa-gun, Iwate, Japan
| | - Yuji Iwadate
- MR Applications and Workflow, GE Healthcare Japan Corporation, Hino, TokyoJapan
| | - Futoshi Mori
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Shiwa-gun, Iwate, Japan
| | - Kota Takeda
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Shiwa-gun, Iwate, Japan
| | - Makoto Sasaki
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Shiwa-gun, Iwate, Japan
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Gokyar S, Zhao C, Ma SJ, Wang DJJ. Deep learning-based local SAR prediction using B 1 maps and structural MRI of the head for parallel transmission at 7 T. Magn Reson Med 2023; 90:2524-2538. [PMID: 37466040 PMCID: PMC10543469 DOI: 10.1002/mrm.29797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 06/03/2023] [Accepted: 06/26/2023] [Indexed: 07/20/2023]
Abstract
PURPOSE To predict subject-specific local specific absorption rate (SAR) distributions of the human head for parallel transmission (pTx) systems at 7 T. THEORY AND METHODS Electromagnetic energy deposition in tissues is nonuniform at 7 T, and interference patterns due to individual channels of pTx systems may result in increased local SAR values, which can only be estimated with very high safety margins. We proposed, designed, and demonstrated a multichannel 3D convolutional neural network (CNN) architecture to predict local SAR maps as well as peak-spatial SAR (ps-SAR) levels. We hypothesized that utilizing a three-channel 3D CNN, in which each channel is fed by aB 1 + $$ {B}_1^{+} $$ map, a phase-reversedB 1 + $$ {B}_1^{+} $$ map, and an MR image, would improve prediction accuracies and decrease uncertainties in the predictions. We generated 10 new head-neck body models, along with 389 3D pTx MRI data having different RF shim settings, with their B1 and local SAR maps to support efforts in this field. RESULTS The proposed three-channel 3D CNN predicted ps-SAR10g levels with an average overestimation error of 20%, which was better than the virtual observation points-based estimation error (i.e., 152% average overestimation). The proposed method decreased prediction uncertainties over 20% (i.e., 22.5%-17.7%) compared to other methods. A safety factor of 1.20 would be enough to avoid underestimations for the dataset generated in this work. CONCLUSION Multichannel 3D CNN networks can be promising in predicting local SAR values and perform predictions within a second, making them clinically useful as an alternative to virtual observation points-based methods.
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Affiliation(s)
- Sayim Gokyar
- Laboratory of FMRI Technology (LOFT), USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, USC, Los Angeles, CA, USA
| | - Chenyang Zhao
- Laboratory of FMRI Technology (LOFT), USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, USC, Los Angeles, CA, USA
| | - Samantha J. Ma
- Siemens Medical Solutions USA, Los Angeles, California, USA
| | - Danny JJ Wang
- Laboratory of FMRI Technology (LOFT), USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, USC, Los Angeles, CA, USA
- Department of Neurology, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
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Solis-Najera S, Ruiz R, Martin R, Vazquez F, Marrufo O, Rodriguez AO. A theoretical and experimental investigation on a volume coil with slotted end-rings for rat MRI at 7 T. MAGMA (NEW YORK, N.Y.) 2023; 36:911-919. [PMID: 37184611 PMCID: PMC10667404 DOI: 10.1007/s10334-023-01096-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2022] [Revised: 04/18/2023] [Accepted: 04/20/2023] [Indexed: 05/16/2023]
Abstract
OBJECTIVE A volume coil with squared slots-end ring was developed to attain improved sensitivity for imaging of rat's brain at 7 T. MATERIAL AND METHODS The principles of the high cavity resonator for the low-pass case and the law of Biot-Savart were used to derive a theoretical expression of [Formula: see text]. The slotted-end ring resonator showed a theoretical 2.22-fold sensitivity improvement over the standard birdcage coil with similar dimensions. Numerical studies were carried out for the electromagnetic fields and specific absorption rates for our coil and a birdcage coil loaded with a saline-filled spherical phantom and a digital brain of a rat. RESULTS An improvement of the signal-to-noise ratio (SNR) can be observed for the slotted volume coil over the birdcage regardless of the load used in the electromagnetic simulations. The specific absorption rate simulations show a decrement for the digital brain and quite similar values with the saline solution phantom. Phantom and rat's brain images were acquired at 7 T to prove the viability of the coil design. The experimental noise figure of our coil design was four times less than the standard birdcage with similar dimensions, which showed a 44.5% increase in experimental SNR. DISCUSSION There is remarkable agreement among the theoretical, numerical and experimental sensitivity values, which all demonstrate that the coil performance for MR imaging of small rodents can be improved using slotted end-rings.
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Affiliation(s)
- Sergio Solis-Najera
- Departamento de Fisica, Facultad de Ciencias, UNAM, 04510, Mexico City, Mexico
| | - Rodrigo Ruiz
- Departamento de Fisica, Facultad de Ciencias, UNAM, 04510, Mexico City, Mexico
| | - Rodrigo Martin
- Departamento de Fisica, Facultad de Ciencias, UNAM, 04510, Mexico City, Mexico
| | - Fabian Vazquez
- Departamento de Fisica, Facultad de Ciencias, UNAM, 04510, Mexico City, Mexico
| | - Oscar Marrufo
- Departamento de Fisica, Facultad de Ciencias, UNAM, 04510, Mexico City, Mexico
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Petzold J, Schmitter S, Silemek B, Winter L, Speck O, Ittermann B, Seifert F. Towards an integrated radiofrequency safety concept for implant carriers in MRI based on sensor-equipped implants and parallel transmission. NMR IN BIOMEDICINE 2023; 36:e4900. [PMID: 36624556 DOI: 10.1002/nbm.4900] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Revised: 10/11/2022] [Accepted: 01/04/2023] [Indexed: 06/15/2023]
Abstract
To protect implant carriers in MRI from excessive radiofrequency (RF) heating it has previously been suggested to assess that hazard via sensors on the implant. Other work recommended parallel transmission (pTx) to actively mitigate implant-related heating. Here, both ideas are integrated into one comprehensive safety concept where native pTx safety (without implant) is ensured by state-of-the-art field simulations and the implant-specific hazard is quantified in situ using physical sensors. The concept is demonstrated by electromagnetic simulations performed on a human voxel model with a simplified spinal-cord implant in an eight-channel pTx body coil at 3 T . To integrate implant and native safety, the sensor signal must be calibrated in terms of an established safety metric (e.g., specific absorption rate [SAR]). Virtual experiments show that E -field and implant-current sensors are well suited for this purpose, while temperature sensors require some caution, and B 1 probes are inadequate. Based on an implant sensor matrix Q s , constructed in situ from sensor readings, and precomputed native SAR limits, a vector space of safe RF excitations is determined where both global (native) and local (implant-related) safety requirements are satisfied. Within this safe-excitation subspace, the solution with the best image quality in terms of B 1 + magnitude and homogeneity is then found by a straightforward optimization algorithm. In the investigated example, the optimized pTx shim provides a 3-fold higher mean B 1 + magnitude compared with circularly polarized excitation for a maximum implant-related temperature increase ∆ T imp ≤ 1 K . To date, sensor-equipped implants interfaced to a pTx scanner exist as demonstrator items in research labs, but commercial devices are not yet within sight. This paper aims to demonstrate the significant benefits of such an approach and how this could impact implant-related RF safety in MRI. Today, the responsibility for safe implant scanning lies with the implant manufacturer and the MRI operator; within the sensor concept, the MRI manufacturer would assume much of the operator's current responsibility.
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Affiliation(s)
- Johannes Petzold
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
- Biomedical Magnetic Resonance, Otto von Guericke University Magdeburg, Magdeburg, Germany
| | - Sebastian Schmitter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Berk Silemek
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Lukas Winter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Oliver Speck
- Biomedical Magnetic Resonance, Otto von Guericke University Magdeburg, Magdeburg, Germany
| | - Bernd Ittermann
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Frank Seifert
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
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Hamilton JI, Truesdell W, Galizia M, Burris N, Agarwal P, Seiberlich N. A low-rank deep image prior reconstruction for free-breathing ungated spiral functional CMR at 0.55 T and 1.5 T. MAGMA (NEW YORK, N.Y.) 2023; 36:451-464. [PMID: 37043121 PMCID: PMC11017470 DOI: 10.1007/s10334-023-01088-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2022] [Revised: 03/02/2023] [Accepted: 04/01/2023] [Indexed: 04/13/2023]
Abstract
OBJECTIVE This study combines a deep image prior with low-rank subspace modeling to enable real-time (free-breathing and ungated) functional cardiac imaging on a commercial 0.55 T scanner. MATERIALS AND METHODS The proposed low-rank deep image prior (LR-DIP) uses two u-nets to generate spatial and temporal basis functions that are combined to yield dynamic images, with no need for additional training data. Simulations and scans in 13 healthy subjects were performed at 0.55 T and 1.5 T using a golden angle spiral bSSFP sequence with images reconstructed using [Formula: see text]-ESPIRiT, low-rank plus sparse (L + S) matrix completion, and LR-DIP. Cartesian breath-held ECG-gated cine images were acquired for reference at 1.5 T. Two cardiothoracic radiologists rated images on a 1-5 scale for various categories, and LV function measurements were compared. RESULTS LR-DIP yielded the lowest errors in simulations, especially at high acceleration factors (R [Formula: see text] 8). LR-DIP ejection fraction measurements agreed with 1.5 T reference values (mean bias - 0.3% at 0.55 T and - 0.2% at 1.5 T). Compared to reference images, LR-DIP images received similar ratings at 1.5 T (all categories above 3.9) and slightly lower at 0.55 T (above 3.4). CONCLUSION Feasibility of real-time functional cardiac imaging using a low-rank deep image prior reconstruction was demonstrated in healthy subjects on a commercial 0.55 T scanner.
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Affiliation(s)
- Jesse I Hamilton
- Department of Radiology, University of Michigan, 1301 Catherine St, Ann Arbor, MI, 48109-1590, USA.
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA.
| | - William Truesdell
- Department of Radiology, University of Michigan, 1301 Catherine St, Ann Arbor, MI, 48109-1590, USA
| | - Mauricio Galizia
- Department of Radiology, University of Michigan, 1301 Catherine St, Ann Arbor, MI, 48109-1590, USA
| | - Nicholas Burris
- Department of Radiology, University of Michigan, 1301 Catherine St, Ann Arbor, MI, 48109-1590, USA
| | - Prachi Agarwal
- Department of Radiology, University of Michigan, 1301 Catherine St, Ann Arbor, MI, 48109-1590, USA
| | - Nicole Seiberlich
- Department of Radiology, University of Michigan, 1301 Catherine St, Ann Arbor, MI, 48109-1590, USA
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
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10
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Qian Z, Liu R, Wu Z, Hsu YC, Fu C, Sun Y, Wu D, Zhang Y. Saturation-prolongated and inhomogeneity-mitigated chemical exchange saturation transfer imaging with parallel transmission. NMR IN BIOMEDICINE 2023; 36:e4689. [PMID: 34994025 DOI: 10.1002/nbm.4689] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2021] [Revised: 12/20/2021] [Accepted: 01/04/2022] [Indexed: 05/23/2023]
Abstract
Chemical exchange saturation transfer (CEST) imaging benefits from a longer saturation duration and a higher saturation duty cycle. Dielectric shading effects occur when the radiofrequency (RF) wavelength approaches the object size. Here, we proposed a simultaneous parallel transmission-based CEST (pTx-CEST) sequence to prolongate the saturation duration at a 100% duty cycle and improve the RF saturation homogeneity in CEST imaging. The simultaneous pTx-CEST sequence was implemented by switching the CEST saturation module from the non-pTx to pTx mode, using the pTx functionality with both transmit channels being driven simultaneously (instead of time-interleaved). The optimization of amplitude ratio and phase difference settings between RF channels for best B1 homogeneity was performed in phantoms of two different sizes mimicking the human brain and abdomen. The optimal amplitude and phase settings generating the best B1 homogeneity in the phantoms were used in pTx-CEST scans of the human study. The comparison of the maximum achievable saturation duration between the non-pTx-CEST and pTx-CEST sequences was performed in a protein phantom, healthy volunteers, and a metastatic brain tumor patient. The optimal amplitude ratio and phase difference setting between transmit channels manifested circular and elliptical polarization in the head-sized and abdomen-sized phantoms. In the brain, the maximum saturation durations achieved at a 100% duty cycle using the simultaneous pTx-CEST sequence were prolonged to 2240, 3220, and 4200 ms compared with 980 ms using the non-pTx-CEST sequence at repetition times of 3, 4, and 5 s, respectively. The longer saturation duration helped improve the image contrast between the tumor and the normal tissue in the patient. The optimized elliptical polarization mode saturation pulses yielded improved uniformity of CEST signals acquired from the human abdomen. The proposed simultaneous pTx-CEST sequence enabled essentially arbitrarily long saturation duration at a 100% duty cycle and helped reduce the dielectric shading effects with the optimized RF setting.
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Affiliation(s)
- Zihua Qian
- Department of Radiology, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
| | - Ruibin Liu
- Key Laboratory for Biomedical Engineering of Ministry of Education, Department of Biomedical Engineering, College of Biomedical Engineering & Instrument Science, Zhejiang University, Hangzhou, Zhejiang, China
| | - Zhe Wu
- Techna Institute, University Health Network, Toronto, Ontario, Canada
| | - Yi-Cheng Hsu
- MR Collaboration, Siemens Healthcare Ltd., Shanghai, China
| | - Caixia Fu
- MR Application Development, Siemens Shenzhen Magnetic Resonance Ltd., Shenzhen, China
| | - Yi Sun
- MR Collaboration, Siemens Healthcare Ltd., Shanghai, China
| | - Dan Wu
- Key Laboratory for Biomedical Engineering of Ministry of Education, Department of Biomedical Engineering, College of Biomedical Engineering & Instrument Science, Zhejiang University, Hangzhou, Zhejiang, China
- Cancer Center, Zhejiang University, Hangzhou, Zhejiang, China
| | - Yi Zhang
- Key Laboratory for Biomedical Engineering of Ministry of Education, Department of Biomedical Engineering, College of Biomedical Engineering & Instrument Science, Zhejiang University, Hangzhou, Zhejiang, China
- Cancer Center, Zhejiang University, Hangzhou, Zhejiang, China
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11
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Ladd ME, Quick HH, Speck O, Bock M, Doerfler A, Forsting M, Hennig J, Ittermann B, Möller HE, Nagel AM, Niendorf T, Remy S, Schaeffter T, Scheffler K, Schlemmer HP, Schmitter S, Schreiber L, Shah NJ, Stöcker T, Uder M, Villringer A, Weiskopf N, Zaiss M, Zaitsev M. Germany's journey toward 14 Tesla human magnetic resonance. MAGMA (NEW YORK, N.Y.) 2023; 36:191-210. [PMID: 37029886 PMCID: PMC10140098 DOI: 10.1007/s10334-023-01085-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Revised: 03/23/2023] [Accepted: 03/27/2023] [Indexed: 04/09/2023]
Abstract
Multiple sites within Germany operate human MRI systems with magnetic fields either at 7 Tesla or 9.4 Tesla. In 2013, these sites formed a network to facilitate and harmonize the research being conducted at the different sites and make this technology available to a larger community of researchers and clinicians not only within Germany, but also worldwide. The German Ultrahigh Field Imaging (GUFI) network has defined a strategic goal to establish a 14 Tesla whole-body human MRI system as a national research resource in Germany as the next progression in magnetic field strength. This paper summarizes the history of this initiative, the current status, the motivation for pursuing MR imaging and spectroscopy at such a high magnetic field strength, and the technical and funding challenges involved. It focuses on the scientific and science policy process from the perspective in Germany, and is not intended to be a comprehensive systematic review of the benefits and technical challenges of higher field strengths.
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Affiliation(s)
- Mark E Ladd
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany.
- Faculty of Medicine, Heidelberg University, Heidelberg, Germany.
- Faculty of Physics and Astronomy, Heidelberg University, Heidelberg, Germany.
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany.
| | - Harald H Quick
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Oliver Speck
- Department of Biomedical Magnetic Resonance, Otto von Guericke University Magdeburg, Magdeburg, Germany
- German Center for Neurodegenerative Diseases (DZNE), Magdeburg, Germany
- Center for Behavioural Brain Sciences, Magdeburg, Germany
- Leibniz Institute for Neurobiology (LIN), Magdeburg, Germany
| | - Michael Bock
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany
| | - Arnd Doerfler
- Department of Neuroradiology, University Hospital Erlangen, Friedrich-Alexander University Erlangen-Nuremberg (FAU), Erlangen, Germany
| | - Michael Forsting
- Institute of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
| | - Jürgen Hennig
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany
| | - Bernd Ittermann
- Medical Physics and Metrological Information Technology, Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany
| | - Harald E Möller
- Methods and Development Group Nuclear Magnetic Resonance, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Armin M Nagel
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany
- Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander University Erlangen-Nuremberg (FAU), Erlangen, Germany
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | - Stefan Remy
- German Center for Neurodegenerative Diseases (DZNE), Magdeburg, Germany
- Leibniz Institute for Neurobiology (LIN), Magdeburg, Germany
| | - Tobias Schaeffter
- Medical Physics and Metrological Information Technology, Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany
| | - Klaus Scheffler
- Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
- Department of Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany
| | | | - Sebastian Schmitter
- Medical Physics and Metrological Information Technology, Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany
| | - Laura Schreiber
- Department of Cardiovascular Imaging, Comprehensive Heart Failure Center, University Hospital Würzburg, Würzburg, Germany
| | - N Jon Shah
- Institute of Neuroscience and Medicine - 4, Forschungszentrum Jülich, Jülich, Germany
| | - Tony Stöcker
- MR Physics, German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany
| | - Michael Uder
- Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander University Erlangen-Nuremberg (FAU), Erlangen, Germany
| | - Arno Villringer
- Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Nikolaus Weiskopf
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
- Felix Bloch Institute for Solid State Physics, Faculty of Physics and Earth Sciences, Leipzig University, Leipzig, Germany
| | - Moritz Zaiss
- Department of Neuroradiology, University Hospital Erlangen, Friedrich-Alexander University Erlangen-Nuremberg (FAU), Erlangen, Germany
| | - Maxim Zaitsev
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany
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12
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Wenz D, Dardano T. Multi-feed, loop-dipole combined dielectric resonator antenna arrays for human brain MRI at 7 T. MAGMA (NEW YORK, N.Y.) 2023; 36:227-243. [PMID: 37017828 PMCID: PMC10140138 DOI: 10.1007/s10334-023-01078-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 10/09/2022] [Revised: 02/28/2023] [Accepted: 03/15/2023] [Indexed: 04/06/2023]
Abstract
OBJECTIVE To determine whether a multi-feed, loop-dipole combined approach can be used to improve performance of rectangular dielectric resonator antenna (DRA) arrays human brain for MRI at 7 T. MATERIALS AND METHODS Electromagnetic field simulations in a spherical phantom and human voxel model "Duke" were conducted for different rectangular DRA geometries and dielectric constants εr. Three types of RF feed were investigated: loop-only, dipole-only and loop-dipole. Additionally, multi-channel array configurations up to 24-channels were simulated. RESULTS The loop-only coupling scheme provided the highest B1+ and SAR efficiency, while the loop-dipole showed the highest SNR in the center of a spherical phantom for both single- and multi-channel configurations. For Duke, 16-channel arrays outperformed an 8-channel bow-tie array with greater B1+ efficiency (1.48- to 1.54-fold), SAR efficiency (1.03- to 1.23-fold) and SNR (1.63- to 1.78). The multi-feed, loop-dipole combined approach enabled the number of channels increase to 24 with 3 channels per block. DISCUSSION This work provides novel insights into the rectangular DRA design for high field MRI and shows that the loop-only feed should be used instead of the dipole-only in transmit mode to achieve the highest B1+ and SAR efficiency, while the loop-dipole should be the best suited in receive mode to obtain the highest SNR in spherical samples of similar size and electrical properties as the human head.
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Affiliation(s)
- Daniel Wenz
- CIBM Center for Biomedical Imaging, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
- Animal Imaging and Technology, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
| | - Thomas Dardano
- CIBM Center for Biomedical Imaging, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
- Animal Imaging and Technology, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
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13
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Lipp I, Kirilina E, Edwards LJ, Pine KJ, Jäger C, Gräßle T, Weiskopf N, Helms G. B 1 + $$ {B}_1^{+} $$ -correction of magnetization transfer saturation maps optimized for 7T postmortem MRI of the brain. Magn Reson Med 2023; 89:1385-1400. [PMID: 36373175 DOI: 10.1002/mrm.29524] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 10/06/2022] [Accepted: 10/25/2022] [Indexed: 11/15/2022]
Abstract
PURPOSE Magnetization transfer saturation ( MTsat $$ \mathrm{MTsat} $$ ) is a useful marker to probe tissue macromolecular content and myelination in the brain. The increased B 1 + $$ {B}_1^{+} $$ -inhomogeneity at ≥ 7 $$ \ge 7 $$ T and significantly larger saturation pulse flip angles which are often used for postmortem studies exceed the limits where previous MTsat $$ \mathrm{MTsat} $$ B 1 + $$ {B}_1^{+} $$ correction methods are applicable. Here, we develop a calibration-based correction model and procedure, and validate and evaluate it in postmortem 7T data of whole chimpanzee brains. THEORY The B 1 + $$ {B}_1^{+} $$ dependence of MTsat $$ \mathrm{MTsat} $$ was investigated by varying the off-resonance saturation pulse flip angle. For the range of saturation pulse flip angles applied in typical experiments on postmortem tissue, the dependence was close to linear. A linear model with a single calibration constant C $$ C $$ is proposed to correct bias in MTsat $$ \mathrm{MTsat} $$ by mapping it to the reference value of the saturation pulse flip angle. METHODS C $$ C $$ was estimated voxel-wise in five postmortem chimpanzee brains. "Individual-based global parameters" were obtained by calculating the mean C $$ C $$ within individual specimen brains and "group-based global parameters" by calculating the means of the individual-based global parameters across the five brains. RESULTS The linear calibration model described the data well, though C $$ C $$ was not entirely independent of the underlying tissue and B 1 + $$ {B}_1^{+} $$ . Individual-based correction parameters and a group-based global correction parameter ( C = 1 . 2 $$ C=1.2 $$ ) led to visible, quantifiable reductions of B 1 + $$ {B}_1^{+} $$ -biases in high-resolution MTsat $$ \mathrm{MTsat} $$ maps. CONCLUSION The presented model and calibration approach effectively corrects for B 1 + $$ {B}_1^{+} $$ inhomogeneities in postmortem 7T data.
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Affiliation(s)
- Ilona Lipp
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Evgeniya Kirilina
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Luke J Edwards
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Kerrin J Pine
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Carsten Jäger
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.,Paul Flechsig Institute of Brain Research, Medical Faculty, Leipzig University, Leipzig, Germany
| | - Tobias Gräßle
- Epidemiology of Highly Pathogenic Microorganisms, Robert Koch-Institute, Berlin, Germany
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- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Nikolaus Weiskopf
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.,Felix Bloch Institute for Solid State Physics, Faculty of Physics and Earth Sciences, Leipzig University, Leipzig, Germany
| | - Gunther Helms
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.,Department of Clinical Sciences and Medical Radiation Physics, Lunds Universitet, Lund, Sweden
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14
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Williams SN, McElhinney P, Gunamony S. Ultra-high field MRI: parallel-transmit arrays and RF pulse design. Phys Med Biol 2023; 68. [PMID: 36410046 DOI: 10.1088/1361-6560/aca4b7] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Accepted: 11/21/2022] [Indexed: 11/22/2022]
Abstract
This paper reviews the field of multiple or parallel radiofrequency (RF) transmission for magnetic resonance imaging (MRI). Currently the use of ultra-high field (UHF) MRI at 7 tesla and above is gaining popularity, yet faces challenges with non-uniformity of the RF field and higher RF power deposition. Since its introduction in the early 2000s, parallel transmission (pTx) has been recognized as a powerful tool for accelerating spatially selective RF pulses and combating the challenges associated with RF inhomogeneity at UHF. We provide a survey of the types of dedicated RF coils used commonly for pTx and the important modeling of the coil behavior by electromagnetic (EM) field simulations. We also discuss the additional safety considerations involved with pTx such as the specific absorption rate (SAR) and how to manage them. We then describe the application of pTx with RF pulse design, including a practical guide to popular methods. Finally, we conclude with a description of the current and future prospects for pTx, particularly its potential for routine clinical use.
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Affiliation(s)
- Sydney N Williams
- Imaging Centre of Excellence, University of Glasgow, Glasgow, United Kingdom
| | - Paul McElhinney
- Imaging Centre of Excellence, University of Glasgow, Glasgow, United Kingdom
| | - Shajan Gunamony
- Imaging Centre of Excellence, University of Glasgow, Glasgow, United Kingdom.,MR CoilTech Limited, Glasgow, United Kingdom
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15
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Shi Z, Zhao X, Zhu S, Miao X, Zhang Y, Han S, Wang B, Zhang B, Ye X, Dai Y, Chen C, Rao S, Lin J, Zeng M, Wang H. Time-of-Flight Intracranial MRA at 3 T versus 5 T versus 7 T: Visualization of Distal Small Cerebral Arteries. Radiology 2023; 306:207-217. [PMID: 36040333 DOI: 10.1148/radiol.220114] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Background Three-dimensional (3D) time-of-flight (TOF) MR angiography (MRA) at 7 T has been reported to have high image quality for visualizing small perforating vessels. However, B1 inhomogeneity and more physiologic considerations limit its applications. Angiography at 5 T may provide another choice for intracranial vascular imaging. Purpose To evaluate the image quality and cerebrovascular visualization of 5-T 3D TOF MRA for visualizing intracranial small branch arteries. Materials and Methods Participants (healthy volunteers or participants with a history of ischemic stroke undergoing intracranial CT angiography or MRA for identifying steno-occlusive disease) were prospectively included from September 2021 to November 2021. Each participant underwent 3-T, 5-T, and 7-T 3D TOF MRA with use of customized MR protocols within 48 hours. Radiologist scoring from 0 (invisible) to 3 (excellent) and quantitative assessment were obtained to evaluate the image quality. The Friedman test was used for comparison of characteristics derived from 3 T, 5 T, and 7 T. Results A total of 12 participants (mean age ± SD, 38 years ± 9; nine men) were included. Visualizations of the distal arteries and small vessels at 5-T TOF MRA were significantly higher than those at 3 T (median score: 3.0 vs 2.0, all P < .001 for distal segments and lenticulostriate artery; median score: 2.0 vs 0, P < .001 for pontine artery). The total length of small vessel branches detected at 5 T was larger than that at 3 T (5.1 m ± 0.7 vs 1.9 m ± 0.4; P < .001). However, there was no evidence of a significant difference compared with 7 T in either the depiction of distal segments and small vessel branches (average median score, 2.5; all P > .05) or the quantitative measurements (total length, 5.6 m ± 0.5; P = .41). Conclusion Three-dimensional time-of-flight MR angiography at 5 T presented the capability to provide superior visualization of distal large arteries and small vessel branches (in terms of subjective and quantitative assessment) to 3 T and had image quality similar to 7 T. © RSNA, 2022 Online supplemental material is available for this article. An earlier incorrect version appeared online. This article was corrected on September 14, 2022.
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Affiliation(s)
- Zhang Shi
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Xueying Zhao
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Shuo Zhu
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Xiyin Miao
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Yunfei Zhang
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Shihong Han
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Bei Wang
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Boyu Zhang
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Xiaodan Ye
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Yongming Dai
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Caizhong Chen
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Shengxiang Rao
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Jiang Lin
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - Mengsu Zeng
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
| | - He Wang
- From the Departments of Radiology (Z.S., S.Z., X.M., X.Y., C.C., S.R., J.L., M.Z.) and Neurology (H.W.), Zhongshan Hospital, Fudan University, No. 180 Fenglin Rd, Xuhui District, Shanghai 200032, China; Shanghai Institute of Medical Imaging, Shanghai, China (Z.S., S.Z., Y.Z., X.Y., C.C., S.R., J.L., M.Z.); Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China (X.Z., B.W., B.Z., H.W.); Central Research Institute, United Imaging Healthcare, Shanghai, China (Y.Z., Y.D.); Shanghai United Imaging Healthcare, Shanghai, China (S.H.)
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16
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Edwards LJ, McColgan P, Helbling S, Zarkali A, Vaculčiaková L, Pine KJ, Dick F, Weiskopf N. Quantitative MRI maps of human neocortex explored using cell type-specific gene expression analysis. Cereb Cortex 2022; 33:5704-5716. [PMID: 36520483 PMCID: PMC10152104 DOI: 10.1093/cercor/bhac453] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Revised: 10/20/2022] [Accepted: 10/21/2022] [Indexed: 12/23/2022] Open
Abstract
Abstract
Quantitative magnetic resonance imaging (qMRI) allows extraction of reproducible and robust parameter maps. However, the connection to underlying biological substrates remains murky, especially in the complex, densely packed cortex. We investigated associations in human neocortex between qMRI parameters and neocortical cell types by comparing the spatial distribution of the qMRI parameters longitudinal relaxation rate (${R_{1}}$), effective transverse relaxation rate (${R_{2}}^{\ast }$), and magnetization transfer saturation (MTsat) to gene expression from the Allen Human Brain Atlas, then combining this with lists of genes enriched in specific cell types found in the human brain. As qMRI parameters are magnetic field strength-dependent, the analysis was performed on MRI data at 3T and 7T. All qMRI parameters significantly covaried with genes enriched in GABA- and glutamatergic neurons, i.e. they were associated with cytoarchitecture. The qMRI parameters also significantly covaried with the distribution of genes enriched in astrocytes (${R_{2}}^{\ast }$ at 3T, ${R_{1}}$ at 7T), endothelial cells (${R_{1}}$ and MTsat at 3T), microglia (${R_{1}}$ and MTsat at 3T, ${R_{1}}$ at 7T), and oligodendrocytes and oligodendrocyte precursor cells (${R_{1}}$ at 7T). These results advance the potential use of qMRI parameters as biomarkers for specific cell types.
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Affiliation(s)
- Luke J Edwards
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences , Leipzig, DE, Germany
| | - Peter McColgan
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences , Leipzig, DE, Germany
- Huntington’s Disease Centre, University College London , London, UK
| | - Saskia Helbling
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences , Leipzig, DE, Germany
- Poeppel Lab, Ernst Strüngmann Institute (ESI) for Neuroscience in Cooperation with Max Planck Society , Frankfurt am Main, DE, Germany
| | - Angeliki Zarkali
- Dementia Research Centre, University College London , London, UK
| | - Lenka Vaculčiaková
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences , Leipzig, DE, Germany
| | - Kerrin J Pine
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences , Leipzig, DE, Germany
| | - Fred Dick
- Birkbeck/UCL Centre for Neuroimaging (BUCNI) , London, UK
| | - Nikolaus Weiskopf
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences , Leipzig, DE, Germany
- Felix Bloch Institute for Solid State Physics, Faculty of Physics and Earth Sciences, Leipzig University , Leipzig, DE, Germany
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17
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Seo JH, Jo YS, Oh CH, Chung JY. A New Combination of Radio-Frequency Coil Configurations Using High-Permittivity Materials and Inductively Coupled Structures for Ultrahigh-Field Magnetic Resonance Imaging. SENSORS (BASEL, SWITZERLAND) 2022; 22:8968. [PMID: 36433565 PMCID: PMC9694602 DOI: 10.3390/s22228968] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/28/2022] [Revised: 11/03/2022] [Accepted: 11/17/2022] [Indexed: 06/16/2023]
Abstract
In ultrahigh-field (UHF) magnetic resonance imaging (MRI) system, the RF power required to excite the nuclei of the target object increases. As the strength of the main magnetic field (B0 field) increases, the improvement of the RF transmit field (B1+ field) efficiency and receive field (B1- field) sensitivity of radio-frequency (RF) coils is essential to reduce their specific absorption rate and power deposition in UHF MRI. To address these problems, we previously proposed a method to simultaneously improve the B1+ field efficiency and B1- field sensitivity of 16-leg bandpass birdcage RF coils (BP-BC RF coils) by combining a multichannel wireless RF element (MCWE) and segmented cylindrical high-permittivity material (scHPM) comprising 16 elements in 7.0 T MRI. In this work, we further improved the performance of transmit/receive RF coils. A new combination of RF coil with wireless element and HPM was proposed by comparing the BP-BC RF coil with the MCWE and the scHPM proposed in the previous study and the multichannel RF coils with a birdcage RF coil-type wireless element (BCWE) and the scHPM proposed in this study. The proposed 16-ch RF coils with the BCWE and scHPM provided excellent B1+ field efficiency and B1- field sensitivity improvement.
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Affiliation(s)
- Jeung-Hoon Seo
- Neuroscience Research Institute, Gachon University, Incheon 21988, Republic of Korea
| | - Young-Seung Jo
- Neuroscience Research Institute, Gachon University, Incheon 21988, Republic of Korea
- Department of Electronics and Information Engineering, Korea University, Sejong 30019, Republic of Korea
| | - Chang-Hyun Oh
- Department of Electronics and Information Engineering, Korea University, Sejong 30019, Republic of Korea
| | - Jun-Young Chung
- Department of Neuroscience, College of Medicine, Gachon University, Incheon 21565, Republic of Korea
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18
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Vaidya MV, Zhang B, Hong D, Brown R, Batsios G, Viswanath P, Paska J, Wulf G, Grant AK, Ronen SM, Larson PEZ. A 13C/ 31P surface coil to visualize metabolism and energetics in the rodent brain at 3 Tesla. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2022; 343:107286. [PMID: 36075133 PMCID: PMC9721620 DOI: 10.1016/j.jmr.2022.107286] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 08/04/2022] [Accepted: 08/24/2022] [Indexed: 06/15/2023]
Abstract
PURPOSE We constructed a 13C/31P surface coil at 3 T for studying cancer metabolism and bioenergetics. In a single scan session, hyperpolarized 13C-pyruvate MRS and 31P MRS was carried out for a healthy rat brain. METHODS All experiments were carried out at 3 Tesla. The multinuclear surface coil was designed as two coplanar loops each tuned to either the 13C or 31P operating frequency with an LCC trap on the 13C loop. A commercial volume proton coil was used for anatomical localization and B0 shimming. Single tuned coils operating at either the 13C or 31P frequency were built to evaluate the relative performance of the multinuclear coil. Coil performance metrics consisted of measuring Q factor ratio, calculating system input power using a single-pulse acquisition, and acquiring SNR and flip angle maps using 2D CSI sequences. To observe in vivo spectra, a bolus of hyperpolarized [1-13C] pyruvate was administered via tail vein. In vivo13C and endogenous 31P spectra were obtained in a single scan session using 1D slice selective acquisitions. RESULTS When compared with single tuned surface coils, the multinuclear coil performance showed a decrease in Q factor ratio, SNR, and transmit efficiency. Flip angle maps showed adequate flip angles within the phantom when the transmit voltage was set using an external phantom. Results show good detection of 13C labeled lactate, alanine, and bicarbonate in addition to ATP from 31P MRS. CONCLUSIONS The coil enables obtaining complementary information within a scan session, thus reducing the number of trials and minimizing biological variability for studies of metabolism and bioenergetics.
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Affiliation(s)
- Manushka V Vaidya
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA.
| | - Bei Zhang
- Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, USA
| | - DongHyun Hong
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA
| | - Ryan Brown
- Center for Advanced Imaging Innovation and Research, and Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA
| | - Georgios Batsios
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA
| | - Pavithra Viswanath
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA
| | - Jan Paska
- Center for Advanced Imaging Innovation and Research, and Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA
| | - Gerburg Wulf
- Department of Hematology-Oncology, Beth Israel Deaconess Medical Center, Boston, MA, USA
| | - Aaron K Grant
- Department of Radiology, Beth Israel Deaconess Medical Center, Boston, MA, USA
| | - Sabrina M Ronen
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA
| | - Peder E Z Larson
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA
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19
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Orzada S, Akash S, Fiedler TM, Kratzer FJ, Ladd ME. An investigation into the dependence of virtual observation point‐based specific absorption rate calculation complexity on number of channels. Magn Reson Med 2022; 89:469-476. [DOI: 10.1002/mrm.29434] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 07/13/2022] [Accepted: 08/10/2022] [Indexed: 11/11/2022]
Affiliation(s)
- Stephan Orzada
- Medical Physics in Radiology German Cancer Research Center (DKFZ) Heidelberg Germany
- Erwin L. Hahn Institute for MRI University Duisburg‐Essen Essen Germany
- Radiation Oncology University Hospital Heidelberg Heidelberg Germany
| | - Safi Akash
- Medical Physics in Radiology German Cancer Research Center (DKFZ) Heidelberg Germany
| | - Thomas M. Fiedler
- Medical Physics in Radiology German Cancer Research Center (DKFZ) Heidelberg Germany
| | - Fabian J. Kratzer
- Medical Physics in Radiology German Cancer Research Center (DKFZ) Heidelberg Germany
| | - Mark E. Ladd
- Medical Physics in Radiology German Cancer Research Center (DKFZ) Heidelberg Germany
- Erwin L. Hahn Institute for MRI University Duisburg‐Essen Essen Germany
- Faculty of Physics and Astronomy Heidelberg University Heidelberg Germany
- Faculty of Medicine Heidelberg University Heidelberg Germany
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20
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Löwen D, Pracht ED, Stirnberg R, Liebig P, Stöcker T. Interleaved binomial kT-Points for water-selective imaging at 7T. Magn Reson Med 2022; 88:2564-2572. [PMID: 35942989 DOI: 10.1002/mrm.29376] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Revised: 06/13/2022] [Accepted: 06/13/2022] [Indexed: 11/07/2022]
Abstract
PURPOSE We present a time-efficient water-selective, parallel transmit RF excitation pulse design for ultra-high field applications. METHODS The proposed pulse design method achieves flip angle homogenization at ultra-high fields by employing spatially nonselective k T $$ {\mathrm{k}}_T $$ -points pulses. In order to introduce water-selection, the concept of binomial pulses is applied. Due to the composite nature of k T $$ {\mathrm{k}}_T $$ -points, the pulse can be split into multiple binomial subpulse blocks shorter than half the precession period of fat, that are played out successively. Additional fat precession turns, that would otherwise impair the spectral response, can thus be avoided. Bloch simulations of the proposed interleaved binomial k T $$ {\mathrm{k}}_T $$ -points pulses were carried out and compared in terms of duration, homogeneity, fat suppression and pulse energy. For validation, in vivo MP-RAGE and 3D-EPI data were acquired. RESULTS Simulation results show that interleaved binomial k T $$ {\mathrm{k}}_T $$ -points pulses achieve shorter total pulse durations, improved flip angle homogeneity and more robust fat suppression compared to available methods. Interleaved binomial k T $$ {\mathrm{k}}_T $$ -points can be customized by changing the number of k T $$ {\mathrm{k}}_T $$ -points, the subpulse duration and the order of the binomial pulse. Using shorter subpulses, the number of k T $$ {\mathrm{k}}_T $$ -points can be increased and hence better homogeneity is achieved, while still maintaining short total pulse durations. Flip angle homogenization and fat suppression of interleaved binomial k T $$ {\mathrm{k}}_T $$ -points pulses is demonstrated in vivo at 7T, confirming Bloch simulation results. CONCLUSION In this work, we present a time efficient and robust parallel transmission technique for nonselective water excitation with simultaneous flip angle homogenization at ultra-high field.
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Affiliation(s)
- Daniel Löwen
- German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany
| | | | | | | | - Tony Stöcker
- German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany
- Department of Physics and Astronomy, University of Bonn, Bonn, Germany
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21
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Le Ster C, Grant A, Van de Moortele PF, Monreal-Madrigal A, Adriany G, Vignaud A, Mauconduit F, Rabrait-Lerman C, Poser BA, Uğurbil K, Boulant N. Magnetic field strength dependent SNR gain at the center of a spherical phantom and up to 11.7T. Magn Reson Med 2022; 88:2131-2138. [PMID: 35849739 PMCID: PMC9420790 DOI: 10.1002/mrm.29391] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2022] [Revised: 06/06/2022] [Accepted: 06/27/2022] [Indexed: 02/05/2023]
Abstract
PURPOSE The SNR at the center of a spherical phantom of known electrical properties was measured in quasi-identical experimental conditions as a function of magnetic field strength between 3 T and 11.7 T. METHODS The SNR was measured at the center of a spherical water saline phantom with a gradient recalled echo sequence. Measurements were performed at NeuroSpin at 3, 7, and 11.7 T. The phantom was then shipped to Maastricht University and then to the University of Minnesota for additional data points at 7, 9.4, and 10.5 T. Experiments were carried out with the exact same type of birdcage volume coil (except at 3 T, where a similar coil was used) to attempt at isolating the evolution of SNR with field strength alone. Phantom electrical properties were characterized over the corresponding frequency range. RESULTS Electrical properties were found to barely vary over the frequency range. Removing the influence of the flip-angle excitation inhomogeneity was crucial, as expected. After such correction, measurements revealed a gain of SNR growing as B0 1.94 ± 0.16 compared with B0 2.13 according to ultimate intrinsic SNR theory. CONCLUSIONS By using quasi-identical experimental setups (RF volume coil, phantom, electrical properties, and protocol), this work reports experimental data between 3 T and 11.7 T, enabling the comparison with SNR theories in which conductivity and permittivity can be assumed to be constant with respect to field strength. According to ultimate SNR theory, these results can be reasonably extrapolated to the performance of receive arrays with greater than about 32 elements for central SNR in the same spherical phantom.
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Affiliation(s)
- Caroline Le Ster
- University of Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif sur Yvette, France
| | - Andrea Grant
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | | | | | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Alexandre Vignaud
- University of Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif sur Yvette, France
| | - Franck Mauconduit
- University of Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif sur Yvette, France
| | | | - Benedikt A Poser
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Nicolas Boulant
- University of Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif sur Yvette, France
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22
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Leitão D, Tomi-Tricot R, Bridgen P, Wilkinson T, Liebig P, Gumbrecht R, Ritter D, Giles SL, Baburamani A, Sedlacik J, Hajnal JV, Malik SJ. Parallel transmit pulse design for saturation homogeneity (PUSH) for magnetization transfer imaging at 7T. Magn Reson Med 2022; 88:180-194. [PMID: 35266204 PMCID: PMC9315051 DOI: 10.1002/mrm.29199] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Revised: 01/25/2022] [Accepted: 01/25/2022] [Indexed: 12/24/2022]
Abstract
PURPOSE This work proposes a novel RF pulse design for parallel transmit (pTx) systems to obtain uniform saturation of semisolid magnetization for magnetization transfer (MT) contrast in the presence of transmit field B1+ inhomogeneities. The semisolid magnetization is usually modeled as being purely longitudinal, with the applied B1+ field saturating but not rotating its magnetization; thus, standard pTx pulse design methods do not apply. THEORY AND METHODS Pulse design for saturation homogeneity (PUSH) optimizes pTx RF pulses by considering uniformity of root-mean squared B1+ , B1rms , which relates to the rate of semisolid saturation. Here we considered designs consisting of a small number of spatially non-selective sub-pulses optimized over either a single 2D plane or 3D. Simulations and in vivo experiments on a 7T Terra system with an 8-TX Nova head coil in five subjects were carried out to study the homogenization of B1rms and of the MT contrast by acquiring MT ratio maps. RESULTS Simulations and in vivo experiments showed up to six and two times more uniform B1rms compared to circular polarized (CP) mode for 2D and 3D optimizations, respectively. This translated into 4 and 1.25 times more uniform MT contrast, consistently for all subjects, where two sub-pulses were enough for the implementation and coil used. CONCLUSION The proposed PUSH method obtains more uniform and higher MT contrast than CP mode within the same specific absorption rate (SAR) budget.
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Affiliation(s)
- David Leitão
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK
| | | | - Pip Bridgen
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK
| | - Tom Wilkinson
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK
| | | | | | | | - Sharon L Giles
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK
| | - Ana Baburamani
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK
| | - Jan Sedlacik
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK.,Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK
| | - Joseph V Hajnal
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK.,Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK
| | - Shaihan J Malik
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK.,Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK
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23
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A Comparative Study of Birdcage RF Coil Configurations for Ultra-High Field Magnetic Resonance Imaging. SENSORS 2022; 22:s22051741. [PMID: 35270889 PMCID: PMC8914904 DOI: 10.3390/s22051741] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 02/14/2022] [Accepted: 02/21/2022] [Indexed: 12/26/2022]
Abstract
Improvements in transmission and reception sensitivities of radiofrequency (RF) coils used in ultra-high field (UHF) magnetic resonance imaging (MRI) are needed to reduce specific absorption rates (SAR) and RF power deposition, albeit without applying high-power RF. Here, we propose a method to simultaneously improve transmission efficiency and reception sensitivity of a band-pass birdcage RF coil (BP-BC RF coil) by combining a multi-channel wireless RF element (MCWE) with a high permittivity material (HPM) in a 7.0 T MRI. Electromagnetic field (EM-field) simulations, performed using two types of phantoms, viz., a cylindrical phantom filled with oil and a human head model, were used to compare the effects of MCWE and HPM on BP-BC RF coils. EM-fields were calculated using the finite difference time-domain (FDTD) method and analyzed using Matlab software. Next, to improve RF transmission efficiency, we compared two HPM structures, namely, a hollow cylinder shape HPM (hcHPM) and segmented cylinder shape HPM (scHPM). The scHPM and MCWE model comprised 16 elements (16-rad BP-BC RF coil) and this coil configuration demonstrated superior RF transmission efficiency and reception sensitivity along with an acceptable SAR. We expect wider clinical application of this combination in 7.0 T MRIs, which were recently approved by the United States Food and Drug Administration.
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24
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Le Ster C, Mauconduit F, Massire A, Boulant N, Gras V. Standardized universal pulse: A fast RF calibration approach to improve flip angle accuracy in parallel transmission. Magn Reson Med 2022; 87:2839-2850. [PMID: 35122302 DOI: 10.1002/mrm.29180] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Revised: 01/10/2022] [Accepted: 01/11/2022] [Indexed: 11/09/2022]
Abstract
PURPOSE In parallel transmission (pTX), subject-tailored RF pulses allow achieving excellent flip angle (FA) accuracy but often require computationally extensive online optimizations, precise characterization of the static field ( Δ B 0 ), and the transmit RF field ( B 1 + ) distributions. This costs time and requires expertise from the MR user. Universal pulses (UPs) have been proposed to reduce this burden, yet, with a penalty in FA accuracy. This study introduces the concept of standardized universal pulses (SUPs), where pulses are designed offline and adjusted to the subject through a fast online calibration scan. METHODS A SUP is designed offline using a so-called standardized database, wherein each B 1 + map has been normalized to a reference transmit RF field distribution. When scanning a new subject, a 3-slice B 1 + acquisition (scan time < 10 s) is performed and used to adjust the SUP to the subject through a linear transform. SUP performance was assessed at 7T with simulations by computing the FA-normalized root mean square error (FA-NRMSE) and the FA pattern stability as measured by the average and coefficient of variation of the FA across 15 control subjects, along with in vivo experiments using an MP2RAGE sequence implementing the SUP variant for the FLASH readout. RESULTS Adjusted SUP improved the FA-NRMSE (8.8 % for UP vs. 7.1 % for adjusted SUP). Experimentally in vivo, this translated in an improved signal homogeneity and more accurate T 1 quantification using MP2RAGE. CONCLUSION The proposed SUP approach improves excitation accuracy (FA-NRMSE) while preserving the same offline pulse design principle as offered by UPs.
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Affiliation(s)
- Caroline Le Ster
- NeuroSpin, CEA, CNRS, BAOBAB, Université Paris-Saclay, Gif-Sur-Yvette, France
| | - Franck Mauconduit
- NeuroSpin, CEA, CNRS, BAOBAB, Université Paris-Saclay, Gif-Sur-Yvette, France
| | | | - Nicolas Boulant
- NeuroSpin, CEA, CNRS, BAOBAB, Université Paris-Saclay, Gif-Sur-Yvette, France
| | - Vincent Gras
- NeuroSpin, CEA, CNRS, BAOBAB, Université Paris-Saclay, Gif-Sur-Yvette, France
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25
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Nazemorroaya A, Aghaeifar A, Shiozawa T, Hirt B, Schulz H, Scheffler K, Hagberg GE. Developing formalin-based fixative agents for post mortem brain MRI at 9.4 T. Magn Reson Med 2021; 87:2481-2494. [PMID: 34931721 DOI: 10.1002/mrm.29122] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Revised: 11/24/2021] [Accepted: 11/25/2021] [Indexed: 11/07/2022]
Abstract
PURPOSE To develop fixative agents for high-field MRI with suitable dielectric properties and measure MR properties in immersion-fixed brain tissue. METHODS Dielectric properties of formalin-based agents were assessed (100 MHz-4.5 GHz), and four candidate fixatives with/without polyvinylpyrrolidone (PVP) and different salt concentrations were formulated. B1 field and MR properties (T1 , R 2 ∗ , R2 , R 2 ' , and magnetic susceptibility [QSM]) were observed in white and gray matter of pig brain samples during 0.5-35 days of immersion fixation. The kinetics were fitted using exponential functions. The immersion time required to reach maximum R 2 ∗ values at different tissue depths was used to estimate the Medawar coefficient for fixative penetration. The effect of replacing the fixatives with Fluoroinert and phosphate-buffered saline as embedding media was also evaluated. RESULTS The dielectric properties of formalin were nonlinearly modified by increasing amounts of additives. With 5% PVP and 0.04% NaCl, the dielectric properties and B1 field reflected in vivo conditions. The highest B1 values were found in white matter with PVP and varied significantly with tissue depth and embedding media, but not with immersion time. The MR properties depended on PVP yielding lower T1 , higher R 2 ∗ , more paramagnetic QSM values, and a lower Medawar coefficient (0.9 mm / h ; without PVP: 1.5). Regardless of fixative, switching to phosphate-buffered saline as embedder caused a paramagnetic shift in QSM and decreased R 2 ∗ that progressed during 1 month of storage, whereas no differences were found with Fluorinert. CONCLUSION In vivo-like B1 fields can be achieved in formalin fixatives using PVP and a low salt concentration, yielding lower T1 , higher R 2 ∗ , and more paramagnetic QSM than without additives. The kinetics of R 2 ∗ allowed estimation of fixative tissue penetration.
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Affiliation(s)
- Azadeh Nazemorroaya
- High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Ali Aghaeifar
- High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Thomas Shiozawa
- Institute of Clinical Anatomy and Cell Analysis, Eberhard Karl's University of Tübingen, Tübingen, Germany
| | - Bernhard Hirt
- Institute of Clinical Anatomy and Cell Analysis, Eberhard Karl's University of Tübingen, Tübingen, Germany
| | - Hildegard Schulz
- High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Klaus Scheffler
- High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.,Institute of Biomedical Magnetic Resonance, Eberhard Karl's University of Tübingen, Tübingen, Germany
| | - Gisela E Hagberg
- High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.,Institute of Biomedical Magnetic Resonance, Eberhard Karl's University of Tübingen, Tübingen, Germany
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A 16-Channel Dipole Antenna Array for Human Head Magnetic Resonance Imaging at 10.5 Tesla. SENSORS 2021; 21:s21217250. [PMID: 34770558 PMCID: PMC8587099 DOI: 10.3390/s21217250] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Revised: 10/28/2021] [Accepted: 10/29/2021] [Indexed: 01/26/2023]
Abstract
For ultra-high field and frequency (UHF) magnetic resonance imaging (MRI), the associated short wavelengths in biological tissues leads to penetration and homogeneity issues at 10.5 tesla (T) and require antenna transmit arrays for efficiently generated 447 MHz B1+ fields (defined as the transmit radiofrequency (RF) magnetic field generated by RF coils). Previously, we evaluated a 16-channel combined loop + dipole antenna (LD) 10.5 T head array. While the LD array configuration did not achieve the desired B1+ efficiency, it showed an improvement of the specific absorption rate (SAR) efficiency compared to the separate 8-channel loop and separate 8-channel dipole antenna arrays at 10.5 T. Here we compare a 16-channel dipole antenna array with a 16-channel LD array of the same dimensions to evaluate B1+ efficiency, 10 g SAR, and SAR efficiency. The 16-channel dipole antenna array achieved a 24% increase in B1+ efficiency in the electromagnetic simulation and MR experiment compared to the LD array, as measured in the central region of a phantom. Based on the simulation results with a human model, we estimate that a 16-channel dipole antenna array for human brain imaging can increase B1+ efficiency by 15% with similar SAR efficiency compared to a 16-channel LD head array.
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Lorking N, Murray AD, O'Brien JT. The use of positron emission tomography/magnetic resonance imaging in dementia: A literature review. Int J Geriatr Psychiatry 2021; 36:1501-1513. [PMID: 34490651 DOI: 10.1002/gps.5586] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2021] [Revised: 04/22/2021] [Accepted: 05/17/2021] [Indexed: 11/08/2022]
Abstract
OBJECTIVES Positron emission tomography-magnetic resonance imaging (PET/MRI) is an emerging hybrid imaging system in clinical nuclear medicine. Research demonstrates a comparative utility to current unimodal and hybrid methods, including PET-computed tomography (PET/CT), in several medical subspecialities such as neuroimaging. The aim of this review is to critically evaluate the literature from 2016 to 2021 using PET/MRI for the investigation of patients with mild cognitive impairment or dementia, and discuss the evidence base for widening its application into clinical practice. METHODS A comprehensive literature search using the PubMed database was conducted to retrieve studies using PET/MRI in relation to the topics of mild cognitive impairment, dementia, or Alzheimer's disease between January 2016 and January 2021. This search strategy enabled studies on all dementia types to be included in the analysis. Studies were required to have a minimum of 10 human subjects and incorporate simultaneous PET/MRI. RESULTS A total of 116 papers were retrieved, with 39 papers included in the final selection. These were broadly categorised into reviews (12), technical/methodological papers (11) and new data studies (16). For the current review, discussion focused on findings from the new data studies. CONCLUSIONS PET/MRI offers additional insight into the underlying anatomical, metabolic and functional changes associated with dementia when compared with unimodal methods and PET/CT, particularly relating to brain regions including the hippocampus and default mode network. Furthermore, the improved diagnostic utility of PET/MRI, as reported by radiologists, offers improved classification of dementia patients, with important implications for clinical management.
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Affiliation(s)
- Nicole Lorking
- School of Medicine, University of Aberdeen, Scotland, UK
| | | | - John T O'Brien
- Department of Psychiatry, University of Cambridge, Cambridge, UK
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28
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Abstract
Especially after the launch of 7 T, the ultrahigh magnetic field (UHF) imaging community achieved critically important strides in our understanding of the physics of radiofrequency interactions in the human body, which in turn has led to solutions for the challenges posed by such UHFs. As a result, the originally obtained poor image quality has progressed to the high-quality and high-resolution images obtained at 7 T and now at 10.5 T in the human torso. Despite these tremendous advances, work still remains to further improve the image quality and fully capitalize on the potential advantages UHF has to offer.
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Abstract
After introduction of the first human 7 tesla (7T) system in 1999, 7T MR systems have been employed as one of the most advanced platforms for human MR research for more than 20 years. Currently, two 7T MR models are approved for clinical use in the U.S.A. The approval facilitated introduction of the 7T system, summing up to around 100 worldwide. The approval in Japan is much awaited. As a clinical MR scanner, the 7T MR system is drawing attention in terms of safety.Several large-sized studies on bioeffects have been reported for vertigo, dizziness, motion disturbances, nausea, and others. Such effects might also be found in MR workers and researchers. Frequency and severity of reported bioeffects will be presented and discussed, including their variances. The high resonance frequency and shorter RF wavelength of 7T increase the concern about the safety. Homogeneous RF pulse excitation is difficult even for the brain, and a multi-channel parallel transmit (pTx) system is considered mandatory. However, pTx may create a hot spot, which makes the estimation of specific absorption rate (SAR) to be difficult. The stronger magnetic field of 7T causes a large force of displacement and heating on metallic implants or devices, and the scan of patients with them should not be conducted at 7T. However, there are some opinions that such patients might be scanned even at 7T, if certain criteria are met. This article provides a brief review on the effect of the static magnetic field on humans (MR subjects, workers, and researchers) and neurons, in addition to scan sound, SAR, and metal implants and devices. Understanding and avoiding adverse effects will contribute to the reduction in safety risks and the prevention of incidents.
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Affiliation(s)
- Tomohisa Okada
- Human Brain Research Center, Graduate School of Medicine, Kyoto University
| | - Thai Akasaka
- Human Brain Research Center, Graduate School of Medicine, Kyoto University
| | - Dinh Hd Thuy
- Human Brain Research Center, Graduate School of Medicine, Kyoto University
| | - Tadashi Isa
- Human Brain Research Center, Graduate School of Medicine, Kyoto University
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30
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Orzada S, Fiedler TM, Quick HH, Ladd ME. Post-processing algorithms for specific absorption rate compression. Magn Reson Med 2021; 86:2853-2861. [PMID: 34216047 DOI: 10.1002/mrm.28909] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Revised: 05/19/2021] [Accepted: 06/10/2021] [Indexed: 11/06/2022]
Abstract
PURPOSE Compression of local specific absorption rate (SAR) matrices is essential for enabling SAR monitoring and efficient pulse calculation in parallel transmission. Improvements in compression result in lower error margin and/or lower number of virtual observation points (VOPs). The purpose of this work is to introduce two algorithms for post-processing of already compressed VOP sets. One calculates individual overestimation matrices for the VOPs to reduce overestimation, the other identifies redundant VOPs. METHODS The first algorithm was evaluated for VOP sets calculated for three different transmit arrays with either 8 or 16 channels. For each array, two different overestimation matrices were used to generate the VOP sets. Each post-processed VOP set was evaluated using one million random excitation vectors and the results compared to the VOP set before post-processing. The second algorithm was evaluated by utilizing the same random excitation vectors and comparing the results after removal of the redundant VOPs with the results before removal to verify that these were identical. RESULTS The first algorithm reduced the mean overestimation by up to four fifths compared to the original set, while keeping the number of VOPs constant. The second algorithm decreased the number of VOPs generated by a compression with Eichfelder and Gebhardt's algorithm by more than 40% in 40% of the investigated cases and by more than 20% in 73% of the investigated cases. CONCLUSION Two post-processing algorithms are presented that enhance previously compressed VOP sets by improving the accuracy per number of VOPs.
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Affiliation(s)
- Stephan Orzada
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Thomas M Fiedler
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Mark E Ladd
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.,Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany.,Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany.,Faculty of Medicine, University of Heidelberg, Heidelberg, Germany
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31
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Fiedler TM, Orzada S, Flöser M, Rietsch SHG, Quick HH, Ladd ME, Bitz AK. Performance analysis of integrated RF microstrip transmit antenna arrays with high channel count for body imaging at 7 T. NMR IN BIOMEDICINE 2021; 34:e4515. [PMID: 33942938 DOI: 10.1002/nbm.4515] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Revised: 02/18/2021] [Accepted: 03/09/2021] [Indexed: 05/12/2023]
Abstract
The aim of the current study was to investigate the performance of integrated RF transmit arrays with high channel count consisting of meander microstrip antennas for body imaging at 7 T and to optimize the position and number of transmit elements. RF simulations using multiring antenna arrays placed behind the bore liner were performed for realistic exposure conditions for body imaging. Simulations were performed for arrays with as few as eight elements and for arrays with high channel counts of up to 48 elements. The B1+ field was evaluated regarding the degrees of freedom for RF shimming in the abdomen. Worst-case specific absorption rate (SARwc ), SAR overestimation in the matrix compression, the number of virtual observation points (VOPs) and SAR efficiency were evaluated. Constrained RF shimming was performed in differently oriented regions of interest in the body, and the deviation from a target B1+ field was evaluated. Results show that integrated multiring arrays are able to generate homogeneous B1+ field distributions for large FOVs, especially for coronal/sagittal slices, and thus enable body imaging at 7 T with a clinical workflow; however, a low duty cycle or a high SAR is required to achieve homogeneous B1+ distributions and to exploit the full potential. In conclusion, integrated arrays allow for high element counts that have high degrees of freedom for the pulse optimization but also produce high SARwc , which reduces the SAR accuracy in the VOP compression for low-SAR protocols, leading to a potential reduction in array performance. Smaller SAR overestimations can increase SAR accuracy, but lead to a high number of VOPs, which increases the computational cost for VOP evaluation and makes online SAR monitoring or pulse optimization challenging. Arrays with interleaved rings showed the best results in the study.
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Affiliation(s)
- Thomas M Fiedler
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Stephan Orzada
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Martina Flöser
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Stefan H G Rietsch
- Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Mark E Ladd
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany
- Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany
- Faculty of Medicine, University of Heidelberg, Heidelberg, Germany
| | - Andreas K Bitz
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Electromagnetic Theory and Applied Mathematics, Faculty of Electrical Engineering and Information Technology, FH Aachen - University of Applied Sciences, Aachen, Germany
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32
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Hess AT, Dragonu I, Chiew M. Accelerated calibrationless parallel transmit mapping using joint transmit and receive low-rank tensor completion. Magn Reson Med 2021; 86:2454-2467. [PMID: 34196031 PMCID: PMC7611890 DOI: 10.1002/mrm.28880] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Revised: 05/04/2021] [Accepted: 05/10/2021] [Indexed: 11/07/2022]
Abstract
Purpose To evaluate an algorithm for calibrationless parallel imaging to reconstruct undersampled parallel transmit field maps for the body and brain. Methods Using a combination of synthetic data and in vivo measurements from brain and body, 3 different approaches to a joint transmit and receive low-rank tensor completion algorithm are evaluated. These methods included: 1) virtual coils using the product of receive and transmit sensitivities, 2) joint-receiver coils that enforces a low rank structure across receive coils of all transmit modes, and 3) transmit low rank that uses a low rank structure for both receive and transmit modes simultaneously. The performance of each is investigated for different noise levels and different acceleration rates on an 8-channel parallel transmit 7 Tesla system. Results The virtual coils method broke down with increasing noise levels or acceleration rates greater than 2, producing normalized RMS error greater than 0.1. The joint receiver coils method worked well up to acceleration factors of 4, beyond which the normalized RMS error exceeded 0.1. Transmit low rank enabled an eightfold acceleration, with most normalized RMS errors remaining below 0.1. Conclusion This work demonstrates that undersampling factors of up to eightfold are feasible for transmit array mapping and can be reconstructed using calibrationless parallel imaging methods.
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Affiliation(s)
- Aaron T. Hess
- Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, Oxford, United Kingdom
| | | | - Mark Chiew
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
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Kořínek R, Pfleger L, Eckstein K, Beiglböck H, Robinson SD, Krebs M, Trattnig S, Starčuk Z, Krššák M. Feasibility of Hepatic Fat Quantification Using Proton Density Fat Fraction by Multi-Echo Chemical-Shift-Encoded MRI at 7T. FRONTIERS IN PHYSICS 2021; 9:665562. [PMID: 34849373 PMCID: PMC7612048 DOI: 10.3389/fphy.2021.665562] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Fat fraction quantification and assessment of its distribution in the hepatic tissue become more important with the growing epidemic of obesity, and the increasing prevalence of diabetes mellitus type 2 and non-alcoholic fatty liver disease. At 3Tesla, the multi-echo, chemical-shift-encoded magnetic resonance imaging (CSE-MRI)-based acquisition allows the measurement of proton density fat-fraction (PDFF) even in clinical protocols. Further improvements in SNR can be achieved by the use of phased array coils and increased static magnetic field. The purpose of the study is to evaluate the feasibility of PDFF imaging using a multi-echo CSE-MRI technique at ultra-high magnetic field (7Tesla). Thirteen volunteers (M/F) with a broad range of age, body mass index, and hepatic PDFF were measured at 3 and 7T by multi-gradient-echo MRI and single-voxel spectroscopy MRS. All measurements were performed in breath-hold (exhalation); the MRI protocols were optimized for a short measurement time, thus minimizing motion-related problems. 7T data were processed off-line using Matlab® (MRI:multi-gradient-echo) and jMRUI (MRS), respectively. For quantitative validation of the PDFF results, a similar protocol was performed at 3T, including on-line data processing provided by the system manufacturer, and correlation analyses between 7 and 3T data were performed off-line. The multi-echo CSE-MRI measurements at 7T with a phased-array coil configuration and an optimal post-processing yielded liver volume coverage ranging from 30 to 90% for high- and low-BMI subjects, respectively. PDFFs ranged between 1 and 20%. We found significant correlations between 7T MRI and -MRS measurements (R2 ≅ 0.97; p < 0.005), and between MRI-PDFF at 7T and 3T fields (R2 ≅ 0.94; p < 0.005) in the evaluated volumes. Based on the measurements and analyses performed, the multi-echo CSE-MRI method using a 32-channel coil at 7T showed its aptitude for MRI-based quantitation of PDFF in the investigated volumes. The results are the first step toward qMRI of the whole liver at 7T with further improvements in hardware.
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Affiliation(s)
- Radim Kořínek
- Magnetic Resonance group, Institute of Scientific Instruments of the Czech Academy of Sciences, Brno, Czechia
| | - Lorenz Pfleger
- Division of Endocrinology and Metabolism, Department of Medicine III, Medical University of Vienna, Vienna, Austria
| | - Korbinian Eckstein
- Department of Biomedical Imaging and Image-Guided Therapy, High-Field Magnetic Resonance Centre, Medical University of Vienna, Vienna, Austria
| | - Hannes Beiglböck
- Division of Endocrinology and Metabolism, Department of Medicine III, Medical University of Vienna, Vienna, Austria
| | - Simon Daniel Robinson
- Department of Biomedical Imaging and Image-Guided Therapy, High-Field Magnetic Resonance Centre, Medical University of Vienna, Vienna, Austria
| | - Michael Krebs
- Division of Endocrinology and Metabolism, Department of Medicine III, Medical University of Vienna, Vienna, Austria
| | - Siegfried Trattnig
- Department of Biomedical Imaging and Image-Guided Therapy, High-Field Magnetic Resonance Centre, Medical University of Vienna, Vienna, Austria
- Christian Doppler Laboratory for Clinical Molecular Imaging, CD Laboratory for Clinical Molecular MR Imaging (MOLIMA), Medical University of Vienna, Vienna, Austria
| | - Zenon Starčuk
- Magnetic Resonance group, Institute of Scientific Instruments of the Czech Academy of Sciences, Brno, Czechia
| | - Martin Krššák
- Division of Endocrinology and Metabolism, Department of Medicine III, Medical University of Vienna, Vienna, Austria
- Department of Biomedical Imaging and Image-Guided Therapy, High-Field Magnetic Resonance Centre, Medical University of Vienna, Vienna, Austria
- Christian Doppler Laboratory for Clinical Molecular Imaging, CD Laboratory for Clinical Molecular MR Imaging (MOLIMA), Medical University of Vienna, Vienna, Austria
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Matsuda T, Uwano I, Iwadate Y, Yoshioka K, Sasaki M. Spatial and temporal variations of flip-angle distributions in the human brain using an eight-channel parallel transmission system at 7T: comparison of three radiofrequency excitation methods. Radiol Phys Technol 2021; 14:161-166. [PMID: 33710499 DOI: 10.1007/s12194-021-00612-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 03/03/2021] [Accepted: 03/04/2021] [Indexed: 10/21/2022]
Abstract
We investigated the spatial and temporal variations of flip-angle (FA) distributions in the human brain from multiple scans, using an eight-channel parallel transmission (pTx) system at 7T. Nine healthy volunteers were scanned in five sessions using three radiofrequency excitation techniques each time: circular polarization (CP), static pTx, and dynamic pTx. We calculated the coefficients of variation of the FA values within the brain area to evaluate the variations, and the maximum intersession differences in the FA values (Dmax), comparing them between the three methods. The coefficients of variation decreased in the following order: CP, static pTx, and dynamic pTx (median: 20.1%, 13.6%, and 5.7%, respectively; p < 0.001). The average Dmax values were significantly higher for the static pTx (5.4°) than for the dynamic pTx (2.8°) and CP (1.7°) methods (p = 0.004 and 0.001, respectively). Compared to the CP method, the dynamic pTx method at 7T can efficiently minimize spatial variations in the FA distribution with a mild increase in temporal variations. The static pTx method exhibited a remarkably wide temporal variation.
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Affiliation(s)
- Tsuyoshi Matsuda
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, 1-1-1 Idaidori Yahaba, Iwate, 028-3694, Japan.
| | - Ikuko Uwano
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, 1-1-1 Idaidori Yahaba, Iwate, 028-3694, Japan
| | - Yuji Iwadate
- MR Applications and Workflow, GE Healthcare Japan Corporation, 4-7-127 Asahigaoka, Hino, Tokyo, 191-0065, Japan
| | - Kunihiro Yoshioka
- Department of Radiology, School of Medicine, Iwate Medical University, 2-1-1 Idaidori Yahaba, Iwate, 028-3695, Japan
| | - Makoto Sasaki
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, 1-1-1 Idaidori Yahaba, Iwate, 028-3694, Japan
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35
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Orzada S, Fiedler TM, Quick HH, Ladd ME. Local SAR compression algorithm with improved compression, speed, and flexibility. Magn Reson Med 2021; 86:561-568. [PMID: 33634530 DOI: 10.1002/mrm.28739] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Revised: 01/12/2021] [Accepted: 01/28/2021] [Indexed: 01/07/2023]
Abstract
PURPOSE Local specific absorption rate (SAR) compression algorithms are essential for enabling online SAR monitoring in parallel transmission. A better compression resulting in a lower number of virtual observation points improves speed of SAR calculation for online supervision and pulse design. METHOD An iterative expansion of an existing algorithm presented by Lee et al is proposed in this work. The original algorithm is used within a loop, making use of the virtual observation points from the previous iteration as the starting subvolume, while decreasing the overestimation with each iteration. This algorithm is evaluated on the SAR matrices of three different simulated arrays. RESULT The number of virtual observation points is approximately halved with the new algorithm, while at the same time the compression time is reduced with speed-up factors of up to 2.5. CONCLUSION The new algorithm improves the original algorithm in terms of compression rate and speed.
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Affiliation(s)
- Stephan Orzada
- Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany
| | - Thomas M Fiedler
- Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Mark E Ladd
- Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany.,Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany.,Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany.,Faculty of Medicine, University of Heidelberg, Heidelberg, Germany
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36
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Marshall H, Stewart NJ, Chan HF, Rao M, Norquay G, Wild JM. In vivo methods and applications of xenon-129 magnetic resonance. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2021; 122:42-62. [PMID: 33632417 PMCID: PMC7933823 DOI: 10.1016/j.pnmrs.2020.11.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Revised: 11/26/2020] [Accepted: 11/29/2020] [Indexed: 05/28/2023]
Abstract
Hyperpolarised gas lung MRI using xenon-129 can provide detailed 3D images of the ventilated lung airspaces, and can be applied to quantify lung microstructure and detailed aspects of lung function such as gas exchange. It is sensitive to functional and structural changes in early lung disease and can be used in longitudinal studies of disease progression and therapy response. The ability of 129Xe to dissolve into the blood stream and its chemical shift sensitivity to its local environment allow monitoring of gas exchange in the lungs, perfusion of the brain and kidneys, and blood oxygenation. This article reviews the methods and applications of in vivo129Xe MR in humans, with a focus on the physics of polarisation by optical pumping, radiofrequency coil and pulse sequence design, and the in vivo applications of 129Xe MRI and MRS to examine lung ventilation, microstructure and gas exchange, blood oxygenation, and perfusion of the brain and kidneys.
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Affiliation(s)
- Helen Marshall
- POLARIS, Imaging Sciences, Department of Infection, Immunity and Cardiovascular Disease, University of Sheffield, Sheffield, United Kingdom
| | - Neil J Stewart
- POLARIS, Imaging Sciences, Department of Infection, Immunity and Cardiovascular Disease, University of Sheffield, Sheffield, United Kingdom
| | - Ho-Fung Chan
- POLARIS, Imaging Sciences, Department of Infection, Immunity and Cardiovascular Disease, University of Sheffield, Sheffield, United Kingdom
| | - Madhwesha Rao
- POLARIS, Imaging Sciences, Department of Infection, Immunity and Cardiovascular Disease, University of Sheffield, Sheffield, United Kingdom
| | - Graham Norquay
- POLARIS, Imaging Sciences, Department of Infection, Immunity and Cardiovascular Disease, University of Sheffield, Sheffield, United Kingdom
| | - Jim M Wild
- POLARIS, Imaging Sciences, Department of Infection, Immunity and Cardiovascular Disease, University of Sheffield, Sheffield, United Kingdom.
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37
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Shao X, Yan L, Ma SJ, Wang K, Wang DJJ. High-Resolution Neurovascular Imaging at 7T: Arterial Spin Labeling Perfusion, 4-Dimensional MR Angiography, and Black Blood MR Imaging. Magn Reson Imaging Clin N Am 2021; 29:53-65. [PMID: 33237015 PMCID: PMC7694883 DOI: 10.1016/j.mric.2020.09.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Ultrahigh field offers increased resolution and contrast for neurovascular imaging. Arterial spin labeling methods benefit from an increased intrinsic signal-to-noise ratio of MR imaging signal and a prolonged tracer half-life at ultrahigh field, allowing the visualization of layer-dependent microvascular perfusion. Arterial spin labeling-based time-resolved 4-dimensional MR angiography at 7T provides a detailed depiction of the vascular architecture and dynamic blood flow pattern with high spatial and temporal resolutions. High-resolution black blood MR imaging at 7T allows detailed characterization of small perforating arteries such as lenticulostriate arteries. All techniques benefit from advances in parallel radiofrequency transmission technologies at ultrahigh field.
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Affiliation(s)
- Xingfeng Shao
- Laboratory of FMRI Technology (LOFT), USC Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, 2025 Zonal Avenue, Los Angeles, CA 90033, USA
| | - Lirong Yan
- Laboratory of FMRI Technology (LOFT), USC Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, 2025 Zonal Avenue, Los Angeles, CA 90033, USA; Department of Neurology, Keck School of Medicine, University of Southern California, 2025 Zonal Avenue, Los Angeles, CA 90033, USA
| | - Samantha J Ma
- Laboratory of FMRI Technology (LOFT), USC Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, 2025 Zonal Avenue, Los Angeles, CA 90033, USA; Siemens Healthcare, Los Angeles, CA, USA
| | - Kai Wang
- Laboratory of FMRI Technology (LOFT), USC Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, 2025 Zonal Avenue, Los Angeles, CA 90033, USA
| | - Danny J J Wang
- Laboratory of FMRI Technology (LOFT), USC Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, 2025 Zonal Avenue, Los Angeles, CA 90033, USA; Department of Neurology, Keck School of Medicine, University of Southern California, 2025 Zonal Avenue, Los Angeles, CA 90033, USA.
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38
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Han J, Gao Y, Nan X, Yu X, Liu F, Xin SX. Effect of radiofrequency inhomogeneity on water-content based electrical properties tomography and its correction by flip angle maps. Magn Reson Imaging 2021; 78:25-34. [PMID: 33450296 DOI: 10.1016/j.mri.2020.12.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 12/24/2020] [Accepted: 12/31/2020] [Indexed: 10/22/2022]
Abstract
Water-content based electrical properties tomography (wEPT) can retrieve electrical properties (EPs) from water-content maps. B1+ field information is not involved in the traditional magnetic resonance electrical properties tomography approach. wEPT can be performed through conventional MR scanning, such as T1-weighted spin-echo imaging, which provides convenient access to multiple clinical applications. However, the inhomogeneous radiofrequency (RF) field induced by RF coils would cause inaccuracy in wEPT reconstructions during MR scanning. We conducted a detailed investigation to evaluate the effect of inhomogeneous RF field on wEPT reconstructions to guarantee that EP mapping is desired for clinical practice. Two important considerations are involved, namely, multiple typical coil configurations and various flip angles (FAs). We proposed a correction scheme with actual FA mapping to calibrate the RF inhomogeneity and finally validated it by using human imaging at 3 T. This study illustrates a detailed evaluation for wEPT under imperfect RF homogeneity and further provides a feasible correction procedure to mitigate it. The profound knowledge of wEPT provided in our work will benefit its performance in clinical applications.
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Affiliation(s)
- Jijun Han
- School of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, China
| | - Yunyu Gao
- School of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, China
| | - Xiang Nan
- Center for Biomedical Engineering, University of Science and Technology of China, Hefei, Anhui, China
| | - Xuefei Yu
- School of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, China
| | - Feng Liu
- School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, QLD, Australia
| | - Sherman Xuegang Xin
- School of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, China; School of Medicine, South China University of Technology, Guangzhou, Guangdong, China.
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Abstract
Magnetic resonance imaging (MRI) is a noninvasive imaging technology that offers unparalleled anatomical and functional detail, along with diagnostic sensitivity. MRI is suitable for longitudinal studies due to the lack of exposure to ionizing radiation. Before undertaking preclinical MRI investigations of the kidney, the appropriate MRI hardware should be carefully chosen to balance the competing demands of image quality, spatial resolution, and imaging speed, tailored to the specific scientific objectives of the investigation. Here we describe the equipment needed to perform renal MRI in rodents, with the aim to guide the appropriate hardware selection to meet the needs of renal MRI applications.This publication is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This chapter on hardware considerations for renal MRI in small animals is complemented by two separate publications describing the experimental procedure and data analysis.
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40
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Georgakis IP, Polimeridis AG, Lattanzi R. A formalism to investigate the optimal transmit efficiency in radiofrequency shimming. NMR IN BIOMEDICINE 2020; 33:e4383. [PMID: 32725650 PMCID: PMC7539236 DOI: 10.1002/nbm.4383] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Revised: 12/18/2019] [Accepted: 06/09/2020] [Indexed: 05/12/2023]
Abstract
Transmit efficiency specifies the amplitude of the magnetic resonance excitation field produced over a region of interest with respect to the radiofrequency (RF) power deposited in the sample. This metric is highly important at ultra-high field magnetic resonance imaging (≥7 T), where excitation inhomogeneities and electric field interference effects could prevent achieving the desired flip angle distribution while satisfying the power safety limits. The aim of this work was to introduce an approach to calculate a theoretical upper bound on the transmit efficiency (OPTXE) for RF shimming, independent from any particular coil design. We computed the OPTXE for head-mimicking uniform spherical samples and a realistic heterogeneous head model by maximizing the square of the net transmit field per unit power deposition. The corresponding RF shimming weights were used to combine the analytical surface current modes into ideal current patterns. OPTXE grew monotonically as the target excitation voxel approached the surface of the object, and overall decreased at higher field strengths, presenting similar trends in both the uniform sphere and heterogeneous head model. Arrays with an increasing number of loops could closely approach OPTXE in the central region of the object, but performance decreased closer to the surface and at higher magnetic field strengths. The performance of 32 loops for a two-dimensional excitation region at 7 T increased from 34% to 93% when they were arranged based on the shape of the ideal current patterns. OPTXE provides an absolute reference to evaluate coil designs and RF shimming algorithms, whereas ideal current patterns could serve as guidelines for novel coil designs at ultra-high field. The uniform sphere model enables rapid analytic simulations and provides a good approximation of the OPTXE distribution in a realistic heterogeneous head model with comparable dimensions.
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Affiliation(s)
- Ioannis P. Georgakis
- Center for Computational and Data-Intensive Science and Engineering (CDISE), Skolkovo Institute of Science and Technology, Moscow, Russian Federation
| | | | - Riccardo Lattanzi
- Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY USA
- The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY USA
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41
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Orzada S, Fiedler TM, Bitz AK, Ladd ME, Quick HH. Local SAR compression with overestimation control to reduce maximum relative SAR overestimation and improve multi-channel RF array performance. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2020; 34:153-163. [PMID: 32964299 PMCID: PMC7910258 DOI: 10.1007/s10334-020-00890-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Revised: 08/31/2020] [Accepted: 09/11/2020] [Indexed: 11/18/2022]
Abstract
Objective In local SAR compression algorithms, the overestimation is generally not linearly dependent on actual local SAR. This can lead to large relative overestimation at low actual SAR values, unnecessarily constraining transmit array performance. Method Two strategies are proposed to reduce maximum relative overestimation for a given number of VOPs. The first strategy uses an overestimation matrix that roughly approximates actual local SAR; the second strategy uses a small set of pre-calculated VOPs as the overestimation term for the compression. Result Comparison with a previous method shows that for a given maximum relative overestimation the number of VOPs can be reduced by around 20% at the cost of a higher absolute overestimation at high actual local SAR values. Conclusion The proposed strategies outperform a previously published strategy and can improve the SAR compression where maximum relative overestimation constrains the performance of parallel transmission.
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Affiliation(s)
- Stephan Orzada
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Kokereiallee 7, 45141, Essen, Germany. .,High-Field and Hybrid MR Imaging, University Hospital Essen, 45147, Essen, Germany.
| | - Thomas M Fiedler
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany
| | - Andreas K Bitz
- Electromagnetic Theory and Applied Mathematics, Faculty of Electrical Engineering and Information Technology, FH Aachen, University of Applied Sciences, 52066, Aachen, Germany
| | - Mark E Ladd
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Kokereiallee 7, 45141, Essen, Germany.,Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany.,Faculty of Physics and Astronomy, University of Heidelberg, Im Neuenheimer Feld 226, 69120, Heidelberg, Germany.,Faculty of Medicine, University of Heidelberg, Im Neuenheimer Feld 672, 69120, Heidelberg, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Kokereiallee 7, 45141, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, 45147, Essen, Germany
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42
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Mao X, Bari S, Love DJ, Rispoli JV. Global and peak local specific absorption rate control on parallel transmit systems using k-means SAR compression model. Magn Reson Med 2020; 85:1093-1103. [PMID: 32810320 DOI: 10.1002/mrm.28456] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Revised: 07/09/2020] [Accepted: 07/10/2020] [Indexed: 12/29/2022]
Abstract
PURPOSE To improve the specific absorption rate (SAR) compression model capability in parallel transmission (pTx) MRI systems. METHODS A k-means clustering method is proposed to group voxels with similar SAR behaviors in the scanned object, providing a controlled upper-bounded estimation of peak local SARs. This k-means compression model and the conventional virtual observation point (VOP) model were tested in a pTx MRI framework. The pTx pulse design with different SAR controlling schemes was simulated using a numerical human head model and an eight-channel 7T coil array. Multiple criteria (including RF power, global and peak local SARs, and excitation accuracy) were compared for the performance testing. RESULTS The k-means compression model generated a narrower overestimation bound, leading to a more accurate local SAR estimation. Among different pTx pulse design approaches, the k-means compression model showed the best trade-off between the SAR and excitation accuracy. CONCLUSIONS The developed SAR compression model is advantageous for pTx framework given the narrower overestimation bound and control over the compression ratio. Results also illustrate that a moderate increase of maximum RF power can be useful for reducing the maximum local SAR deposition.
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Affiliation(s)
- Xianglun Mao
- School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN, USA
| | - Sumra Bari
- School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN, USA
| | - David J Love
- School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN, USA
| | - Joseph V Rispoli
- School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN, USA.,Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, USA
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43
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Zhao X, Lee H, Song HK, Cheng CC, Wehrli FW. Impact of gradient imperfections on bone water quantification with UTE MRI. Magn Reson Med 2020; 84:2034-2047. [PMID: 32307749 DOI: 10.1002/mrm.28272] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Revised: 02/06/2020] [Accepted: 03/11/2020] [Indexed: 01/14/2023]
Abstract
PURPOSE The impact of gradient imperfections on UTE images and UTE image-derived bone water quantification was investigated at 3 T field strength. METHODS The effects of simple gradient time delays and eddy currents on UTE images, as well as the effects of gradient error corrections, were studied with simulation and phantom experiments. The k-space trajectory was mapped with a 2D sequence with phase encoding on both spatial axes by measuring the phase of the signal in small time increments during ramp-up of the read gradient. In vivo 3D UTE images were reconstructed with and without gradient error compensation to determine the bias in bone water quantification. Finally, imaging was performed on 2 equally configured Siemens TIM Trio systems (Siemens Medical Solutions, Erlangen, Germany) to investigate the impact of such gradient imperfections on inter-scanner measurement bias. RESULTS Compared to values derived from UTE images with full gradient error compensation, total bone water was found to deviate substantially with no (up to 17%) or partial (delay-only) compensation (up to 10.8%). Bound water, obtained with inversion recovery-prepared UTE, was somewhat less susceptible to gradient errors (up to 2.2% for both correction strategies). Inter-scanner comparison indicated a statistically significant bias between measurements from the 2 MR systems for both total and bound water, which either vanished or was substantially reduced following gradient error correction. CONCLUSION Gradient imperfections impose spatially dependent artifacts on UTE images, which compromise not only bone water quantification accuracy but also inter-scanner measurement agreement if left uncompensated.
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Affiliation(s)
- Xia Zhao
- Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Hyunyeol Lee
- Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Hee Kwon Song
- Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Cheng-Chieh Cheng
- Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Felix W Wehrli
- Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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44
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Restivo MC, Ramasawmy R, Bandettini WP, Herzka DA, Campbell-Washburn AE. Efficient spiral in-out and EPI balanced steady-state free precession cine imaging using a high-performance 0.55T MRI. Magn Reson Med 2020; 84:2364-2375. [PMID: 32291845 DOI: 10.1002/mrm.28278] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 03/10/2020] [Accepted: 03/13/2020] [Indexed: 12/22/2022]
Abstract
PURPOSE Low-field MRI offers favorable physical properties for SNR-efficient long readout acquisitions such as spiral and EPI. We used a 0.55 tesla (T) MRI system equipped with high-performance hardware to increase the sampling duty cycle and extend the TR of balanced steady-state free precession (bSSFP) cardiac cine acquisitions, which typically are limited by banding artifacts. METHODS We developed a high-efficiency spiral in-out bSSFP acquisition, with zeroth- and first-gradient moment nulling, and an EPI bSSFP acquisition for cardiac cine imaging using a contemporary MRI system modified to operate at 0.55T. Spiral in-out and EPI bSSFP cine protocols, with TR = 8 ms, were designed to maintain both spatiotemporal resolution and breath-hold length. Simulations, phantom imaging, and healthy volunteer imaging studies (n = 12) were performed to assess SNR and image quality using these high sampling duty-cycle bSSFP sequences. RESULTS Spiral in-out bSSFP performed favorably at 0.55T and generated good image quality, whereas EPI bSSFP suffered motion and flow artifacts. There was no difference in ejection fraction comparing spiral in-out with standard Cartesian imaging. Moreover, human images demonstrated a 79% ± 21% increase in myocardial SNR using spiral in-out bSSFP and 50% ± 14% increase in SNR using EPI bSSFP as compared with the reference Cartesian acquisition. Spiral in-out acquisitions at 0.55T recovered 69% ± 14% of the myocardial SNR at 1.5T. CONCLUSION Efficient bSSFP spiral in-out provided high-quality cardiac cine imaging and SNR recovery on a high-performance 0.55T MRI system.
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Affiliation(s)
- Matthew C Restivo
- Cardiovascular Branch, Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Rajiv Ramasawmy
- Cardiovascular Branch, Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - W Patricia Bandettini
- Cardiovascular Branch, Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Daniel A Herzka
- Cardiovascular Branch, Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Adrienne E Campbell-Washburn
- Cardiovascular Branch, Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
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Basiri R, Federico P, Lebel RM. Transverse relaxometry with transmit field-constrained stimulated echo compensation. MAGMA (NEW YORK, N.Y.) 2019; 32:669-677. [PMID: 31338627 DOI: 10.1007/s10334-019-00769-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Revised: 06/26/2019] [Accepted: 07/15/2019] [Indexed: 06/10/2023]
Abstract
OBJECTIVE Purely exponential decay is rarely observed in conventional mono-exponential T2 mapping due to transmit field inhomogeneity and calibration errors, which collectively introduce stimulated and indirect echo pathways. Stimulated echo correction (SEC) requires an additional fit parameter for the transmit field, resulting in greater uncertainty in T2 relative to mono-exponential fitting. The aim of this study was to develop an accurate and precise method for T2 mapping using SEC. METHODS The proposed method, called two-step SEC (tSEC), leverages spatial correlations in the transmit field to reduce the number of fully independent fitting parameters from three to two. The method involves a two-pass fit: the first pass involves a fast but standard SEC fit. The initially estimated transmit field is smoothed and provided as a fixed input to the second pass. RESULTS Simulations and in vivo experiments demonstrated up to 38% and 27% decreases in relative T2 variance with tSEC relative to SEC. Average T2 values were unchanged between tSEC and SEC fits. The proposed method uses the same input data as SEC and exponential fits, so it is applicable to existing data. DISCUSSION The proposed method generates reliable and reproducible quantitative T2 maps and should be considered for future relaxometry studies.
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Affiliation(s)
- Reza Basiri
- Biomedical Engineering, University of Calgary, 2500 University Dr NW, Calgary, AB, T2N 1N4, Canada.
- Hotchkiss Brain Institute, University of Calgary, 2500 University Dr NW, Calgary, AB, T2N 1N4, Canada.
- Seaman Family Centre, Foothills Medical Centre, MRG 020A, 3330 Hospital Drive NW, Calgary, AB, T2N 2T9, Canada.
| | - Paolo Federico
- Hotchkiss Brain Institute, University of Calgary, 2500 University Dr NW, Calgary, AB, T2N 1N4, Canada
- Department of Clinical Neuroscience, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
- Department of Radiology, University of Calgary, 2500 University Dr NW, Calgary, AB, Canada
- Seaman Family Centre, Foothills Medical Centre, MRG 020A, 3330 Hospital Drive NW, Calgary, AB, T2N 2T9, Canada
| | - Robert Marc Lebel
- Biomedical Engineering, University of Calgary, 2500 University Dr NW, Calgary, AB, T2N 1N4, Canada
- Department of Radiology, University of Calgary, 2500 University Dr NW, Calgary, AB, Canada
- GE Healthcare, Calgary, AB, Canada
- Seaman Family Centre, Foothills Medical Centre, MRG 020A, 3330 Hospital Drive NW, Calgary, AB, T2N 2T9, Canada
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Gao Y, Han J, Zhu Y, Wang J, Wei X, Xin X. Channel-combination method for phase-based |B 1+| mapping techniques. Magn Reson Imaging 2019; 65:1-7. [PMID: 31670236 DOI: 10.1016/j.mri.2019.09.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Revised: 09/06/2019] [Accepted: 09/15/2019] [Indexed: 10/25/2022]
Abstract
PURPOSE The aim of this study was to propose a channel combination method for |B1+| mapping methods using phase difference to reconstruct |B1+| map. THEORY AND METHODS Phase-based |B1+| mapping methods commonly consider the phase difference of two scans to measure |B1+|. Multiple receiver coils acquire a number of images and the phase difference at each channel is theoretically the same in the absence of noise. Affected by noise, phase difference is approximately governed by Gaussian distribution. Considering data from all channels as samples, estimation can be achieved by maximum likelihood method. With this method, all phase differences at each channel are combined into one. In this study, the proposed method is applied with Bloch-Siegert shift |B1+| mapping method. Simulations are performed to illustrate the phase difference distribution and demonstrate the feasibility and facility of the proposed method. Phantom and vivo experiments are carried out at 1.5 T scanner equipped with 8-channel receiver coil. In all experiments, the proposed method is compared with weighted averaging (WA) method. RESULTS Simulations revealed appropriateness of approximating the distribution of phase difference to Gaussian distribution. Compared with WA method, the proposed method reduces errors of |B1+| calculation. Phantom and vivo experiments provide further validation. CONCLUSION Considering phase noise distribution, the proposed method achieves channel combination by finding the estimation from data acquired by multiple receivers coil. The proposed method reduces |B1+| reconstruction errors caused by noise.
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Affiliation(s)
- Yunyu Gao
- School of Biomedical Engineering, Southern Medical University, No. 1023-1063 Shatai South Road, Baiyun district, Guangzhou City, Guangdong Province 510515, China
| | - Jijun Han
- School of Biomedical Engineering, Southern Medical University, No. 1023-1063 Shatai South Road, Baiyun district, Guangzhou City, Guangdong Province 510515, China
| | - Yurong Zhu
- School of Biomedical Engineering, Southern Medical University, No. 1023-1063 Shatai South Road, Baiyun district, Guangzhou City, Guangdong Province 510515, China
| | - Jiajia Wang
- School of Biomedical Engineering, Southern Medical University, No. 1023-1063 Shatai South Road, Baiyun district, Guangzhou City, Guangdong Province 510515, China
| | - Xinhua Wei
- Department of Radiology, Guangzhou First People's Hospital, South China University of Technology, No. 1 Panfu Road, Yuexiu District, Guangzhou City, Guangzhou Province 510180, China
| | - Xuegang Xin
- School of Biomedical Engineering, Southern Medical University, No. 1023-1063 Shatai South Road, Baiyun district, Guangzhou City, Guangdong Province 510515, China; School of Medicine, South China University of Technology, Guangzhou Higher Education Mega Centre, Panyu District, Guangzhou City, Guangzhou Province 510006, China.
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47
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Abstract
Abstract
Despite all major breakthroughs in recent years of research, we are still unsuccessful to effectively diagnose and treat cancer that has express and metastasizes. Thus, the development of a novel approach for cancer detection and treatment is crucial. Recent progress in Glyconanotechnology has allowed the use of glycans and lectins as bio-functional molecules for many biological and biomedical applications. With the known advantages of quantum dots (QDs) and versatility of carbohydrates and lectins, Glyco-functionalised QD is a new prospect in constructing biomedical imaging platform for cancer behaviour study as well as treatment. In this review, we aim to describe the current utilisation of Glyco-functionalised QDs as well as their future prospective to interpret and confront cancer.
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48
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Orzada S, Solbach K, Gratz M, Brunheim S, Fiedler TM, Johst S, Bitz AK, Shooshtary S, Abuelhaija A, Voelker MN, Rietsch SHG, Kraff O, Maderwald S, Flöser M, Oehmigen M, Quick HH, Ladd ME. A 32-channel parallel transmit system add-on for 7T MRI. PLoS One 2019; 14:e0222452. [PMID: 31513637 PMCID: PMC6742215 DOI: 10.1371/journal.pone.0222452] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Accepted: 08/29/2019] [Indexed: 02/07/2023] Open
Abstract
PURPOSE A 32-channel parallel transmit (pTx) add-on for 7 Tesla whole-body imaging is presented. First results are shown for phantom and in-vivo imaging. METHODS The add-on system consists of a large number of hardware components, including modulators, amplifiers, SAR supervision, peripheral devices, a control computer, and an integrated 32-channel transmit/receive body array. B1+ maps in a phantom as well as B1+ maps and structural images in large volunteers are acquired to demonstrate the functionality of the system. EM simulations are used to ensure safe operation. RESULTS Good agreement between simulation and experiment is shown. Phantom and in-vivo acquisitions show a field of view of up to 50 cm in z-direction. Selective excitation with 100 kHz sampling rate is possible. The add-on system does not affect the quality of the original single-channel system. CONCLUSION The presented 32-channel parallel transmit system shows promising performance for ultra-high field whole-body imaging.
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Affiliation(s)
- Stephan Orzada
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany
- * E-mail:
| | - Klaus Solbach
- RF & Microwave Technology, University of Duisburg-Essen, Duisburg, Germany
| | - Marcel Gratz
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Sascha Brunheim
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Thomas M. Fiedler
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Sören Johst
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany
| | - Andreas K. Bitz
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Electromagnetic Theory and Applied Mathematics, Faculty of Electrical Engineering and Information Technology, FH Aachen – University of Applied Sciences, Aachen, Germany
| | - Samaneh Shooshtary
- RF & Microwave Technology, University of Duisburg-Essen, Duisburg, Germany
| | - Ashraf Abuelhaija
- RF & Microwave Technology, University of Duisburg-Essen, Duisburg, Germany
| | - Maximilian N. Voelker
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Stefan H. G. Rietsch
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Oliver Kraff
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany
| | - Stefan Maderwald
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany
| | - Martina Flöser
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Mark Oehmigen
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Harald H. Quick
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Mark E. Ladd
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Faculty of Physics and Astronomy and Faculty of Medicine, University of Heidelberg, Heidelberg, Germany
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Connell IRO, Menon RS. Shape Optimization of an Electric Dipole Array for 7 Tesla Neuroimaging. IEEE TRANSACTIONS ON MEDICAL IMAGING 2019; 38:2177-2187. [PMID: 30908199 DOI: 10.1109/tmi.2019.2906507] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Radio-frequency (RF) arrays constructed using electric dipoles have potential benefits for transmit and receive applications using the ultra-high field (UHF) MRI. This paper examines some of the implementation barriers regarding dipole RF arrays for human head imaging at 7 T. The dipole array was constructed with conformal, meandered dipoles with dimensions selected utilizing an evolutionary-based optimization routine to shape-optimize the dipole structure. Coupling matrix synthesis (CMS) was utilized to decouple the dipole array. Mean and worst-case transmission between nearest-neighbour dipoles was -17.2 and -15.5 dB, respectively (±2.4 dB). Transmit efficiencies of 24.6 nT/V for the entire brain and 26.0 nT/V across the axial slice were observed. The total and peak 10-g SAR, normalized to 1 Watt accepted input power per channel, was 0.163 and 0.601 W/kg, respectively. Maximum and mean noise correlations were -17 dB and -32 dB, respectively. The use of both CMS and a novel shape optimization routine to design a dipole array translated into sufficient transmit uniformity with a simultaneous reduction in 10-g SAR in comparison to a non-optimized dipole array of the same geometry. As a receiver, the dipole array maintained high orthogonality between elements, resulting in strong parallel imaging performance.
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50
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Knowles BR, Friedrich F, Fischer C, Paech D, Ladd ME. Beyond T2 and 3T: New MRI techniques for clinicians. Clin Transl Radiat Oncol 2019; 18:87-97. [PMID: 31341982 PMCID: PMC6630188 DOI: 10.1016/j.ctro.2019.04.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Revised: 04/11/2019] [Accepted: 04/11/2019] [Indexed: 12/12/2022] Open
Abstract
Technological advances in Magnetic Resonance Imaging (MRI) in terms of field strength and hybrid MR systems have led to improvements in tumor imaging in terms of anatomy and functionality. This review paper discusses the applications of such advances in the field of radiation oncology with regards to treatment planning, therapy guidance and monitoring tumor response and predicting outcome.
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Affiliation(s)
- Benjamin R. Knowles
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Florian Friedrich
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Department of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany
| | - Carola Fischer
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Department of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany
| | - Daniel Paech
- Department of Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Mark E. Ladd
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Department of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany
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