101
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Chadzynski GL, Bause J, Shajan G, Pohmann R, Scheffler K, Ehses P. Fast and efficient free induction decay MR spectroscopic imaging of the human brain at 9.4 Tesla. Magn Reson Med 2016; 78:1281-1295. [PMID: 27900794 DOI: 10.1002/mrm.26539] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Revised: 10/11/2016] [Accepted: 10/12/2016] [Indexed: 12/14/2022]
Abstract
PURPOSE The purpose of this work was to develop a fast and efficient MRSI-FID acquisition scheme and test its performance in vivo. The aim was to find a trade-off between the minimal total acquisition time and signal-to-noise ratio of the acquired spectra. METHODS Measurements were performed on a 9.4 Tesla system. Sequence optimization included redesign of water suppression, optimization of the sequence gradients, and improvement of the sampling efficiency by minimizing the read-out time. This resulted in an acquisition time of 2:47 and 22:13 minutes for 2D (TR = 57 ms; 3-mm in-plane resolution) and 3D MRSI (TR = 57 ms; 16 slices; 3-mm isotropic resolution), respectively. RESULTS Despite strong T1 weighting and first-order phase problems, it was possible to obtain spectra of an acceptable quality. The average line width calculated for the tCr peak across the entire field of view was 26.9 ± 9.6 Hz for 2D and 30.0 ± 11.3 Hz for 3D MRSI. In 3D measurements, the percent fraction of voxels fitted with Cramer-Rao lower bounds below 10% was 53.3 ± 4.1%, 63.4 ± 8.4%, and 81.0 ± 2.9% for Glu, tCr, and tNAA, respectively. CONCLUSION Considering the typically long duration of high-resolution MRSI, the proposed technique may be of interest for clinical applications and/or studies that focus on following the biochemistry of dynamic processes. Magn Reson Med 78:1281-1295, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Grzegorz L Chadzynski
- Department of Biomedical Magnetic Resonance, Eberhard-Karls University of Tübingen, Tübingen, Germany.,High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Jonas Bause
- High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.,Graduate Training Centre of Neuroscience, Eberhard-Karls University of Tübingen, Tübingen, Germany
| | - Gunamony Shajan
- High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Rolf Pohmann
- High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Klaus Scheffler
- Department of Biomedical Magnetic Resonance, Eberhard-Karls University of Tübingen, Tübingen, Germany.,High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Philipp Ehses
- Department of Biomedical Magnetic Resonance, Eberhard-Karls University of Tübingen, Tübingen, Germany.,High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
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102
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Tse DHY, Wiggins CJ, Poser BA. High-resolution gradient-recalled echo imaging at 9.4T using 16-channel parallel transmit simultaneous multislice spokes excitations with slice-by-slice flip angle homogenization. Magn Reson Med 2016; 78:1050-1058. [PMID: 27774641 PMCID: PMC5574011 DOI: 10.1002/mrm.26501] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Revised: 08/30/2016] [Accepted: 09/17/2016] [Indexed: 11/26/2022]
Abstract
Purpose In order to fully benefit from the improved signal‐to‐noise and contrast‐to‐noise ratios at 9.4T, the challenges of
B1+ inhomogeneity and the long acquisition time of high‐resolution 2D gradient‐recalled echo (GRE) imaging were addressed. Theory and Methods Flip angle homogenized excitations were achieved by parallel transmission (pTx) of 3‐spoke pulses, designed by magnitude least‐squares optimization in a slice‐by‐slice fashion; the acquisition time reduction was achieved by simultaneous multislice (SMS) pulses. The slice‐specific spokes complex radiofrequency scaling factors were applied to sinc waveforms on a per‐channel basis and combined with the other pulses in an SMS slice group to form the final SMS‐pTX pulse. Optimal spokes locations were derived from simulations. Results Flip angle maps from presaturation TurboFLASH showed improvement of flip angle homogenization with 3‐spoke pulses over CP‐mode excitation (normalized root‐mean‐square error [NRMSE] 0.357) as well as comparable excitation homogeneity across the single‐band (NRMSE 0.119), SMS‐2 (NRMSE 0.137), and SMS‐3 (NRMSE 0.132) 3‐spoke pulses. The application of the 3‐spoke SMS‐3 pulses in a 48‐slice GRE protocol, which has an in‐plane resolution of 0.28 × 0.28 mm, resulted in a 50% reduction of scan duration (total acquisition time 6:52 min including reference scans). Conclusion Time‐efficient flip angle homogenized high‐resolution GRE imaging at 9.4T was accomplished by using slice‐specific SMS‐pTx spokes excitations. Magn Reson Med 78:1050–1058, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Desmond H Y Tse
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands
| | | | - Benedikt A Poser
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands
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103
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Connell IRO, Menon RS. General Coupling Matrix Synthesis for Decoupling MRI RF Arrays. IEEE TRANSACTIONS ON MEDICAL IMAGING 2016; 35:2229-2242. [PMID: 27093549 DOI: 10.1109/tmi.2016.2553844] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Multi-channel radio-frequency (RF) arrays, composed of multiple resonant coils, provide significant benefits for MRI during both signal reception (receive) and excitation (transmit). Demonstration of increased signal-to-noise ratio (SNR) and acceleration factors during parallel acquisitions has lead to the development of receive arrays. Conversely, transmit arrays have demonstrated considerable potential for mitigating excitation inhomogeneity arising at ultra-high magnetic field strengths ( ≥ 7 T) , present due to wave-like interactions inside the sample. Due to geometric constraints, the design of both receive and transmit arrays requires the resonating coils to be closely spaced. Significant overlap in the near-field distributions from each coil results in coupling. Without an adequate decoupling strategy applied between individual elements in an RF array, the MRI performance of the array can be significantly degraded. This work presents a method to design decoupling networks for arbitrarily large RF arrays based on direct synthesis of a coupling matrix. Reflection coefficients are fitted to transfer polynomials with transmission coefficients simultaneously minimized through a nonlinear optimization. The method demonstrates the design of nth-order distributed filters and lumped element networks that compensate for all first-order and cross-coupling terms arising in an RF array suitable for MRI. The synthesis results are computed for 4-, 8-, and 32-channel RF arrays. Monte Carlo analyses and experimental results for two RF array constructions demonstrate the robustness of this approach.
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104
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Le Garrec M, Gras V, Hang MF, Ferrand G, Luong M, Boulant N. Probabilistic analysis of the specific absorption rate intersubject variability safety factor in parallel transmission MRI. Magn Reson Med 2016; 78:1217-1223. [PMID: 27670737 DOI: 10.1002/mrm.26468] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Revised: 08/22/2016] [Accepted: 08/26/2016] [Indexed: 11/08/2022]
Abstract
PURPOSE Specific absorption rate (SAR) calculations in parallel transmission are commonly performed by using electromagnetic simulations on generic models. In this study, we propose a probabilistic analysis to study the safety factor employed to account for SAR intersubject variability versus risk relationship in head imaging at 7T. METHODS Thirty-three finite-element electromagnetic simulations were conducted to sample the four-dimensional parameter space consisting of the head length, head breadth, and shifts in Z and Y random variables. Based on the SAR matrices for each configuration, a multivariate second-order polynomial of the SAR versus the different parameters was reconstructed for different types of radiofrequency pulses. A Monte Carlo calculation was then performed to compute the probability of occurrence of a given SAR value. RESULTS By testing a large number of radiofrequency excitation pulses, the SAR calculated for the average model amplified by a safety margin of 1.5 was found to return a probability of less than 1% to be exceeded across the adult Caucasian population given the investigated parameters. CONCLUSION The proposed method to study SAR intersubject variability uses a reasonable number of electromagnetic simulations. Look-ahead SAR safety margins can be deduced based on risk/benefit ratio assessments. Magn Reson Med 78:1217-1223, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
| | - Vincent Gras
- CEA, DRF, I2BM, NeuroSpin, Unirs, Gif sur Yvette, France
| | | | | | - Michel Luong
- CEA, DRF, Irfu, SACM, Unirs, Gif sur Yvette, France
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105
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Loureiro JR, Hagberg GE, Ethofer T, Erb M, Bause J, Ehses P, Scheffler K, Himmelbach M. Depth-dependence of visual signals in the human superior colliculus at 9.4 T. Hum Brain Mapp 2016; 38:574-587. [PMID: 27659062 DOI: 10.1002/hbm.23404] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Revised: 09/04/2016] [Accepted: 09/06/2016] [Indexed: 11/08/2022] Open
Abstract
The superior colliculus (SC) is a layered structure located in the midbrain. We exploited the improved spatial resolution and BOLD signal strength available at 9.4 T to investigate the depth profile of visual BOLD responses in the human SC based on distortion-corrected EPI data with a 1 mm isotropic resolution. We used high resolution (350 µm in-plane) anatomical images to determine regions-of-interest of the SC and applied a semi-automated method to segment it into superficial, intermediate, and deep zones. A greater than linear increase in sensitivity of the functional signal at 9.4 T allowed us to detect a statistically significant depth pattern in a group analysis with a 20 min stimulation paradigm. Descriptive data showed consistent depth profiles also in single individuals. The highest signals were localized to the superficial layers of the right and left SC during contralateral stimulation, which was in good agreement with its functional architecture known from non-human primates. This study thus demonstrates the potential of 9.4 T MRI for functional neuroimaging even in deeply located, particularly challenging brain structures such as the SC. Hum Brain Mapp 38:574-587, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Joana R Loureiro
- High-Field MR, Max Planck Institute for Biological Cybernetics, Tuebingen, DE, Germany.,Biomedical Magnetic Resonance, University Hospital Tuebingen, Tuebingen, DE, Germany.,Graduate School of Neural and Behavioural Sciences/International Max Planck Research School, University of Tuebingen, Tuebingen, DE, Germany.,Division of Neuropsychology, Centre for Neurology, Hertie-Institute for Clinical Brain Research, Tuebingen, DE, Germany
| | - Gisela E Hagberg
- High-Field MR, Max Planck Institute for Biological Cybernetics, Tuebingen, DE, Germany.,Biomedical Magnetic Resonance, University Hospital Tuebingen, Tuebingen, DE, Germany
| | - Thomas Ethofer
- Biomedical Magnetic Resonance, University Hospital Tuebingen, Tuebingen, DE, Germany.,Department of Psychiatry and Psychotherapy, University of Tuebingen, Tuebingen, DE, Germany
| | - Michael Erb
- Biomedical Magnetic Resonance, University Hospital Tuebingen, Tuebingen, DE, Germany
| | - Jonas Bause
- High-Field MR, Max Planck Institute for Biological Cybernetics, Tuebingen, DE, Germany
| | - Philipp Ehses
- High-Field MR, Max Planck Institute for Biological Cybernetics, Tuebingen, DE, Germany.,Biomedical Magnetic Resonance, University Hospital Tuebingen, Tuebingen, DE, Germany
| | - Klaus Scheffler
- High-Field MR, Max Planck Institute for Biological Cybernetics, Tuebingen, DE, Germany.,Biomedical Magnetic Resonance, University Hospital Tuebingen, Tuebingen, DE, Germany
| | - Marc Himmelbach
- Graduate School of Neural and Behavioural Sciences/International Max Planck Research School, University of Tuebingen, Tuebingen, DE, Germany.,Division of Neuropsychology, Centre for Neurology, Hertie-Institute for Clinical Brain Research, Tuebingen, DE, Germany
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106
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O'Reilly TPA, Webb AG, Brink WM. Practical improvements in the design of high permittivity pads for dielectric shimming in neuroimaging at 7T. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 270:108-114. [PMID: 27434779 DOI: 10.1016/j.jmr.2016.07.003] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Revised: 06/15/2016] [Accepted: 07/08/2016] [Indexed: 06/06/2023]
Abstract
Improvements are proposed for practical design and use of high permittivity materials in high field neuroimaging in three different areas: (i) a simple formula to predict the permittivity of tri-component aqueous-based perovskite suspensions with relative permittivities between 110 and 300, (ii) characterization of addition of a hydroxyethyl-cellulose gelling agent to improve the long-term stability and material properties of "dielectric pads", and (iii) investigation of the integration of, for example, headphones into the dielectric pads to increase patient comfort within tightly-fitting receive coil arrays.
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Affiliation(s)
- T P A O'Reilly
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands
| | - A G Webb
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands.
| | - W M Brink
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands
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107
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Webb AG, Van de Moortele PF. The technological future of 7 T MRI hardware. NMR IN BIOMEDICINE 2016; 29:1305-1315. [PMID: 25974894 DOI: 10.1002/nbm.3315] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Revised: 02/07/2015] [Accepted: 04/07/2015] [Indexed: 06/04/2023]
Abstract
In this article we present our projections of future hardware developments on 7 T human MRI systems. These include compact cryogen-light magnets, improved gradient performance, integrated RF-receive and direct current shimming coil arrays, new RF technology with adaptive impedance matching, patient-specific specific absorption rate estimation and monitoring, and increased integration of physiological monitoring systems. Copyright © 2015 John Wiley & Sons, Ltd.
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Affiliation(s)
- A G Webb
- C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - P F Van de Moortele
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, MN, USA
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108
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Padormo F, Beqiri A, Hajnal JV, Malik SJ. Parallel transmission for ultrahigh-field imaging. NMR IN BIOMEDICINE 2016; 29:1145-61. [PMID: 25989904 PMCID: PMC4995736 DOI: 10.1002/nbm.3313] [Citation(s) in RCA: 124] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2014] [Revised: 03/27/2015] [Accepted: 03/29/2015] [Indexed: 05/24/2023]
Abstract
The development of MRI systems operating at or above 7 T has provided researchers with a new window into the human body, yielding improved imaging speed, resolution and signal-to-noise ratio. In order to fully realise the potential of ultrahigh-field MRI, a range of technical hurdles must be overcome. The non-uniformity of the transmit field is one of such issues, as it leads to non-uniform images with spatially varying contrast. Parallel transmission (i.e. the use of multiple independent transmission channels) provides previously unavailable degrees of freedom that allow full spatial and temporal control of the radiofrequency (RF) fields. This review discusses the many ways in which these degrees of freedom can be used, ranging from making more uniform transmit fields to the design of subject-tailored RF pulses for both uniform excitation and spatial selection, and also the control of the specific absorption rate. © 2015 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.
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Affiliation(s)
- Francesco Padormo
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
| | - Arian Beqiri
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
| | - Joseph V Hajnal
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
- Centre for the Developing Brain, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
| | - Shaihan J Malik
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
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109
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Guérin B, Stockmann JP, Baboli M, Torrado-Carvajal A, Stenger AV, Wald LL. Robust time-shifted spoke pulse design in the presence of large B0 variations with simultaneous reduction of through-plane dephasing, B1+ effects, and the specific absorption rate using parallel transmission. Magn Reson Med 2016; 76:540-54. [PMID: 26444717 PMCID: PMC4824674 DOI: 10.1002/mrm.25902] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Revised: 07/29/2015] [Accepted: 07/30/2015] [Indexed: 11/09/2022]
Abstract
PURPOSE To design parallel transmission spokes pulses with time-shifted profiles for joint mitigation of intensity variations due to B1+ effects, signal loss due to through-plane dephasing, and the specific absorption rate (SAR) at 7T. METHODS We derived a slice-averaged small tip angle (SA-STA) approximation of the magnetization signal at echo time that depends on the B1+ transmit profiles, the through-slice B0 gradient and the amplitude and time-shifts of the spoke waveforms. We minimize a magnitude least-squares objective based on this signal equation using a fast interior-point approach with analytical expressions of the Jacobian and Hessian. RESULTS Our algorithm runs in less than three minutes for the design of two-spoke pulses subject to hundreds of local SAR constraints. On a B0/B1+ head phantom, joint optimization of the channel-dependent time-shifts and spoke amplitudes allowed signal recovery in high-B0 regions at no increase of SAR. Although the method creates uniform magnetization profiles (ie, uniform intensity), the flip angle varies across the image, which makes it ill-suited to T1-weighted applications. CONCLUSIONS The SA-STA approach presented in this study is best suited to T2*-weighted applications with long echo times that require signal recovery around high B0 regions. Magn Reson Med 76:540-554, 2016. © 2015 Wiley Periodicals, Inc.
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Affiliation(s)
- Bastien Guérin
- Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
| | - Jason P Stockmann
- Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
- Physics Department, Harvard University, Cambridge, Massachusetts, USA
| | - Mehran Baboli
- John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, USA
| | - Angel Torrado-Carvajal
- Medical Image Analysis and Biometry Laboratory, University Rey Juan Carlos, Mostoles Spain
- Madrid-MIT M+ Vision Consortium, Madrid, Spain
| | - Andrew V Stenger
- John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, USA
| | - Lawrence L Wald
- Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
- Harvard-MIT Division of Health Sciences Technology, Cambridge, Massachusetts, USA
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110
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Yan X, Zhang X, Xue R, Gore JC, Grissom WA. Optimizing the ICE decoupling element distance to improve monopole antenna arrays for 7 Tesla MRI. Magn Reson Imaging 2016; 34:1264-1268. [PMID: 27469314 DOI: 10.1016/j.mri.2016.07.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2016] [Revised: 07/19/2016] [Accepted: 07/21/2016] [Indexed: 11/15/2022]
Abstract
The induced current elimination (ICE) method has been previously applied to decouple monopole coil arrays in ultrahigh field MRI. However, the method creates low B1+ spots near the decoupling elements. In this study, we aim to improve the performance of ICE-decoupled monopole array in human head imaging at 7 Tesla. Eight-channel ICE-decoupled monopole arrays were optimized by varying the position of the decoupling elements. A series of numerical studies were performed using the co-simulation method. In simulation, decoupling performance, quality (Q-) values and transmit field (B1+) were comparatively investigated. In addition, we constructed an optimized ICE-decoupled monopole array and compared its performance with the unoptimized array. The simulation results showed that a good trade-off between decoupling and B1+ loss can be obtained when decoupling elements were moved 2.5-cm away from coil elements. This was validated by in-vivo MR imaging using the constructed array. Compared with the unoptimized ICE decoupled monopole array, the optimized array had a more homogeneous transmit field and no dark spots or signal cancellations in the MR images.
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Affiliation(s)
- Xinqiang Yan
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA; Department of Radiology, Vanderbilt University, Nashville, TN, USA.
| | - Xiaoliang Zhang
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA; UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, CA, USA
| | - Rong Xue
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - John C Gore
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA; Department of Radiology, Vanderbilt University, Nashville, TN, USA
| | - William A Grissom
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
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111
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Tse DHY, Wiggins CJ, Ivanov D, Brenner D, Hoffmann J, Mirkes C, Shajan G, Scheffler K, Uludağ K, Poser BA. Volumetric imaging with homogenised excitation and static field at 9.4 T. MAGMA (NEW YORK, N.Y.) 2016; 29:333-45. [PMID: 26995492 PMCID: PMC4891373 DOI: 10.1007/s10334-016-0543-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Revised: 02/26/2016] [Accepted: 02/29/2016] [Indexed: 11/29/2022]
Abstract
OBJECTIVES To overcome the challenges of B0 and RF excitation inhomogeneity at ultra-high field MRI, a workflow for volumetric B0 and flip-angle homogenisation was implemented on a human 9.4 T scanner. MATERIALS AND METHODS Imaging was performed with a 9.4 T human MR scanner (Siemens Medical Solutions, Erlangen, Germany) using a 16-channel parallel transmission system. B0- and B1-mapping were done using a dual-echo GRE and transmit phase-encoded DREAM, respectively. B0 shims and a small-tip-angle-approximation kT-points pulse were calculated with an off-line routine and applied to acquire T1- and T 2 (*) -weighted images with MPRAGE and 3D EPI, respectively. RESULTS Over six in vivo acquisitions, the B0-distribution in a region-of-interest defined by a brain mask was reduced down to a full-width-half-maximum of 0.10 ± 0.01 ppm (39 ± 2 Hz). Utilising the kT-points pulses, the normalised RMSE of the excitation was decreased from CP-mode's 30.5 ± 0.9 to 9.2 ± 0.7 % with all B 1 (+) voids eliminated. The SNR inhomogeneities and contrast variations in the T1- and T 2 (*) -weighted volumetric images were greatly reduced which led to successful tissue segmentation of the T1-weighted image. CONCLUSION A 15-minute B0- and flip-angle homogenisation workflow, including the B0- and B1-map acquisitions, was successfully implemented and enabled us to reduce intensity and contrast variations as well as echo-planar image distortions in 9.4 T images.
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Affiliation(s)
- Desmond H Y Tse
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.
| | | | - Dimo Ivanov
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Daniel Brenner
- German Centre for Neurodegenerative Diseases (DZNE), Bonn, Germany
| | - Jens Hoffmann
- High Field MR Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
| | - Christian Mirkes
- High Field MR Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
- Department for Biomedical Magnetic Resonance, University of Tuebingen, Tuebingen, Germany
| | - Gunamony Shajan
- High Field MR Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
| | - Klaus Scheffler
- High Field MR Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
- Department for Biomedical Magnetic Resonance, University of Tuebingen, Tuebingen, Germany
| | - Kâmil Uludağ
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
- Scannexus BV, Maastricht, The Netherlands
| | - Benedikt A Poser
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
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112
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Electrodynamics and radiofrequency antenna concepts for human magnetic resonance at 23.5 T (1 GHz) and beyond. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2016; 29:641-56. [PMID: 27097905 DOI: 10.1007/s10334-016-0559-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Revised: 04/04/2016] [Accepted: 04/06/2016] [Indexed: 10/21/2022]
Abstract
OBJECTIVE This work investigates electrodynamic constraints, explores RF antenna concepts and examines the transmission fields (B 1 (+) ) and RF power deposition of dipole antenna arrays for (1)H magnetic resonance of the human brain at 1 GHz (23.5 T). MATERIALS AND METHODS Electromagnetic field (EMF) simulations are performed in phantoms with average tissue simulants for dipole antennae using discrete frequencies [300 MHz (7.0 T) to 3 GHz (70.0 T)]. To advance to a human setup EMF simulations are conducted in anatomical human voxel models of the human head using a 20-element dipole array operating at 1 GHz. RESULTS Our results demonstrate that transmission fields suitable for (1)H MR of the human brain can be achieved at 1 GHz. An increase in transmit channel density around the human head helps to enhance B 1 (+) in the center of the brain. The calculated relative increase in specific absorption rate at 23.5 versus 7.0 T was below 1.4 (in-phase phase setting) and 2.7 (circular polarized phase setting) for the dipole antennae array. CONCLUSION The benefits of multi-channel dipole antennae at higher frequencies render MR at 23.5 T feasible from an electrodynamic standpoint. This very preliminary finding opens the door on further explorations that might be catalyzed into a 20-T class human MR system.
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113
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Yan X, Cao Z, Grissom WA. Experimental implementation of array-compressed parallel transmission at 7 tesla. Magn Reson Med 2016; 75:2545-52. [PMID: 27080331 DOI: 10.1002/mrm.26239] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 03/12/2016] [Accepted: 03/18/2016] [Indexed: 12/13/2022]
Abstract
PURPOSE To implement and validate a hardware-based array-compressed parallel transmission (acpTx) system. METHODS In array-compressed parallel transmission, a small number of transmit channels drive a larger number of transmit coils, which are connected via an array compression network that implements optimized coil-to-channel combinations. A two channel-to-eight coil array compression network was developed using power splitters, attenuators and phase shifters, and a simulation was performed to investigate the effects of coil coupling on power dissipation in a simplified network. An eight coil transmit array was constructed using induced current elimination decoupling, and the coil and network were validated in benchtop measurements, B1+ mapping scans, and an accelerated spiral excitation experiment. RESULTS The developed attenuators came within 0.08 dB of the desired attenuations, and reflection coefficients were -22 dB or better. The simulation demonstrated that up to 3× more power was dissipated in the network when coils were poorly isolated (-9.6 dB), versus well-isolated (-31 dB). Compared to split circularly-polarized coil combinations, the additional degrees of freedom provided by the array compression network led to 54% lower squared excitation error in the spiral experiment. CONCLUSION Array-compressed parallel transmission was successfully implemented in a hardware system. Further work is needed to develop remote network tuning and to minimize network power dissipation. Magn Reson Med 75:2545-2552, 2016. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Xinqiang Yan
- Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.,Department of Radiology, Vanderbilt University, Nashville, Tennessee, USA
| | - Zhipeng Cao
- Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.,Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
| | - William A Grissom
- Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.,Department of Radiology, Vanderbilt University, Nashville, Tennessee, USA.,Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.,Department of Electrical Engineering, Vanderbilt University, Nashville, Tennessee, USA
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114
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Bisdas S, Chadzynski GL, Braun C, Schittenhelm J, Skardelly M, Hagberg GE, Ethofer T, Pohmann R, Shajan G, Engelmann J, Tabatabai G, Ziemann U, Ernemann U, Scheffler K. MR spectroscopy for in vivo assessment of the oncometabolite 2-hydroxyglutarate and its effects on cellular metabolism in human brain gliomas at 9.4T. J Magn Reson Imaging 2016; 44:823-33. [PMID: 26970248 DOI: 10.1002/jmri.25221] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 02/22/2016] [Indexed: 12/27/2022] Open
Abstract
PURPOSE To examine in vivo metabolic alterations in the isocitrate dehydrogenase (IDH) mutated gliomas using magnetic resonance spectroscopy (MRS) at magnetic field 9.4T. MATERIALS AND METHODS Spectra were acquired with a 9.4T whole-body scanner with the use of a custom-built head coil (16 channel transmit and 31 channel receive). A modified stimulated echo acquisition mode (STEAM) sequence was used for localization. Eighteen patients with brain tumors of probable glial origin participated in this study. The study was performed in accordance with the guidelines of the local Ethics Committee. RESULTS The increased spectral resolution allowed us to directly address metabolic alterations caused by the specific pathophysiology of IDH mutations including the presence of the oncometabolite 2-hydroxglutarate (2HG) and a significant decrease of the pooled glutamate and glutamine (20%, P = 0.024), which probably reflects an attempt to replenish α-ketoglutarate lost by conversion to 2HG. We also observed significantly reduced glutathione (GSH) levels (39%, P = 0.019), which could be similarly caused by depletion of dihydronicotinamide-adenine dinucleotide phosphate (NADPH) during this conversion in IDH mutant gliomas. CONCLUSION We demonstrate that MRS at 9.4T provides a noninvasive measure of 2HG in vivo, which may be used for therapy planning and prognostication, and may provide insights into related pathophysiologic metabolic alterations associated with IDH mutations. J. MAGN. RESON. IMAGING 2016;44:823-833.
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Affiliation(s)
- Sotirios Bisdas
- Department of Neuroradiology, Eberhard-Karls University Tübingen, Tübingen, Germany.,Department of Neuroradiology, National Hospital for Neurology and Neurosurgery, University College London Hospitals, London, UK.,Center for CNS tumors, Comprehensive Cancer Center Tübingen-Stuttgart, University Hospital Tübingen, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Grzegorz L Chadzynski
- Department of Biomedical Magnetic Resonance, Eberhard-Karls University Tübingen, Tübingen, Germany. .,High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.
| | - Christian Braun
- Center for CNS tumors, Comprehensive Cancer Center Tübingen-Stuttgart, University Hospital Tübingen, Eberhard Karls University Tübingen, Tübingen, Germany.,Department of Neurology & Stroke, Hertie Institute for Clinical Brain Research, Eberhard-Karls University Tübingen, Tübingen, Germany.,Interdisciplinary Division of Neuro-Oncology, University Hospital Tübingen, Hertie Institute for Clinical Brain Research, Eberahrd Karls University, Tübingen, Germany
| | - Jens Schittenhelm
- Center for CNS tumors, Comprehensive Cancer Center Tübingen-Stuttgart, University Hospital Tübingen, Eberhard Karls University Tübingen, Tübingen, Germany.,Interdisciplinary Division of Neuro-Oncology, University Hospital Tübingen, Hertie Institute for Clinical Brain Research, Eberahrd Karls University, Tübingen, Germany.,Department of Neuropathology, Eberhard-Karls University Tübingen, Tübingen, Germany.,Center for Personalized Medicine, Eberhard Karls University, Tübingen, Germany
| | - Marco Skardelly
- Center for CNS tumors, Comprehensive Cancer Center Tübingen-Stuttgart, University Hospital Tübingen, Eberhard Karls University Tübingen, Tübingen, Germany.,Interdisciplinary Division of Neuro-Oncology, University Hospital Tübingen, Hertie Institute for Clinical Brain Research, Eberahrd Karls University, Tübingen, Germany.,Center for Personalized Medicine, Eberhard Karls University, Tübingen, Germany.,Department of Neurosurgery, Eberhard-Karls University Tübingen, Tübingen, Germany
| | - Gisela E Hagberg
- Department of Biomedical Magnetic Resonance, Eberhard-Karls University Tübingen, Tübingen, Germany.,High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Thomas Ethofer
- Department of Biomedical Magnetic Resonance, Eberhard-Karls University Tübingen, Tübingen, Germany.,Clinic for Psychiatry and Psychotherapy, Eberhard-Karls University Tübingen, Tübingen, Germany
| | - Rolf Pohmann
- High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - G Shajan
- High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Jörn Engelmann
- Department of Biomedical Magnetic Resonance, Eberhard-Karls University Tübingen, Tübingen, Germany.,High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Ghazaleh Tabatabai
- Center for CNS tumors, Comprehensive Cancer Center Tübingen-Stuttgart, University Hospital Tübingen, Eberhard Karls University Tübingen, Tübingen, Germany.,Department of Neurology & Stroke, Hertie Institute for Clinical Brain Research, Eberhard-Karls University Tübingen, Tübingen, Germany.,Interdisciplinary Division of Neuro-Oncology, University Hospital Tübingen, Hertie Institute for Clinical Brain Research, Eberahrd Karls University, Tübingen, Germany.,Center for Personalized Medicine, Eberhard Karls University, Tübingen, Germany.,German Cancer Consortium (DKTK), DKFZ partner site Tübingen, Tübingen, Germany
| | - Ulf Ziemann
- Center for CNS tumors, Comprehensive Cancer Center Tübingen-Stuttgart, University Hospital Tübingen, Eberhard Karls University Tübingen, Tübingen, Germany.,Department of Neurology & Stroke, Hertie Institute for Clinical Brain Research, Eberhard-Karls University Tübingen, Tübingen, Germany.,Center for Personalized Medicine, Eberhard Karls University, Tübingen, Germany
| | - Ulrike Ernemann
- Department of Neuroradiology, Eberhard-Karls University Tübingen, Tübingen, Germany.,Center for CNS tumors, Comprehensive Cancer Center Tübingen-Stuttgart, University Hospital Tübingen, Eberhard Karls University Tübingen, Tübingen, Germany.,Center for Personalized Medicine, Eberhard Karls University, Tübingen, Germany
| | - Klaus Scheffler
- Department of Biomedical Magnetic Resonance, Eberhard-Karls University Tübingen, Tübingen, Germany.,High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
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115
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Mirkes C, Shajan G, Chadzynski G, Buckenmaier K, Bender B, Scheffler K. (31)P CSI of the human brain in healthy subjects and tumor patients at 9.4 T with a three-layered multi-nuclear coil: initial results. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2016; 29:579-89. [PMID: 26811174 DOI: 10.1007/s10334-016-0524-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Revised: 12/20/2015] [Accepted: 01/04/2016] [Indexed: 12/15/2022]
Abstract
OBJECTIVE Investigation of the feasibility and performance of phosphorus ((31)P) magnetic resonance spectroscopic imaging (MRSI) at 9.4 T with a three-layered phosphorus/proton coil in human normal brain tissue and tumor. MATERIALS AND METHODS A multi-channel (31)P coil was designed to enable MRSI of the entire human brain. The performance of the coil was evaluated by means of electromagnetic field simulations and actual measurements. A 3D chemical shift imaging approach with a variable repetition time and flip angle was used to increase the achievable signal-to-noise ratio of the acquired (31)P spectra. The impact of the resulting k-space modulation was investigated by simulations. Three tumor patients and three healthy volunteers were scanned and differences between spectra from healthy and cancerous tissue were evaluated qualitatively. RESULTS The high sensitivity provided by the 27-channel (31)P coil allowed acquiring CSI data in 22 min with a nominal voxel size of 15 × 15 × 15 mm(3). Shimming and anatomical localization could be performed with the integrated four-channel proton dipole array. The amplitudes of the phosphodiesters and phosphoethanolamine appeared reduced in tumorous tissue for all three patients. A neutral or slightly alkaline pH was measured within the brain lesions. CONCLUSION These initial results demonstrate that (31)P 3D CSI is feasible at 9.4 T and could be performed successfully in healthy subjects and tumor patients in under 30 min.
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Affiliation(s)
- Christian Mirkes
- Department for Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany. .,High-Field MR Center, Max Planck Institute for Biological Cybernetics, Spemannstr. 41, 72076, Tübingen, Germany.
| | - Gunamony Shajan
- High-Field MR Center, Max Planck Institute for Biological Cybernetics, Spemannstr. 41, 72076, Tübingen, Germany
| | - Grzegorz Chadzynski
- Department for Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany.,High-Field MR Center, Max Planck Institute for Biological Cybernetics, Spemannstr. 41, 72076, Tübingen, Germany
| | - Kai Buckenmaier
- High-Field MR Center, Max Planck Institute for Biological Cybernetics, Spemannstr. 41, 72076, Tübingen, Germany
| | - Benjamin Bender
- Department of Diagnostic and Interventional Neuroradiology, University Hospital Tübingen, Tübingen, Germany
| | - Klaus Scheffler
- Department for Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany.,High-Field MR Center, Max Planck Institute for Biological Cybernetics, Spemannstr. 41, 72076, Tübingen, Germany
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116
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Brown R, Lakshmanan K, Madelin G, Parasoglou P. A nested phosphorus and proton coil array for brain magnetic resonance imaging and spectroscopy. Neuroimage 2016; 124:602-611. [PMID: 26375209 PMCID: PMC4651763 DOI: 10.1016/j.neuroimage.2015.08.066] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2015] [Revised: 08/04/2015] [Accepted: 08/28/2015] [Indexed: 02/02/2023] Open
Abstract
A dual-nuclei radiofrequency coil array was constructed for phosphorus and proton magnetic resonance imaging and spectroscopy of the human brain at 7T. An eight-channel transceive degenerate birdcage phosphorus module was implemented to provide whole-brain coverage and significant sensitivity improvement over a standard dual-tuned loop coil. A nested eight-channel proton module provided adequate sensitivity for anatomical localization without substantially sacrificing performance on the phosphorus module. The developed array enabled phosphorus spectroscopy, a saturation transfer technique to calculate the global creatine kinase forward reaction rate, and single-metabolite whole-brain imaging with 1.4cm nominal isotropic resolution in 15min (2.3cm actual resolution), while additionally enabling 1mm isotropic proton imaging. This study demonstrates that a multi-channel array can be utilized for phosphorus and proton applications with improved coverage and/or sensitivity over traditional single-channel coils. The efficient multi-channel coil array, time-efficient pulse sequences, and the enhanced signal strength available at ultra-high fields can be combined to allow volumetric assessment of the brain and could provide new insights into the underlying energy metabolism impairment in several neurodegenerative conditions, such as Alzheimer's and Parkinson's diseases, as well as mental disorders such as schizophrenia.
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Affiliation(s)
- Ryan Brown
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA; Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, NY, USA; NYU WIRELESS, Polytechnic Institute of New York University, 2 Metro Tech Center, Brooklyn, NY 11201, USA.
| | - Karthik Lakshmanan
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA; Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, NY, USA
| | - Guillaume Madelin
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA; Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, NY, USA
| | - Prodromos Parasoglou
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, USA; Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, NY, USA
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117
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Lee SK, Mathieu JB, Graziani D, Piel J, Budesheim E, Fiveland E, Hardy CJ, Tan ET, Amm B, Foo TKF, Bernstein MA, Huston J, Shu Y, Schenck JF. Peripheral nerve stimulation characteristics of an asymmetric head-only gradient coil compatible with a high-channel-count receiver array. Magn Reson Med 2015; 76:1939-1950. [PMID: 26628078 DOI: 10.1002/mrm.26044] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Revised: 10/18/2015] [Accepted: 10/20/2015] [Indexed: 11/07/2022]
Abstract
PURPOSE To characterize peripheral nerve stimulation (PNS) of an asymmetric head-only gradient coil that is compatible with a commercial high-channel-count receive-only array. METHODS Two prototypes of an asymmetric head-only gradient coil set with a 42-cm inner diameter were constructed for brain imaging at 3T with maximum performance specifications of up to 85 mT/m and 708 T/m/s. Tests were performed in 24 volunteers to measure PNS thresholds with the transverse (x = left-right; y = anterior-posterior [A/P]) gradient coils of both prototypes. Fourteen of these 24 volunteers were also tested for the z-gradient PNS in the second prototype and were scanned with high-slew-rate echo planar imaging (EPI) immediately after the PNS tests. RESULTS For both prototypes, the y-gradient PNS threshold was markedly higher than the x-gradient threshold. The z-gradient threshold was intermediate between those for the x- and y-coils. Of the 24 volunteers, only two experienced y-gradient PNS at 80 mT/m and 500 T/m/s. All volunteers underwent the EPI scan without PNS when the readout direction was set to A/P. CONCLUSION Measured PNS characteristics of asymmetric head-only gradient coil prototypes indicate that such coils, especially in the A/P direction, can be used for fast EPI readout in high-performance neuroimaging scans with substantially reduced PNS concerns compared with conventional whole body gradient coils. Magn Reson Med 76:1939-1950, 2016. © 2015 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
| | | | | | - Joseph Piel
- GE Global Research Center, Niskayuna, New York, USA
| | | | | | | | - Ek Tsoon Tan
- GE Global Research Center, Niskayuna, New York, USA
| | - Bruce Amm
- GE Global Research Center, Niskayuna, New York, USA
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118
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Avdievich NI, Giapitzakis IA, Henning A. Novel splittable N-Tx/2N-Rx transceiver phased array to optimize both signal-to-noise ratio and transmit efficiency at 9.4T. Magn Reson Med 2015; 76:1621-1628. [DOI: 10.1002/mrm.26051] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Revised: 09/28/2015] [Accepted: 10/23/2015] [Indexed: 11/07/2022]
Affiliation(s)
- Nikolai I. Avdievich
- High-Field MR Center, Max Planck Institute for Biological Cybernetics; Tübingen Germany
| | | | - Anke Henning
- High-Field MR Center, Max Planck Institute for Biological Cybernetics; Tübingen Germany
- Institute for Biomedical Engineering, UZH and ETH Zurich; Zurich Switzerland
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119
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Yan X, Xue R, Zhang X. Closely-spaced double-row microstrip RF arrays for parallel MR imaging at ultrahigh fields. APPLIED MAGNETIC RESONANCE 2015; 46:1239-1248. [PMID: 26508810 PMCID: PMC4617305 DOI: 10.1007/s00723-015-0712-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Radiofrequency (RF) coil arrays with high count of elements, e.g., closely-spaced multi-row arrays, exhibit superior parallel imaging performance in MRI. However, it is technically challenging and time-consuming to build multi-row arrays due to complex coupling issues. This paper presents a novel and simple method for closely-spaced multi-row RF array designs. Induced current elimination (ICE) decoupling method has shown the capability of reducing coupling between microstrip elements from different rows. In this study, its capability for decoupling array elements from the same row was investigated and validated by bench tests, with an isolation improvement from -8.9 dB to -20.7 dB. Based on this feature, a closely-spaced double-row microstrip array with 16 elements was built at 7T. S21 between any two elements of the 16-channel closely-spaced was better than -14 dB. In addition, its feasibility and performance was validated by MRI experiments. No significant image reconstruction- related noise amplifications were observed for parallel imaging even when reduced factor (R) achieves 4. The experimental results demonstrated that the proposed design might be a simple and efficient approach in fabricating closely-spaced multi-row RF arrays.
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Affiliation(s)
- Xinqiang Yan
- Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
- Beijing Engineering Research Center of Radiographic Techniques and Equipment, Beijing 100049, China
| | - Rong Xue
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Xiaoliang Zhang
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California 94158, USA
- UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, California 94158, USA
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120
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Bluemink JJ, Raaijmakers AJE, Koning W, Andreychenko A, Rivera DS, Luijten PR, Klomp DWJ, van den Berg CAT. Dielectric waveguides for ultrahigh field magnetic resonance imaging. Magn Reson Med 2015; 76:1314-24. [DOI: 10.1002/mrm.26007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Revised: 09/11/2015] [Accepted: 09/12/2015] [Indexed: 11/09/2022]
Affiliation(s)
- Johanna J. Bluemink
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Alexander J. E. Raaijmakers
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Wouter Koning
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Anna Andreychenko
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Debra S. Rivera
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Peter R. Luijten
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Dennis W. J. Klomp
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Cornelis A. T. van den Berg
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
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121
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Barth M, Breuer F, Koopmans PJ, Norris DG, Poser BA. Simultaneous multislice (SMS) imaging techniques. Magn Reson Med 2015; 75:63-81. [PMID: 26308571 PMCID: PMC4915494 DOI: 10.1002/mrm.25897] [Citation(s) in RCA: 357] [Impact Index Per Article: 39.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 07/25/2015] [Accepted: 07/27/2015] [Indexed: 12/25/2022]
Abstract
Simultaneous multislice imaging (SMS) using parallel image reconstruction has rapidly advanced to become a major imaging technique. The primary benefit is an acceleration in data acquisition that is equal to the number of simultaneously excited slices. Unlike in‐plane parallel imaging this can have only a marginal intrinsic signal‐to‐noise ratio penalty, and the full acceleration is attainable at fixed echo time, as is required for many echo planar imaging applications. Furthermore, for some implementations SMS techniques can reduce radiofrequency (RF) power deposition. In this review the current state of the art of SMS imaging is presented. In the Introduction, a historical overview is given of the history of SMS excitation in MRI. The following section on RF pulses gives both the theoretical background and practical application. The section on encoding and reconstruction shows how the collapsed multislice images can be disentangled by means of the transmitter pulse phase, gradient pulses, and most importantly using multichannel receiver coils. The relationship between classic parallel imaging techniques and SMS reconstruction methods is explored. The subsequent section describes the practical implementation, including the acquisition of reference data, and slice cross‐talk. Published applications of SMS imaging are then reviewed, and the article concludes with an outlook and perspective of SMS imaging. Magn Reson Med 75:63–81, 2016. © 2015 The Authors. Magnetic Resonance in Medicine Published by Wiley Periodicals, Inc. on behalf of International Society of Medicine in Resonance.
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Affiliation(s)
- Markus Barth
- Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia.,Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands
| | - Felix Breuer
- Research Center Magnetic Resonance Bavaria (MRB), Würzburg, Germany
| | - Peter J Koopmans
- Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands.,FMRIB Centre, University of Oxford, Oxford, United Kingdom
| | - David G Norris
- Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands.,Erwin L. Hahn Institute for Magnetic Resonance Imaging, UNESCO-Weltkulturerbe Zollverein, Leitstand Kokerei Zollverein, Essen, Germany.,MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands
| | - Benedikt A Poser
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.,Maastricht Brain Imaging Center (M-BIC), Maastricht University, Maastricht, The Netherlands
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122
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Scheffler K, Ehses P. High-resolution mapping of neuronal activation with balanced SSFP at 9.4 tesla. Magn Reson Med 2015; 76:163-71. [DOI: 10.1002/mrm.25890] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Revised: 07/10/2015] [Accepted: 07/24/2015] [Indexed: 11/10/2022]
Affiliation(s)
- Klaus Scheffler
- Department for Biomedical Magnetic Resonance; University of Tübingen; Tübingen Germany
- High-Field MR Center, Max Planck Institute for Biological Cybernetics; Tübingen Germany
| | - Philipp Ehses
- Department for Biomedical Magnetic Resonance; University of Tübingen; Tübingen Germany
- High-Field MR Center, Max Planck Institute for Biological Cybernetics; Tübingen Germany
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123
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Graessl A, Ruehle A, Waiczies H, Resetar A, Hoffmann SH, Rieger J, Wetterling F, Winter L, Nagel AM, Niendorf T. Sodium MRI of the human heart at 7.0 T: preliminary results. NMR IN BIOMEDICINE 2015; 29:1131-44. [PMID: 26082025 DOI: 10.1002/nbm.3290] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Revised: 02/25/2015] [Accepted: 02/25/2015] [Indexed: 05/05/2023]
Abstract
The objective of this work was to examine the feasibility of three-dimensional (3D) and whole heart coverage (23)Na cardiac MRI at 7.0 T including single-cardiac-phase and cinematic (cine) regimes. A four-channel transceiver RF coil array tailored for (23)Na MRI of the heart at 7.0 T (f = 78.5 MHz) is proposed. An integrated bow-tie antenna building block is used for (1)H MR to support shimming, localization and planning in a clinical workflow. Signal absorption rate simulations and assessment of RF power deposition were performed to meet the RF safety requirements. (23) Na cardiac MR was conducted in an in vivo feasibility study. 3D gradient echo (GRE) imaging in conjunction with Cartesian phase encoding (total acquisition time T(AQ) = 6 min 16 s) and whole heart coverage imaging employing a density-adapted 3D radial acquisition technique (T(AQ) = 18 min 20 s) were used. For 3D GRE-based (23)Na MRI, acquisition of standard views of the heart using a nominal in-plane resolution of (5.0 × 5.0) mm(2) and a slice thickness of 15 mm were feasible. For whole heart coverage 3D density-adapted radial (23)Na acquisitions a nominal isotropic spatial resolution of 6 mm was accomplished. This improvement versus 3D conventional GRE acquisitions reduced partial volume effects along the slice direction and enabled retrospective image reconstruction of standard or arbitrary views of the heart. Sodium cine imaging capabilities were achieved with the proposed RF coil configuration in conjunction with 3D radial acquisitions and cardiac gating. Cardiac-gated reconstruction provided an enhancement in blood-myocardium contrast of 20% versus the same data reconstructed without cardiac gating. The proposed transceiver array enables (23)Na MR of the human heart at 7.0 T within clinical acceptable scan times. This capability is in positive alignment with the needs of explorations that are designed to examine the potential of (23)Na MRI for the assessment of cardiovascular and metabolic diseases.
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Affiliation(s)
- Andreas Graessl
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Anjuli Ruehle
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | | | - Ana Resetar
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Stefan H Hoffmann
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | | | | | - Lukas Winter
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Armin M Nagel
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
- Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max-Delbrück Center for Molecular Medicine, Berlin, Germany
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124
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Connell IRO, Gilbert KM, Abou-Khousa MA, Menon RS. MRI RF array decoupling method with magnetic wall distributed filters. IEEE TRANSACTIONS ON MEDICAL IMAGING 2015; 34:825-835. [PMID: 25838388 DOI: 10.1109/tmi.2014.2378695] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Multi-channel radio-frequency (RF) transmit coil arrays have been developed to mitigate many of the RF challenges associated with ultra-high field ( ≥ 7T) magnetic resonance imaging (MRI). These arrays can be used for parallel RF transmission to produce spatially tailored RF excitation over the field of view. However, the realization of such arrays remains a challenge due to significant reactive interaction between the array coils, i.e., mutual coupling. In this paper, a novel bandstop filter ("magnetic wall") is used in an MRI RF transmit array to decouple individual coils. The proposed decoupling method is inspired by periodic resonator designs commonly used in frequency selective surfaces and is used as a distributed RF filter to suppress the transmission of RF energy between coils in an array. The decoupling of the magnetic wall (MW) is analyzed in terms of equivalent circuits that include terms for both magnetic and electric coupling for an arbitrary number of MW resonant conductors. Both frequency-and time-domain full-wave simulations were performed to analyze a specific MW structure. The performance of the proposed method is experimentally validated for both first-order coupling and higher-order coupling with a three-coil 7T array setup. Analysis and measurements confirm that the rejection band of the MW can be tuned to provide high isolation in the presence of cross coupling between RF array coils.
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125
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Pohmann R, Speck O, Scheffler K. Signal-to-noise ratio and MR tissue parameters in human brain imaging at 3, 7, and 9.4 tesla using current receive coil arrays. Magn Reson Med 2015; 75:801-9. [PMID: 25820458 DOI: 10.1002/mrm.25677] [Citation(s) in RCA: 227] [Impact Index Per Article: 25.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2014] [Revised: 02/04/2015] [Accepted: 02/09/2015] [Indexed: 12/18/2022]
Abstract
PURPOSE Relaxation times, transmit homogeneity, signal-to-noise ratio (SNR) and parallel imaging g-factor were determined in the human brain at 3T, 7T, and 9.4T, using standard, tight-fitting coil arrays. METHODS The same human subjects were scanned at all three field strengths, using identical sequence parameters and similar 31- or 32-channel receive coil arrays. The SNR of three-dimensional (3D) gradient echo images was determined using a multiple replica approach and corrected with measured flip angle and T2 (*) distributions and the T1 of white matter to obtain the intrinsic SNR. The g-factor maps were derived from 3D gradient echo images with several GRAPPA accelerations. RESULTS As expected, T1 values increased, T2 (*) decreased and the B1 -homogeneity deteriorated with increasing field. The SNR showed a distinctly supralinear increase with field strength by a factor of 3.10 ± 0.20 from 3T to 7T, and 1.76 ± 0.13 from 7T to 9.4T over the entire cerebrum. The g-factors did not show the expected decrease, indicating a dominating role of coil design. CONCLUSION In standard experimental conditions, SNR increased supralinearly with field strength (SNR ∼ B0 (1.65) ). To take full advantage of this gain, the deteriorating B1 -homogeneity and the decreasing T2 (*) have to be overcome.
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Affiliation(s)
- Rolf Pohmann
- Max Planck Institute for Biological Cybernetics, Magnetic Resonance Center, Tübingen, Germany
| | - Oliver Speck
- Department of Biomedical Magnetic Resonance, Otto-von-Guericke University Magdeburg, Germany.,German Centre for Neurodegenerative Diseases (DZNE), Site Magdeburg, Germany.,Leibniz Institute for Neurobiology, Magdeburg, Germany.,Center for Behavioral Brain Sciences, Magdeburg, Germany
| | - Klaus Scheffler
- Max Planck Institute for Biological Cybernetics, Magnetic Resonance Center, Tübingen, Germany.,Department for Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany
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126
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Hoffmann J, Mirkes C, Shajan G, Scheffler K, Pohmann R. Combination of a multimode antenna and TIAMO for traveling-wave imaging at 9.4 Tesla. Magn Reson Med 2015; 75:452-62. [PMID: 25732895 DOI: 10.1002/mrm.25614] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2014] [Revised: 12/15/2014] [Accepted: 12/18/2014] [Indexed: 11/09/2022]
Abstract
PURPOSE To investigate the performance of a multimode antenna combined with time-interleaved acquisition of modes (TIAMO) for improved (1)H image homogeneity as compared to conventional traveling-wave imaging in the human brain at 9.4 Tesla (T). METHODS An adjustable three-port antenna was built to stimulate the propagation of three basic waveguide modes within a 9.4 T scanner bore. For TIAMO, two time-interleaved acquisitions using different linear combinations of these modes were optimized to achieve a homogeneous rooted sum-of-squares combination of their B1+ patterns ( B1,RSS+). The antenna's transmit and receive performance, as well as local specific absorption rate, were analyzed using experiments and numerical simulations. RESULTS The optimized TIAMO B1,RSS+ combination was superior to radiofrequency shimming. Across the entire brain, it improved the homogeneity of the excitation field by a factor of two and its maximum-to-minimum ratio by almost a factor of five as compared to the circularly polarized mode. The two-fold increase in "virtual" receive channels enhanced the parallel imaging performance and enabled the use of higher acceleration factors. CONCLUSION Despite the limited number of channels, a remote three-port antenna combined with TIAMO represents an easily implementable setup to achieve void-free (1)H images from the entire brain at 9.4 T, which can be used for anatomical localization and B0 shimming.
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Affiliation(s)
- Jens Hoffmann
- High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.,Graduate School of Neural and Behavioural Sciences, Tübingen, Germany
| | - Christian Mirkes
- High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.,Department for Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany
| | - G Shajan
- High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Klaus Scheffler
- High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.,Department for Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany
| | - Rolf Pohmann
- High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
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127
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Yan X, Pedersen JO, Wei L, Zhang X, Xue R. Multichannel Double-Row Transmission Line Array for Human MR Imaging at Ultrahigh Fields. IEEE Trans Biomed Eng 2015; 62:1652-9. [PMID: 25706499 DOI: 10.1109/tbme.2015.2401976] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
OBJECTIVE In microstrip transmission line (MTL) transmit/receive (transceive) arrays used for ultrahigh field MRI, the array length is often constrained by the required resonant frequency, limiting the image coverage. The purpose of this study is to increase the imaging coverage and also improve its parallel imaging capability by utilizing a double-row design. METHODS A 16-channel double-row MTL transceive array was designed, constructed, and tested for human head imaging at 7 T. Array elements between two rows were decoupled by using the induced current elimination or magnetic wall decoupling technique. In vivo human head images were acquired, and g-factor results were calculated to evaluate the performance of this double-row array. RESULTS Testing results showed that all coil elements were well decoupled with a better than -18 dB transmission coefficient between any two elements. The double-row array improves the imaging quality of the lower portion of the human head, and has low g-factors even at high acceleration rates. CONCLUSION Compared with a regular single-row MTL array, the double-row array demonstrated a larger imaging coverage along the z-direction with improved parallel imaging capability. SIGNIFICANCE The proposed technique is particularly suitable for the design of large-sized transceive arrays with large channel counts, which ultimately benefits the imaging performance in human MRI.
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128
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Ehses P, Bause J, Shajan G, Scheffler K. Efficient generation of T2*-weighted contrast by interslice echo-shifting for human functional and anatomical imaging at 9.4 Tesla. Magn Reson Med 2014; 74:1698-704. [DOI: 10.1002/mrm.25570] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Revised: 10/21/2014] [Accepted: 11/02/2014] [Indexed: 11/10/2022]
Affiliation(s)
- Philipp Ehses
- Department of Biomedical Magnetic Resonance; University of Tübingen; Tübingen Germany
- High-Field Magnetic Resonance Center; Max Planck Institute for Biological Cybernetics; Tübingen Germany
| | - Jonas Bause
- High-Field Magnetic Resonance Center; Max Planck Institute for Biological Cybernetics; Tübingen Germany
| | - G. Shajan
- High-Field Magnetic Resonance Center; Max Planck Institute for Biological Cybernetics; Tübingen Germany
| | - Klaus Scheffler
- Department of Biomedical Magnetic Resonance; University of Tübingen; Tübingen Germany
- High-Field Magnetic Resonance Center; Max Planck Institute for Biological Cybernetics; Tübingen Germany
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129
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Chadzynski GL, Pohmann R, Shajan G, Kolb R, Bisdas S, Klose U, Scheffler K. In vivo proton magnetic resonance spectroscopic imaging of the healthy human brain at 9.4 T: initial experience. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2014; 28:239-49. [PMID: 25248946 DOI: 10.1007/s10334-014-0460-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2014] [Revised: 08/22/2014] [Accepted: 08/22/2014] [Indexed: 11/26/2022]
Abstract
OBJECT In this study, the feasibility of in vivo proton magnetic resonance spectroscopic imaging ((1)H MRSI) of the healthy human brain at a field strength of 9.4 T, using conventional acquisition techniques, is examined and the initial experience is summarized. MATERIALS AND METHODS MRSI measurements were performed on a 9.4 T MR scanner (Siemens, Erlangen, Germany) equipped with head-only gradient insert (AC84, Siemens) and custom-developed, 8-channel transmit/24-channel receive, and 16-channel transmit/31-channel receive coils. Spectra were acquired from the superior part of the human brain with a modified STEAM sequence. Spectral quantification was done with LCModel software. RESULTS Reasonable quality and signal-to-noise ratio of the acquired spectra allowed reliable quantification of 12 metabolites (Cramer-Rao lower bounds < 20 %), some of which may be difficult to quantify at field strengths below 7 T due to overlapping resonances or low concentrations. CONCLUSION While further developments are necessary to minimize chemical shift displacement and homogeneity of the transmit field, it is demonstrated that in vivo (1)H MRSI at a field strength of 9.4 T is possible. However, further studies applying up-to-date techniques to overcome high-field specific problems are needed in order to assess the potential gain in sensitivity that may be offered by MRSI at 9.4 T.
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Affiliation(s)
- Grzegorz L Chadzynski
- Biomedical Magnetic Resonance, University Hospital Tuebingen, Hoppe-Seyler-Str. 3, 72076, Tübingen, Germany,
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Heule R, Bär P, Mirkes C, Scheffler K, Trattnig S, Bieri O. Triple-echo steady-state T2 relaxometry of the human brain at high to ultra-high fields. NMR IN BIOMEDICINE 2014; 27:1037-1045. [PMID: 24986791 DOI: 10.1002/nbm.3152] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Revised: 04/23/2014] [Accepted: 05/21/2014] [Indexed: 06/03/2023]
Abstract
Quantitative MRI techniques, such as T2 relaxometry, have demonstrated the potential to detect changes in the tissue microstructure of the human brain with higher specificity to the underlying pathology than in conventional morphological imaging. At high to ultra-high field strengths, quantitative MR-based tissue characterization benefits from the higher signal-to-noise ratio traded for either improved resolution or reduced scan time, but is impaired by severe static (B0 ) and transmit (B1 ) field heterogeneities. The objective of this study was to derive a robust relaxometry technique for fast T2 mapping of the human brain at high to ultra-high fields, which is highly insensitive to B0 and B1 field variations. The proposed method relies on a recently presented three-dimensional (3D) triple-echo steady-state (TESS) imaging approach that has proven to be suitable for fast intrinsically B1 -insensitive T2 relaxometry of rigid targets. In this work, 3D TESS imaging is adapted for rapid high- to ultra-high-field two-dimensional (2D) acquisitions. The achieved short scan times of 2D TESS measurements reduce motion sensitivity and make TESS-based T2 quantification feasible in the brain. After validation in vitro and in vivo at 3 T, T2 maps of the human brain were obtained at 7 and 9.4 T. Excellent agreement between TESS-based T2 measurements and reference single-echo spin-echo data was found in vitro and in vivo at 3 T, and T2 relaxometry based on TESS imaging was proven to be feasible and reliable in the human brain at 7 and 9.4 T. Although prominent B0 and B1 field variations occur at ultra-high fields, the T2 maps obtained show no B0 - or B1 -related degradations. In conclusion, as a result of the observed robustness, TESS T2 may emerge as a valuable measure for the early diagnosis and progression monitoring of brain diseases in high-resolution 2D acquisitions at high to ultra-high fields.
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Affiliation(s)
- Rahel Heule
- Division of Radiological Physics, Department of Radiology, University of Basel Hospital, Basel, Switzerland
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131
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Shao Y, Zeng P, Wang S. Statistical simulation of SAR variability with geometric and tissue property changes by using the unscented transform. Magn Reson Med 2014; 73:2357-62. [PMID: 25046818 DOI: 10.1002/mrm.25367] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Revised: 06/18/2014] [Accepted: 06/24/2014] [Indexed: 11/07/2022]
Abstract
PURPOSE The local specific absorption rate (SAR) is critical to the safety of radio frequency transmit coils. A statistical simulation approach is introduced to address the local SAR variability related to tissue property and geometric variations. METHODS The local SAR is modeled as the output of a nonlinear transformation with factors that may affect its value being treated as random input variables. Instead of using the Monte Carlo method with a large number of sample points, the unscented transform is applied with a small set of deterministic sample points. A sensitivity analysis is further performed to determine the significance of each input variable. Electromagnetic simulations are carried out by the finite-difference time-domain method implemented on graphic processing unit. RESULTS The local SAR variability of a 7 Tesla square loop coil for spine imaging and a 16-element brain imaging array as the result of tissue property and geometric changes were examined respectively. SAR limits were determined based on their means and standard deviations. CONCLUSION The proposed approach is efficient and general for the study of local SAR variability.
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Affiliation(s)
- Yu Shao
- Department of Electrical and Computer Engineering, Auburn University, Alabama, USA
| | - Peng Zeng
- Department of Mathematics and Statistics, Auburn University, Auburn, Alabama, USA
| | - Shumin Wang
- Department of Electrical and Computer Engineering, Auburn University, Alabama, USA
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133
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Multicenter Study of Subjective Acceptance During Magnetic Resonance Imaging at 7 and 9.4 T. Invest Radiol 2014; 49:249-59. [DOI: 10.1097/rli.0000000000000035] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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134
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Guérin B, Gebhardt M, Serano P, Adalsteinsson E, Hamm M, Pfeuffer J, Nistler J, Wald LL. Comparison of simulated parallel transmit body arrays at 3 T using excitation uniformity, global SAR, local SAR, and power efficiency metrics. Magn Reson Med 2014; 73:1137-50. [PMID: 24752979 DOI: 10.1002/mrm.25243] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Revised: 03/14/2014] [Accepted: 03/17/2014] [Indexed: 01/24/2023]
Abstract
PURPOSE We compare the performance of eight parallel transmit (pTx) body arrays with up to 32 channels and a standard birdcage design. Excitation uniformity, local specific absorption rate (SAR), global SAR, and power metrics are analyzed in the torso at 3 T for radiofrequency (RF)-shimming and 2-spoke excitations. METHODS We used a fast cosimulation strategy for field calculation in the presence of coupling between transmit channels. We designed spoke pulses using magnitude least squares optimization with explicit constraint of SAR and power and compared the performance of the different pTx coils using the L-curve method. RESULTS PTx arrays outperformed the conventional birdcage coil in all metrics except peak and average power efficiency. The presence of coupling exacerbated this power efficiency problem. At constant excitation fidelity, the pTx array with 24 channels arranged in three z-rows could decrease local SAR more than 4-fold (2-fold) for RF-shimming (2-spoke) compared to the birdcage coil for pulses of equal duration. Multi-row pTx coils had a marked performance advantage compared to single row designs, especially for coronal imaging. CONCLUSION PTx coils can simultaneously improve the excitation uniformity and reduce SAR compared to a birdcage coil when SAR metrics are explicitly constrained in the pulse design.
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Affiliation(s)
- Bastien Guérin
- Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
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