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Budé LMI, Steensma BR, Zivkovic I, Raaijmakers AJE. The coax monopole antenna: A flexible end-fed antenna for ultrahigh field transmit/receive arrays. Magn Reson Med 2024; 92:361-373. [PMID: 38376359 DOI: 10.1002/mrm.30036] [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: 08/01/2023] [Revised: 01/15/2024] [Accepted: 01/15/2024] [Indexed: 02/21/2024]
Abstract
PURPOSE The coax monopole antenna is presented for body imaging at 7 T. The antenna is fed at one end, eliminating the possibility of cable-coil coupling and simplifying cable routing. Additionally, its flexibility improves loading to the subject. METHODS Like the coax dipole antenna, an interruption in the shield of the coaxial cable allows the current to extend to the outside of the shield, generating a B1 + field. Matching is achieved using a single inductor at the distal side, and a cable trap enforces the desired antenna length. Finite difference time domain simulations are employed to optimize the design parameters. Phantom measurements are conducted to determine the antenna's B1 + efficiency and to find the S-parameters in straight and bent positions. Eight-channel simulations and measurements are performed for prostate imaging. RESULTS The optimal configuration is a length of 360 mm with a gap position of 40 mm. Simulation data show higher B1 + levels for the coax monopole (20% in the prostate), albeit with a 5% lower specific absorbance rate efficiency, compared to the fractionated dipole antenna. The S11 of the coax monopole exhibits remarkable robustness to loading changes. In vivo prostate imaging demonstrates B1 + levels of 10-14 μT with an input power of 8 × 800 W, which is comparable to the fractionated dipole antenna. High-quality images and acceptable coupling levels were achieved. CONCLUSION The coax monopole is a novel, flexible antenna for body imaging at 7 T. Its simple design incorporates a single inductor at the distal side to achieve matching, and one-sided feeding greatly simplifies cable routing.
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Affiliation(s)
- Lyanne M I Budé
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
- Department of Electrical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Bart R Steensma
- Division of Imaging and Oncology, UMC Utrecht, Utrecht, The Netherlands
| | - Irena Zivkovic
- Department of Electrical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Alexander J E Raaijmakers
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
- Division of Imaging and Oncology, UMC Utrecht, Utrecht, The Netherlands
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2
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Cap V, Rocha dos Santos VR, Repnin K, Červený D, Laistler E, Meyerspeer M, Frass-Kriegl R. Combining Dipole and Loop Coil Elements for 7 T Magnetic Resonance Studies of the Human Calf Muscle. SENSORS (BASEL, SWITZERLAND) 2024; 24:3309. [PMID: 38894105 PMCID: PMC11174775 DOI: 10.3390/s24113309] [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: 03/15/2024] [Revised: 04/26/2024] [Accepted: 05/17/2024] [Indexed: 06/21/2024]
Abstract
Combining proton and phosphorus magnetic resonance spectroscopy offers a unique opportunity to study the oxidative and glycolytic components of metabolism in working muscle. This paper presents a 7 T proton calf coil design that combines dipole and loop elements to achieve the high performance necessary for detecting metabolites with low abundance and restricted visibility, specifically lactate, while including the option of adding a phosphorus array. We investigated the transmit, receive, and parallel imaging performance of three transceiver dipoles with six pair-wise overlap-decoupled standard or twisted pair receive-only coils. With a higher SNR and more efficient transmission decoupling, standard loops outperformed twisted pair coils. The dipoles with standard loops provided a four-fold-higher image SNR than a multinuclear reference coil comprising two proton channels and 32% more than a commercially available 28-channel proton knee coil. The setup enabled up to three-fold acceleration in the right-left direction, with acceptable g-factors and no visible aliasing artefacts. Spectroscopic phantom measurements revealed a higher spectral SNR for lactate with the developed setup than with either reference coil and fewer restrictions in voxel placement due to improved transmit homogeneity. This paper presents a new use case for dipoles and highlights their advantages for the integration in multinuclear calf coils.
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Affiliation(s)
- Veronika Cap
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria
| | - Vasco Rafael Rocha dos Santos
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria
| | - Kostiantyn Repnin
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria
| | - David Červený
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria
- Institute for Clinical and Experimental Medicine, 140 21 Prague, Czech Republic
- Institute of Biophysics and Informatics, First Faculty of Medicine, Charles University, 121 08 Prague, Czech Republic
| | - Elmar Laistler
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria
| | - Martin Meyerspeer
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria
| | - Roberta Frass-Kriegl
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria
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3
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Nurzed B, Kuehne A, Aigner CS, Schmitter S, Niendorf T, Eigentler TW. Radiofrequency antenna concepts for human cardiac MR at 14.0 T. MAGMA (NEW YORK, N.Y.) 2023; 36:257-277. [PMID: 36920549 PMCID: PMC10140016 DOI: 10.1007/s10334-023-01075-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 02/23/2023] [Accepted: 02/27/2023] [Indexed: 04/28/2023]
Abstract
OBJECTIVE To examine the feasibility of human cardiac MR (CMR) at 14.0 T using high-density radiofrequency (RF) dipole transceiver arrays in conjunction with static and dynamic parallel transmission (pTx). MATERIALS AND METHODS RF arrays comprised of self-grounded bow-tie (SGBT) antennas, bow-tie (BT) antennas, or fractionated dipole (FD) antennas were used in this simulation study. Static and dynamic pTx were applied to enhance transmission field (B1+) uniformity and efficiency in the heart of the human voxel model. B1+ distribution and maximum specific absorption rate averaged over 10 g tissue (SAR10g) were examined at 7.0 T and 14.0 T. RESULTS At 14.0 T static pTx revealed a minimum B1+ROI efficiency of 0.91 μT/√kW (SGBT), 0.73 μT/√kW (BT), and 0.56 μT/√kW (FD) and maximum SAR10g of 4.24 W/kg, 1.45 W/kg, and 2.04 W/kg. Dynamic pTx with 8 kT points indicate a balance between B1+ROI homogeneity (coefficient of variation < 14%) and efficiency (minimum B1+ROI > 1.11 µT/√kW) at 14.0 T with a maximum SAR10g < 5.25 W/kg. DISCUSSION MRI of the human heart at 14.0 T is feasible from an electrodynamic and theoretical standpoint, provided that multi-channel high-density antennas are arranged accordingly. These findings provide a technical foundation for further explorations into CMR at 14.0 T.
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Affiliation(s)
- Bilguun Nurzed
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin Ultrahigh Field Facility (B.U.F.F.), Robert Rössle Strasse 10, 13125, Berlin, Germany
| | | | | | | | - Thoralf Niendorf
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin Ultrahigh Field Facility (B.U.F.F.), Robert Rössle Strasse 10, 13125, Berlin, Germany.
- MRI.TOOLS GmbH, Berlin, Germany.
- Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
| | - Thomas Wilhelm Eigentler
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin Ultrahigh Field Facility (B.U.F.F.), Robert Rössle Strasse 10, 13125, Berlin, Germany
- Chair of Medical Engineering, Technische Universität Berlin, Berlin, Germany
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4
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Terekhov M, Elabyad IA, Lohr D, Hofmann U, Schreiber LM. High-resolution imaging of the excised porcine heart at a whole-body 7 T MRI system using an 8Tx/16Rx pTx coil. MAGMA (NEW YORK, N.Y.) 2023; 36:279-293. [PMID: 37027119 PMCID: PMC10140105 DOI: 10.1007/s10334-023-01077-z] [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: 10/01/2022] [Revised: 03/09/2023] [Accepted: 03/14/2023] [Indexed: 04/28/2023]
Abstract
INTRODUCTION MRI of excised hearts at ultra-high field strengths ([Formula: see text]≥7 T) can provide high-resolution, high-fidelity ground truth data for biomedical studies, imaging science, and artificial intelligence. In this study, we demonstrate the capabilities of a custom-built, multiple-element transceiver array customized for high-resolution imaging of excised hearts. METHOD A dedicated 16-element transceiver loop array was implemented for operation in parallel transmit (pTx) mode (8Tx/16Rx) of a clinical whole-body 7 T MRI system. The initial adjustment of the array was performed using full-wave 3D-electromagnetic simulation with subsequent final fine-tuning on the bench. RESULTS We report the results of testing the implemented array in tissue-mimicking liquid phantoms and excised porcine hearts. The array demonstrated high efficiency of parallel transmits characteristics enabling efficient pTX-based B1+-shimming. CONCLUSION The receive sensitivity and parallel imaging capability of the dedicated coil were superior to that of a commercial 1Tx/32Rx head coil in both SNR and T2*-mapping. The array was successfully tested to acquire ultra-high-resolution (0.1 × 0.1 × 0.8 mm voxel) images of post-infarction scar tissue. High-resolution (isotropic 1.6 mm3 voxel) diffusion tensor imaging-based tractography provided high-resolution information about normal myocardial fiber orientation.
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Affiliation(s)
- Maxim Terekhov
- Comprehensive Heart Failure Center (CHFC), Department of Cardiovascular Imaging, University Hospital Würzburg, Am Schwarzenberg 15, 97078, Würzburg, Germany.
| | - Ibrahim A Elabyad
- Comprehensive Heart Failure Center (CHFC), Department of Cardiovascular Imaging, University Hospital Würzburg, Am Schwarzenberg 15, 97078, Würzburg, Germany
| | - David Lohr
- Comprehensive Heart Failure Center (CHFC), Department of Cardiovascular Imaging, University Hospital Würzburg, Am Schwarzenberg 15, 97078, Würzburg, Germany
| | - Ulrich Hofmann
- Department of Internal Medicine I / Cardiology, University Hospital Würzburg, Oberdürrbacher Straße 6, 97080, Würzburg, Germany
| | - Laura M Schreiber
- Comprehensive Heart Failure Center (CHFC), Department of Cardiovascular Imaging, University Hospital Würzburg, Am Schwarzenberg 15, 97078, Würzburg, Germany
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5
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Kikken MWI, Steensma BR, van den Berg CAT, Raaijmakers AJE. Multi-echo MR thermometry in the upper leg at 7 T using near-harmonic 2D reconstruction for initialization. Magn Reson Med 2023; 89:2347-2360. [PMID: 36688273 DOI: 10.1002/mrm.29591] [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: 09/09/2022] [Revised: 01/02/2023] [Accepted: 01/03/2023] [Indexed: 01/24/2023]
Abstract
PURPOSE The aim of this work is the development of a thermometry method to measure temperature increases in vivo, with a precision and accuracy sufficient for validation against thermal simulations. Such an MR thermometry model would be a valuable tool to get an indication on one of the major safety concerns in MR imaging: the tissue heating occurring due to radiofrequency (RF) exposure. To prevent excessive temperature rise, RF power deposition, expressed as specific absorption rate, cannot exceed predefined thresholds. Using these thresholds, MRI has demonstrated an extensive history of safe usage. Nevertheless, MR thermometry would be a valuable tool to address some of the unmet needs in the area of RF safety assessment, such as validation of specific absorption rate and thermal simulations, investigation of local peak temperatures during scanning, or temperature-based safety guidelines. METHODS The harmonic initialized model-based multi-echo approach is proposed. The method combines a previously published model-based multi-echo water/fat separated approach with an also previously published near-harmonic 2D reconstruction method. The method is tested on the human thigh with a multi-transmit array at 7 T, in three volunteers, and for several RF shims. RESULTS Precision and accuracy are improved considerably compared to a previous fat-referenced method (precision: 0.09 vs. 0.19°C). Comparison of measured temperature rise distributions to subject-specific simulated counterparts show good relative agreement for multiple RF shim settings. CONCLUSION The high precision shows promising potential for validation purposes and other RF safety applications.
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Affiliation(s)
- Mathijs W I Kikken
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Bart R Steensma
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Cornelis A T van den Berg
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.,Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Alexander J E Raaijmakers
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.,Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
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6
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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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7
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Zheng M, Gao Y, Quan Z, Zhang X. The design and evaluation of single-channel loopole coils at 7T MRI. Phys Med Biol 2022; 67. [DOI: 10.1088/1361-6560/ac8fdf] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2022] [Accepted: 09/06/2022] [Indexed: 11/12/2022]
Abstract
Abstract
Objective. Improving the local uniformity of
B
1
+
field for awake monkey brain magnetic resonance imaging (MRI) at ultra-high fields while facilitating convenient placement and fixation of MRI-compatible multimodal devices for neuroscience study, can eventually advance our understanding of the primate’s brain organization. Approach. A group of single-channel RF coils including conventional loop coils and loopole coils sharing the same size and shape were designed for comparison; their performance as the transmit coil was quantitatively evaluated through a series of numerical electromagnetic (EM) simulations, and further verified by using 7T MRI over a saline phantom and a monkey in vivo. Main results. Compared to conventional loop coils, the optimized loopole coil brought up to 23.5%
B
1
+
uniformity improvement for monkey brain imaging in EM simulations, and this performance was further verified over monkey brain imaging at 7T in vivo. Importantly, we have systematically explored the underlying mechanism regarding the relationship between loopole coils’ current density distribution and
B
1
+
uniformity, observing that it can be approximated as a sinusoidal curve. Significance. The proposed loopole coil design can improve the imaging quality in awake and behaving monkeys, thus benefiting advanced brain research at UHF.
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8
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Clément J, Tomi-Tricot R, Malik SJ, Webb A, Hajnal JV, Ipek Ö. Towards an integrated neonatal brain and cardiac examination capability at 7 T: electromagnetic field simulations and early phantom experiments using an 8-channel dipole array. MAGMA (NEW YORK, N.Y.) 2022; 35:765-778. [PMID: 34997396 PMCID: PMC9463228 DOI: 10.1007/s10334-021-00988-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 12/06/2021] [Accepted: 12/06/2021] [Indexed: 11/27/2022]
Abstract
OBJECTIVE Neonatal brain and cardiac imaging would benefit from the increased signal-to-noise ratio levels at 7 T compared to lower field. Optimal performance might be achieved using purpose designed RF coil arrays. In this study, we introduce an 8-channel dipole array and investigate, using simulations, its RF performances for neonatal applications at 7 T. METHODS The 8-channel dipole array was designed and evaluated for neonatal brain/cardiac configurations in terms of SAR efficiency (ratio between transmit-field and maximum specific-absorption-rate level) using adjusted dielectric properties for neonate. A birdcage coil operating in circularly polarized mode was simulated for comparison. Validation of the simulation model was performed on phantom for the coil array. RESULTS The 8-channel dipole array demonstrated up to 46% higher SAR efficiency levels compared to the birdcage coil in neonatal configurations, as the specific-absorption-rate levels were alleviated. An averaged normalized root-mean-square-error of 6.7% was found between measured and simulated transmit field maps on phantom. CONCLUSION The 8-channel dipole array design integrated for neonatal brain and cardiac MR was successfully demonstrated, in simulation with coverage of the baby and increased SAR efficiency levels compared to the birdcage. We conclude that the 8Tx-dipole array promises safe operating procedures for MR imaging of neonatal brain and heart at 7 T.
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Affiliation(s)
- Jérémie Clément
- Department of Biomedical Engineering, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK
| | | | - Shaihan J Malik
- Department of Biomedical Engineering, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK.,Centre for the Developing Brain, King's College London, London, UK
| | - Andrew Webb
- Department of Radiology, C. J Gorter Center for High Field MRI, Leiden University Medical Center, Leiden, The Netherlands
| | - Joseph V Hajnal
- Department of Biomedical Engineering, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK.,Centre for the Developing Brain, King's College London, London, UK
| | - Özlem Ipek
- Department of Biomedical Engineering, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK.
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9
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Avdievich NI, Nikulin AV, Ruhm L, Magill AW, Glang F, Henning A, Scheffler K. A 32-element loop/dipole hybrid array for human head imaging at 7 T. Magn Reson Med 2022; 88:1912-1926. [PMID: 35766426 DOI: 10.1002/mrm.29347] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Revised: 05/16/2022] [Accepted: 05/16/2022] [Indexed: 11/09/2022]
Abstract
PURPOSE To improve whole-brain SNR at 7 Tesla, a novel 32-element hybrid human head array coil was developed, constructed, and tested. METHODS Our general design strategy is based on 2 major ideas: Firstly, following suggestions of previous works based on the ultimate intrinsic SNR theory, we combined loops and dipoles for improvement of SNR near the head center. Secondly, we minimized the total number of array elements by using a hybrid combination of transceive (TxRx) and receive (Rx) elements. The new hybrid array consisted of 8 folded-end TxRx-dipole antennas and 3 rows of 24 Rx-loops all placed in a single layer on the surface of a tight-fit helmet. RESULTS The developed array significantly improved SNR in vivo both near the center (∼20%) and at the periphery (∼20% to 80%) in comparison to a common commercial array coil with 8 transmit (Tx) and 32 Rx-elements. Whereas 24 loops alone delivered central SNR very similar to that of the commercial coil, the addition of complementary dipole structures provided further improvement. The new array also provided ∼15% higher Tx efficiency and better longitudinal coverage than that of the commercial array. CONCLUSION The developed array coil demonstrated advantages in combining complementary TxRx and Rx resonant structures, that is, TxRx-dipoles and Rx-loops all placed in a single layer at the same distance to the head. This strategy improved both SNR and Tx-performance, as well as simplified the total head coil design, making it more robust.
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Affiliation(s)
- Nikolai I Avdievich
- High-Field MR Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Anton V Nikulin
- High-Field MR Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.,Department for Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany
| | - Loreen Ruhm
- High-Field MR Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Arthur W Magill
- Department for Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Felix Glang
- High-Field MR Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Anke Henning
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX
| | - Klaus Scheffler
- High-Field MR Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.,Department for Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany
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He X, Schmidt S, Zbýň Š, Haluptzok T, Moeller S, Metzger GJ. Improved TSE imaging at ultrahigh field using nonlocalized efficiency RF shimming and acquisition modes optimized for refocused echoes (AMORE). Magn Reson Med 2022; 88:1702-1719. [PMID: 35692053 PMCID: PMC9339473 DOI: 10.1002/mrm.29318] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Revised: 05/07/2022] [Accepted: 05/10/2022] [Indexed: 11/06/2022]
Abstract
Purpose To develop and evaluate a novel RF shimming optimization strategy tailored to improve the transmit efficiency in turbo spin echo imaging when performing time‐interleaved acquisition of modes (TIAMO) at ultrahigh fields. Theory and Methods A nonlocalized efficiency shimming cost function is proposed and extended to perform TIAMO using acquisition modes optimized for refocused echoes (AMORE). The nonlocalized efficiency shimming was demonstrated in brain and knee imaging at 7 Tesla. Phantom and in vivo torso imaging studies were performed to compare the performance between AMORE and previously proposed TIAMO mode optimizations with and without localized constraints in turbo spin echo and gradient echo acquisitions. Results The proposed nonlocalized efficiency RF shimming produced a circularly polarized‐like field with fewer signal dropouts in the brain and knee. For larger targets, AMORE was used and required a significantly lower transmitter voltage to produce a similar contrast to existing TIAMO mode design approaches for turbo spin echo as well as gradient echo acquisitions. In vivo, AMORE effectively reduced signal dropout in the interior torso while providing more uniform contrast with reduced transmit power. A local constraint further improved performance for a target region while maintaining performance in the larger FOV. Conclusion AMORE based on the presented nonlocalized efficiency shimming cost function demonstrated improved contrast and SNR uniformity as well as increased transmit efficiency for both gradient echo and turbo spin echo acquisitions. Click here for author‐reader discussions
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Affiliation(s)
- Xiaoxuan He
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | - Simon Schmidt
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | - Štefan Zbýň
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | - Tobey Haluptzok
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | - Steen Moeller
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
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Tenbergen CJA, Metzger GJ, Scheenen TWJ. Ultra-high-field MR in Prostate cancer: Feasibility and Potential. MAGNETIC RESONANCE MATERIALS IN PHYSICS, BIOLOGY AND MEDICINE 2022; 35:631-644. [PMID: 35579785 PMCID: PMC9113077 DOI: 10.1007/s10334-022-01013-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Revised: 03/31/2022] [Accepted: 04/07/2022] [Indexed: 02/07/2023]
Abstract
Multiparametric MRI of the prostate at clinical magnetic field strengths (1.5/3 Tesla) has emerged as a reliable noninvasive imaging modality for identifying clinically significant cancer, enabling selective sampling of high-risk regions with MRI-targeted biopsies, and enabling minimally invasive focal treatment options. With increased sensitivity and spectral resolution, ultra-high-field (UHF) MRI (≥ 7 Tesla) holds the promise of imaging and spectroscopy of the prostate with unprecedented detail. However, exploiting the advantages of ultra-high magnetic field is challenging due to inhomogeneity of the radiofrequency field and high local specific absorption rates, raising local heating in the body as a safety concern. In this work, we review various coil designs and acquisition strategies to overcome these challenges and demonstrate the potential of UHF MRI in anatomical, functional and metabolic imaging of the prostate and pelvic lymph nodes. When difficulties with power deposition of many refocusing pulses are overcome and the full potential of metabolic spectroscopic imaging is used, UHF MR(S)I may aid in a better understanding of the development and progression of local prostate cancer. Together with large field-of-view and low-flip-angle anatomical 3D imaging, 7 T MRI can be used in its full strength to characterize different tumor stages and help explain the onset and spatial distribution of metastatic spread.
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Affiliation(s)
- Carlijn J A Tenbergen
- Department of Medical Imaging, Radboud University Medical Center, PO Box 9101, 6500 HB, Nijmegen, The Netherlands.
| | - Gregory J Metzger
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN, USA
| | - Tom W J Scheenen
- Department of Medical Imaging, Radboud University Medical Center, PO Box 9101, 6500 HB, Nijmegen, The Netherlands
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany
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12
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In Vivo Magnetic Resonance Spectroscopy Methods for Investigating Cardiac Metabolism. Metabolites 2022; 12:metabo12020189. [PMID: 35208262 PMCID: PMC8877606 DOI: 10.3390/metabo12020189] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 02/14/2022] [Accepted: 02/15/2022] [Indexed: 11/17/2022] Open
Abstract
Magnetic resonance spectroscopy (MRS) is a non-invasive and non-ionizing technique, enabling in vivo investigation of cardiac metabolism in normal and diseased hearts. In vivo measurement tools are critical for studying mechanisms that regulate cardiac energy metabolism in disease developments and to assist in early response assessments to novel therapies. For cardiac MRS, proton (1H), phosphorus (31P), and hyperpolarized 13-carbon (13C) provide valuable metabolic information for diagnosis and treatment assessment purposes. Currently, low sensitivity and some technical limitations limit the utility of MRS. An essential step in translating MRS for clinical use involves further technological improvements, particularly in coil design, improving the signal-to-noise ratios, field homogeneity, and optimizing radiofrequency sequences. This review addresses the recent advances in metabolic imaging by MRS from primarily the literature published since 2015.
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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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14
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van Leeuwen CC, Steensma BR, Klomp DWJ, van den Berg CAT, Raaijmakers AJE. The Coax Dipole: A fully flexible coaxial cable dipole antenna with flattened current distribution for body imaging at 7 Tesla. Magn Reson Med 2021; 87:528-540. [PMID: 34411327 PMCID: PMC9292881 DOI: 10.1002/mrm.28983] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 07/14/2021] [Accepted: 08/04/2021] [Indexed: 01/26/2023]
Abstract
Purpose The coax dipole antenna, a flexible antenna for body imaging at 7T is presented. Similar to the high impedance coil, this coaxial cable antenna is fed on the central conductor and through gaps in the shield, the current passes to the outside of the antenna to generate B1 field. This could achieve more favorable current distributions and better adaptation to the body curvature. Methods Finite difference time domain (FDTD) simulations are performed to optimize the positions of the gaps in the shield for a flat current profile. Lumped inductors are added to each end to reduce losses. The performance of a single antenna is compared to a fractionated dipole using B1 maps and MR thermometry. Finally, an array of eight coax dipoles is evaluated in simulations and used for in‐vivo scanning. Results An optimal configuration is found with gaps located at 10 cm from the center and inductor values of 28 nH. In comparison to the fractionated dipole antenna, in single antenna phantom measurements the coax dipole achieves similar B1 amplitude with 18% lower peak temperature. In simulations, the eight‐channel array of coax dipoles improved B1 homogeneity by 18%, along with small improvements in transmit efficiency and specific absorption rate (SAR). MRI measurements on three volunteers show more consistent performance for the coax dipoles. Conclusion The coax dipole is a novel antenna design with a flattened current distribution resulting in beneficial properties. Also, the flexible design of the coax dipoles allows better adaptation to the body curvature and can potentially be used for a wide range of imaging targets.
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Affiliation(s)
- Carel C van Leeuwen
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Bart R Steensma
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Dennis W J Klomp
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | | | - Alexander J E Raaijmakers
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.,Biomedical Engineering Department, Eindhoven University of Technology, Eindhoven, The Netherlands
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15
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Reiter T, Lohr D, Hock M, Ankenbrand MJ, Stefanescu MR, Kosmala A, Kaspar M, Juchem C, Terekhov M, Schreiber LM. On the way to routine cardiac MRI at 7 Tesla - a pilot study on consecutive 84 examinations. PLoS One 2021; 16:e0252797. [PMID: 34297720 PMCID: PMC8301632 DOI: 10.1371/journal.pone.0252797] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2020] [Accepted: 05/23/2021] [Indexed: 11/29/2022] Open
Abstract
INTRODUCTION Cardiac magnetic resonance (CMR) at ultrahigh field (UHF) offers the potential of high resolution and fast image acquisition. Both technical and physiological challenges associated with CMR at 7T require specific hardware and pulse sequences. This study aimed to assess the current status and existing, publicly available technology regarding the potential of a clinical application of 7T CMR. METHODS Using a 7T MRI scanner and a commercially available radiofrequency coil, a total of 84 CMR examinations on 72 healthy volunteers (32 males, age 19-70 years, weight 50-103 kg) were obtained. Both electrocardiographic and acoustic triggering were employed. The data were analyzed regarding the diagnostic image quality and the influence of patient and hardware dependent factors. 50 complete short axis stacks and 35 four chamber CINE views were used for left ventricular (LV) and right ventricular (RV), mono-planar LV function, and RV fractional area change (FAC). Twenty-seven data sets included aortic flow measurements that were used to calculate stroke volumes. Subjective acceptance was obtained from all volunteers with a standardized questionnaire. RESULTS Functional analysis showed good functions of LV (mean EF 56%), RV (mean EF 59%) and RV FAC (mean FAC 52%). Flow measurements showed congruent results with both ECG and ACT triggering. No significant influence of experimental parameters on the image quality of the LV was detected. Small fractions of 5.4% of LV and 2.5% of RV segments showed a non-diagnostic image quality. The nominal flip angle significantly influenced the RV image quality. CONCLUSION The results demonstrate that already now a commercially available 7T MRI system, without major methods developments, allows for a solid morphological and functional analysis similar to the clinically established CMR routine approach. This opens the door towards combing routine CMR in patients with development of advanced 7T technology.
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Affiliation(s)
- Theresa Reiter
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
- Department of Internal Medicine I, Cardiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - David Lohr
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Michael Hock
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Markus Johannes Ankenbrand
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Maria Roxana Stefanescu
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Aleksander Kosmala
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
- Department of Radiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Mathias Kaspar
- Department of Health Services Research, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Christoph Juchem
- Departments of Biomedical Engineering and Radiology, Columbia University, New York, New York, United States of America
| | - Maxim Terekhov
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Laura Maria Schreiber
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
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16
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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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17
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Steensma BR, Meliadò EF, Luijten P, Klomp DWJ, van den Berg CAT, Raaijmakers AJE. SAR and temperature distributions in a database of realistic human models for 7 T cardiac imaging. NMR IN BIOMEDICINE 2021; 34:e4525. [PMID: 33955061 PMCID: PMC8244032 DOI: 10.1002/nbm.4525] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Revised: 03/23/2021] [Accepted: 03/27/2021] [Indexed: 06/12/2023]
Abstract
PURPOSE To investigate inter-subject variability of B1+ , SAR and temperature rise in a database of human models using a local transmit array for 7 T cardiac imaging. METHODS Dixon images were acquired of 14 subjects and segmented in dielectric models with an eight-channel local transmit array positioned around the torso for cardiac imaging. EM simulations were done to calculate SAR distributions. Based on the SAR distributions, temperature simulations were performed for exposure times of 6 min and 30 min. Peak local SAR and temperature rise levels were calculated for different RF shim settings. A statistical analysis of the resulting peak local SAR and temperature rise levels was performed to arrive at safe power limits. RESULTS For RF shim vectors with random phase and uniformly distributed power, a safe average power limit of 35.7 W was determined (first level controlled mode). When RF amplitude and phase shimming was performed on the heart, a safe average power limit of 35.0 W was found. According to Pennes' model, our numerical study suggests a very low probability of exceeding the absolute local temperature limit of 40 °C for a total exposure time of 6 min and a peak local SAR of 20 W/kg. For a 30 min exposure time at 20 W/kg, it was shown that the absolute temperature limit can be exceeded in the case where perfusion does not change with temperature. CONCLUSION Safe power constraints were found for 7 T cardiac imaging with an eight-channel local transmit array, while considering the inter-subject variability of B1+ , SAR and temperature rise.
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Affiliation(s)
- Bart R Steensma
- Center for Image Sciences, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Ettore F Meliadò
- Center for Image Sciences, University Medical Center Utrecht, Utrecht, The Netherlands
- Tesla Dynamic Coils, Zaltbommel, The Netherlands
| | - Peter Luijten
- Center for Image Sciences, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Dennis W J Klomp
- Center for Image Sciences, University Medical Center Utrecht, Utrecht, The Netherlands
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18
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Eigentler TW, Kuehne A, Boehmert L, Dietrich S, Els A, Waiczies H, Niendorf T. 32-Channel self-grounded bow-tie transceiver array for cardiac MR at 7.0T. Magn Reson Med 2021; 86:2862-2879. [PMID: 34169546 DOI: 10.1002/mrm.28885] [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: 02/24/2021] [Revised: 04/20/2021] [Accepted: 05/18/2021] [Indexed: 12/17/2022]
Abstract
PURPOSE Design, implementation, evaluation, and application of a 32-channel Self-Grounded Bow-Tie (SGBT) transceiver array for cardiac MR (CMR) at 7.0T. METHODS The array consists of 32 compact SGBT building blocks. Transmission field ( B 1 + ) shimming and radiofrequency safety assessment were performed with numerical simulations and benchmarked against phantom experiments. In vivo B 1 + efficiency mapping was conducted with actual flip angle imaging. The array's applicability for accelerated high spatial resolution 2D FLASH CINE imaging of the heart was examined in a volunteer study (n = 7). RESULTS B 1 + shimming provided a uniform field distribution suitable for female and male subjects. Phantom studies demonstrated an excellent agreement between simulated and measured B 1 + efficiency maps (7% mean difference). The SGBT array afforded a spatial resolution of (0.8 × 0.8 × 2.5) mm3 for 2D CINE FLASH which is by a factor of 12 superior to standardized cardiovascular MR (CMR) protocols. The density of the SGBT array supports 1D acceleration of up to R = 4 (mean signal-to-noise ratio (whole heart) ≥ 16.7, mean contrast-to-noise ratio ≥ 13.5) without impairing image quality significantly. CONCLUSION The compact SGBT building block facilitates a modular high-density array that supports accelerated and high spatial resolution CMR at 7.0T. The array provides a technological basis for future clinical assessment of parallel transmission techniques.
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Affiliation(s)
- Thomas Wilhelm Eigentler
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.,Chair of Medical Engineering, Technische Universität Berlin, Berlin, Germany
| | | | - Laura Boehmert
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | - Sebastian Dietrich
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Antje Els
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | | | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.,MRI.TOOLS GmbH, Berlin, Germany.,Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
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19
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Gosselink M, Hoogduin H, Froeling M, Klomp DWJ. No need to detune transmitters in 32-channel receiver arrays at 7 T. NMR IN BIOMEDICINE 2021; 34:e4491. [PMID: 33567471 PMCID: PMC8244117 DOI: 10.1002/nbm.4491] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/26/2020] [Revised: 12/16/2020] [Accepted: 01/25/2021] [Indexed: 06/12/2023]
Abstract
Ultrahigh field magnetic resonance imaging facilitates high spatiotemporal resolution that benefits from increasing the number of receiver elements. Because high-density receiver arrays have a relatively small element size compared with the transmitter, a side effect is that such setups cause low flux coupling between the transmitter and receiver. Moreover, when transmitters are designed in a multitransmit configuration, their relative size is much smaller than the sample, reducing coupling to the sample and thereby potentially also the coupling to the receivers. Transmitters are traditionally detuned during reception. In this study, we investigate, for a 32-channel receiver head array at 7 T, if transmitter detuning of a quadrature birdcage or of an eight-channel transmit coil can be omitted without substantially sacrificing signal-to-noise ratio (SNR). The transmit elements are operated once with and once without detuning and, in the latter, the received signals are either merged with the array or excluded for image reconstruction. For each of the three measurements, SNR and 1/g-factor maps are investigated. The tuning of the quadrature and eight-channel transmit coils during signal reception introduced a 10.1% and 6.5% penalty in SNR, respectively, relative to the SNR received with detuned transmitters. When also incorporating the signal of the transmit coils, the SNR was regained to 98.5% or 101.4% for the quadrature and eight-channel coil, respectively, relative to the detuned transmitters, while the 1/g-factor maps improved slightly. For the 32-channel receive coil used the SNR penalty can become negligible when omitting detuning of the transmit coils. This not only simplifies transmit coil designs, potentially increasing their efficiency, but also enables the transmitters to be used as receivers in parallel to the receiver array, thus increasing parallel imaging performance.
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Affiliation(s)
- Mark Gosselink
- Department of RadiologyUniversity Medical Center UtrechtUtrechtthe Netherlands
| | - Hans Hoogduin
- Department of RadiologyUniversity Medical Center UtrechtUtrechtthe Netherlands
| | - Martijn Froeling
- Department of RadiologyUniversity Medical Center UtrechtUtrechtthe Netherlands
| | - Dennis W. J. Klomp
- Department of RadiologyUniversity Medical Center UtrechtUtrechtthe Netherlands
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20
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Bourfiss M, Steensma BR, Te Riele ASJM, Leiner T, Velthuis BK, Raaijmakers AJE. Feature-tracking cardiac magnetic resonance of the right ventricle: Effect of field strength, resolution and imaging sequence. Eur J Radiol 2021; 138:109671. [PMID: 33773860 DOI: 10.1016/j.ejrad.2021.109671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Accepted: 03/18/2021] [Indexed: 11/28/2022]
Affiliation(s)
- Mimount Bourfiss
- Department of Cardiology, University Medical Center Utrecht, Heidelberglaan 100, 3584CX, Utrecht, the Netherlands.
| | - Bart R Steensma
- Department of Radiology, University Medical Center Utrecht, Heidelberglaan 100, 3584CX, Utrecht, the Netherlands
| | - Anneline S J M Te Riele
- Department of Cardiology, University Medical Center Utrecht, Heidelberglaan 100, 3584CX, Utrecht, the Netherlands
| | - Tim Leiner
- Department of Radiology, University Medical Center Utrecht, Heidelberglaan 100, 3584CX, Utrecht, the Netherlands
| | - Birgitta K Velthuis
- Department of Radiology, University Medical Center Utrecht, Heidelberglaan 100, 3584CX, Utrecht, the Netherlands
| | - Alexander J E Raaijmakers
- Department of Radiology, University Medical Center Utrecht, Heidelberglaan 100, 3584CX, Utrecht, the Netherlands; Eindhoven University of Technology, Department of Biomedical Engineering, Den Dolech 2, 5612AZ, Eindhoven, the Netherlands
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21
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Zhang B, Adriany G, Delabarre L, Radder J, Lagore R, Rutt B, Yang QX, Ugurbil K, Lattanzi R. Effect of radiofrequency shield diameter on signal-to-noise ratio at ultra-high field MRI. Magn Reson Med 2021; 85:3522-3530. [PMID: 33464649 DOI: 10.1002/mrm.28670] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2020] [Revised: 11/23/2020] [Accepted: 12/14/2020] [Indexed: 02/01/2023]
Abstract
PURPOSE In this work, we investigated how the position of the radiofrequency (RF) shield can affect the signal-to-noise ratio (SNR) of a receive RF coil. Our aim was to obtain physical insight for the design of a 10.5T 32-channel head coil, subject to the constraints on the diameter of the RF shield imposed by the head gradient coil geometry. METHOD We used full-wave numerical simulations to investigate how the SNR of an RF receive coil depends on the diameter of the RF shield at ultra-high magnetic field (UHF) strengths (≥7T). RESULTS Our simulations showed that there is an SNR-optimal RF shield size at UHF strength, whereas at low field the SNR monotonically increases with the shield diameter. For a 32-channel head coil at 10.5T, an optimally sized RF shield could act as a cylindrical waveguide and increase the SNR in the brain by 27% compared to moving the shield as far as possible from the coil. Our results also showed that a separate transmit array between the RF shield and the receive array could considerably reduce SNR even if they are decoupled. CONCLUSION At sufficiently high magnetic field strength, the design of local RF coils should be optimized together with the design of the RF shield to benefit from both near field and resonant modes.
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Affiliation(s)
- Bei Zhang
- Center for Advanced Imaging Innovation and Research (CAI2R), New York University School of Medicine, New York, New York, USA.,Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, New York, USA.,Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, Texas, USA
| | - Gregor Adriany
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Lance Delabarre
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Jerahmie Radder
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Russell Lagore
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Brian Rutt
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Qing X Yang
- Department of Radiology, Pennsylvania State College of Medicine, Hershey, Pennsylvania, USA
| | - Kamil Ugurbil
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Riccardo Lattanzi
- Center for Advanced Imaging Innovation and Research (CAI2R), New York University School of Medicine, New York, New York, USA.,Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, New York, USA
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22
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Ibrahim ESH, Arpinar VE, Muftuler LT, Stojanovska J, Nencka AS, Koch KM. Cardiac functional magnetic resonance imaging at 7T: Image quality optimization and ultra-high field capabilities. World J Radiol 2020; 12:231-246. [PMID: 33240463 PMCID: PMC7653183 DOI: 10.4329/wjr.v12.i10.231] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 09/27/2020] [Accepted: 10/14/2020] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND 7T cardiac magnetic resonance imaging (MRI) introduces several advantages, as well as some limitations, compared to lower-field imaging. The capabilities of ultra-high field (UHF) MRI have not been fully exploited in cardiac functional imaging.
AIM To optimize 7T cardiac MRI functional imaging without the need for conducting B1 shimming or subject-specific tuning, which improves scan efficiency. In this study, we provide results from phantom and in vivo scans using a multi-channel transceiver modular coil.
METHODS We investigated the effects of adding a dielectric pad at different locations next to the imaged region of interest on improving image quality in subjects with different body habitus. We also investigated the effects of adjusting the imaging flip angle in cine and tagging sequences on improving image quality, B1 field homogeneity, signal-to-noise ratio (SNR), blood-myocardium contrast-to-noise ratio (CNR), and tagging persistence throughout the cardiac cycle.
RESULTS The results showed the capability of achieving improved image quality with high spatial resolution (0.75 mm × 0.75 mm × 2 mm), high temporal resolution (20 ms), and increased tagging persistence (for up to 1200 ms cardiac cycle duration) at 7T cardiac MRI after adjusting scan set-up and imaging parameters. Adjusting the imaging flip angle was essential for achieving optimal SNR and myocardium-to-blood CNR. Placing a dielectric pad at the anterior left position of the chest resulted in improved B1 homogeneity compared to other positions, especially in subjects with small chest size.
CONCLUSION Improved regional and global cardiac functional imaging can be achieved at 7T MRI through simple scan set-up adjustment and imaging parameter optimization, which would allow for more streamlined and efficient UHF cardiac MRI.
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Affiliation(s)
- El-Sayed H Ibrahim
- Department of Radiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States
| | - V Emre Arpinar
- Department of Radiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States
| | - L Tugan Muftuler
- Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, WI 53226, United States
| | - Jadranka Stojanovska
- Department of Radiology, University of Michigan, Ann Arbor, MI 48109, United States
| | - Andrew S Nencka
- Department of Radiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States
| | - Kevin M Koch
- Department of Radiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States
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23
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Ibrahim ESH, Arpinar VE, Muftuler LT, Stojanovska J, Nencka AS, Koch KM. Cardiac functional magnetic resonance imaging at 7T: Image quality optimization and ultra-high field capabilities. World J Radiol 2020. [DOI: 10.4329/wjr.v12.i10.229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
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24
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Wilcox M, Wright SM, McDougall M. A Review of Non- 1H RF Receive Arrays in Magnetic Resonance Imaging and Spectroscopy. IEEE OPEN JOURNAL OF ENGINEERING IN MEDICINE AND BIOLOGY 2020; 1:290-300. [PMID: 35402958 PMCID: PMC8975242 DOI: 10.1109/ojemb.2020.3030531] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Revised: 09/15/2020] [Accepted: 09/25/2020] [Indexed: 11/16/2022] Open
Abstract
It is now common practice to use radiofrequency (RF) coils to increase the signal-to-noise ratio (SNR) in 1H magnetic resonance imaging and spectroscopy experiments. Use of array coils for non-1H experiments, however, has been historically more limited despite the fact that these nuclei suffer inherently lower sensitivity and could benefit greatly from an increased SNR. Recent advancements in receiver technology and increased support from scanner manufacturers have now opened greater options for the use of array coils for non-1H magnetic resonance experiments. This paper reviews the research in adopting array coil technology with an emphasis on studies of the most commonly studied non-1H nuclei including 31P, 13C, 23Na, and 19F. These nuclei offer complementary information to 1H imaging and spectroscopy and have proven themselves important in the study of numerous disease processes. While recent work with non-1H array coils has shown promising results, the technology is not yet widely utilized and should see substantial developments in the coming years.
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25
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Xavier A, Arteaga de Castro C, Andia ME, Luijten PR, Klomp DW, Fillmer A, Prompers JJ. Metabolite cycled liver 1 H MRS on a 7 T parallel transmit system. NMR IN BIOMEDICINE 2020; 33:e4343. [PMID: 32515151 PMCID: PMC7379278 DOI: 10.1002/nbm.4343] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2019] [Revised: 05/08/2020] [Accepted: 05/12/2020] [Indexed: 05/03/2023]
Abstract
INTRODUCTION Single-voxel 1 H MRS in body applications often suffers from respiratory and other motion induced phase and frequency shifts, which lead to incoherent averaging and hence to suboptimal results. METHODS Here we show the application of metabolite cycling (MC) for liver STEAM-localized 1 H MRS on a 7 T parallel transmit system, using eight transmit-receive fractionated dipole antennas with 16 additional, integrated receive loops. MC-STEAM measurements were made in six healthy, lean subjects and compared with STEAM measurements using VAPOR water suppression. Measurements were performed during free breathing and during synchronized breathing, for which the subjects did breathe in between the MRS acquisitions. Both intra-session repeatability and inter-session reproducibility of liver lipid quantification with MC-STEAM and VAPOR-STEAM were determined. RESULTS The preserved water signal in MC-STEAM allowed for robust phase and frequency correction of individual acquisitions before averaging, which resulted in in vivo liver spectra that were of equal quality when measurements were made with free breathing or synchronized breathing. Intra-session repeatability and inter-session reproducibility of liver lipid quantification were better for MC-STEAM than for VAPOR-STEAM. This may also be explained by the more robust phase and frequency correction of the individual MC-STEAM acquisitions as compared with the VAPOR-STEAM acquisitions, for which the low-signal-to-noise ratio lipid signals had to be used for the corrections. CONCLUSION Non-water-suppressed MC-STEAM on a 7 T system with parallel transmit is a promising approach for 1 H MRS applications in the body that are affected by motion, such as in the liver, and yields better repeatability and reproducibility compared with water-suppressed measurements.
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Affiliation(s)
- Aline Xavier
- Department of Radiology, Imaging DivisionUniversity Medical Center UtrechtUtrechtThe Netherlands
- Biomedical Imaging Center, Pontificia Universidad Católica de ChileSantiagoChile
- Millennium Nucleus for Cardiovascular Magnetic ResonanceSantiagoChile
| | | | - Marcelo E. Andia
- Biomedical Imaging Center, Pontificia Universidad Católica de ChileSantiagoChile
- Millennium Nucleus for Cardiovascular Magnetic ResonanceSantiagoChile
| | - Peter R. Luijten
- Department of Radiology, Imaging DivisionUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Dennis W. Klomp
- Department of Radiology, Imaging DivisionUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Ariane Fillmer
- Department of Radiology, Imaging DivisionUniversity Medical Center UtrechtUtrechtThe Netherlands
- Physikalisch‐Technische Bundesanstalt (PTB)BerlinGermany
| | - Jeanine J. Prompers
- Department of Radiology, Imaging DivisionUniversity Medical Center UtrechtUtrechtThe Netherlands
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26
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Maunder A, Rao M, Robb F, Wild JM. An 8-element Tx/Rx array utilizing MEMS detuning combined with 6 Rx loops for 19 F and 1 H lung imaging at 1.5T. Magn Reson Med 2020; 84:2262-2277. [PMID: 32281139 DOI: 10.1002/mrm.28260] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Revised: 02/27/2020] [Accepted: 02/27/2020] [Indexed: 12/24/2022]
Abstract
PURPOSE To firstly improve the attainable image SNR of 19 F and 1 H C3 F8 lung imaging at 1.5 tesla using an 8-element transmit/receive (Tx/Rx) flexible vest array combined with a 6-element Rx-only array, and to secondly evaluate microelectromechanical systems for switching the array elements between the 2 resonant frequencies. METHODS The Tx efficiency and homogeneity of the 8-element array were measured and simulated for 1 H imaging in a cylindrical phantom and then evaluated for in vivo 19 F/1 H imaging. The added improvement provided by the 6-element Rx-only array was quantified through simulation and measurement and compared to the ultimate SNR. It was verified through the measurement of isolation that microelectromechanical systems switches provided broadband isolation of Tx/Rx circuitry such that the 19 F tuned Tx/Rx array could be effectively used for both 19 F and 1 H nuclei. RESULTS For 1 H imaging, the measured Tx efficiency/homogeneity (mean ± percent SD; 6.79 μ T / kW ± 26 % ) was comparable to that simulated ( 7.57 μ T / kW ± 20 % ). The 6 additional Rx-only loops increased the mean Rx sensitivity when compared to the 8-element array by a factor of 1.41× and 1.45× in simulation and measurement, respectively. In regions central to the thorax, the simulated SNR of the 14-element array achieves ≥70% of the ultimate SNR when including noise from the matching circuits and preamplifiers. A measured microelectromechanical systems switching speed of 12 µs and added minimum 22 dB of isolation between Tx and Rx were sufficient for Tx/Rx switching in this application. CONCLUSION The described single-tuned array driven at 19 F and 1 H, utilizing microelectromechanical systems technology, provides excellent results for 19 F and 1 H dual-nuclear lung ventilation imaging.
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Affiliation(s)
- Adam Maunder
- POLARIS, Imaging Group, Department of IICD, University of Sheffield, Sheffield, United Kingdom
| | - Madhwesha Rao
- POLARIS, Imaging Group, Department of IICD, University of Sheffield, Sheffield, United Kingdom
| | - Fraser Robb
- POLARIS, Imaging Group, Department of IICD, University of Sheffield, Sheffield, United Kingdom.,GE Healthcare, Aurora, OH, USA
| | - Jim M Wild
- POLARIS, Imaging Group, Department of IICD, University of Sheffield, Sheffield, United Kingdom
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27
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A Novel Mono-surface Antisymmetric 8Tx/16Rx Coil Array for Parallel Transmit Cardiac MRI in Pigs at 7T. Sci Rep 2020; 10:3117. [PMID: 32080274 PMCID: PMC7033245 DOI: 10.1038/s41598-020-59949-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Accepted: 01/30/2020] [Indexed: 02/01/2023] Open
Abstract
A novel mono-surface antisymmetric 16-element transmit/receive (Tx/Rx) coil array was designed, simulated, constructed, and tested for cardiac magnetic resonance imaging (cMRI) in pigs at 7 T. The cardiac array comprised of a mono-surface 16-loops with two central elements arranged anti-symmetrically and flanked by seven elements on either side. The array was configured for parallel transmit (pTx) mode to have an eight channel transmit and 16-channel receive (8Tx/16Rx) coil array. Electromagnetic (EM) simulations, bench-top measurements, phantom, and MRI experiments with two pig cadavers (68 and 46 kg) were performed. Finally, the coil was used in pilot in-vivo measurements with a 60 kg pig. Flip angle (FA), geometry factor (g-factor), signal-to-noise ratio (SNR) maps, and high-resolution cardiac images were acquired with an in-plane resolution of 0.6 mm × 0.6 mm (in-vivo) and 0.3 mm × 0.3 mm (ex-vivo). The mean g-factor over the heart was 1.26 (R = 6). Static phase [Formula: see text] shimming in a pig body phantom with the optimal phase vectors makes possible to improve the [Formula: see text] homogeneity by factor > 2 and transmit efficiency by factor > 3 compared to zero phases (before RF shimming). Parallel imaging performed in the in-vivo measurements demonstrated well preserved diagnostic quality of the resulting images at acceleration factors up to R = 6. The described hardware design can be adapted for arrays optimized for animals and humans with a larger number of elements (32-64) while maintaining good decoupling for various MRI applications at UHF (e.g., cardiac, head, and spine).
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Lakshmanan K, Cloos M, Brown R, Lattanzi R, Sodickson DK, Wiggins GC. The "Loopole" Antenna: A Hybrid Coil Combining Loop and Electric Dipole Properties for Ultra-High-Field MRI. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2020; 2020:8886543. [PMID: 34140840 PMCID: PMC8207246 DOI: 10.1155/2020/8886543] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
PURPOSE To revisit the "loopole," an unusual coil topology whose unbalanced current distribution captures both loop and electric dipole properties, which can be advantageous in ultra-high-field MRI. METHODS Loopole coils were built by deliberately breaking the capacitor symmetry of traditional loop coils. The corresponding current distribution, transmit efficiency, and signal-to-noise ratio (SNR) were evaluated in simulation and experiments in comparison to those of loops and electric dipoles at 7 T (297 MHz). RESULTS The loopole coil exhibited a hybrid current pattern, comprising features of both loops and electric dipole current patterns. Depending on the orientation relative to B0, the loopole demonstrated significant performance boost in either the transmit efficiency or SNR at the center of a dielectric sample when compared to a traditional loop. Modest improvements were observed when compared to an electric dipole. CONCLUSION The loopole can achieve high performance by supporting both divergence-free and curl-free current patterns, which are both significant contributors to the ultimate intrinsic performance at ultra-high field. While electric dipoles exhibit similar hybrid properties, loopoles maintain the engineering advantages of loops, such as geometric decoupling and reduced resonance frequency dependence on sample loading.
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Affiliation(s)
- Karthik Lakshmanan
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
- Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
| | - Martijn Cloos
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
- Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
| | - Ryan Brown
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
- Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
| | - Riccardo Lattanzi
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
- Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
| | - Daniel K. Sodickson
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
- Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
- Tech4Health, NYU Langone Health, New York, NY, USA
| | - Graham C. Wiggins
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
- Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA
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He X, Ertürk MA, Grant A, Wu X, Lagore RL, DelaBarre L, Eryaman Y, Adriany G, Auerbach EJ, Van de Moortele PF, Uğurbil K, Metzger GJ. First in-vivo human imaging at 10.5T: Imaging the body at 447 MHz. Magn Reson Med 2019; 84:289-303. [PMID: 31846121 DOI: 10.1002/mrm.28131] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Revised: 11/25/2019] [Accepted: 11/26/2019] [Indexed: 01/31/2023]
Abstract
PURPOSE To investigate the feasibility of imaging the human torso and to evaluate the performance of several radiofrequency (RF) management strategies at 10.5T. METHODS Healthy volunteers were imaged on a 10.5T whole-body scanner in multiple target anatomies, including the prostate, hip, kidney, liver, and heart. Phase-only shimming and spoke pulses were used to demonstrate their performance in managing the B 1 + inhomogeneity present at 447 MHz. Imaging protocols included both qualitative and quantitative acquisitions to show the feasibility of imaging with different contrasts. RESULTS High-quality images were acquired and demonstrated excellent overall contrast and signal-to-noise ratio. The experimental results matched well with predictions and suggested good translational capabilities of the RF management strategies previously developed at 7T. Phase-only shimming provided increased efficiency, but showed pronounced limitations in homogeneity, demonstrating the need for the increased degrees of freedom made possible through single- and multispoke RF pulse design. CONCLUSION The first in-vivo human imaging was successfully performed at 10.5T using previously developed RF management strategies. Further improvement in RF coils, transmit chain, and full integration of parallel transmit functionality are needed to fully realize the benefits of 10.5T.
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Affiliation(s)
- Xiaoxuan He
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - M Arcan Ertürk
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Andrea Grant
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Xiaoping Wu
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Russell L Lagore
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Lance DelaBarre
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Yiğitcan Eryaman
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Eddie J Auerbach
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | | | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
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30
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Meliadò EF, Raaijmakers AJE, Sbrizzi A, Steensma BR, Maspero M, Savenije MHF, Luijten PR, van den Berg CAT. A deep learning method for image-based subject-specific local SAR assessment. Magn Reson Med 2019; 83:695-711. [PMID: 31483521 PMCID: PMC6899474 DOI: 10.1002/mrm.27948] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2019] [Revised: 07/23/2019] [Accepted: 07/24/2019] [Indexed: 12/31/2022]
Abstract
Purpose Local specific absorption rate (SAR) cannot be measured and is usually evaluated by offline numerical simulations using generic body models that of course will differ from the patient's anatomy. An additional safety margin is needed to include this intersubject variability. In this work, we present a deep learning–based method for image‐based subject‐specific local SAR assessment. We propose to train a convolutional neural network to learn a “surrogate SAR model” to map the relation between subject‐specific B1+ maps and the corresponding local SAR. Method Our database of 23 subject‐specific models with an 8–transmit channel body array for prostate imaging at 7 T was used to build 5750 training samples. These synthetic complex B1+ maps and local SAR distributions were used to train a conditional generative adversarial network. Extra penalization for local SAR underestimation errors was included in the loss function. In silico and in vivo validation were performed. Results In silico cross‐validation shows a good qualitative and quantitative match between predicted and ground‐truth local SAR distributions. The peak local SAR estimation error distribution shows a mean overestimation error of 15% with 13% probability of underestimation. The higher accuracy of the proposed method allows the use of less conservative safety factors compared with standard procedures. In vivo validation shows that the method is applicable with realistic measurement data with impressively good qualitative and quantitative agreement to simulations. Conclusion The proposed deep learning method allows online image‐based subject‐specific local SAR assessment. It greatly reduces the uncertainty in current state‐of‐the‐art SAR assessment methods, reducing the time in the examination protocol by almost 25%.
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Affiliation(s)
- E F Meliadò
- Department of Radiology, University Medical Center Utrecht, Utrecht, Netherlands.,Computational Imaging Group for MR Diagnostics & Therapy, Center for Image Sciences, University Medical Center Utrecht, Netherlands.,Tesla Dynamic Coils, Zaltbommel, Netherlands
| | - A J E Raaijmakers
- Department of Radiology, University Medical Center Utrecht, Utrecht, Netherlands.,Computational Imaging Group for MR Diagnostics & Therapy, Center for Image Sciences, University Medical Center Utrecht, Netherlands.,Biomedical Image Analysis, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands
| | - A Sbrizzi
- Department of Radiology, University Medical Center Utrecht, Utrecht, Netherlands.,Computational Imaging Group for MR Diagnostics & Therapy, Center for Image Sciences, University Medical Center Utrecht, Netherlands
| | - B R Steensma
- Department of Radiology, University Medical Center Utrecht, Utrecht, Netherlands.,Computational Imaging Group for MR Diagnostics & Therapy, Center for Image Sciences, University Medical Center Utrecht, Netherlands
| | - M Maspero
- Division of Imaging & Oncology, Department of Radiotherapy, University Medical Center Utrecht, Netherlands.,Computational Imaging Group for MR Diagnostics & Therapy, Center for Image Sciences, University Medical Center Utrecht, Netherlands
| | - M H F Savenije
- Division of Imaging & Oncology, Department of Radiotherapy, University Medical Center Utrecht, Netherlands.,Computational Imaging Group for MR Diagnostics & Therapy, Center for Image Sciences, University Medical Center Utrecht, Netherlands
| | - P R Luijten
- Department of Radiology, University Medical Center Utrecht, Utrecht, Netherlands
| | - C A T van den Berg
- Division of Imaging & Oncology, Department of Radiotherapy, University Medical Center Utrecht, Netherlands.,Computational Imaging Group for MR Diagnostics & Therapy, Center for Image Sciences, University Medical Center Utrecht, Netherlands
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31
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Elabyad IA, Terekhov M, Stefanescu MR, Lohr D, Fischer M, Schreiber LM. Design of a novel antisymmetric coil array for parallel transmit cardiac MRI in pigs at 7 T. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 305:195-208. [PMID: 31306985 DOI: 10.1016/j.jmr.2019.07.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Revised: 06/12/2019] [Accepted: 07/04/2019] [Indexed: 05/12/2023]
Abstract
The design, simulation, assembly and testing of a novel dedicated antisymmetric transmit/receive (Tx/Rx) coil array to demonstrate the feasibility of cardiac magnetic resonance imaging (cMRI) in pigs at 7 T was described. The novel antisymmetric array is composed of eight elements based on mirrored and reversed loop orientations to generate varying B1+ field harmonics for RF shimming. The central four loop elements formed together a pair of antisymmetric L-shaped channels to allow good decoupling between all neighboring elements of the entire array. The antisymmetric array was compared to a standard symmetric rectilinear loop array with an identical housing dimension. Both arrays were driven in the parallel transmit (pTx) mode forming an 8-channel transmit and 16-channel receive (8Tx/16Rx) coil array, where the same posterior array was combined with both anterior arrays. The hardware and imaging performance of the dedicated cardiac arrays were validated and compared by means of electromagnetic (EM) simulations, bench-top measurements, phantom, and ex-vivo MRI experiments with 46 kg female pig. Combined signal-to-noise ratio (SNR), geometry factor (g-factor), noise correlation maps, and high resolution ex-vivo cardiac images were acquired with an in-plane resolution of 0.3 mm × 0.3 mm using both arrays. The novel antisymmetric array enhanced the SNR within the heart by about two times and demonstrated good decoupling and improved control of the B1+ field distributions for RF shimming compared to the standard coil array. Parallel imaging with acceleration factor (R) up to 4 was possible using the novel antisymmetric coil array while maintaining the mean g-factor within the heart region of 1.13.
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Affiliation(s)
- Ibrahim A Elabyad
- Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center (CHFC), University Hospital Wuerzburg, D-97078 Wuerzburg, Germany; Department of Electronics and Communications Engineering, Thebes Higher Institute of Engineering, Cairo, Egypt.
| | - M Terekhov
- Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center (CHFC), University Hospital Wuerzburg, D-97078 Wuerzburg, Germany.
| | - M R Stefanescu
- Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center (CHFC), University Hospital Wuerzburg, D-97078 Wuerzburg, Germany.
| | - D Lohr
- Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center (CHFC), University Hospital Wuerzburg, D-97078 Wuerzburg, Germany.
| | - M Fischer
- Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center (CHFC), University Hospital Wuerzburg, D-97078 Wuerzburg, Germany.
| | - L M Schreiber
- Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center (CHFC), University Hospital Wuerzburg, D-97078 Wuerzburg, Germany.
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32
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Erturk MA, Li X, Van de Moortele PF, Ugurbil K, Metzger GJ. Evolution of UHF Body Imaging in the Human Torso at 7T: Technology, Applications, and Future Directions. Top Magn Reson Imaging 2019; 28:101-124. [PMID: 31188271 PMCID: PMC6587233 DOI: 10.1097/rmr.0000000000000202] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/13/2023]
Abstract
The potential value of ultrahigh field (UHF) magnetic resonance imaging (MRI) and spectroscopy to biomedical research and in clinical applications drives the development of technologies to overcome its many challenges. The increased difficulties of imaging the human torso compared with the head include its overall size, the dimensions and location of its anatomic targets, the increased prevalence and magnitude of physiologic effects, the limited availability of tailored RF coils, and the necessary transmit chain hardware. Tackling these issues involves addressing notoriously inhomogeneous transmit B1 (B1) fields, limitations in peak B1, larger spatial variations of the static magnetic field B0, and patient safety issues related to implants and local RF power deposition. However, as research institutions and vendors continue to innovate, the potential gains are beginning to be realized. Solutions overcoming the unique challenges associated with imaging the human torso are reviewed as are current studies capitalizing on the benefits of UHF in several anatomies and applications. As the field progresses, strategies associated with the RF system architecture, calibration methods, RF pulse optimization, and power monitoring need to be further integrated into the MRI systems making what are currently complex processes more streamlined. Meanwhile, the UHF MRI community must seize the opportunity to build upon what have been so far proof of principle and feasibility studies and begin to further explore the true impact in both research and the clinic.
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Affiliation(s)
- M Arcan Erturk
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
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33
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Abstract
Radiofrequency (RF) coils are an essential part of the magnetic resonance (MR) system. To exploit the inherently higher signal-to-noise ratio at ultrahigh magnetic fields (UHF), research sites were forced to build up expertise in RF coil development, as the number of commercially available RF coils were limited. In addition, an integrated transmit body RF coil, which is well-established at MR systems of lower field strength, is still missing at UHF due to technical and physical constraints. This review article provides a brief recapitulation of RF characteristics and RF coils in general to introduce terminology and RF-related parameters, and will then provide an extensive overview of current state-of-the-art RF coils used for MRI from head to toe at 7 Tesla. Finally, a section on RF safety will briefly discuss challenges in performing a safety assessment for custom-designed RF coils, and issues arising from the interaction of the RF field and potentially implanted medical devices.
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Affiliation(s)
- Oliver Kraff
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
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Clément J, Gruetter R, Ipek Ö. A combined 32-channel receive-loops/8-channel transmit-dipoles coil array for whole-brain MR imaging at 7T. Magn Reson Med 2019; 82:1229-1241. [PMID: 31081176 PMCID: PMC6618274 DOI: 10.1002/mrm.27808] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Revised: 04/17/2019] [Accepted: 04/18/2019] [Indexed: 12/24/2022]
Abstract
Purpose Multichannel receive arrays provide high SNR and parallel‐imaging capabilities, while transmit‐only dipole arrays have been shown to achieve a large coverage of the whole‐brain including the cerebellum. The aim of this study was to develop and characterize the performances of a 32‐channel receive‐only loop array combined with an 8‐channel dipole coil array at 7T for the first time. Methods The 8Tx‐dipoles/32Rx‐loops coil array was characterized by the SNR, g‐factors, noise correlation matrix, accelerated image quality, and B1+ maps, and compared with a commercial 1Tx‐birdcage/32Rx‐loops array. Simulated and measured B1+ maps were shown for the 8Tx‐dipoles/32Rx‐loops coil array and compared with the 8Tx/Rx dipole array. Results The in‐house built 32‐channel receive coil demonstrated a large longitudinal coverage of the brain, particularly the upper neck area. G‐factors and accelerated MR acquisitions demonstrated robust performances up to R = 4 in 2D, and R = 8 (4 × 2) in 3D. A 83% increase in SNR was measured over the cerebellum with the in‐house built 8Tx/32Rx coil array compared to the commercial 1Tx/32Rx, while similar performances were obtained in the cerebral cortex. Conclusions The combined 32‐channel receive/8‐channel transmit coil array demonstrated high transmit‐receive performances compared to the commercial receive array at 7T, notably in the cerebellum. We conclude that in combination with parallel transmit capabilities, this coil is particularly suitable for whole‐brain MR studies at 7T.
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Affiliation(s)
- Jérémie Clément
- LIFMET, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Rolf Gruetter
- LIFMET, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.,Department of Radiology, University of Geneva, Geneva, Switzerland.,Department of Radiology, University of Lausanne, Lausanne, Switzerland
| | - Özlem Ipek
- CIBM-AIT, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.,School of Biomedical Engineering & Imaging, King's College London, London, United Kingdom
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35
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Steensma BR, Luttje M, Voogt IJ, Klomp DW, Luijten PR, van den Berg CA, Raaijmakers AJ. Comparing signal-to-noise ratio for prostate imaging at 7T and 3T. J Magn Reson Imaging 2019; 49:1446-1455. [PMID: 30350388 PMCID: PMC6587835 DOI: 10.1002/jmri.26527] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2018] [Revised: 09/12/2018] [Accepted: 09/12/2018] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND In MRI, the signal-to-noise ratio (SNR) theoretically increases with B0 field strength. However, because of attenuation of the radiofrequency (RF) fields at 7T, it is not certain if this SNR gain can be realized for prostate imaging. PURPOSE/HYPOTHESIS To investigate the SNR gain in prostate imaging at 7T as compared with 3T. It is expected that SNR will improve for prostate imaging at 7T compared with 3T. STUDY TYPE Prospective. SUBJECTS Four healthy volunteers and one prostate cancer patient. FIELD STRENGTH/SEQUENCE All subjects were scanned at 3T and at 7T using optimal coil setups for both field strengths. For all volunteers, proton density-weighted images were acquired for SNR analysis and actual flip angle imaging (AFI) B 1 + | maps were acquired for correction of measured SNR values. In the patient, a T2 -weighted (T2 w) image was acquired at 3T and at 7T. ASSESSMENT SNR was calculated in the prostate region for all volunteers. SNR was normalized for flip angle, receiver bandwidth, and voxel volume. SNR was also calculated for different sensitivity encoding (SENSE) acceleration factors. STATISTICAL TESTING SNR values are represented as the arithmetic mean of SNR values in the prostate. Estimated SNR in the T2 w image is calculated as the arithmetic mean of the signal intensity (SI) divided by the standard deviation of the SI in a specified zone. Tumor-to-tissue contrast is calculated as (SItumor +SIzone )/( SItumor -SIzone ). RESULTS An increase in SNR ranging from 1.7-fold to 2.8-fold was measured in the prostate at 7T in comparison to 3T for four volunteers. At 7T, it is possible to achieve a 4-fold SENSE acceleration in the left-right direction with similar SNR to a nonaccelerated 3T image. T2 w imaging was done at 3T and 7T in one patient, where improved tumor-to-tissue contrast was demonstrated at 7T. DATA CONCLUSION SNR improves for prostate imaging at 7T as compared with 3T. LEVEL OF EVIDENCE 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:1446-1455.
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Affiliation(s)
- Bart R. Steensma
- University Medical Center UtrechtDepartment of RadiologyUtrechtThe Netherlands
| | - Mariska Luttje
- University Medical Center UtrechtDepartment of RadiologyUtrechtThe Netherlands
| | - Ingmar J. Voogt
- University Medical Center UtrechtDepartment of RadiologyUtrechtThe Netherlands
| | - Dennis W.J. Klomp
- University Medical Center UtrechtDepartment of RadiologyUtrechtThe Netherlands
| | - Peter R. Luijten
- University Medical Center UtrechtDepartment of RadiologyUtrechtThe Netherlands
| | | | - Alexander J.E. Raaijmakers
- University Medical Center UtrechtDepartment of RadiologyUtrechtThe Netherlands
- Eindhoven University of TechnologyDepartment of Biomedical EngineeringUtrechtThe Netherlands
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Rietsch SHG, Brunheim S, Orzada S, Voelker MN, Maderwald S, Bitz AK, Gratz M, Ladd ME, Quick HH. Development and evaluation of a 16-channel receive-only RF coil to improve 7T ultra-high field body MRI with focus on the spine. Magn Reson Med 2019; 82:796-810. [PMID: 30924181 DOI: 10.1002/mrm.27731] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 01/02/2019] [Accepted: 01/27/2019] [Indexed: 12/21/2022]
Abstract
PURPOSE A 16-channel receive (16Rx) radiofrequency (RF) array for 7T ultra-high field body MR imaging is presented. The coil is evaluated in conjunction with a 16-channel transmit/receive (16TxRx) coil and additionally with a 32-channel transmit/receive (32TxRx) remote body coil for RF transmit and serving as receive references. METHODS The 16Rx array consists of 16 octagonal overlapping loops connected to custom-built detuning boards with preamplifiers. Performance metrics like noise correlation, g-factors, and signal-to-noise ratio gain were compared between 4 different RF coil configurations. In vivo body imaging was performed in volunteers using radiofrequency shimming, time interleaved acquisition of modes (TIAMO), and 2D spatially selective excitation using parallel transmit (pTx) in the spine. RESULTS Lower g-factors were obtained when using the 16Rx coil in addition to the 16TxRx array coil configuration versus the 16TxRx array alone. Distinct signal-to-noise ratio gain using the 16Rx coil could be demonstrated in the spine region both for a comparison with the 16TxRx coil (>50% gain) in vivo and the 32TxRx coil (>240% gain) in a phantom. The 16Rx coil was successfully applied to improve anatomical imaging in the abdomen and 2D spatially selective excitation in the spine of volunteers. CONCLUSION The novel 16-channel Rx-array as an add-on to multichannel TxRx RF coil configurations provides increased signal-to-noise ratio, lower g-factors, and thus improves 7T ultra-high field body MR imaging.
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Affiliation(s)
- Stefan H G Rietsch
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Sascha Brunheim
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Stephan Orzada
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany
| | - Maximilian N Voelker
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Stefan Maderwald
- Erwin L. Hahn Institute for MR Imaging, 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, University of Applied Sciences Aachen, Aachen, Germany
| | - Marcel Gratz
- Erwin L. Hahn Institute for MR Imaging, 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 MR Imaging, 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
| | - Harald H Quick
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
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Maunder A, Rao M, Robb F, Wild JM. Optimization of steady-state free precession MRI for lung ventilation imaging with 19 F C 3 F 8 at 1.5T and 3T. Magn Reson Med 2019; 81:1130-1142. [PMID: 30387911 PMCID: PMC6491987 DOI: 10.1002/mrm.27479] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Revised: 06/26/2018] [Accepted: 07/11/2018] [Indexed: 12/12/2022]
Abstract
PURPOSE To optimize 19 F imaging pulse sequences for perfluoropropane (C3 F8 ) gas human lung ventilation MRI considering intrinsic in vivo relaxation parameters at both 1.5T and 3T. METHODS Optimization of the imaging parameters for both 3D spoiled gradient (SPGR) and steady-state free precession (SSFP) 19 F imaging sequences with inhaled 79% C3 F8% and 21% oxygen was performed. Phantom measurements were used to validate simulations of SNR. In vivo parameter mapping and sequence optimization and comparison was performed by imaging the lungs of a healthy adult volunteer. T1 and T2* mapping was performed in vivo to optimize sequence parameters for in vivo lung MRI. The performance of SSFP and SPGR was then evaluated in vivo at 1.5T and 3T. RESULTS The in vivo T2* of C3 F8 was shown to be dependent upon lung inflation level (2.04 ms ± 36% for residual volume and 3.14 ms ± 28% for total lung capacity measured at 3T), with lower T2* observed near the susceptibility interfaces of the diaphragm and around pulmonary blood vessels. Simulation and phantom measurements indicate that a factor of ~2-3 higher SNR can be achieved with SSFP when compared with optimized SPGR. In vivo lung imaging showed a 1.7 factor of improvement in SNR achieved at 1.5T, while the theoretical improvement at 3T was not attained due to experimental SAR constraints, shorter in vivo T1 , and B0 inhomogeneity. CONCLUSION SSFP imaging provides increased SNR in lung ventilation imaging of C3 F8 demonstrated at 1.5T with optimized SSFP similar to the SNR that can be obtained at 3T with optimized SPGR.
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Affiliation(s)
- Adam Maunder
- POLARIS, Unit of Academic Radiology, Department of IICDUniversity of SheffieldSheffieldUnited Kingdom
| | - Madhwesha Rao
- POLARIS, Unit of Academic Radiology, Department of IICDUniversity of SheffieldSheffieldUnited Kingdom
| | - Fraser Robb
- POLARIS, Unit of Academic Radiology, Department of IICDUniversity of SheffieldSheffieldUnited Kingdom
- GE HealthcareAuroraOhio
| | - Jim M. Wild
- POLARIS, Unit of Academic Radiology, Department of IICDUniversity of SheffieldSheffieldUnited Kingdom
- Insigneo Institute for In silico medicineSheffieldUnited Kingdom
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Hosseinnezhadian S, Frass-Kriegl R, Goluch-Roat S, Pichler M, Sieg J, Vít M, Poirier-Quinot M, Darrasse L, Moser E, Ginefri JC, Laistler E. A flexible 12-channel transceiver array of transmission line resonators for 7 T MRI. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 296:47-59. [PMID: 30205313 DOI: 10.1016/j.jmr.2018.08.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Revised: 08/08/2018] [Accepted: 08/30/2018] [Indexed: 06/08/2023]
Abstract
A flexible transceiver array based on transmission line resonators (TLRs) combining the advantages of coil arrays with the possibility of form-fitting targeting cardiac MRI at 7 T is presented. The design contains 12 elements which are fabricated on a flexible substrate with rigid PCBs attached on the center of each element to place the interface components, i.e. transmit/receive (T/R) switch, power splitter, pre-amplifier and capacitive tuning/matching circuitry. The mutual coupling between elements is cancelled using a decoupling ring-based technique. The performance of the developed array is evaluated by 3D electromagnetic simulations, bench tests, and MR measurements using phantoms. Efficient inter-element decoupling is demonstrated in flat configuration on a box-shaped phantom (Sij < -19 dB), and bent on a human torso phantom (Sij < -16 dB). Acceleration factors up to 3 can be employed in bent configuration with reasonable g-factors (<1.7) in an ROI at the position of the heart. The array enables geometrical conformity to bodies within a large range of size and shape and is compatible with parallel imaging and parallel transmission techniques.
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Affiliation(s)
- Sajad Hosseinnezhadian
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria; MR Centre of Excellence, Medical University of Vienna, Lazarettgasse 14, 1090 Vienna, Austria; IR4M (Imagerie par Résonance Magnétique Médicale et Multi-Modalités), Bât 220, Univ. Paris-Sud, CNRS, Université Paris-Saclay, 91405 Orsay, France
| | - Roberta Frass-Kriegl
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria; MR Centre of Excellence, Medical University of Vienna, Lazarettgasse 14, 1090 Vienna, Austria
| | - Sigrun Goluch-Roat
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria; MR Centre of Excellence, Medical University of Vienna, Lazarettgasse 14, 1090 Vienna, Austria
| | - Michael Pichler
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria; MR Centre of Excellence, Medical University of Vienna, Lazarettgasse 14, 1090 Vienna, Austria
| | - Jürgen Sieg
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria; MR Centre of Excellence, Medical University of Vienna, Lazarettgasse 14, 1090 Vienna, Austria
| | - Martin Vít
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria; MR Centre of Excellence, Medical University of Vienna, Lazarettgasse 14, 1090 Vienna, Austria; IKEM (Institute for Clinical and Experimental Medicine), Vídeňská 1958/9, 140 21 Praha 4, Czech Republic
| | - Marie Poirier-Quinot
- IR4M (Imagerie par Résonance Magnétique Médicale et Multi-Modalités), Bât 220, Univ. Paris-Sud, CNRS, Université Paris-Saclay, 91405 Orsay, France
| | - Luc Darrasse
- IR4M (Imagerie par Résonance Magnétique Médicale et Multi-Modalités), Bât 220, Univ. Paris-Sud, CNRS, Université Paris-Saclay, 91405 Orsay, France
| | - Ewald Moser
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria; MR Centre of Excellence, Medical University of Vienna, Lazarettgasse 14, 1090 Vienna, Austria
| | - Jean-Christophe Ginefri
- IR4M (Imagerie par Résonance Magnétique Médicale et Multi-Modalités), Bât 220, Univ. Paris-Sud, CNRS, Université Paris-Saclay, 91405 Orsay, France
| | - Elmar Laistler
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria; MR Centre of Excellence, Medical University of Vienna, Lazarettgasse 14, 1090 Vienna, Austria.
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Leiner T, Strijkers G. Advances in cardiovascular MR imaging. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2018; 31:3-6. [PMID: 29411168 DOI: 10.1007/s10334-018-0676-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
- Tim Leiner
- Department of Radiology, Utrecht University Medical Center, Utrecht, The Netherlands.
| | - Gustav Strijkers
- Department of Biomedical Engineering and Physics, Academic Medical Center, Amsterdam, The Netherlands
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