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Lu M, Sengupta S, Gore JC, Grissom WA, Yan X. High-Density MRI RF Arrays Using Mixed Dipole Antennas and Microstrip Transmission Line Resonators. IEEE Trans Biomed Eng 2022; 69:3243-3252. [PMID: 35404807 PMCID: PMC9587496 DOI: 10.1109/tbme.2022.3166279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
OBJECTIVE High-density multi-coil arrays are desirable in MRI because they provide high signal-to-noise ratios (SNR), enable highly accelerated parallel imaging, and provide more uniform transmit fields at high fields. For high-density arrays such as a head array with 16 elements in a row, popular dipole antennas and microstrip transmission line (also referred to as "MTL") resonators both have severe coupling issues. METHODS In this work, we show that dipoles and MTLs have naturally low coupling and propose a novel array configuration in which they are interleaved. We first show the electromagnetic (EM) coupling between a single dipole and a single MTL across different separations in bench tests. Then we validate and analyze this through EM simulations. Finally, we construct a 16-channel mixed dipole and MTL array and evaluate its performance on the bench and through MRI experiments. RESULTS Without any decoupling treatments, the worst coupling between a dipole and an MTL was only -15.8 dB when their center-to-center distance was 4.7 cm (versus -5.4 dB for two dipole antennas and -6.0 dB for two MTL resonators). Even in a dense 16-channel mixed array, the inter-element isolation among all elements was better than -14 dB. CONCLUSION This study reveals, analyzes, and validates a novel finding that the popular dipole antennas and MTL resonators used in ultrahigh field MRI have naturally low coupling. SIGNIFICANCE These findings will simplify the construction of high-density arrays, enable new applications, and benefit imaging performance in ultrahigh field MRI.
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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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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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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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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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6
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Ipek Ö. Radio-frequency coils for ultra-high field magnetic resonance. Anal Biochem 2017; 529:10-16. [DOI: 10.1016/j.ab.2017.03.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 03/24/2017] [Accepted: 03/27/2017] [Indexed: 10/19/2022]
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O'Reilly TPA, Ruytenberg T, Webb AG. Modular transmit/receive arrays using very-high permittivity dielectric resonator antennas. Magn Reson Med 2017. [PMID: 28635034 PMCID: PMC5811774 DOI: 10.1002/mrm.26784] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
PURPOSE Dielectric resonator antenna (DRAs) are compact structures that exhibit low coupling between adjacent elements and therefore can be used as MRI transmit arrays. In this study, we use very high permittivity materials to construct modular flexible transceive arrays of a variable numbers of elements for operation at 7T. METHODS DRAs were constructed using rectangular blocks of ceramic (lead zirconate titanate, εr = 1070) with the transverse electric (TE)01 mode tuned to 298 MHz. Finite-difference time-domain simulations were used to determine the B1 and specific absorption rate distributions. B1+ maps were acquired in a phantom to validate the simulations. Performance was compared to an equally sized surface coil. In vivo images were acquired of the wrist (four elements), ankle (seven elements), and calf muscle (16 elements). RESULTS Coupling between DRAs spaced 5 mm apart on a phantom was -18.2 dB compared to -9.1 dB for equivalently spaced surface coils. DRAs showed a higher B1+ intensity close to the antenna but a lower penetration depth compared to the surface coil. CONCLUSION DRAs show very low coupling compared to equally sized surface coils and can be used in transceive arrays without requiring decoupling networks. The penetration depth of the current DRA geometry means they are ideally suited to imaging of extremities. Magn Reson Med 79:1781-1788, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
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Affiliation(s)
- Thomas P A O'Reilly
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Thomas Ruytenberg
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Andrew G Webb
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
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Ertürk MA, Wu X, Eryaman Y, Van de Moortele PF, Auerbach EJ, Lagore RL, DelaBarre L, Vaughan JT, Uğurbil K, Adriany G, Metzger GJ. Toward imaging the body at 10.5 tesla. Magn Reson Med 2016; 77:434-443. [PMID: 27770469 DOI: 10.1002/mrm.26487] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 09/08/2016] [Accepted: 09/11/2016] [Indexed: 01/29/2023]
Abstract
PURPOSE To explore the potential of performing body imaging at 10.5 Tesla (T) compared with 7.0T through evaluating the transmit/receive performance of similarly configured dipole antenna arrays. METHODS Fractionated dipole antenna elements for 10.5T body imaging were designed and evaluated using numerical simulations. Transmit performance of antenna arrays inside the prostate, kidneys and heart were investigated and compared with those at 7.0T using both phase-only radiofrequency (RF) shimming and multi-spoke pulses. Signal-to-noise ratio (SNR) comparisons were also performed. A 10-channel antenna array was constructed to image the abdomen of a swine at 10.5T. Numerical methods were validated with phantom studies at both field strengths. RESULTS Similar power efficiencies were observed inside target organs with phase-only shimming, but RF nonuniformity was significantly higher at 10.5T. Spokes RF pulses allowed similar transmit performance with accompanying local specific absorption rate increases of 25-90% compared with 7.0T. Relative SNR gains inside the target anatomies were calculated to be >two-fold higher at 10.5T, and 2.2-fold SNR gain was measured in a phantom. Gradient echo and fast spin echo imaging demonstrated the feasibility of body imaging at 10.5T with the designed array. CONCLUSION While comparable power efficiencies can be achieved using dipole antenna arrays with static shimming at 10.5T; increasing RF nonuniformities underscore the need for efficient, robust, and safe parallel transmission methods. Magn Reson Med 77:434-443, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- M Arcan Ertürk
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Xiaoping Wu
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Yiğitcan Eryaman
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | | | - Edward J Auerbach
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Russell L Lagore
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Lance DelaBarre
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - J Thomas Vaughan
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.,Department of Biomedical Engineering in The Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, New York, USA
| | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
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Niendorf T, Paul K, Oezerdem C, Graessl A, Klix S, Huelnhagen T, Hezel F, Rieger J, Waiczies H, Frahm J, Nagel AM, Oberacker E, Winter L. W(h)ither human cardiac and body magnetic resonance at ultrahigh fields? technical advances, practical considerations, applications, and clinical opportunities. NMR IN BIOMEDICINE 2016; 29:1173-97. [PMID: 25706103 DOI: 10.1002/nbm.3268] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Revised: 12/26/2014] [Accepted: 01/13/2015] [Indexed: 05/12/2023]
Abstract
The objective of this study was to document and review advances and groundbreaking progress in cardiac and body MR at ultrahigh fields (UHF, B0 ≥ 7.0 T) with the goal to attract talent, clinical adopters, collaborations and resources to the biomedical and diagnostic imaging communities. This review surveys traits, advantages and challenges of cardiac and body MR at 7.0 T. The considerations run the gamut from technical advances to clinical opportunities. Key concepts, emerging technologies, practical considerations, frontier applications and future directions of UHF body and cardiac MR are provided. Examples of UHF cardiac and body imaging strategies are demonstrated. Their added value over the kindred counterparts at lower fields is explored along with an outline of research promises. The achievements of cardiac and body UHF-MR are powerful motivators and enablers, since extra speed, signal and imaging capabilities may be invested to overcome the fundamental constraints that continue to hamper traditional cardiac and body MR applications. If practical obstacles, concomitant physics effects and technical impediments can be overcome in equal measure, sophisticated cardiac and body UHF-MR will help to open the door to new MRI and MRS approaches for basic research and clinical science, with the lessons learned at 7.0 T being transferred into broad clinical use including diagnostics and therapy guiding at lower fields. Copyright © 2015 John Wiley & Sons, Ltd.
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Affiliation(s)
- Thoralf Niendorf
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
- DZHK (German Centre for Cardiovascular Research), Partner Site, Berlin, Germany
| | - Katharina Paul
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Celal Oezerdem
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Andreas Graessl
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Sabrina Klix
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Till Huelnhagen
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Fabian Hezel
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | | | | | - Jens Frahm
- Biomedizinische NMR Forschungs GmbH, am Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany
- DZHK (German Centre for Cardiovascular Research), Partner Site, Göttingen, Germany
| | - Armin M Nagel
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Eva Oberacker
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Lukas Winter
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
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Electrodynamics and radiofrequency antenna concepts for human magnetic resonance at 23.5 T (1 GHz) and beyond. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2016; 29:641-56. [PMID: 27097905 DOI: 10.1007/s10334-016-0559-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Revised: 04/04/2016] [Accepted: 04/06/2016] [Indexed: 10/21/2022]
Abstract
OBJECTIVE This work investigates electrodynamic constraints, explores RF antenna concepts and examines the transmission fields (B 1 (+) ) and RF power deposition of dipole antenna arrays for (1)H magnetic resonance of the human brain at 1 GHz (23.5 T). MATERIALS AND METHODS Electromagnetic field (EMF) simulations are performed in phantoms with average tissue simulants for dipole antennae using discrete frequencies [300 MHz (7.0 T) to 3 GHz (70.0 T)]. To advance to a human setup EMF simulations are conducted in anatomical human voxel models of the human head using a 20-element dipole array operating at 1 GHz. RESULTS Our results demonstrate that transmission fields suitable for (1)H MR of the human brain can be achieved at 1 GHz. An increase in transmit channel density around the human head helps to enhance B 1 (+) in the center of the brain. The calculated relative increase in specific absorption rate at 23.5 versus 7.0 T was below 1.4 (in-phase phase setting) and 2.7 (circular polarized phase setting) for the dipole antennae array. CONCLUSION The benefits of multi-channel dipole antennae at higher frequencies render MR at 23.5 T feasible from an electrodynamic standpoint. This very preliminary finding opens the door on further explorations that might be catalyzed into a 20-T class human MR system.
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Ertürk MA, Raaijmakers AJE, Adriany G, Uğurbil K, Metzger GJ. A 16-channel combined loop-dipole transceiver array for 7 Tesla body MRI. Magn Reson Med 2016; 77:884-894. [PMID: 26887533 DOI: 10.1002/mrm.26153] [Citation(s) in RCA: 112] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Revised: 12/21/2015] [Accepted: 01/17/2016] [Indexed: 12/17/2022]
Abstract
PURPOSE To develop a 16-channel transceive body imaging array at 7.0 T with improved transmit, receive, and specific absorption rate (SAR) performance by combining both loop and dipole elements and using their respective and complementary near and far field characteristics. METHODS A 16-channel radiofrequency (RF) coil array consisting of eight loop-dipole blocks (16LD) was designed and constructed. Transmit and receive performance was quantitatively investigated in phantom and human model simulations, and experiments on five healthy volunteers inside the prostate. Comparisons were made with 16-channel microstrip line (16ML) and 10-channel fractionated dipole antenna (10DA) arrays. The 16LD was used to acquire anatomic and functional images of the prostate, kidneys, and heart. RESULTS The 16LD provided > 14% improvements in the signal-to-noise ratio (SNR), peak B1+, B1+ transmit, and SAR efficiencies over the 16ML and 10DA in simulations inside the prostate. Experimentally, the 16LD had > 20% higher SNR and B1+ transmit efficiency compared with other arrays, and achieved up to 51.8% higher peak B1+ compared with 10DA. CONCLUSION Combining loop and dipole elements provided a body imaging array with high channel count and density while limiting inter-element coupling. The 16LD improved both near and far-field performance compared with existing 7.0T body arrays and provided high-quality MRI of the prostate kidneys and heart. Magn Reson Med 77:884-894, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- M Arcan Ertürk
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | | | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
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12
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Ertürk MA, Tian J, Van de Moortele PF, Adriany G, Metzger GJ. Development and evaluation of a multichannel endorectal RF coil for prostate MRI at 7T in combination with an external surface array. J Magn Reson Imaging 2015; 43:1279-87. [PMID: 26584144 DOI: 10.1002/jmri.25099] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Revised: 09/18/2015] [Accepted: 09/21/2015] [Indexed: 11/05/2022] Open
Abstract
PURPOSE To develop and evaluate a sterilizable multichannel endorectal coil (ERC) for use in combination with an external surface array (ESA) for high-resolution anatomical and functional studies of the prostate at 7T. MATERIALS AND METHODS A two-loop ERC (ERC-2L) and a microstrip-loop ERC (ERC-ML) were compared at 7T in terms of transmit and receive performance. The best-performing ERC was evaluated alone and in combination with the ESA through 1) simulations on both phantom and an anatomically correct numerical human model to assess B1+ transmit and specific absorption rate (SAR) efficiencies, and 2) phantom experiments to calculate B1+ transmit efficiency and signal-to-noise ratio (SNR). Phantom studies were also performed to look at heating when using the ERC as a transmitter and for comparing the new coil against a single-channel balloon-type ERC (ERC-b). High-resolution magnetic resonance imaging (MRI) acquisitions were performed on a single healthy subject using the two-channel ERC combined with the ESA. RESULTS Compared to the ERC-ML, the ERC-2L demonstrated 20% higher SAR efficiency and higher SNR 3 cm from the coil. The presence of a tuned and detuned ERC-2L did not alter the peak local SAR of the ESA alone; however, the detuned ERC-2L had 45% less peak local SAR around the rectum compared to the tuned ERC-2L. The receive-only version of the ERC-2L improved the SNR 4.7-fold and 1.3-fold compared to the ESA and ERC-b, respectively. In combination with the ESA, the ERC-2L supported in-plane voxel-size of 0.36 × 0.36 mm(2) in T2 -weighted anatomic imaging. CONCLUSION The reusable ERC-2L combined with an ESA offers a high SNR imaging platform for translational studies of the prostate at 7T. J. Magn. Reson. Imaging 2016;43:1279-1287.
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Affiliation(s)
- M Arcan Ertürk
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Jinfeng Tian
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | | | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA
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Duan Q, Nair G, Gudino N, de Zwart JA, van Gelderen P, Murphy-Boesch J, Reich DS, Duyn JH, Merkle H. A 7T spine array based on electric dipole transmitters. Magn Reson Med 2015; 74:1189-97. [PMID: 26190585 DOI: 10.1002/mrm.25817] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Revised: 04/30/2015] [Accepted: 05/27/2015] [Indexed: 11/10/2022]
Abstract
PURPOSE The goal of this study was to explore the feasibility of using an array of electric dipole antennas for RF transmission in spine MRI at high fields. METHOD A two-channel transmit array based on an electric dipole design was quantitatively optimized for 7T spine imaging and integrated with a receive array combining eight loop coils. Using B1+ mapping, the transmit efficiency of the dipole array was compared with a design using quadrature loop pairs. The radiofrequency energy deposition for each array was measured using a home-built dielectric phantom and MR thermometry. The performance of the proposed array was qualitatively demonstrated in human studies. RESULTS The results indicate dramatically improved transmit efficiency for the dipole design compared with the loop excitation. A gain of up to 76% was achieved within the spinal region. CONCLUSION For imaging of the spine, electric dipole-based transmitters provide an attractive alternative to the traditional loop-based design. Easy integration with existing receive array technology facilitates practical use at high fields.
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Affiliation(s)
- Qi Duan
- Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
| | - Govind Nair
- Division of Neuroimmunology and Neurovirology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
| | - Natalia Gudino
- Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
| | - Jacco A de Zwart
- Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
| | - Peter van Gelderen
- Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
| | - Joe Murphy-Boesch
- Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
| | - Daniel S Reich
- Division of Neuroimmunology and Neurovirology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
| | - Jeff H Duyn
- Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
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15
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Oezerdem C, Winter L, Graessl A, Paul K, Els A, Weinberger O, Rieger J, Kuehne A, Dieringer M, Hezel F, Voit D, Frahm J, Niendorf T. 16-channel bow tie antenna transceiver array for cardiac MR at 7.0 tesla. Magn Reson Med 2015; 75:2553-65. [PMID: 26183320 DOI: 10.1002/mrm.25840] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Revised: 05/22/2015] [Accepted: 06/20/2015] [Indexed: 02/03/2023]
Abstract
PURPOSE To design, evaluate, and apply a bow tie antenna transceiver radiofrequency (RF) coil array tailored for cardiac MRI at 7.0 Tesla (T). METHODS The radiofrequency (RF) coil array comprises 16 building blocks each containing a bow tie shaped λ/2-dipole antenna. Numerical simulations were used for transmission field homogenization and RF safety validation. RF characteristics were examined in a phantom study. The array's suitability for high spatial resolution two-dimensional (2D) CINE imaging and for real time imaging of the heart was examined in a volunteer study. RESULTS The arrays transmission fields and RF characteristics are suitable for cardiac MRI at 7.0T. The coil performance afforded a spatial resolution as good as (0.8 × 0.8 × 2.5) mm(3) for segmented 2D CINE MRI at 7.0T which is by a factor of 12 superior versus standardized protocols used in clinical practice at 1.5T. The proposed transceiver array supports 1D acceleration factors of up to R = 6 without impairing image quality significantly. CONCLUSION The 16-channel bow tie antenna transceiver array supports accelerated and high spatial resolution cardiac MRI. The array is compatible with multichannel transmission and provides a technological basis for future clinical assessment of parallel transmission techniques at 7.0 Tesla. Magn Reson Med 75:2553-2565, 2016. © 2015 Wiley Periodicals, Inc.
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Affiliation(s)
- Celal Oezerdem
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Lukas Winter
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Andreas Graessl
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Katharina Paul
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Antje Els
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Oliver Weinberger
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | | | | | - Matthias Dieringer
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Berlin, Germany
| | - Fabian Hezel
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany
| | - Dirk Voit
- Biomedizinische NMR Forschungs GmbH am Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany
| | - Jens Frahm
- Biomedizinische NMR Forschungs GmbH am Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Göttingen, Germany
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Berlin, Germany
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16
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Rivera DS, Wijnen JP, van der Kemp WJM, Raaijmakers AJ, Luijten PR, Klomp DWJ. MRI and 31
P magnetic resonance spectroscopy hardware for axillary lymph node investigation at 7T. Magn Reson Med 2014; 73:2038-46. [DOI: 10.1002/mrm.25304] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Revised: 05/07/2014] [Accepted: 05/07/2014] [Indexed: 12/19/2022]
Affiliation(s)
- Debra S. Rivera
- Department of Neurophysics; Max Planck Institute for Human Cognitive and Brain Sciences; Leipzig Germany
| | - Jannie P. Wijnen
- Department of Radiology; University Medical Center Utrecht; Utrecht the Netherlands
| | | | | | - Peter R. Luijten
- Department of Radiology; University Medical Center Utrecht; Utrecht the Netherlands
| | - Dennis W. J. Klomp
- Department of Radiology; University Medical Center Utrecht; Utrecht the Netherlands
- Department of Radiology; University Medical Center Nijmegen; Nijmegen the Netherlands
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17
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Ipek O, Raaijmakers AJ, Lagendijk JJ, Luijten PR, van den Berg CAT. Intersubject local SAR variation for 7T prostate MR imaging with an eight-channel single-side adapted dipole antenna array. Magn Reson Med 2013; 71:1559-67. [PMID: 23754584 DOI: 10.1002/mrm.24794] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2012] [Revised: 03/27/2013] [Accepted: 04/13/2013] [Indexed: 11/07/2022]
Abstract
PURPOSE Surface transmit arrays used in ultra-high field body MRI require local specific absorption rate (SAR) assessment. As local SAR cannot be measured directly, local SAR is determined by simulations using dielectric patient models. In this study, the inter-patient local SAR variation is investigated for 7T prostate imaging with the single-side adapted dipole antenna array. METHOD Four-dedicated dielectric models were created by segmenting Dixon water-fat separated images that were obtained from four subjects with a 1.5T scanner and the surface array in place. Electromagnetic simulations were performed to calculate the SAR distribution for each model. Radio frequency (RF) exposure variations were determined by analyzing the SAR(10g) distributions (1) with one element active, (2) using a Q-matrix eigenvalue/eigenvector approach, (3) with the maximum potential SAR in each voxel, and (4) for a phase shimmed prostate measurement. RESULTS Maximum potential local SAR levels for 1 W time-averaged accepted power per transmit channel range from 4.1 to 7.1 W/kg. CONCLUSION These variations show that one model is not sufficient to determine safe scan settings. For the operation of the surface array conservative power settings were derived based on a worst-case SAR evaluation and the most SAR-sensitive body model.
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Affiliation(s)
- Ozlem Ipek
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, the Netherlands
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