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Du F, Li N, Yang X, Zhang B, Zhang X, Li Y. Design and construction of an 8-channel transceiver coil array for rat imaging at 9.4 T. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 351:107302. [PMID: 37116433 DOI: 10.1016/j.jmr.2022.107302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 08/27/2022] [Accepted: 09/11/2022] [Indexed: 05/29/2023]
Abstract
Ultra-high field (UHF) small animal magnetic resonance imaging (MRI) is a crucial tool permitting investigation of metabolic diseases and identification of imaging biomarkers suitable for clinical diagnosis and translation. Radiofrequency (RF) coils are critical components in enabling acquisition of high-quality rat abdomen MRI data. However, efficient RF coils with high-channel count, capable of sensitive and accelerated rat abdomen imaging at 9.4 T, are not available commercially. The SNR of the commonly-used 9.4 T birdcage coil is relatively weak, particularly in the peripheral area of the subject. In addition, the birdcage is not readily to perform parallel imaging due to unavailability of the required multiple channels. Consequently, the extended scanning duration may cause unnecessary hazards to the rat. In this work, an 8-channel transceiver coil array was designed and constructed to provide good image quality and large coverage for rat abdomen imaging at 9.4 T. The structure and the performance of the developed array was optimized and evaluated by numerical electromagnetic simulations and bench tests, respectively. The MR imaging experiments in phantoms and rat models were also performed on a Bruker 9.4 T preclinical MRI system to validate the feasibility of the proposed design. The coil array supports a one-dimensional acceleration factor up to R = 4, providing good parallel imaging capabilities. These results demonstrated that the proposed 8-channel transceiver coil array for rat imaging has the ability to obtain high spatial resolution of rat abdomen anatomical structure images at 9.4 T.
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Affiliation(s)
- Feng Du
- Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China; Key Laboratory for Magnetic Resonance and Multimodality Imaging of Guangdong Province, Shenzhen 518055, Guang Dong, China
| | - Nan Li
- Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China; Key Laboratory for Magnetic Resonance and Multimodality Imaging of Guangdong Province, Shenzhen 518055, Guang Dong, China
| | - Xing Yang
- Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China; Key Laboratory for Magnetic Resonance and Multimodality Imaging of Guangdong Province, Shenzhen 518055, Guang Dong, China
| | - Baogui Zhang
- State Key Laboratory of Brain and Cognitive Sciences, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; University of Chinese Academy of Sciences, Beijing, China; Brainnetome Center, Institute of Automation, Chinese Academy of Sciences, Beijing 100190, China
| | - Xiaoliang Zhang
- Department of Biomedical Engineering, State University of New York at Buffalo, NY, United States., Buffalo, NY, United States
| | - Ye Li
- Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China; Key Laboratory for Magnetic Resonance and Multimodality Imaging of Guangdong Province, Shenzhen 518055, Guang Dong, China.
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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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Yang Z, Lu M, Drake G, Wang F, Yang PF, Chen LM, Gore JC, Yan X. RF shielding designs for birdcage coils for preclinical MRI at 9.4 T. Magn Reson Imaging 2022; 94:1-6. [PMID: 36075493 DOI: 10.1016/j.mri.2022.08.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Revised: 08/19/2022] [Accepted: 08/31/2022] [Indexed: 11/19/2022]
Abstract
Birdcage coils are widely used in preclinical MRI as they perform well, allow for quadrature drive, and can provide a homogeneous transmit field. Unlike in larger bore scanners, an RF shield is essential to avoid strong cross-talk with gradient coils that are in close proximity. However, gradient switching induces eddy currents that heat the shield and coil and impair the temporal signal-to-noise ratio (tSNR). The motivation of this study is to investigate the performance of different designs of RF shields on a birdcage coil used for high resolution functional MRI of small primates at 9.4 T. We found the choice of materials for RF shields significantly affected ghosting and tSNR in fMRI scans. Both ultrathin foils and a slotted pattern reduce eddy currents and improve imaging quality. Our results also demonstrate that a 9-um-thick copper foil is sufficiently thin to reduce the eddy current effects for high-resolution fMRI scans and there is no need for high-cost 4-um-thick foil. For slotted shields, our results demonstrate that the number of slots should be carefully considered, and an excessive number of slots can lead to a lower SNR and tSNR. We believe the results from this study can be used as a reference to design future RF coil shields selection for preclinical scanners.
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Affiliation(s)
- Zhangyan Yang
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
| | - Ming Lu
- College of Nuclear Equipment and Nuclear Engineering, Yantai University, Yantai, Shandong, China
| | - Gary Drake
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Feng Wang
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Pai-Feng Yang
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Li Min Chen
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
| | - John C Gore
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA; Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
| | - Xinqiang Yan
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA.
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Abstract
Purpose: We proposed and developed a new microstrip transmission line radiofrequency (RF) coil for a positron emission tomography (PET) insert for MRI, which has low electrical interactions with PET shield boxes. We performed imaging experiments using a single-channel and a four-channel proposed RF coils for proof-of-concept. Methods: A conventional microstrip coil consists of a microstrip conductor, a ground conductor, and a dielectric between the two conductors. We proposed a microstrip coil for the PET insert that replaced the conventional single-layer ground conductor with the RF shield of the PET insert. A dielectric material, which could otherwise attenuate gamma photons radiated from the PET imaging tracer, was not used. As proof-of-concept, we compared conventional and the proposed single-channel coils. To study multichannel performance, we further developed a four-channel proposed RF coil. Since the MRI system had a single-channel transmission port, an interfacing four-way RF power division circuit was designed. The coils were implemented as both RF transmitters and receivers in a cylindrical frame of diameter 150 mm. Coil bench performances were tested with a network analyzer (Rohde & Schwarz, Germany), and a homogeneous phantom study was conducted for gradient echo imaging and RF field (B1) mapping in a 3T clinical MRI system (Verio, Siemens, Erlangen, Germany). Results: For all coils, the power reflection coefficient was below −30 dB, and the transmission coefficients in the four-channel configuration were near or below −20 dB. The comparative single-channel coil study showed good similarity between the conventional and proposed coils. The gradient echo image of the four-channel coil showed expected flashing image intensity near the coils and no phase distortion was visible. Transmit B1 field map resembled the image performance. Conclusion: The proposed PET-microstrip coil performed similarly to the conventional microstrip transmission line coil and is promising for the development of a compact coil-PET system capable of simultaneous PET/MRI analysis with an existing MRI system.
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Affiliation(s)
- Md Shahadat Hossain Akram
- National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology
| | - Takayuki Obata
- National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology
| | - Taiga Yamaya
- National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology
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Connell IRO, Menon RS. Shape Optimization of an Electric Dipole Array for 7 Tesla Neuroimaging. IEEE TRANSACTIONS ON MEDICAL IMAGING 2019; 38:2177-2187. [PMID: 30908199 DOI: 10.1109/tmi.2019.2906507] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Radio-frequency (RF) arrays constructed using electric dipoles have potential benefits for transmit and receive applications using the ultra-high field (UHF) MRI. This paper examines some of the implementation barriers regarding dipole RF arrays for human head imaging at 7 T. The dipole array was constructed with conformal, meandered dipoles with dimensions selected utilizing an evolutionary-based optimization routine to shape-optimize the dipole structure. Coupling matrix synthesis (CMS) was utilized to decouple the dipole array. Mean and worst-case transmission between nearest-neighbour dipoles was -17.2 and -15.5 dB, respectively (±2.4 dB). Transmit efficiencies of 24.6 nT/V for the entire brain and 26.0 nT/V across the axial slice were observed. The total and peak 10-g SAR, normalized to 1 Watt accepted input power per channel, was 0.163 and 0.601 W/kg, respectively. Maximum and mean noise correlations were -17 dB and -32 dB, respectively. The use of both CMS and a novel shape optimization routine to design a dipole array translated into sufficient transmit uniformity with a simultaneous reduction in 10-g SAR in comparison to a non-optimized dipole array of the same geometry. As a receiver, the dipole array maintained high orthogonality between elements, resulting in strong parallel imaging performance.
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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: 6] [Impact Index Per Article: 1.0] [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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Rispoli JV, Wilcox MD, By S, Wright SM, McDougall MP. Effects of coplanar shielding for high field MRI. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2017; 2016:6250-6253. [PMID: 28269680 DOI: 10.1109/embc.2016.7592157] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
This work investigates the efficacy of "coplanar shielding," in which copper shields are oriented concentric and coplanar to the RF coils rather than implemented as a full ground plane behind them. Following FDTD simulations to determine optimal shielding parameters, two coil geometries were constructed: a circular loop surface coil and a half-volume five-element receive array. Each was evaluated using bench measurements with and without coplanar shielding. Imaging, including accelerated SENSE imaging, was performed with the shielded and unshielded receive arrays on a whole-body 7T scanner. Results from modeled and fabricated coils showed good agreement with improvements in Q factors for all cases. Imaging showed substantial improvements in SNR and g-factors for the coplanar shielded array.
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Yan X, Xue R, Zhang X. Closely-spaced double-row microstrip RF arrays for parallel MR imaging at ultrahigh fields. APPLIED MAGNETIC RESONANCE 2015; 46:1239-1248. [PMID: 26508810 PMCID: PMC4617305 DOI: 10.1007/s00723-015-0712-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Radiofrequency (RF) coil arrays with high count of elements, e.g., closely-spaced multi-row arrays, exhibit superior parallel imaging performance in MRI. However, it is technically challenging and time-consuming to build multi-row arrays due to complex coupling issues. This paper presents a novel and simple method for closely-spaced multi-row RF array designs. Induced current elimination (ICE) decoupling method has shown the capability of reducing coupling between microstrip elements from different rows. In this study, its capability for decoupling array elements from the same row was investigated and validated by bench tests, with an isolation improvement from -8.9 dB to -20.7 dB. Based on this feature, a closely-spaced double-row microstrip array with 16 elements was built at 7T. S21 between any two elements of the 16-channel closely-spaced was better than -14 dB. In addition, its feasibility and performance was validated by MRI experiments. No significant image reconstruction- related noise amplifications were observed for parallel imaging even when reduced factor (R) achieves 4. The experimental results demonstrated that the proposed design might be a simple and efficient approach in fabricating closely-spaced multi-row RF arrays.
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Affiliation(s)
- Xinqiang Yan
- Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
- Beijing Engineering Research Center of Radiographic Techniques and Equipment, Beijing 100049, China
| | - Rong Xue
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Xiaoliang Zhang
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California 94158, USA
- UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, California 94158, USA
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Woo MK, Hong SM, Lee J, Kang CK, Park SY, Son YD, Kim YB, Cho ZH. Extended Monopole antenna Array with individual Shield (EMAS) coil: An improved monopole antenna design for brain imaging at 7 tesla MRI. Magn Reson Med 2015. [PMID: 26198163 DOI: 10.1002/mrm.25837] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
PURPOSE To propose a new Extended Monopole antenna Array with individual Shields (EMAS) coil that improves the B1 field coverage and uniformity along the z-direction. METHODS To increase the spatial coverage of Monopole antenna Array (MA) coil, each monopole antenna was shielded and extended in length. Performance of this new coil, which is referred to as EMAS coil, was compared with the original MA coil and an Extended Monopole antenna Array coil with no shield (EMA). For comparison, flip angle, signal-to-noise ratio (SNR), and receive sensitivity maps were measured at multiple regions of interest (ROIs) in the brain. RESULTS The EMAS coil demonstrated substantially larger flip angle and receive sensitivity than the MA and EMA coils in the inferior aspect of the brain. In the brainstem ROI, for example, the flip angle in the EMAS coil was increased by 45.5% (or 60.0%) and the receive sensitivity was increased by 26.9% (or 14.9%), resulting in an SNR gain of 84.8% (or 76.3%) when compared with the MA coil (or EMA). CONCLUSION The EMAS coil provided 25.7% (or 24.4%) more uniform B1+ field distribution compared with the MA (or EMA) coil in sagittal. The EMAS coil successfully extended the imaging volume in lower part of the brain. Magn Reson Med 75:2566-2572, 2016. © 2015 Wiley Periodicals, Inc.
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Affiliation(s)
- Myung-Kyun Woo
- Department of Electrical and Computer Engineering, Seoul National University, Seoul, Republic of Korea
| | - Suk-Min Hong
- Institute of Neuroscience and Medicine-4, Forschungszentrum Jülich, Jülich, Germany
| | - Jongho Lee
- Department of Electrical and Computer Engineering, Seoul National University, Seoul, Republic of Korea
| | - Chang-Ki Kang
- Neuroscience Research Institute, Gachon University, Incheon, Republic of Korea; Department of Radiological Science, College of Health Science, Gachon University, Incheon, Republic of Korea
| | - Sung-Yeon Park
- Neuroscience Research Institute, Gachon University, Incheon, Republic of Korea
| | - Young-Don Son
- Neuroscience Research Institute, Gachon University, Incheon, Republic of Korea; Department of Biomedical Engineering, College of Health Science, Gachon University, Incheon, Republic of Korea
| | - Young-Bo Kim
- Neuroscience Research Institute, Gachon University, Incheon, Republic of Korea
| | - Zang-Hee Cho
- Graduate School of Convergence Science and Technology, Seoul National University, Suwon, Republic of Korea
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Yan X, Wei L, Xue R, Zhang X. Hybrid monopole/loop coil array for human head MR imaging at 7T. APPLIED MAGNETIC RESONANCE 2015; 46:541-550. [PMID: 26120252 PMCID: PMC4479412 DOI: 10.1007/s00723-015-0656-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The monopole coil and loop coil have orthogonal radiofrequency (RF) fields and thus are intrinsically decoupled electromagnetically if they are laid out appropriately. In this study, we proposed a hybrid monopole/loop technique which could combine the advantages of both loop arrays and monopole arrays. To investigate this technique, a hybrid RF coil array containing 4 monopole channels and 4 loop channels was developed for human head MR imaging at 7T. In vivo MR imaging and g-factor results using monopole-only channels, loop-only channels and all channels of the hybrid array were acquired and evaluated. Compared with the monopole-only and loop-only channels, the proposed hybrid array has higher SNR and better parallel imaging performance. Sufficient electromagnetic decoupling and diverse RF magnetic field (B1) distributions of monopole channels and loop channels may contribute to this performance improvement. From experimental results, the hybrid monopole/loop array has low g-factor and excellent SNR at both periphery and center of the brain, which is valuable for human head imaging at ultrahigh fields.
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Affiliation(s)
- Xinqiang Yan
- Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
- Beijing Engineering Research Center of Radiographic Techniques and Equipment, Beijing 100049, China
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Long Wei
- Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
- Beijing Engineering Research Center of Radiographic Techniques and Equipment, Beijing 100049, China
| | - Rong Xue
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- China and Beijing Institute for Brain Disorders, Beijing 100053, China
| | - Xiaoliang Zhang
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California 94158, USA
- UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, California 94158, USA
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Connell IRO, Gilbert KM, Abou-Khousa MA, Menon RS. Design of a parallel transmit head coil at 7T with magnetic wall distributed filters. IEEE TRANSACTIONS ON MEDICAL IMAGING 2015; 34:836-845. [PMID: 25415982 DOI: 10.1109/tmi.2014.2370533] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Ultra-high field magnetic resonance imaging (MRI) scanners ( ≥ 7T) require radio-frequency (RF) coils to operate in the range of the electromagnetic spectrum where the effective wavelength in the tissue approaches the patient dimensions. Multi-channel transmit arrays, driven in parallel, have been developed to increase the transmit field (B1(+)) uniformity in this wavelength regime. However, the closely packed array elements interact through mutual coupling. This paper expands on the ability of a distributed planar filter (the "magnetic wall") to decouple individual elements in an entire array. A transmit RF coil suitable for neuroimaging at 7T was constructed. The transmit coil, composed of 10 individual surface coil elements, was decoupled with magnetic walls. A separate receive coil array was used for signal reception. The hardware and imaging performance of the transmit coil was validated with electromagnetic simulation, bench-top measurements, and in vivo MRI experiments. Analysis and measurements confirmed that the magnetic wall decoupling method provides high isolation between transmit channels, while minimally affecting the B1(+) field profiles. Electromagnetic simulations confirmed that the decoupling method did not correlate to local specific absorption rate (SAR) "hot spots" or increase local-to-global SAR fractions in comparison to previously reported 7T multi-channel transmit arrays employing different decoupling methods.
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12
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Yan X, Pedersen JO, Wei L, Zhang X, Xue R. Multichannel Double-Row Transmission Line Array for Human MR Imaging at Ultrahigh Fields. IEEE Trans Biomed Eng 2015; 62:1652-9. [PMID: 25706499 DOI: 10.1109/tbme.2015.2401976] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
OBJECTIVE In microstrip transmission line (MTL) transmit/receive (transceive) arrays used for ultrahigh field MRI, the array length is often constrained by the required resonant frequency, limiting the image coverage. The purpose of this study is to increase the imaging coverage and also improve its parallel imaging capability by utilizing a double-row design. METHODS A 16-channel double-row MTL transceive array was designed, constructed, and tested for human head imaging at 7 T. Array elements between two rows were decoupled by using the induced current elimination or magnetic wall decoupling technique. In vivo human head images were acquired, and g-factor results were calculated to evaluate the performance of this double-row array. RESULTS Testing results showed that all coil elements were well decoupled with a better than -18 dB transmission coefficient between any two elements. The double-row array improves the imaging quality of the lower portion of the human head, and has low g-factors even at high acceleration rates. CONCLUSION Compared with a regular single-row MTL array, the double-row array demonstrated a larger imaging coverage along the z-direction with improved parallel imaging capability. SIGNIFICANCE The proposed technique is particularly suitable for the design of large-sized transceive arrays with large channel counts, which ultimately benefits the imaging performance in human MRI.
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Zhao Y, Zhao T, Raval SB, Krishnamurthy N, Zheng H, Harris CT, Handler WB, Chronik BA, Ibrahim TS. Dual optimization method of radiofrequency and quasistatic field simulations for reduction of eddy currents generated on 7T radiofrequency coil shielding. Magn Reson Med 2014; 74:1461-9. [PMID: 25367703 DOI: 10.1002/mrm.25424] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Revised: 06/26/2014] [Accepted: 08/04/2014] [Indexed: 01/20/2023]
Abstract
PURPOSE To optimize the design of radiofrequency (RF) shielding of transmit coils at 7T and reduce eddy currents generated on the RF shielding when imaging with rapid gradient waveforms. METHODS One set of a four-element, 2 × 2 Tic-Tac-Toe head coil structure was selected and constructed to study eddy currents on the RF coil shielding. The generated eddy currents were quantitatively studied in the time and frequency domains. The RF characteristics were studied using the finite difference time domain method. Five different kinds of RF shielding were tested on a 7T MRI scanner with phantoms and in vivo human subjects. RESULTS The eddy current simulation method was verified by the measurement results. Eddy currents induced by solid/intact and simple-structured slotted RF shielding significantly distorted the gradient fields. Echo-planar images, B1+ maps, and S matrix measurements verified that the proposed slot pattern suppressed the eddy currents while maintaining the RF characteristics of the transmit coil. CONCLUSION The presented dual-optimization method could be used to design RF shielding and reduce the gradient field-induced eddy currents while maintaining the RF characteristics of the transmit coil.
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Affiliation(s)
- Yujuan Zhao
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Tiejun Zhao
- Siemens Medical Solutions, Pittsburgh, Pennsylvania, USA
| | - Shailesh B Raval
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.,Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | | | - Hai Zheng
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Chad T Harris
- Department of Physics and Astronomy, University of Western Ontario, London, Canada
| | - William B Handler
- Department of Physics and Astronomy, University of Western Ontario, London, Canada
| | - Blaine A Chronik
- Department of Physics and Astronomy, University of Western Ontario, London, Canada
| | - Tamer S Ibrahim
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.,Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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Hong SM, Park JH, Woo MK, Kim YB, Cho ZH. New design concept of monopole antenna array for UHF 7T MRI. Magn Reson Med 2013; 71:1944-52. [PMID: 23818275 DOI: 10.1002/mrm.24844] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2013] [Revised: 05/15/2013] [Accepted: 05/23/2013] [Indexed: 11/06/2022]
Abstract
PURPOSE We have developed and evaluated a monopole antenna array that can increase sensitivity at the center of the brain for 7T MRI applications. METHODS We have developed a monopole antenna array that has half the length of a conventional dipole antenna with eight channels for brain imaging with a 7T MRI. The eight-channel monopole antenna array and conventional eight-channel transceiver surface coil array were evaluated and compared in terms of transmit properties, specific absorption ratio (SAR), and sensitivity. The sensitivity maps were generated by dividing the SNR map by the flip angle distribution. RESULTS A single surface coil provides asymmetric sensitivity resulting in reduced sensitivity at the center of the brain. In contrast, a single monopole antenna provides higher sensitivity at the center of the brain. Moreover, the monopole antenna array provides uniform sensitivity over the entire brain, and the sensitivity gain was 1.5 times higher at the center of the brain compared with the surface coil array. CONCLUSION The monopole antenna array is a promising candidate for MRI applications, especially for brain imaging in a 7T MRI because it provides increased sensitivity at the center of the brain.
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Affiliation(s)
- Suk-Min Hong
- Neuroscience Research Institute, Gachon University, Incheon, Korea
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15
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Pang Y, Zhang X. Precompensation for mutual coupling between array elements in parallel excitation. Quant Imaging Med Surg 2012; 1:4-10. [PMID: 23243630 DOI: 10.3978/j.issn.2223-4292.2011.11.02] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Accepted: 11/09/2011] [Indexed: 11/14/2022]
Abstract
Parallel transmission or excitation has been suggested to perform multi-dimensional spatial selective excitation to shorten the pulse width using a coil array and the sensitivity information. The mutual coupling between array elements has been a critical technical issue in RF array designs, which can cause artifacts on the excitation profile, leading to degraded excitation performance and image quality. In this work, a precompensation method is proposed to address the mutual coupling effect in parallel transmission by introducing the mutual coupling coefficient matrix into the RF pulses design procedure of the parallel transmission. 90° RF pulses have been designed using both the original transmit SENSE method and the proposed precompensation method for RF arrays with non-negligible mutual coupling, and their excitation profiles are generated by simulating the Bloch equation. The results show that the mutual coupling effect can be effectively compensated by using the proposed method, yielding enhanced tolerance to insufficient mutual decoupling of RF arrays in parallel excitation, ultimately, providing improved performance and accuracy of parallel excitation.
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Affiliation(s)
- Yong Pang
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States
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16
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Multi-reception strategy with improved SNR for multichannel MR imaging. PLoS One 2012; 7:e42237. [PMID: 22879921 PMCID: PMC3411773 DOI: 10.1371/journal.pone.0042237] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Accepted: 07/04/2012] [Indexed: 12/03/2022] Open
Abstract
A multi-reception strategy with extended GRAPPA is proposed in this work to improve MR imaging performance at ultra-high field MR systems with limited receiver channels. In this method, coil elements are separated to two or more groups under appropriate grouping criteria. Those groups are enabled in sequence for imaging first, and then parallel acquisition is performed to compensate for the redundant scan time caused by the multiple receptions. To efficiently reconstruct the data acquired from elements of each group, a specific extended GRAPPA was developed. This approach was evaluated by using a 16-element head array on a 7 Tesla whole-body MRI scanner with 8 receive channels. The in-vivo experiments demonstrate that with the same scan time, the 16-element array with twice receptions and acceleration rate of 2 can achieve significant SNR gain in the periphery area of the brain and keep nearly the same SNR in the center area over an eight-element array, which indicates the proposed multi-reception strategy and extended GRAPPA are feasible to improve image quality for MRI systems with limited receive channels. This study also suggests that it is advantageous for a MR system with N receiver channels to utilize a coil array with more than N elements if an appropriate acquisition strategy is applied.
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Khan AF, Drozd JJ, Moreland RK, Ta RM, Borrie MJ, Bartha R. A novel MRI-compatible brain ventricle phantom for validation of segmentation and volumetry methods. J Magn Reson Imaging 2012; 36:476-82. [DOI: 10.1002/jmri.23612] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Accepted: 01/11/2012] [Indexed: 11/08/2022] Open
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18
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Jin J, Li Y, Liu F, Weber E, Crozier S. A comparison study of different RF shields for an 8-element transceive small animal array at 9.4T. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2012; 2011:543-6. [PMID: 22254368 DOI: 10.1109/iembs.2011.6090100] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
In this study, three types of radio-frequency shields are studied and compared in the context of ultra-high field small-animal magnetic resonance imaging. It has been demonstrated that the coil penetration depth and mutual coupling between the coils depend heavily on the type of shield employed. The results were used to guide the design of a 9.4T 8-element transceive small animal array, which provides high overall coil penetration.
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Affiliation(s)
- Jin Jin
- School of Information Technology and Electrical Engineering, the University of Queensland, Queensland 4072, Australia.
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Wu B, Zhang X, Wang C, Li Y, Pang Y, Lu J, Xu D, Majumdar S, Nelson SJ, Vigneron DB. Flexible transceiver array for ultrahigh field human MR imaging. Magn Reson Med 2012; 68:1332-8. [PMID: 22246803 DOI: 10.1002/mrm.24121] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2010] [Revised: 11/18/2011] [Accepted: 11/28/2011] [Indexed: 11/05/2022]
Abstract
A flexible transceiver array, capable of multiple-purpose imaging applications in vivo at ultrahigh magnetic fields was designed, implemented and tested on a 7 T MR scanner. By alternately placing coil elements with primary and secondary harmonics, improved decoupling among coil elements was accomplished without requiring decoupling circuitry between resonant elements, which is commonly required in high-frequency transceiver arrays to achieve sufficient element-isolation during radiofrequency excitation. This flexible array design is capable of maintaining the required decoupling among resonant elements in different array size and geometry and is scalable in coil size and number of resonant elements (i.e., number of channels), yielding improved filling factors for various body parts with different geometry and size. To investigate design feasibility, flexibility, and array performance, a multichannel, 16-element transceiver array was designed and constructed, and in vivo images of the human head, knee, and hand were acquired using a whole-body 7 T MR system. Seven Tesla parallel imaging with generalized autocalibrating partially parallel acquisitions (GRAPPA) performed using this flexible transceiver array was also presented.
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Affiliation(s)
- Bing Wu
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California 94158, USA
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Curtis AT, Gilbert KM, Klassen LM, Gati JS, Menon RS. Slice-by-slice B
1
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shimming at 7 T. Magn Reson Med 2011; 68:1109-16. [DOI: 10.1002/mrm.23319] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2011] [Revised: 10/20/2011] [Accepted: 11/15/2011] [Indexed: 11/08/2022]
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21
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Gilbert KM, Belliveau JG, Curtis AT, Gati JS, Klassen LM, Menon RS. A conformal transceive array for 7 T neuroimaging. Magn Reson Med 2011; 67:1487-96. [DOI: 10.1002/mrm.23124] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2011] [Revised: 06/21/2011] [Accepted: 07/07/2011] [Indexed: 01/06/2023]
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