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Payne K, Zhao Y, Bhosale AA, Zhang X. Dual-Tuned Coaxial-Transmission-Line RF Coils for Hyperpolarized 13C and Deuterium 2H Metabolic MRS Imaging at Ultrahigh Fields. IEEE Trans Biomed Eng 2024; 71:1521-1530. [PMID: 38090865 PMCID: PMC11095995 DOI: 10.1109/tbme.2023.3341760] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2023]
Abstract
OBJECTIVE Information on the metabolism of tissues in healthy and diseased states plays a significant role in the detection and understanding of tumors, neurodegenerative diseases, diabetes, and other metabolic disorders. Hyperpolarized carbon-13 magnetic resonance imaging (13C-HPMRI) and deuterium metabolic imaging (2H-DMI) are two emerging X-nuclei used as practical imaging tools to investigate tissue metabolism. However due to their low gyromagnetic ratios (ɣ13C = 10.7 MHz/T; ɣ2H = 6.5 MHz/T) and natural abundance, such method required a sophisticated dual-tuned radiofrequency (RF) coil. METHODS Here, we report a dual-tuned coaxial transmission line (CTL) RF coil agile for metabolite information operating at 7T with independent tuning capability. The design analysis has demonstrated how both resonant frequencies can be individually controlled by simply varying the constituent of the design parameters. RESULTS Numerical results have demonstrated a broadband tuning range capability, covering most of the X-nucleus signal, especially the 13C and 2H spectra at 7T. Furthermore, in order to validate the feasibility of the proposed design, both dual-tuned 1H/13C and 1H/2H CTLs RF coils are fabricated using a semi-flexible RG-405 .086" coaxial cable and bench test results (scattering parameters and magnetic field efficiency/distribution) are successfully obtained. CONCLUSION The proposed dual-tuned RF coils reveal highly effective magnetic field obtained from both proton and heteronuclear signal which is crucial for accurate and detailed imaging. SIGNIFICANCE The successful development of this new dual-tuned RF coil technique would provide a tangible and efficient tool for ultrahigh field metabolic MR imaging.
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Zhao Y, Bhosale AA, Zhang X. Multimodal surface coils for low field MR imaging. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2024:2024.04.14.24305802. [PMID: 38699318 PMCID: PMC11065021 DOI: 10.1101/2024.04.14.24305802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2024]
Abstract
Low field MRI is safer and more cost effective than the high field MRI. One of the inherent problems of low field MRI is its low signal-to-noise ratio or sensitivity. In this work, we introduce a multimodal surface coil technique for signal excitation and reception to improve the RF magnetic field (B 1 ) efficiency and potentially improve MR sensitivity. The proposed multimodal surface coil consists of multiple identical resonators that are electromagnetically coupled to form a multimodal resonator. The field distribution of its lowest frequency mode is suitable for MR imaging applications. The prototype multimodal surface coils are built, and the performance is investigated and validated through numerical simulation, standard RF measurements and tests, and comparison with the conventional surface coil at low fields. Our results show that the B 1 efficiency of the multimodal surface coil outperforms that of the conventional surface coil which is known to offer the highest B 1 efficiency among all coil categories, i.e., volume coil, half-volume coil and surface coil. In addition, in low-field MRI, the required low-frequency coils often use large value capacitance to achieve the low resonant frequency which makes frequency tuning difficult. The proposed multimodal surface coil can be conveniently tuned to the required low frequency for low-field MRI with significantly reduced capacitance value, demonstrating excellent low-frequency operation capability over the conventional surface coil.
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Payne K, Bhosale AA, Zhang X. Double cross magnetic wall decoupling for quadrature transceiver RF array coils using common-mode differential-mode resonators. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 353:107498. [PMID: 37295282 PMCID: PMC10527004 DOI: 10.1016/j.jmr.2023.107498] [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: 03/17/2023] [Revised: 05/09/2023] [Accepted: 05/31/2023] [Indexed: 06/12/2023]
Abstract
In contrast to linearly polarized RF coil arrays, quadrature transceiver coil arrays are capable of improving signal-to-noise ratio (SNR), spatial resolution, and parallel imaging performance. Owing to a reduced excitation power, a low specific absorption rate can also be obtained using quadrature RF coils. However, due to the complex nature of their structure and their electromagnetic properties, it is challenging to achieve sufficient electromagnetic decoupling while designing multichannel quadrature RF coil arrays, particularly in ultra-high fields. In this work, we proposed a double-cross magnetic wall decoupling for quadrature transceiver RF arrays and implemented the decoupling method on common-mode differential mode quadrature (CMDM) quadrature transceiver arrays at an ultrahigh field of 7 T. The proposed magnetic decoupling wall, comprised of two intrinsically decoupled loops, is used to reduce the mutual coupling between all the multi-mode currents present in the quadrature CMDM array. The decoupling network has no physical connection with the CMDMs' resonators, which provides less design constraint over size-adjustable RF arrays. To validate the feasibility of the proposed cross-magnetic decoupling wall, systematic studies on the decoupling performance based on the impedance of two intrinsic loops are numerically performed. A pair of quadrature transceiver CMDMs is constructed along with the proposed decoupling network, and their scattering matrix is characterized using a network analyzer. The measured results indicate that all the current modes from coupling are simultaneously suppressed using the proposed cross-magnetic wall. Moreover, field distribution and local specific absorption rate (SAR) are numerically obtained for a well-decoupled 8-channel quadrature knee-coil array.
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Affiliation(s)
- Komlan Payne
- Department of Biomedical Engineering, State University of New York at Buffalo, Buffalo, NY 14260, USA.
| | - Aditya Ashok Bhosale
- Department of Biomedical Engineering, State University of New York at Buffalo, Buffalo, NY 14260, USA.
| | - Xiaoliang Zhang
- Department of Biomedical Engineering, State University of New York at Buffalo, Buffalo, NY 14260, USA; Department of Electrical Engineering, State University of New York at Buffalo, Buffalo, NY 14260, USA.
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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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Hong SM, Choi CH, Shah NJ, Felder J. Design of a Folded, Double-Tuned Loop Coil for ¹H/X-Nuclei MRI Applications. IEEE TRANSACTIONS ON MEDICAL IMAGING 2023; 42:1424-1430. [PMID: 37015697 DOI: 10.1109/tmi.2022.3228305] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
MR measurement using a combination of X-nuclei and proton MRI is of great interest as the information provided by the two nuclei is highly complementary, with the X-nuclei signal giving metabolic data relating to potential biomarkers and the proton signal affording anatomical details. Due to the relatively weak signal obtained from X-nuclei, combining an X-nuclei coil with a proton coil is also advantageous for [Formula: see text] shimming and scout images. One approach to building a double-resonant coil is to modify the coil geometry. Here, to achieve double-resonance, a 2× 1 ladder network was designed and tuned at both proton and X-nuclei frequencies successfully. Due to coupling between closed wires, the double-tuned coil generates a shifted transmit efficiency pattern compared to that of the single-tuned loop at the 7T MRI proton frequency. To compensate for the shifted pattern, one part of the 2× 1 ladder network was folded, and the tuning and performance of the folded double-tuned coil were evaluated in simulations and MR measurements. The proposed structure was further evaluated with overlapped decoupling in a receive-only array. The results show that our proposed folded double-tuned coil moderated the shifted pattern of a straight double-tuned loop coil and provided minimum losses at both proton and X-nuclei frequencies. The proposed folded double-tuned loop coil has also been further extended to a receive-only array.
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Hadley JR, Odéen H, Merrill R, Adams SI, Rieke V, Payne A, Parker DL. Improving image quality in transcranial magnetic resonance guided focused ultrasound using a conductive screen. Magn Reson Imaging 2021; 83:41-49. [PMID: 34242694 PMCID: PMC8449813 DOI: 10.1016/j.mri.2021.07.002] [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: 05/21/2021] [Accepted: 07/03/2021] [Indexed: 10/20/2022]
Abstract
Transcranial Magnetic Resonance guided Focused Ultrasound (TcMRgFUS) has been proven to be an effective treatment for some neurological disorders such as essential and Parkinson's tremor. However, magnetic resonance guidance at 3 Tesla (3T) frequencies and using the large hemispherical transducers required for TcMRgFUS results in artifactual low-signal bands that pass through key regions of the brain. The purpose of this work was to investigate the use of a circular conductive Radio Frequency (RF) screen, that is bent to have a 12 cm radius in one direction and positioned near the top or back of the head, to reduce or remove these artifactual low-signal bands in TcMRgFUS. The impact of using an RF screen to remove these low signal bands was studied in both imaging experiments and electromagnetic simulations. Hydrophone measurements of the acoustic transparency of the bronze 2 mm diameter square mesh screen used in the imaging studies were compared with temperature measurements with and without the screen in heating studies in the TcMRgFUS system. The imaging and simulation studies both show that for the different screen configurations studied in this work, RF screen removes the low-signal bands and increases both homogeneity and signal-to-noise ratio (SNR) throughout the region of the brain. Hydrophone and heating studies indicate that even a 2 mm wire mesh provides minimal attenuation to the ultrasound beam. Simulation results also suggest that a 1 cm mesh will provide adequate artifact suppression with even less ultrasound attenuation. An RF screen that disrupts the natural waveguide nature of the transducer in the 3T MR environment can change the electromagnetic field profile to reduce unwanted artifacts and provide an imaging region which has more homogeneity and higher SNR throughout the brain.
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Affiliation(s)
- J R Hadley
- Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, USA.
| | - H Odéen
- Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, USA.
| | - R Merrill
- Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, USA.
| | - S I Adams
- Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, USA.
| | - V Rieke
- Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, USA.
| | - A Payne
- Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, USA.
| | - D L Parker
- Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, USA.
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Beck MJ, Parker DL, Hadley JR. Quasistatic Solutions versus Full-Wave Solutions of Single-Channel Circular RF Receive Coils on Phantoms of Varying Conductivities at 3 Tesla. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2021; 2021:6638576. [PMID: 34899097 PMCID: PMC8665417 DOI: 10.1155/2021/6638576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
PURPOSE Although full-wave simulations could be used to aid in RF coil design, the algorithms may be too slow for an iterative optimization algorithm. If quasistatic simulations are accurate within the design tolerance, then their use could reduce simulation time by orders of magnitude compared to full-wave simulations. This paper examines the accuracy of quasistatic and full-wave simulations at 3 Tesla. METHODS Three sets of eight coils ranging from 3-10 cm (24 total) were used to measure SNR on three phantoms with conductivities of 0.3, 0.6, and 0.9 S/m. The phantom conductivities were chosen to represent those typically found in human tissues. The range of coil element sizes represents the sizes of coil elements seen in typical coil designs. SNR was determined using the magnetic and electric fields calculated by quasistatic and full-wave simulations. Each simulated SNR dataset was scaled to minimize the root mean squared error (RMSE) when compared against measured SNR data. In addition, the noise values calculated by each simulation were compared against benchtop measured noise values. RESULTS The RMSE was 0.285 and 0.087 for the quasistatic and full-wave simulations, respectively. The maximum and minimum quotient values, when taking the ratio of simulated to measured SNR values, were 1.69 and 0.20 for the quasistatic simulations and 1.29 and 0.75 for the full-wave simulations, respectively. The ratio ranges, for the calculated quasistatic and full-wave total noise values compared to benchtop measured noise values, were 0.83-1.06 and 0.27-3.02, respectively. CONCLUSIONS Full-wave simulations were on average 3x more accurate than the quasistatic simulations. Full-wave simulations were more accurate in characterizing the wave effects within the sample, though they were not able to fully account for the skin effect when calculating coil noise.
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Affiliation(s)
- Michael J Beck
- Department of Radiology and Imaging Sciences, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City 84132, USA
| | - Dennis L Parker
- Department of Radiology and Imaging Sciences, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City 84132, USA
| | - J Rock Hadley
- Department of Radiology and Imaging Sciences, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City 84132, USA
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Han J, Gao Y, Nan X, Yu X, Liu F, Xin SX. Effect of radiofrequency inhomogeneity on water-content based electrical properties tomography and its correction by flip angle maps. Magn Reson Imaging 2021; 78:25-34. [PMID: 33450296 DOI: 10.1016/j.mri.2020.12.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 12/24/2020] [Accepted: 12/31/2020] [Indexed: 10/22/2022]
Abstract
Water-content based electrical properties tomography (wEPT) can retrieve electrical properties (EPs) from water-content maps. B1+ field information is not involved in the traditional magnetic resonance electrical properties tomography approach. wEPT can be performed through conventional MR scanning, such as T1-weighted spin-echo imaging, which provides convenient access to multiple clinical applications. However, the inhomogeneous radiofrequency (RF) field induced by RF coils would cause inaccuracy in wEPT reconstructions during MR scanning. We conducted a detailed investigation to evaluate the effect of inhomogeneous RF field on wEPT reconstructions to guarantee that EP mapping is desired for clinical practice. Two important considerations are involved, namely, multiple typical coil configurations and various flip angles (FAs). We proposed a correction scheme with actual FA mapping to calibrate the RF inhomogeneity and finally validated it by using human imaging at 3 T. This study illustrates a detailed evaluation for wEPT under imperfect RF homogeneity and further provides a feasible correction procedure to mitigate it. The profound knowledge of wEPT provided in our work will benefit its performance in clinical applications.
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Affiliation(s)
- Jijun Han
- School of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, China
| | - Yunyu Gao
- School of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, China
| | - Xiang Nan
- Center for Biomedical Engineering, University of Science and Technology of China, Hefei, Anhui, China
| | - Xuefei Yu
- School of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, China
| | - Feng Liu
- School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, QLD, Australia
| | - Sherman Xuegang Xin
- School of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, China; School of Medicine, South China University of Technology, Guangzhou, Guangdong, China.
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Choi CH, Felder T, Felder J, Tellmann L, Hong SM, Wegener HP, Shah NJ, Ziemons K. Design, evaluation and comparison of endorectal coils for hybrid MR-PET imaging of the prostate. Phys Med Biol 2020; 65:115005. [PMID: 32268314 DOI: 10.1088/1361-6560/ab87f8] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Prostate cancer is one of the most common cancers among men and its early detection is critical for its successful treatment. The use of multimodal imaging, such as MR-PET, is most advantageous as it is able to provide detailed information about the prostate. However, as the human prostate is flexible and can move into different positions under external conditions, it is important to localise the focused region-of-interest using both MRI and PET under identical circumstances. In this work, we designed five commonly used linear and quadrature radiofrequency surface coils suitable for hybrid MR-PET use in endorectal applications. Due to the endorectal design and the shielded PET insert, the outer face of the coils investigated was curved and the region to be imaged was outside the volume of the coil. The tilting angles of the coils were varied with respect to the main magnetic field direction. This was done to approximate the various positions from which the prostate could be imaged. The transmit efficiencies and safety excitation efficiencies from simulations, together with the signal-to-noise ratios from the MR images were calculated and analysed. Overall, it was found that the overlapped loops driven in quadrature were superior to the other types of coils we tested. In order to determine the effect of the different coil designs on PET, transmission scans were carried out, and it was observed that the differences between attenuation maps with and without the coils were negligible. The findings of this work can provide useful guidance for the integration of such coil designs into MR-PET hybrid systems in the future.
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Affiliation(s)
- Chang-Hoon Choi
- Institute of Neuroscience and Medicine - 4, Forschungszentrum Jülich, Jülich, Germany
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Duan S, Zhu Y, Liu F, Xin SX. Numerical Experiments on the Contrast Capability of Magnetic Resonance Electrical Property Tomography. Magn Reson Med Sci 2020; 19:77-85. [PMID: 31019159 PMCID: PMC7067912 DOI: 10.2463/mrms.mp.2018-0167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Purpose: Magnetic resonance electrical property tomography (MR EPT) is a technique for non-invasively obtaining the electric property (EP) distribution of biological tissues, with a promising potential for application in the early detection of tumors. However, the contrast capability (CC) of this technique has not been fully studied. This work aims to theoretically explore the CC for detecting the variation of EP values and the size of the imaging region. Methods: A simulation scheme was specifically designed to evaluate the CC of MR EPT. The simulation study has the advantage that the magnetic field can be accurately obtained. EP maps of the designed phantom embedded with target regions of designated various sizes and EPs were reconstructed using the homogeneous Helmholtz equation based on B1+ with different signal-to-noise ratios (SNRs). The CC was estimated by determining the smallest detectable EP contrast when the target region size was as large as the Laplacian kernel and the smallest detectable target region size when the EP contrast was the same as the difference between healthy and malignant tissues in the brain, based on the reconstructed EP maps. Results: Using noise free B1+, the smallest detectable contrastσ and contrastεr were 1% and 3%, respectively, and the smallest detectable target region size was 1 mesh unit (the base unit size used in the simulation) for conductivity and relative permittivity. The smallest detectable EP contrast and target region size were decreased as the B1+ SNR increased. Conclusion: The CC of MR EPT was related with the SNR of the magnetic field. A small EP contrast and size were necessary for detection at a high-SNR magnetic field. Obtaining a high-SNR magnetic field is important for improving the CC of MR EPT.
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Affiliation(s)
- Song Duan
- Department of Radiation Oncology, Sun Yat-sen Memorial Hospital, Sun Yat-sen University
| | - Yurong Zhu
- Department of Biomedical Engineering, Southern Medical University
| | - Feng Liu
- School of Information Technology and Electrical Engineering, University of Queensland
| | - Sherman Xuegang Xin
- School of Medicine, South China University of Technology, Guangzhou Higher Education Mega Centre
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Abstract
In this article, an overview of the current developments and research applications for non-proton magnetic resonance imaging (MRI) at ultrahigh magnetic fields (UHFs) is given. Due to technical and methodical advances, efficient MRI of physiologically relevant nuclei, such as Na, Cl, Cl, K, O, or P has become feasible and is of interest to obtain spatially and temporally resolved information that can be used for biomedical and diagnostic applications. Sodium (Na) MRI is the most widespread multinuclear imaging method with applications ranging over all regions of the human body. Na MRI yields the second largest in vivo NMR signal after the clinically used proton signal (H). However, other nuclei such as O and P (energy metabolism) or Cl and K (cell viability) are used in an increasing number of MRI studies at UHF. One major advancement has been the increased availability of whole-body MR scanners with UHFs (B0 ≥7T) expanding the range of detectable nuclei. Nevertheless, efforts in terms of pulse sequence and post-processing developments as well as hardware designs must be made to obtain valuable information in clinically feasible measurement times. This review summarizes the available methods in the field of non-proton UHF MRI, especially for Na MRI, as well as introduces potential applications in clinical research.
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Affiliation(s)
- Sebastian C Niesporek
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Armin M Nagel
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
- Institute of Medical Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Tanja Platt
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
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Hendriks AD, Luijten PR, Klomp DWJ, Petridou N. Potential acceleration performance of a 256-channel whole-brain receive array at 7 T. Magn Reson Med 2018; 81:1659-1670. [PMID: 30257049 PMCID: PMC6585755 DOI: 10.1002/mrm.27519] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 08/09/2018] [Accepted: 08/11/2018] [Indexed: 11/21/2022]
Abstract
Purpose Assess the potential gain in acceleration performance of a 256‐channel versus 32‐channel receive coil array at 7 T in combination with a 2D CAIPIRINHA sequence for 3D data sets. Methods A 256‐channel receive setup was simulated by placing 2 small 16‐channel high‐density receive arrays at 2 × 8 different locations on the head of healthy participants. Multiple consecutive measurements were performed and coil sensitivity maps were combined to form a complete 256‐channel data set. This setup was compared with a standard 32‐channel head coil, in terms of SNR, noise correlation, and acceleration performance (g‐factor). Results In the periphery of the brain, the receive SNR was on average a factor 1.5 higher (ranging up to a factor 2.7 higher) than the 32‐channel coil; in the center of the brain the SNR was comparable or lower, depending on the size of the region of interest, with a factor 1.0 on average (ranging from 0.7 up to a factor of 1.6). The average noise correlation between coil elements was 3% for the 256‐channel coil, and 5% for the 32‐channel coil. At acceptable g‐factors (< 2), the achievable acceleration factor using SENSE and 2D CAIPIRINHA was 24 and 28, respectively, versus 9 and 12 for the 32‐channel coil. Conclusion The receive performance of the simulated 256 channel array was better than the 32‐channel reference. Combined with 2D CAIPIRINHA, a peak acceleration factor of 28 was assessed, showing great potential for high‐density receive arrays.
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Affiliation(s)
- Arjan D Hendriks
- Department of Radiology, Imaging Division, University Medical Center Utrecht, Utrecht, Netherlands
| | - Peter R Luijten
- Department of Radiology, Imaging Division, University Medical Center Utrecht, Utrecht, Netherlands
| | - Dennis W J Klomp
- Department of Radiology, Imaging Division, University Medical Center Utrecht, Utrecht, Netherlands
| | - Natalia Petridou
- Department of Radiology, Imaging Division, University Medical Center Utrecht, Utrecht, Netherlands
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Quantitative 19F MRI of perfluoro-15-crown-5-ether using uniformity correction of the spin excitation and signal reception. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2018; 32:25-36. [DOI: 10.1007/s10334-018-0696-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 07/10/2018] [Accepted: 07/23/2018] [Indexed: 12/26/2022]
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14
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Watanabe H, Takaya N. Quantitation Error in 1H MRS Caused by B 1 Inhomogeneity and Chemical Shift Displacement. Magn Reson Med Sci 2018; 17:244-250. [PMID: 29118306 PMCID: PMC6039773 DOI: 10.2463/mrms.mp.2017-0062] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Purpose: The quantitation accuracy in proton magnetic resonance spectroscopy (1H MRS) improves at higher B0 field. However, a larger chemical shift displacement (CSD) and stronger B1 inhomogeneity exist. In this work, we evaluate the quantitation accuracy for the spectra of metabolite mixtures in phantom experiments at 4.7T. We demonstrate a position-dependent error in quantitation and propose a correction method by measuring water signals. Materials and Methods: All experiments were conducted on a whole-body 4.7T MR system with a quadrature volume coil for transmission and reception. We arranged three bottles filled with metabolite solutions of N-acetyl aspartate (NAA) and creatine (Cr) in a vertical row inside a cylindrical phantom filled with water. Peak areas of three singlets of NAA and Cr were measured on three 1H spectra at three volume of interests (VOIs) inside three bottles. We also measured a series of water spectra with a shifted carrier frequency and measured a reception sensitivity map. Results: The ratios of NAA and Cr at 3.92 ppm to Cr at 3.01 ppm differed amongst the three VOIs in peak area, which leads to a position-dependent error. The nature of slope depicting the relationship between peak areas and the shifted values of frequency was like that between the reception sensitivities and displacement at every VOI. Conclusion: CSD and inhomogeneity of reception sensitivity cause amplitude modulation along the direction of chemical shift on the spectra, resulting in a quantitation error. This error may be more significant at higher B0 field where CSD and B1 inhomogeneity are more severe. This error may also occur in reception using a surface coil having inhomogeneous B1. Since this type of error is around a few percent, the data should be analyzed with greater attention while discussing small differences in the studies of 1H MRS.
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Affiliation(s)
- Hidehiro Watanabe
- Center for Environmental Measurement and Analysis, National Institutes for Environmental Studies
| | - Nobuhiro Takaya
- Center for Environmental Measurement and Analysis, National Institutes for Environmental Studies
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15
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Ha Y, Choi CH, Shah NJ. Development and Implementation of a PIN-Diode Controlled, Quadrature-Enhanced, Double-Tuned RF Coil for Sodium MRI. IEEE TRANSACTIONS ON MEDICAL IMAGING 2018; 37:1626-1631. [PMID: 29969413 DOI: 10.1109/tmi.2017.2786466] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Sodium (23Na) MRI provides complementary cellular and metabolic information. However, the intrinsic MR sensitivity of 23Na is considerably lower compared with that of the proton, making it difficult to measure MR-detectable sodium signals. It is therefore important to maintain the signal-to-noise ratio (SNR) of the sodium signal as high as possible. Double-tuned coils are often employed in combinationwith a 1H coil, providing structural images and B0 shimming capability. The double-tuned coil design can be achieved with the use of two geometrically decoupled coils whose B1 field directions are perpendicular to each other. This can be used to design quadrature-driven, single-nucleus coils to improve SNR, and additionally, this coil can also be utilized as a linear-driven double-resonant mode. Here, we have developed and evaluateda quadrature-enhanced, double-tuned coil. The novel coil uses PIN-diode switches, inserted only in the loop coil, to shift the resonance frequency between 1H and 23Na so that 23Na signals can be acquired in quadrature and the capability of using 1H function remains. Consequently, the 23Na SNR values obtained with the double-tuned coil are nearly 33% and 17% higher in comparison with geometrically identical single-tuned coils. SNR plots also show the superiority of double-tuned coil in 23Na.
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16
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Zoelch N, Hock A, Henning A. Quantitative magnetic resonance spectroscopy at 3T based on the principle of reciprocity. NMR IN BIOMEDICINE 2018; 31:e3875. [PMID: 29465821 DOI: 10.1002/nbm.3875] [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: 05/31/2017] [Revised: 10/06/2017] [Accepted: 11/10/2017] [Indexed: 05/22/2023]
Abstract
Quantification of magnetic resonance spectroscopy signals using the phantom replacement method requires an adequate correction of differences between the acquisition of the reference signal in the phantom and the measurement in vivo. Applying the principle of reciprocity, sensitivity differences can be corrected at low field strength by measuring the RF transmitter gain needed to obtain a certain flip angle in the measured volume. However, at higher field strength the transmit sensitivity may vary from the reception sensitivity, which leads to wrongly estimated concentrations. To address this issue, a quantification approach based on the principle of reciprocity for use at 3T is proposed and validated thoroughly. In this approach, the RF transmitter gain is determined automatically using a volume-selective power optimization and complemented with information from relative reception sensitivity maps derived from contrast-minimized images to correct differences in transmission and reception sensitivity. In this way, a reliable measure of the local sensitivity was obtained. The proposed method is used to derive in vivo concentrations of brain metabolites and tissue water in two studies with different coil sets in a total of 40 healthy volunteers. Resulting molar concentrations are compared with results using internal water referencing (IWR) and Electric REference To access In vivo Concentrations (ERETIC). With the proposed method, changes in coil loading and regional sensitivity due to B1 inhomogeneities are successfully corrected, as demonstrated in phantom and in vivo measurements. For the tissue water content, coefficients of variation between 2% and 3.5% were obtained (0.6-1.4% in a single subject). The coefficients of variation of the three major metabolites ranged from 3.4-14.5%. In general, the derived concentrations agree well with values estimated with IWR. Hence, the presented method is a valuable alternative for IWR, without the need for additional hardware such as ERETIC and with potential advantages in diseased tissue.
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Affiliation(s)
- Niklaus Zoelch
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
- Institute of Forensic Medicine, University of Zurich, Zurich, Switzerland
- Hospital of Psychiatry, Department of Psychiatry, Psychotherapy and Psychosomatics, University of Zurich, Zurich, Switzerland
| | - Andreas Hock
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
- Hospital of Psychiatry, Department of Psychiatry, Psychotherapy and Psychosomatics, University of Zurich, Zurich, Switzerland
| | - Anke Henning
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
- Max Plank Institute for Biological Cybernetics, Tuebingen, Germany
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17
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Zhang X, Martin A, Jordan C, Lillaney P, Losey A, Pang Y, Hu J, Wilson M, Cooke D, Hetts SW. Design of catheter radio frequency coils using coaxial transmission line resonators for interventional neurovascular MR imaging. Quant Imaging Med Surg 2017; 7:187-194. [PMID: 28516044 DOI: 10.21037/qims.2016.12.05] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
BACKGROUND It is technically challenging to design compact yet sensitive miniature catheter radio frequency (RF) coils for endovascular interventional MR imaging. METHODS In this work, a new design method for catheter RF coils is proposed based on the coaxial transmission line resonator (TLR) technique. Due to its distributed circuit, the TLR catheter coil does not need any lumped capacitors to support its resonance, which simplifies the practical design and construction and provides a straightforward technique for designing miniature catheter-mounted imaging coils that are appropriate for interventional neurovascular procedures. The outer conductor of the TLR serves as an RF shield, which prevents electromagnetic energy loss, and improves coil Q factors. It also minimizes interaction with surrounding tissues and signal losses along the catheter coil. To investigate the technique, a prototype catheter coil was built using the proposed coaxial TLR technique and evaluated with standard RF testing and measurement methods and MR imaging experiments. Numerical simulation was carried out to assess the RF electromagnetic field behavior of the proposed TLR catheter coil and the conventional lumped-element catheter coil. RESULTS The proposed TLR catheter coil was successfully tuned to 64 MHz for proton imaging at 1.5 T. B1 fields were numerically calculated, showing improved magnetic field intensity of the TLR catheter coil over the conventional lumped-element catheter coil. MR images were acquired from a dedicated vascular phantom using the TLR catheter coil and also the system body coil. The TLR catheter coil is able to provide a significant signal-to-noise ratio (SNR) increase (a factor of 200 to 300) over its imaging volume relative to the body coil. CONCLUSIONS Catheter imaging RF coil design using the proposed coaxial TLR technique is feasible and advantageous in endovascular interventional MR imaging applications.
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Affiliation(s)
- Xiaoliang Zhang
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA.,UC Berkeley/UCSF Joint Bioengineering Program, University of California, Berkeley, San Francisco, CA, USA
| | - Alastair Martin
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA
| | - Caroline Jordan
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA
| | - Prasheel Lillaney
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA
| | - Aaron Losey
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA
| | - Yong Pang
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA
| | - Jeffrey Hu
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA
| | - Mark Wilson
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA
| | - Daniel Cooke
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA
| | - Steven W Hetts
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA
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18
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Duan S, Xu C, Deng G, Wang J, Liu F, Xin SX. Quantitative analysis of the reconstruction errors of the currently popular algorithm of magnetic resonance electrical property tomography at the interfaces of adjacent tissues. NMR IN BIOMEDICINE 2016; 29:744-750. [PMID: 27037715 DOI: 10.1002/nbm.3522] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Revised: 01/27/2016] [Accepted: 02/26/2016] [Indexed: 06/05/2023]
Abstract
This work quantitatively analyzed the reconstruction errors (REs) of electrical property (EP) images using a currently popular algorithm of magnetic resonance electrical property tomography (MREPT), which occurred along the tissue interfaces. Transmitted magnetic fields B1+ were acquired at 3 T using a birdcage coil loaded with a phantom consisting of various adjacent tissues. Homogeneous Helmholtz was employed to calculate the EP maps by Laplacian computation of central differences. The maps of absolute REs (aREs) and relative REs (rREs) were calculated. The maximum and mean rREs, in addition to rRE distributions at the interfaces, were presented. Reconstructed EP maps showed various REs along different interface boundaries. Among all the investigated tissue interfaces, the kidney-fat interface presented the maximum mean rREs for both conductivity and relative permittivity. The minimum mean rRE of conductivity was observed at the spleen-muscle interface, and the minimum mean rRE of relative permittivity was detected along the lung-heart interface. The mean rREs ranged from 0.3986 to 36.11 for conductivity and 0.2218 to 11.96 for relative permittivity. Overall, this research indicates that different REs occur at various tissue boundaries, as shown by the currently popular algorithm of MREPT. Thus, REs should be considered when applying MREPT to reconstruct the EP distributions inside the human body. Copyright © 2016 John Wiley & Sons, Ltd.
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Affiliation(s)
- Song Duan
- Biomedical Engineering Department and Guangdong Provincial Key Laboratory of Medical Image Processing, Southern Medical University, Guangzhou, Guangdong, China
| | - Chao Xu
- Biomedical Engineering Department and Guangdong Provincial Key Laboratory of Medical Image Processing, Southern Medical University, Guangzhou, Guangdong, China
| | - Guanhua Deng
- Biomedical Engineering Department and Guangdong Provincial Key Laboratory of Medical Image Processing, Southern Medical University, Guangzhou, Guangdong, China
| | - Jiajia Wang
- Biomedical Engineering Department and Guangdong Provincial Key Laboratory of Medical Image Processing, Southern Medical University, Guangzhou, Guangdong, China
| | - Feng Liu
- School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, Qld, Australia
| | - Sherman Xuegang Xin
- Biomedical Engineering Department and Guangdong Provincial Key Laboratory of Medical Image Processing, Southern Medical University, Guangzhou, Guangdong, China
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Yan X, Wei L, Chu S, Xue R, Zhang X. Eight-Channel Monopole Array Using ICE Decoupling for Human Head MR Imaging at 7 T. APPLIED MAGNETIC RESONANCE 2016; 47:527-538. [PMID: 29033501 PMCID: PMC5638452 DOI: 10.1007/s00723-016-0775-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Revised: 03/09/2016] [Indexed: 06/03/2023]
Abstract
Due to the unique structure of radiative coil elements, traditional decoupling methods face technical challenges in reducing the electromagnetic coupling of the radiative arrays. In this study, we aim to investigate the possibility of using the recently introduced induced current elimination (ICE) decoupling technique for cylindrical shaped radiative coil array designs. To evaluate the method, an eight-channel transmit/receive monopole array with the ICE decoupling, suitable for human head imaging at 7 T, was built and comparatively investigated. In vivo human head images were acquired and geometry factor maps were measured and calculated to evaluate the performance of the ICE-decoupled monopole array. Compared with the monopole array without decoupling methods, the ICE-decoupled monopole array had a higher signal-to-noise ratio and demonstrated improved parallel imaging ability. The experimental results indicate that the ICE decoupling method is a promising solution to addressing the coupling issue of radiative array at ultrahigh fields.
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Affiliation(s)
- Xinqiang Yan
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- 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, 19B Yuquan Road, Shijingshan District, Beijing 100049, 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, 19B Yuquan Road, Shijingshan District, Beijing 100049, China
| | - Suoda Chu
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, 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
- Beijing Institute for Brain Disorders, Beijing 100053, China
| | - Xiaoliang Zhang
- Department of Radiology and Biomedical Imaging, University of California San Francisco, Byers Hall, Room 102, 1700 4th ST, San Francisco, CA 941582330, USA
- UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, CA 94158, USA
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20
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Vaidya MV, Collins CM, Sodickson DK, Brown R, Wiggins GC, Lattanzi R. Dependence of B1+ and B1- Field Patterns of Surface Coils on the Electrical Properties of the Sample and the MR Operating Frequency. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2016; 46:25-40. [PMID: 27795697 PMCID: PMC5082994 DOI: 10.1002/cmr.b.21319] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
In high field MRI, the spatial distribution of the radiofrequency magnetic ( B1) field is usually affected by the presence of the sample. For hardware design and to aid interpretation of experimental results, it is important both to anticipate and to accurately simulate the behavior of these fields. Fields generated by a radiofrequency surface coil were simulated using dyadic Green's functions, or experimentally measured over a range of frequencies inside an object whose electrical properties were varied to illustrate a variety of transmit [Formula: see text] and receive [Formula: see text] field patterns. In this work, we examine how changes in polarization of the field and interference of propagating waves in an object can affect the B1 spatial distribution. Results are explained conceptually using Maxwell's equations and intuitive illustrations. We demonstrate that the electrical conductivity alters the spatial distribution of distinct polarized components of the field, causing "twisted" transmit and receive field patterns, and asymmetries between [Formula: see text] and [Formula: see text]. Additionally, interference patterns due to wavelength effects are observed at high field in samples with high relative permittivity and near-zero conductivity, but are not present in lossy samples due to the attenuation of propagating EM fields. This work provides a conceptual framework for understanding B1 spatial distributions for surface coils and can provide guidance for RF engineers.
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Affiliation(s)
- Manushka V Vaidya
- Department of Radiology, Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY 10016; The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY 10016; NYU WIRELESS, Polytechnic Institute of New York University, Brooklyn, NY 11201
| | - Christopher M Collins
- Department of Radiology, Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY 10016; The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY 10016; NYU WIRELESS, Polytechnic Institute of New York University, Brooklyn, NY 11201
| | - Daniel K Sodickson
- Department of Radiology, Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY 10016; The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY 10016; NYU WIRELESS, Polytechnic Institute of New York University, Brooklyn, NY 11201
| | - Ryan Brown
- Department of Radiology, Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY 10016; NYU WIRELESS, Polytechnic Institute of New York University, Brooklyn, NY 11201
| | - Graham C Wiggins
- Department of Radiology, Center for Advanced Imaging Innovation and Research (CAI R) and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY 10016
| | - Riccardo Lattanzi
- Department of Radiology, Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY 10016; The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY 10016; NYU WIRELESS, Polytechnic Institute of New York University, Brooklyn, NY 11201
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21
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Rodgers CT, Robson MD. Coil combination for receive array spectroscopy: Are data-driven methods superior to methods using computed field maps? Magn Reson Med 2016; 75:473-87. [PMID: 25820303 PMCID: PMC4744755 DOI: 10.1002/mrm.25618] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Revised: 12/01/2014] [Accepted: 12/22/2014] [Indexed: 11/12/2022]
Abstract
PURPOSE Combining spectra from receive arrays, particularly X-nuclear spectra with low signal-to-noise ratios (SNRs), is challenging. We test whether data-driven combination methods are better than using computed coil sensitivities. THEORY Several combination algorithms are recast into the notation of Roemer's classic formula, showing that they differ primarily in their estimation of coil receive sensitivities. This viewpoint reveals two extensions of the whitened singular-value decomposition (WSVD) algorithm, using temporal or temporal + spatial apodization to improve the coil sensitivities, and thus the combined spectral SNR. METHODS Radiofrequency fields from an array were simulated and used to make synthetic spectra. These were combined with 10 algorithms. The combined spectra were then assessed in terms of their SNR. Validation used phantoms and cardiac (31) P spectra from five subjects at 3T. RESULTS Combined spectral SNRs from simulations, phantoms, and humans showed the same trends. In phantoms, the combined SNR using computed coil sensitivities was lower than with WSVD combination whenever the WSVD SNR was >14 (or >11 with temporal apodization, or >9 with temporal + spatial apodization). These new apodized WSVD methods gave higher SNRs than other data-driven methods. CONCLUSION In the human torso, at frequencies ≥49 MHz, data-driven combination is preferable to using computed coil sensitivities. Magn Reson, 2015. © 2015 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 License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Magn Reson Med 75:473-487, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Christopher T. Rodgers
- Oxford Centre for Clinical Magnetic Resonance ResearchUniversity of Oxford, John Radcliffe HospitalOxfordUnited Kingdom
| | - Matthew D. Robson
- Oxford Centre for Clinical Magnetic Resonance ResearchUniversity of Oxford, John Radcliffe HospitalOxfordUnited Kingdom
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22
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Wen Q, Kelley DAC, Banerjee S, Lupo JM, Chang SM, Xu D, Hess CP, Nelson SJ. Clinically feasible NODDI characterization of glioma using multiband EPI at 7 T. NEUROIMAGE-CLINICAL 2015; 9:291-9. [PMID: 26509116 PMCID: PMC4579286 DOI: 10.1016/j.nicl.2015.08.017] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Revised: 08/08/2015] [Accepted: 08/27/2015] [Indexed: 12/22/2022]
Abstract
Recent technological progress in the multiband echo planer imaging (MB EPI) technique enables accelerated MR diffusion weighted imaging (DWI) and allows whole brain, multi-b-value diffusion imaging to be acquired within a clinically feasible time. However, its applications at 7 T have been limited due to B1 field inhomogeneity and increased susceptibility artifact. It is an ongoing debate whether DWI at 7 T can be performed properly in patients, and a systematic SNR comparison for multiband spin-echo EPI between 3 T and 7 T has not been methodically studied. The goal of this study was to use MB EPI at 7 T in order to obtain 90-directional multi-shell DWI within a clinically feasible acquisition time for patients with glioma. This study included an SNR comparison between 3 T and 7 T, and the application of B1 mapping and distortion correction procedures for reducing the impact of variations in B0 and B1. The optimized multiband sequence was applied in 20 patients with glioma to generate both DTI and NODDI maps for comparison of values in tumor and normal appearing white matter (NAWM). Our SNR analysis showed that MB EPI at 7 T was comparable to that at 3 T, and the data quality acquired in patients was clinically acceptable. NODDI maps provided unique contrast within the T2 lesion that was not seen in anatomical images or DTI maps. Such contrast may reflect the complexity of tissue compositions associated with disease progression and treatment effects. The ability to consistently obtain high quality diffusion data at 7 T will contribute towards the implementation of a comprehensive brain MRI examination at ultra-high field. NODDI characterization of glioma at 7 T within 6 min with multiband EPI An SNR comparison was performed between 7 T and 3 T SE-EPI. SNR was comparable between 7 T and 3 T multiband SE-EPI. NODDI maps provided unique contrast within the glioma T2 lesion.
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Affiliation(s)
- Qiuting Wen
- UCSF/UCB Joint Graduate Group in Bioengineering, University of California, San Francisco (UCSF), San Francisco, CA, USA ; Department of Radiology and Biomedical Imaging, University of California, San Francisco (UCSF), San Francisco, CA, USA
| | | | | | - Janine M Lupo
- Department of Radiology and Biomedical Imaging, University of California, San Francisco (UCSF), San Francisco, CA, USA
| | - Susan M Chang
- Department of Neurological Surgery, University of California, San Francisco (UCSF), San Francisco, CA, USA
| | - Duan Xu
- Department of Radiology and Biomedical Imaging, University of California, San Francisco (UCSF), San Francisco, CA, USA
| | - Christopher P Hess
- Department of Radiology and Biomedical Imaging, University of California, San Francisco (UCSF), San Francisco, CA, USA
| | - Sarah J Nelson
- UCSF/UCB Joint Graduate Group in Bioengineering, University of California, San Francisco (UCSF), San Francisco, CA, USA ; Department of Radiology and Biomedical Imaging, University of California, San Francisco (UCSF), San Francisco, CA, USA ; Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, San Francisco, CA, USA
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23
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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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24
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Li M, Jin J, Zuo Z, Liu F, Trakic A, Weber E, Zhuo Y, Xue R, Crozier S. In vivo sensitivity estimation and imaging acceleration with rotating RF coil arrays at 7 Tesla. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2015; 252:29-40. [PMID: 25635352 DOI: 10.1016/j.jmr.2014.12.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Revised: 12/11/2014] [Accepted: 12/13/2014] [Indexed: 06/04/2023]
Abstract
Using a new rotating SENSitivity Encoding (rotating-SENSE) algorithm, we have successfully demonstrated that the rotating radiofrequency coil array (RRFCA) was capable of achieving a significant reduction in scan time and a uniform image reconstruction for a homogeneous phantom at 7 Tesla. However, at 7 Tesla the in vivo sensitivity profiles (B1(-)) become distinct at various angular positions. Therefore, sensitivity maps at other angular positions cannot be obtained by numerically rotating the acquired ones. In this work, a novel sensitivity estimation method for the RRFCA was developed and validated with human brain imaging. This method employed a library database and registration techniques to estimate coil sensitivity at an arbitrary angular position. The estimated sensitivity maps were then compared to the acquired sensitivity maps. The results indicate that the proposed method is capable of accurately estimating both magnitude and phase of sensitivity at an arbitrary angular position, which enables us to employ the rotating-SENSE algorithm to accelerate acquisition and reconstruct image. Compared to a stationary coil array with the same number of coil elements, the RRFCA was able to reconstruct images with better quality at a high reduction factor. It is hoped that the proposed rotation-dependent sensitivity estimation algorithm and the acceleration ability of the RRFCA will be particularly useful for ultra high field MRI.
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Affiliation(s)
- Mingyan Li
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia.
| | - Jin Jin
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Zhentao Zuo
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Centre for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China.
| | - Feng Liu
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Adnan Trakic
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Ewald Weber
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Yan Zhuo
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Centre for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
| | - Rong Xue
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Centre for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
| | - Stuart Crozier
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
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25
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Yan X, Xue R, Zhang X. A monopole/loop dual-tuned RF coil for ultrahigh field MRI. Quant Imaging Med Surg 2014; 4:225-31. [PMID: 25202657 DOI: 10.3978/j.issn.2223-4292.2014.08.03] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Accepted: 08/06/2014] [Indexed: 01/27/2023]
Abstract
Proton and heteronuclear MRI/MRS using dual-tuned (DT) coils could provide both anatomical and metabolic images without repositioning the subject. However, it is technologically challenging to attain sufficiently electromagnetic (EM) decoupling between the heteronuclear channel and proton channel, and keep the imaging areas and profiles of two nuclear channels highly matched. In this study, a hybrid monopole/loop technique was proposed for DT coil design and this technique was validated by implementing and testing a DT (1)H/(23)Na coil for MR imaging at 7T. The RF fields of the monopole ((1)H channel) and regular L/C loop ((23)Na channel) were orthogonal and intrinsically EM decoupled. Bench measurement results demonstrated the isolation between the two nuclear channels was better than -28 dB at both nuclear frequencies. Compared with the conventional DT coil using trap circuits, the monopole/loop DT coil had higher MR sensitivity for sodium imaging. The experimental results indicated that the monopole/loop technique might be a simple and efficient design for multinuclear imaging at ultrahigh fields. Additionally, the proposed DT coils based on the monopole/loop technique can be used as building blocks in designing multichannel DT coil arrays.
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Affiliation(s)
- Xinqiang Yan
- 1 State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China ; 2 Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China ; 3 Beijing Engineering Research Center of Radiographic Techniques and Equipment, Beijing 100049, China ; 4 Beijing Institute for Brain Disorders, Beijing 100053, China ; 5 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California 94158, USA ; 6 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, California 94158, USA
| | - Rong Xue
- 1 State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China ; 2 Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China ; 3 Beijing Engineering Research Center of Radiographic Techniques and Equipment, Beijing 100049, China ; 4 Beijing Institute for Brain Disorders, Beijing 100053, China ; 5 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California 94158, USA ; 6 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, California 94158, USA
| | - Xiaoliang Zhang
- 1 State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China ; 2 Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China ; 3 Beijing Engineering Research Center of Radiographic Techniques and Equipment, Beijing 100049, China ; 4 Beijing Institute for Brain Disorders, Beijing 100053, China ; 5 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California 94158, USA ; 6 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, California 94158, USA
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Yan X, Zhang X, Wei L, Xue R. Magnetic wall decoupling method for monopole coil array in ultrahigh field MRI: a feasibility test. Quant Imaging Med Surg 2014; 4:79-86. [PMID: 24834419 DOI: 10.3978/j.issn.2223-4292.2014.04.10] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2014] [Accepted: 04/21/2014] [Indexed: 11/14/2022]
Abstract
Ultrahigh field (UHF) MR imaging of deeply located target in high dielectric biological samples faces challenges due to the reduced penetration depth at the corresponding high frequencies. Radiative coils, e.g., dipole and monopole coils, have recently been applied for UHF MRI applications to obtain better signal-noise-ratio (SNR) in the area deep inside the human head and body. However, due to the unique structure of radiative coil elements, electromagnetic (EM) coupling between elements in radiative coil arrays cannot be readily addressed by using traditional decoupling methods such as element overlapping and L/C decoupling network. A new decoupling method based on induced current elimination (ICE) or magnetic wall technique has recently been proposed and has demonstrated feasibility in designing microstrip transmission line (MTL) arrays and L/C loop arrays. In this study, an array of two monopole elements decoupled using magnetic wall decoupling technique was designed, constructed and analyzed numerically and experimentally to investigate the feasibility of the decoupling technique in radiative coil array designs for MR imaging at 7 T. An L-shaped capacitive network was employed as the matching circuit and the reflection coefficients (S11) of the monopole element achieved -30 dB or better. Isolation between the two monopole elements was improved from about -10 dB (without decoupling treatment) to better than -30 dB with the ICE/magnetic wall decoupling method. B1 maps and MR images of the phantom were acquired and SNR maps were measured and calculated to evaluate the performance of the ICE/magnetic wall decoupling method. Compared with the monopole elements without decoupling methods, the ICE-decoupled array demonstrated more independent image profiles from each element and had a higher SNR in the peripheral area of the imaging subject. The experimental and simulation results indicate that the ICE/magnetic wall decoupling technique might be a promising solution to reducing the EM coupling of monopole arrays for UHF MRI.
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Affiliation(s)
- Xinqiang Yan
- 1 State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China ; 2 Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China ; 3 Beijing Engineering Research Center of Radiographic Techniques and Equipment, Beijing 100049, China ; 4 University of Chinese Academy of Sciences, Beijing 100049, China ; 5 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California 94158, USA ; 6 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, California 94158, USA
| | - Xiaoliang Zhang
- 1 State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China ; 2 Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China ; 3 Beijing Engineering Research Center of Radiographic Techniques and Equipment, Beijing 100049, China ; 4 University of Chinese Academy of Sciences, Beijing 100049, China ; 5 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California 94158, USA ; 6 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, California 94158, USA
| | - Long Wei
- 1 State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China ; 2 Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China ; 3 Beijing Engineering Research Center of Radiographic Techniques and Equipment, Beijing 100049, China ; 4 University of Chinese Academy of Sciences, Beijing 100049, China ; 5 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California 94158, USA ; 6 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, California 94158, USA
| | - Rong Xue
- 1 State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China ; 2 Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China ; 3 Beijing Engineering Research Center of Radiographic Techniques and Equipment, Beijing 100049, China ; 4 University of Chinese Academy of Sciences, Beijing 100049, China ; 5 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California 94158, USA ; 6 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, California 94158, USA
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Pang Y, Wong EWH, Yu B, Zhang X. Design and numerical evaluation of a volume coil array for parallel MR imaging at ultrahigh fields. Quant Imaging Med Surg 2014; 4:50-6. [PMID: 24649435 DOI: 10.3978/j.issn.2223-4292.2014.02.07] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Accepted: 02/26/2014] [Indexed: 11/14/2022]
Abstract
In this work, we propose and investigate a volume coil array design method using different types of birdcage coils for MR imaging. Unlike the conventional radiofrequency (RF) coil arrays of which the array elements are surface coils, the proposed volume coil array consists of a set of independent volume coils including a conventional birdcage coil, a transverse birdcage coil, and a helix birdcage coil. The magnetic fluxes of these three birdcage coils are intrinsically cancelled, yielding a highly decoupled volume coil array. In contrast to conventional non-array type volume coils, the volume coil array would be beneficial in improving MR signal-to-noise ratio (SNR) and also gain the capability of implementing parallel imaging. The volume coil array is evaluated at the ultrahigh field of 7T using FDTD numerical simulations, and the g-factor map at different acceleration rates was also calculated to investigate its parallel imaging performance.
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Affiliation(s)
- Yong Pang
- 1 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA ; 2 Agilent Technologies, Santa Clara, CA, USA ; 3 Magwale, Palo Alto, CA, USA ; 4 UC Berkeley/UCSF Joint Graduate Group in Bioengineering, San Francisco & Berkeley, CA, USA ; 5 California Institute for Quantitative Biosciences (QB3), San Francisco, CA, USA
| | - Ernest W H Wong
- 1 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA ; 2 Agilent Technologies, Santa Clara, CA, USA ; 3 Magwale, Palo Alto, CA, USA ; 4 UC Berkeley/UCSF Joint Graduate Group in Bioengineering, San Francisco & Berkeley, CA, USA ; 5 California Institute for Quantitative Biosciences (QB3), San Francisco, CA, USA
| | - Baiying Yu
- 1 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA ; 2 Agilent Technologies, Santa Clara, CA, USA ; 3 Magwale, Palo Alto, CA, USA ; 4 UC Berkeley/UCSF Joint Graduate Group in Bioengineering, San Francisco & Berkeley, CA, USA ; 5 California Institute for Quantitative Biosciences (QB3), San Francisco, CA, USA
| | - Xiaoliang Zhang
- 1 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA ; 2 Agilent Technologies, Santa Clara, CA, USA ; 3 Magwale, Palo Alto, CA, USA ; 4 UC Berkeley/UCSF Joint Graduate Group in Bioengineering, San Francisco & Berkeley, CA, USA ; 5 California Institute for Quantitative Biosciences (QB3), San Francisco, CA, USA
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Hu X, Chen X, Liu X, Zheng H, Li Y, Zhang X. Parallel imaging performance investigation of an 8-channel common-mode differential-mode (CMDM) planar array for 7T MRI. Quant Imaging Med Surg 2014; 4:33-42. [PMID: 24649433 DOI: 10.3978/j.issn.2223-4292.2014.02.05] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Accepted: 02/24/2014] [Indexed: 11/14/2022]
Abstract
An 8-channel planar phased array was proposed based on the common-mode differential-mode (CMDM) structure for ultrahigh field MRI. The parallel imaging performance of the 8-channel CMDM planar array was numerically investigated based on electromagnetic simulations and Cartesian sensitivity encoding (SENSE) reconstruction. The signal-to-noise ratio (SNR) of multichannel images combined using root-sum-of-squares (rSoS) and covariance weighted root-sum-of-squares (Cov-rSoS) at various reduction factors were compared between 8-channel CMDM array and 4-channel CM and DM array. The results of the study indicated the 8-channel CMDM array excelled the 4-channel CM and DM in SNR. The g-factor maps and artifact power were calculated to evaluate parallel imaging performance of the proposed 8-channel CMDM array. The artifact power of 8-channel CMDM array was reduced dramatically compared with the 4-channel CM and DM arrays demonstrating the parallel imaging feasibility of the CMDM array.
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Affiliation(s)
- Xiaoqing Hu
- 1 Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology of Chinese Academy of Sciences, Shenzhen 518055, China ; 2 Shenzhen Key Laboratory for MRI, Shenzhen 518055, China ; 3 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA ; 4 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, CA, USA
| | - Xiao Chen
- 1 Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology of Chinese Academy of Sciences, Shenzhen 518055, China ; 2 Shenzhen Key Laboratory for MRI, Shenzhen 518055, China ; 3 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA ; 4 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, CA, USA
| | - Xin Liu
- 1 Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology of Chinese Academy of Sciences, Shenzhen 518055, China ; 2 Shenzhen Key Laboratory for MRI, Shenzhen 518055, China ; 3 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA ; 4 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, CA, USA
| | - Hairong Zheng
- 1 Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology of Chinese Academy of Sciences, Shenzhen 518055, China ; 2 Shenzhen Key Laboratory for MRI, Shenzhen 518055, China ; 3 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA ; 4 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, CA, USA
| | - Ye Li
- 1 Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology of Chinese Academy of Sciences, Shenzhen 518055, China ; 2 Shenzhen Key Laboratory for MRI, Shenzhen 518055, China ; 3 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA ; 4 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, CA, USA
| | - Xiaoliang Zhang
- 1 Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology of Chinese Academy of Sciences, Shenzhen 518055, China ; 2 Shenzhen Key Laboratory for MRI, Shenzhen 518055, China ; 3 Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA ; 4 UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, CA, USA
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Wu X, Schmitter S, Auerbach EJ, Uğurbil K, Van de Moortele PF. Mitigating transmit B 1 inhomogeneity in the liver at 7T using multi-spoke parallel transmit RF pulse design. Quant Imaging Med Surg 2014; 4:4-10. [PMID: 24649429 DOI: 10.3978/j.issn.2223-4292.2014.02.06] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2014] [Accepted: 02/26/2014] [Indexed: 11/14/2022]
Abstract
In this work, the use of multi-spoke slice-selective parallel transmit (pTX) RF pulse was explored to address B 1+ inhomogeneity in the largest transverse section of the liver at 7T. The impact of the number of spokes was specifically investigated, considering RF pulses consisting of 2, 3 and 4 spokes, as well as single-spoke RF pulses corresponding to static B 1 shimming. Healthy volunteers were imaged on a whole body MR scanner equipped with an eight-channel transmit system. A robust and fast transmit B 1 (B 1+) estimation method was employed to obtain the eight-channel B 1+ maps within a single breath hold. Gradient echo (GRE) images of the liver were acquired using the four different RF pulses and the results were compared. The use of static B 1 shimming (i.e., 1-spoke RF pulse) resulted in partial improvement but significant signal dropouts were still observed in the target region. By comparison, the use of multi-spoke pTX RF pulse design gave rise to much improved excitation homogeneity without signal dropouts. These results demonstrate the effectiveness of multi-spoke pTX RF pulse design in B 1+ homogenization for liver magnetic resonance imaging (MRI) at 7T. The current findings at 7T may have implications for body imaging applications in clinical settings at 3T where B 1+ inhomogeneities are also known for degrading image quality in the torso.
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Affiliation(s)
- Xiaoping Wu
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Sebastian Schmitter
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Edward J Auerbach
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Pierre-François Van de Moortele
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
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30
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Li M, Zuo Z, Jin J, Xue R, Trakic A, Weber E, Liu F, Crozier S. Highly accelerated acquisition and homogeneous image reconstruction with rotating RF coil array at 7T-A phantom based study. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 240:102-112. [PMID: 24365100 DOI: 10.1016/j.jmr.2013.11.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Revised: 11/01/2013] [Accepted: 11/05/2013] [Indexed: 06/03/2023]
Abstract
Parallel imaging (PI) is widely used for imaging acceleration by means of coil spatial sensitivities associated with phased array coils (PACs). By employing a time-division multiplexing technique, a single-channel rotating radiofrequency coil (RRFC) provides an alternative method to reduce scan time. Strategically combining these two concepts could provide enhanced acceleration and efficiency. In this work, the imaging acceleration ability and homogeneous image reconstruction strategy of 4-element rotating radiofrequency coil array (RRFCA) was numerically investigated and experimental validated at 7T with a homogeneous phantom. Each coil of RRFCA was capable of acquiring a large number of sensitivity profiles, leading to a better acceleration performance illustrated by the improved geometry-maps that have lower maximum values and more uniform distributions compared to 4- and 8-element stationary arrays. A reconstruction algorithm, rotating SENSitivity Encoding (rotating SENSE), was proposed to provide image reconstruction. Additionally, by optimally choosing the angular sampling positions and transmit profiles under the rotating scheme, phantom images could be faithfully reconstructed. The results indicate that, the proposed technique is able to provide homogeneous reconstructions with overall higher and more uniform signal-to-noise ratio (SNR) distributions at high reduction factors. It is hoped that, by employing the high imaging acceleration and homogeneous imaging reconstruction ability of RRFCA, the proposed method will facilitate human imaging for ultra high field MRI.
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Affiliation(s)
- Mingyan Li
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Zhentao Zuo
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Centre for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Jin Jin
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Rong Xue
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Centre for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Adnan Trakic
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Ewald Weber
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Feng Liu
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Stuart Crozier
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia.
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31
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Moon CH, Kim JH, Zhao T, Bae KT. Quantitative23Na MRI of human knee cartilage using dual-tuned1H/23Na transceiver array radiofrequency coil at 7 tesla. J Magn Reson Imaging 2013; 38:1063-72. [DOI: 10.1002/jmri.24030] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Accepted: 12/12/2012] [Indexed: 12/20/2022] Open
Affiliation(s)
- Chan Hong Moon
- Department of Radiology; University of Pittsburgh; Pittsburgh, Pennsylvania USA
| | - Jung-Hwan Kim
- Department of Radiology; University of Pittsburgh; Pittsburgh, Pennsylvania USA
| | - Tiejun Zhao
- MR Research Support; Siemens Healthcare; Pittsburgh, Pennsylvania USA
| | - Kyongtae Ty Bae
- Department of Radiology; University of Pittsburgh; Pittsburgh, Pennsylvania USA
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32
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Li Y, Wang C, Yu B, Vigneron D, Chen W, Zhang X. Image homogenization using pre-emphasis method for high field MRI. Quant Imaging Med Surg 2013; 3:217-23. [PMID: 24040618 DOI: 10.3978/j.issn.2223-4292.2013.07.01] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2013] [Accepted: 07/16/2013] [Indexed: 11/14/2022]
Abstract
Radiofrequency (RF) field (B 1) inhomogeneity due to shortened wavelength at high field is a major cause of magnetic resonance imaging (MRI) nonuniformity in high dielectric biological samples (e.g., human body). In this work, we propose a method to improve the B 1 and MRI homogeneity by using pre-emphasized non-uniform B 1 distribution. The intrinsic B 1 distribution that could be generated by a RF volume coil, specifically a microstrip transmission line (MTL) coil used in this work, was pre-emphasized in the sample's periphery region of interest to compensate for the central brightness induced by high frequency interference effect due to shortened wave length. This pre-emphasized non-uniform B 1 can be realized by varying the parameters of microstrip elements, such as the substrate thickness of MTL volume coil. Both numerical simulation and phantom MR imaging studies were carried out to investigate the feasibility and merit of the proposed method in achieving homogeneous MR images. The simulation results demonstrate that by using a pre-emphasized B 1 distribution generated by the MTL volume coil, relatively uniform B 1 distribution and homogeneous MR image (98% homogeneity) within the spherical phantom (15 cm diameter) were achieved with 4.5 mm thickness. The B 1 and MRI intensity distributions of a 16-element MTL volume coil with fixed substrate thickness and five varied saline loads were modeled and experimentally tested. Similar results from both simulation and experiments were obtained, suggesting substantial improvements of B 1 and MRI homogeneities within the phantom containing 125 mM saline. The overall results demonstrate an efficient B 1 shimming approach for improving high field MRI.
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Affiliation(s)
- Ye Li
- Department of Radiology and Biomedical Imaging, UC San Francisco, San Francisco, CA, USA
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Cao Z, Oh S, Sica CT, McGarrity JM, Horan T, Luo W, Collins CM. Bloch-based MRI system simulator considering realistic electromagnetic fields for calculation of signal, noise, and specific absorption rate. Magn Reson Med 2013; 72:237-47. [PMID: 24006153 DOI: 10.1002/mrm.24907] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2013] [Revised: 07/10/2013] [Accepted: 07/10/2013] [Indexed: 01/09/2023]
Abstract
PURPOSE To describe and introduce new software capable of accurately simulating MR signal, noise, and specific absorption rate (SAR) given arbitrary sample, sequence, static magnetic field distribution, and radiofrequency magnetic and electric field distributions for each transmit and receive coil. THEORY AND METHODS Using fundamental equations for nuclear precession and relaxation, signal reception, noise reception, and calculation of SAR, a versatile MR simulator was developed. The resulting simulator was tested with simulation of a variety of sequences demonstrating several common imaging contrast types and artifacts. The simulation of intravoxel dephasing and rephasing with both tracking of the first order derivatives of each magnetization vector and multiple magnetization vectors was examined to ensure adequate representation of the MR signal. A quantitative comparison of simulated and experimentally measured SNR was also performed. RESULTS The simulator showed good agreement with our expectations, theory, and experiment. CONCLUSION With careful design, an MR simulator producing realistic signal, noise, and SAR for arbitrary sample, sequence, and fields has been created. It is hoped that this tool will be valuable in a wide variety of applications.
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Affiliation(s)
- Zhipeng Cao
- Department of Bioengineering, The Pennsylvania State University, Hershey, Pennsylvania, USA; Department of Radiology, The Pennsylvania State University, Hershey, 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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35
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Reiss-Zimmermann M, Gutberlet M, Köstler H, Fritzsch D, Hoffmann KT. Improvement of SNR and acquisition acceleration using a 32-channel head coil compared to a 12-channel head coil at 3T. Acta Radiol 2013; 54:702-8. [PMID: 23474767 DOI: 10.1177/0284185113479051] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Magnetic resonance imaging (MRI) techniques continue to improve in manifold ways. Besides field strength and sequence optimization, technical advances in coil design and sensitivity yield to increase the signal detection and therefore improve image quality. PURPOSE To evaluate the performance of signal-to-noise ratio (SNR) and parallel acquisition technique (PAT) acceleration of a dedicated 32-channel head coil compared with a standard 12-channel head coil. MATERIAL AND METHODS In a clinical 3T setting, spatial resolved SNR values for unaccelerated imaging and PAT with acceleration factors of 2-6 of a 32-channel head coil were evaluated in relation to a 12-channel head coil. SNR was determined quantitatively using proton-density-weighted in-vivo examinations in five healthy volunteers. Quantitative SNR maps for unaccelerated and PAT imaging were calculated using unfiltered MR raw data. RESULTS Up to three-fold higher SNR values were achieved with the 32-channel head coil, which diminished towards the center to an increase of 40% compared with the 12-channel head coil. When using PAT, the 32-channel head coil resulted in a lower spatial-dependent quantitative noise enhancement, varying between 0% at R = 2 and 33% at R = 5. CONCLUSION The 32-channel head coil provided superior SNR both with and without PAT compared with a 12-channel head coil, especially close to the brain surface. Using PAT, the unavoidable noise enhancement is diminished up to acceleration factors of 6 for the 32-channel head coil. Therefore, the 32-channel head coil is considered as a preferable tool for high-resolution neuroradiological imaging.
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Affiliation(s)
| | | | - Herbert Köstler
- Institute of Radiology, University of Würzburg, Würzburg, Germany
| | - Dominik Fritzsch
- Department of Neuroradiology, University Hospital Leipzig, Leipzig
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36
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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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Jin J, Liu F, Weber E, Crozier S. Improving SAR estimations in MRI using subject-specific models. Phys Med Biol 2012; 57:8153-71. [PMID: 23174940 DOI: 10.1088/0031-9155/57/24/8153] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
To monitor and strategically control energy deposition in magnetic resonance imaging (MRI), measured as a specific absorption rate (SAR), numerical methods using generic human models have been employed to estimate worst-case values. Radiofrequency (RF) sequences are therefore often designed conservatively with large safety margins, potentially hindering the full potential of high-field systems. To more accurately predict the patient SAR values, we propose the use of image registration techniques, in conjunction with high-resolution image and tissue libraries, to create patient-specific voxel models. To test this, a matching model from the archives was first selected. Its tissue information was then warped to the patient's coordinates by registering the high-resolution library image to the pilot scan of the patient. Results from studying the models' 1 g SAR distribution suggest that the developed patient model can predict regions of elevated SAR within the patient with remarkable accuracy. Additionally, this work also proposes a voxel analytical metric that can assist in the construction of a patient library and the selection of the matching model from the library for a patient. It is hoped that, by developing voxel models with high accuracy in patient-specific anatomy and positioning, the proposed method can accurately predict the safety margins for high-field human applications and, therefore maximize the safe use of RF sequence power in high-field MRI systems.
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Affiliation(s)
- Jin Jin
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
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38
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Watanabe H. Experimental demonstration of the proportionality of the RF reception field to a complex conjugate of B₁⁻. Magn Reson Med Sci 2012; 11:193-6. [PMID: 23037564 DOI: 10.2463/mrms.11.193] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
We demonstrated that the radiofrequency (RF) reception field is proportional to B₁⁻* straightforwardly in magnetic resonance (MR) imaging experiments at 4.7 T. We compared maps of the reception field and the B₁⁻ of a saline phantom in magnitude and phase. First, we measured the image using an adiabatic spin echo (ASE) sequence with homogeneous excitation. That image corresponds to a map of the reception field. Next, we rotated the RF coil with the sample 180° around the vertical axis to measure the map of the transmission field that corresponded to B₁⁻ in the original configuration. The magnitude of the distribution fields of the reception field and B₁⁻ maps was almost identical. Examining the phases of the ASE images in the original and inverted configurations, we observed almost the same distribution in both phase maps, which indicated the proportionality of the reception field to B₁⁻*.
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Affiliation(s)
- Hidehiro Watanabe
- Center for Environmental Measurement and Analysis, National Institutes for Environmental Studies, Tsukuba, Ibaraki, Japan.
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39
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Yoo H, Gopinath A, Vaughan JT. A method to localize RF B₁ field in high-field magnetic resonance imaging systems. IEEE Trans Biomed Eng 2012; 59:3365-71. [PMID: 22929360 DOI: 10.1109/tbme.2012.2208965] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
In high-field magnetic resonance imaging (MRI) systems, B₀ fields of 7 and 9.4 T, the RF field shows greater inhomogeneity compared to clinical MRI systems with B₀ fields of 1.5 and 3.0 T. In multichannel RF coils, the magnitude and phase of the input to each coil element can be controlled independently to reduce the nonuniformity of the RF field. The convex optimization technique has been used to obtain the optimum excitation parameters with iterative solutions for homogeneity in a selected region of interest. The pseudoinverse method has also been used to find a solution. The simulation results for 9.4- and 7-T MRI systems are discussed in detail for the head model. Variation of the simulation results in a 9.4-T system with the number of RF coil elements for different positions of the regions of interest in a spherical phantom are also discussed. Experimental results were obtained in a phantom in the 9.4-T system and are compared to the simulation results and the specific absorption rate has been evaluated.
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Affiliation(s)
- Hyoungsuk Yoo
- Department of Electrical and Computer Engineering and the Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA.
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40
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Jin J, Liu F, Zuo Z, Xue R, Li M, Li Y, Weber E, Crozier S. Inverse field-based approach for simultaneous B₁ mapping at high fields - a phantom based study. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 217:27-35. [PMID: 22391489 DOI: 10.1016/j.jmr.2012.02.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2011] [Revised: 01/16/2012] [Accepted: 02/08/2012] [Indexed: 05/31/2023]
Abstract
Based on computational electromagnetics and multi-level optimization, an inverse approach of attaining accurate mapping of both transmit and receive sensitivity of radiofrequency coils is presented. This paper extends our previous study of inverse methods of receptivity mapping at low fields, to allow accurate mapping of RF magnetic fields (B(1)) for high-field applications. Accurate receive sensitivity mapping is essential to image domain parallel imaging methods, such as sensitivity encoding (SENSE), to reconstruct high quality images. Accurate transmit sensitivity mapping will facilitate RF-shimming and parallel transmission techniques that directly address the RF inhomogeneity issue, arguably the most challenging issue of high-field magnetic resonance imaging (MRI). The inverse field-based approach proposed herein is based on computational electromagnetics and iterative optimization. It fits an experimental image to the numerically calculated signal intensity by iteratively optimizing the coil-subject geometry to better resemble the experiments. Accurate transmit and receive sensitivities are derived as intermediate results of the optimization process. The method is validated by imaging studies using homogeneous saline phantom at 7T. A simulation study at 300MHz demonstrates that the proposed method is able to obtain receptivity mapping with errors an order of magnitude less than that of the conventional method. The more accurate receptivity mapping and simultaneously obtained transmit sensitivity mapping could enable artefact-reduced and intensity-corrected image reconstructions. It is hoped that by providing an approach to the accurate mapping of both transmit and receive sensitivity, the proposed method will facilitate a range of applications in high-field MRI and parallel imaging.
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Affiliation(s)
- Jin Jin
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
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41
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Webb AG. Visualization and characterization of pure and coupled modes in water-based dielectric resonators on a human 7T scanner. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 216:107-113. [PMID: 22341210 DOI: 10.1016/j.jmr.2012.01.013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2011] [Revised: 12/19/2011] [Accepted: 01/22/2012] [Indexed: 05/31/2023]
Abstract
MRI represents a unique method to visualize directly different resonant modes of arbitrarily-shaped dielectric resonators in the radiofrequency spectrum via construction of resonators filled with distilled, deionized water which has a low conductivity and high relative permittivity. The required dimensions, particularly for higher order modes, are large and so a high field whole-body MRI system is needed to visualize these modes. In this study, using a simple cylindrical geometry, many higher order modes were identified and confirmed using electromagnetic simulations. In addition, coupled modes between more than one resonator were investigated, with possible future applications including direct visualization of fields in metamaterials.
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Affiliation(s)
- A G Webb
- Department of Radiology, C3-Q, Leiden University Medical Center, Albinusdreef 2, Leiden 2333 ZA, The Netherlands.
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42
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The road to functional imaging and ultrahigh fields. Neuroimage 2012; 62:726-35. [PMID: 22333670 DOI: 10.1016/j.neuroimage.2012.01.134] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Revised: 01/24/2012] [Accepted: 01/30/2012] [Indexed: 11/23/2022] Open
Abstract
The Center for Magnetic Resonance (CMRR) at the University of Minnesota was one of the laboratories where the work that simultaneously and independently introduced functional magnetic resonance imaging (fMRI) of human brain activity was carried out. However, unlike other laboratories pursuing fMRI at the time, our work was performed at 4T magnetic field and coincided with the effort to push human magnetic resonance imaging to field strength significantly beyond 1.5T which was the high-end standard of the time. The human fMRI experiments performed in CMRR were planned between two colleagues who had known each other and had worked together previously in Bell Laboratories, namely Seiji Ogawa and myself, immediately after the Blood Oxygenation Level Dependent (BOLD) contrast was developed by Seiji. We were waiting for our first human system, a 4T system, to arrive in order to attempt at imaging brain activity in the human brain and these were the first experiments we performed on the 4T instrument in CMRR when it became marginally operational. This was a prelude to a subsequent systematic push we initiated for exploiting higher magnetic fields to improve the accuracy and sensitivity of fMRI maps, first going to 9.4T for animal model studies and subsequently developing a 7T human system for the first time. Steady improvements in high field instrumentation and ever expanding armamentarium of image acquisition and engineering solutions to challenges posed by ultrahigh fields have brought fMRI to submillimeter resolution in the whole brain at 7T, the scale necessary to reach cortical columns and laminar differentiation in the whole brain. The solutions that emerged in response to technological challenges posed by 7T also propagated and continues to propagate to lower field clinical systems, a major advantage of the ultrahigh fields effort that is underappreciated. Further improvements at 7T are inevitable. Further translation of these improvements to lower field clinical systems to achieve new capabilities and to magnetic fields significantly higher than 7T to enable human imaging is inescapable.
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43
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Seo JK, Kim MO, Lee J, Choi N, Woo EJ, Kim HJ, Kwon OI, Kim DH. Error analysis of nonconstant admittivity for MR-based electric property imaging. IEEE TRANSACTIONS ON MEDICAL IMAGING 2012; 31:430-437. [PMID: 21990329 DOI: 10.1109/tmi.2011.2171000] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Magnetic resonance electrical property tomography (MREPT) is a new imaging modality to visualize a distribution of admittivity γ = σ+iωε inside the human body where σ and ε denote electrical conductivity and permittivity, respectively. Using B1 maps acquired by an magnetic resonance imaging scanner, it produces cross-sectional images of σ and ε at the Larmor frequency. Since current MREPT methods rely on an assumption of a locally homogeneous admittivity, there occurs a reconstruction error where this assumption fails. Rigorously analyzing the reconstruction error in MREPT, we showed that the error is fundamental and may cause technical difficulties in interpreting MREPT images of a general inhomogeneous object. We performed numerical simulations and phantom experiments to quantitatively support the error analysis. We compared the MREPT image reconstruction problem with that of magnetic resonance electrical impedance tomography (MREIT) to highlight distinct features of both methods to probe the same object in terms of its high- and low-frequency conductivity distributions, respectively. MREPT images showed large errors along boundaries where admittivity values changed whereas MREIT images showed no such boundary effects. Noting that MREIT makes use of the term neglected in MREPT, a novel MREPT admittivity image reconstruction method is proposed to deal with the boundary effects, which requires further investigation on the complex directional derivative in the real Euclidian space [Formula: see text].
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Affiliation(s)
- Jin Keun Seo
- Department of Computational Science and Engineering, Yonsei University, Seoul 120-749, South Korea.
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44
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Kim JH, Moon CH, Park BW, Furlan A, Zhao T, Bae KT. Multichannel transceiver dual-tuned RF coil for proton/sodium MR imaging of knee cartilage at 3 T. Magn Reson Imaging 2012; 30:562-71. [PMID: 22297242 DOI: 10.1016/j.mri.2011.12.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2011] [Revised: 11/08/2011] [Accepted: 12/04/2011] [Indexed: 10/14/2022]
Abstract
Sodium magnetic resonance (MR) imaging is a promising technique for detecting changes of proteoglycan (PG) content in cartilage associated with knee osteoarthritis. Despite its potential clinical benefit, sodium MR imaging in vivo is challenging because of intrinsically low sodium concentration and low MR signal sensitivity. Some of the challenges in sodium MR imaging may be eliminated by the use of a high-sensitivity radiofrequency (RF) coil, specifically, a dual-tuned (DT) proton/sodium RF coil which facilitates the co-registration of sodium and proton MR images and the evaluation of both physiochemical and structural properties of knee cartilage. Nevertheless, implementation of a DT proton/sodium RF coil is technically difficult because of the coupling effect between the coil elements (particularly at high field) and the required compact design with improved coil sensitivity. In this study, we applied a multitransceiver RF coil design to develop a DT proton/sodium coil for knee cartilage imaging at 3 T. With the new design, the size of the coil was minimized, and a high signal-to-noise ratio (SNR) was achieved. DT coil exhibited high levels of reflection S11 (∼-21 dB) and transmission coefficient S12 (∼-19 dB) for both the proton and sodium coils. High SNR (range 27-38) and contrast-to-noise ratio (CNR) (range 15-21) were achieved in sodium MR imaging of knee cartilage in vivo at 3-mm(3) isotropic resolution. This DT coil performance was comparable to that measured using a sodium-only birdcage coil (SNR of 28 and CNR of 20). Clinical evaluation of the DT coil on four normal subjects demonstrated a consistent acquisition of high-resolution proton images and measurement of relative sodium concentrations of knee cartilages without repositioning of the subjects during the same MR scanning session.
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Affiliation(s)
- Jung-Hwan Kim
- Department of Radiology, Magnetic Resonance Research Center, University of Pittsburgh, Pittsburgh, PA 15213, USA
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45
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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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46
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WATANABE H. Investigation of the Asymmetric Distributions of RF Transmission and Reception Fields at High Static Field. Magn Reson Med Sci 2012; 11:129-35. [DOI: 10.2463/mrms.11.129] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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47
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Kim KN, Kim YB, Cho ZH. Improvement of a 4-Channel Spiral-Loop RF Coil Array for TMJ MR Imaging at 7T. ACTA ACUST UNITED AC 2012. [DOI: 10.13104/jksmrm.2012.16.2.103] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
Affiliation(s)
- Kyoung-Nam Kim
- Neuroscience Research Institute, Gachon University, Incheon, Republic of Korea
| | - Young-Bo Kim
- Neuroscience Research Institute, Gachon University, Incheon, Republic of Korea
| | - Zang-Hee Cho
- Neuroscience Research Institute, Gachon University, Incheon, Republic of Korea
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48
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Watanabe H, Takaya N, Mitsumori F. Non-uniformity correction of human brain imaging at high field by RF field mapping of B1+ and B1-. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2011; 212:426-430. [PMID: 21889379 DOI: 10.1016/j.jmr.2011.08.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2011] [Revised: 07/28/2011] [Accepted: 08/05/2011] [Indexed: 05/31/2023]
Abstract
A new method of non-uniform image correction is proposed. Image non-uniformity is originated from the spatial distribution of RF transmission and reception fields, represented as B(1)(+) and B(1)(-), respectively. In our method, B(1)(+) mapping was performed invivo by a phase method. In B(1)(-) mapping, images with multiple TEs were acquired with a multi-echo adiabatic spin echo (MASE) sequence which enables homogeneous excitation. By T(2) fitting of these images an M(0) map (M(0)(MASE)) was obtained, in which signal intensity was expressed as the product of B(1)(-) and M₀(1-e⁻(TR/T¹)) . The ratio of this M(0)(MASE) map to the B(1)(+) map showed a similar spatial pattern in different human brains. These ratios of M(0)(MASE) to B(1)(+) in 24 subjects were averaged and then fitted with a spatially polynomial function to obtain a ratio map of B(1)(-)/B(1)(+)(α). Uniform image was achieved in spin echo (SE), MASE and inversion recovery turboFLASH (IRTF) images using measured B(1)(+) and calculated B(1)(-) by αB(1)(+). Water fractions in gray and white matters obtained from the M(0) images corrected by this method were in good agreement with previously reported values. From these experimental results, the proposed method of non-uniformity correction is validated at 4.7 T imaging.
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Affiliation(s)
- Hidehiro Watanabe
- Center for Environmental Measurement and Analysis, National Institutes for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
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49
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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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50
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Gilbert KM, Curtis AT, Gati JS, Klassen LM, Menon RS. A radiofrequency coil to facilitate B₁⁺ shimming and parallel imaging acceleration in three dimensions at 7 T. NMR IN BIOMEDICINE 2011; 24:815-823. [PMID: 21834005 DOI: 10.1002/nbm.1627] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2010] [Revised: 07/29/2010] [Accepted: 09/21/2010] [Indexed: 05/31/2023]
Abstract
A 15-channel transmit-receive (transceive) radiofrequency (RF) coil was developed to image the human brain at 7 T. A hybrid decoupling scheme was implemented that used both capacitive decoupling and the partial geometric overlapping of adjacent coil elements. The decoupling scheme allowed coil elements to be arrayed along all three Cartesian axes; this facilitated shimming of the transmit field, B₁⁺, and parallel imaging acceleration along the longitudinal direction in addition to the standard transverse directions. Each channel was independently controlled during imaging using a 16-channel console and a 16 × 1-kW RF amplifier-matrix. The mean isolation between all combinations of coil elements was 18 ± 7 dB. After B₁⁺ shimming, the standard deviation of the transmit field uniformity was 11% in an axial plane and 32% over the entire brain superior to the mid-cerebellum. Transmit uniformity was sufficient to acquire fast spin echo images of this region of the brain with a single B₁⁺ shim solution. Signal-to-noise ratio (SNR) maps showed higher SNR in the periphery vs center of the brain, and higher SNR in the occipital and temporal lobes vs the frontal lobe. Parallel imaging acceleration in a rostral-caudal oblique plane was demonstrated. The implication of the number of channels in a transmit-receive coil was discussed: it was determined that improvements in SNR and B₁⁺ shimming can be expected when using more than 15 independently controlled transmit-receive channels.
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Affiliation(s)
- Kyle M Gilbert
- Robarts Research Institute, The University of Western Ontario, London, ON, Canada.
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