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Matsuda T, Iwadate Y, Mori F, Takeda K, Sasaki M. Using Phase Difference Information to Detect Errors in the Flip Angle Measured with Actual Flip Angle Imaging at 7T. Magn Reson Med Sci 2024; 23:102-109. [PMID: 36450525 PMCID: PMC10838719 DOI: 10.2463/mrms.tn.2022-0053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Accepted: 09/25/2022] [Indexed: 01/05/2024] Open
Abstract
Flip angle (FA) measurements using the actual flip angle imaging (AFI) method may induce significant errors in ultrahigh fields. We aimed to develop a method for detecting errors in FA measurements using phase information at 7 tesla. We performed computer simulations to elucidate the relationship between the FA calculation errors and the phase difference between the two AFI source images. We then examined whether a method based on the phase difference could detect FA calculation errors and determine the prescribed nominal FA of the scanner for accurate measurements in phantoms and healthy volunteers. The simulations confirmed that the calculated FA values erroneously decreased when the longitudinal magnetization and phase in one of the source images were inverted. Tests on phantoms and human subjects demonstrated that the phase difference information between the source images with a cut-off of 90° could readily detect FA calculation errors in the AFI method.
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Affiliation(s)
- Tsuyoshi Matsuda
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Shiwa-gun, Iwate, Japan
| | - Yuji Iwadate
- MR Applications and Workflow, GE Healthcare Japan Corporation, Hino, TokyoJapan
| | - Futoshi Mori
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Shiwa-gun, Iwate, Japan
| | - Kota Takeda
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Shiwa-gun, Iwate, Japan
| | - Makoto Sasaki
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Shiwa-gun, Iwate, Japan
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Abstract
Clinical MRI systems have continually improved over the years since their introduction in the 1980s. In MRI technical development, the developments in each MRI system component, including data acquisition, image reconstruction, and hardware systems, have impacted the others. Progress in each component has induced new technology development opportunities in other components. New technologies outside of the MRI field, for example, computer science, data processing, and semiconductors, have been immediately incorporated into MRI development, which resulted in innovative applications. With high performance computing and MR technology innovations, MRI can now provide large volumes of functional and anatomical image datasets, which are important tools in various research fields. MRI systems are now combined with other modalities, such as positron emission tomography (PET) or therapeutic devices. These hybrid systems provide additional capabilities. In this review, MRI advances in the last two decades will be considered. We will discuss the progress of MRI systems, the enabling technology, established applications, current trends, and the future outlook.
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Affiliation(s)
- Hiroyuki Kabasawa
- Department of Radiological Sciences, School of Health Sciences at Narita, International University of Health and Welfare
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Matsuda T, Uwano I, Iwadate Y, Yoshioka K, Sasaki M. Spatial and temporal variations of flip-angle distributions in the human brain using an eight-channel parallel transmission system at 7T: comparison of three radiofrequency excitation methods. Radiol Phys Technol 2021; 14:161-166. [PMID: 33710499 DOI: 10.1007/s12194-021-00612-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 03/03/2021] [Accepted: 03/04/2021] [Indexed: 10/21/2022]
Abstract
We investigated the spatial and temporal variations of flip-angle (FA) distributions in the human brain from multiple scans, using an eight-channel parallel transmission (pTx) system at 7T. Nine healthy volunteers were scanned in five sessions using three radiofrequency excitation techniques each time: circular polarization (CP), static pTx, and dynamic pTx. We calculated the coefficients of variation of the FA values within the brain area to evaluate the variations, and the maximum intersession differences in the FA values (Dmax), comparing them between the three methods. The coefficients of variation decreased in the following order: CP, static pTx, and dynamic pTx (median: 20.1%, 13.6%, and 5.7%, respectively; p < 0.001). The average Dmax values were significantly higher for the static pTx (5.4°) than for the dynamic pTx (2.8°) and CP (1.7°) methods (p = 0.004 and 0.001, respectively). Compared to the CP method, the dynamic pTx method at 7T can efficiently minimize spatial variations in the FA distribution with a mild increase in temporal variations. The static pTx method exhibited a remarkably wide temporal variation.
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Affiliation(s)
- Tsuyoshi Matsuda
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, 1-1-1 Idaidori Yahaba, Iwate, 028-3694, Japan.
| | - Ikuko Uwano
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, 1-1-1 Idaidori Yahaba, Iwate, 028-3694, Japan
| | - Yuji Iwadate
- MR Applications and Workflow, GE Healthcare Japan Corporation, 4-7-127 Asahigaoka, Hino, Tokyo, 191-0065, Japan
| | - Kunihiro Yoshioka
- Department of Radiology, School of Medicine, Iwate Medical University, 2-1-1 Idaidori Yahaba, Iwate, 028-3695, Japan
| | - Makoto Sasaki
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, 1-1-1 Idaidori Yahaba, Iwate, 028-3694, Japan
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Abstract
Magnetic resonance imaging (MRI) has been driven toward ultrahigh magnetic fields (UHF) in order to benefit from correspondingly higher signal-to-noise ratio and spectral resolution. Technological challenges associated with UHF, such as increased radiofrequency (RF) energy deposition and RF excitation inhomogeneity, limit realization of the full potential of these benefits. Parallel RF transmission (pTx) enables decreases in the inhomogeneity of RF excitations and in RF energy deposition by using multiple-transmit RF coils driven independently and operating simultaneously. pTx plays a fundamental role in UHF MRI by bringing the potential applications of UHF into reality. In this review article, we review the recent developments in pTx pulse design and RF safety in pTx. Simultaneous multislice imaging and inner volume imaging using pTx are reviewed with a focus on UHF applications. Emerging pTx design approaches using improved pTx design frameworks and calibrations are reviewed together with calibration-free approaches that remove the necessity of time-consuming calibrations necessary for successful pTx. Lastly, we focus on the safety of pTx that is improved by using intersubject variability analysis, proactively managing pTx and temperature-based pTx approaches.
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Affiliation(s)
- Cem M. Deniz
- Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY
- RF Test Labs, LLC, New York, NY
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Kameda H, Kudo K, Matsuda T, Harada T, Iwadate Y, Uwano I, Yamashita F, Yoshioka K, Sasaki M, Shirato H. Improvement of the repeatability of parallel transmission at 7T using interleaved acquisition in the calibration scan. J Magn Reson Imaging 2017; 48:94-101. [PMID: 29205623 DOI: 10.1002/jmri.25903] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Accepted: 11/07/2017] [Indexed: 11/07/2022] Open
Abstract
BACKGROUND Respiration-induced phase shift affects B0 /B1+ mapping repeatability in parallel transmission (pTx) calibration for 7T brain MRI, but is improved by breath-holding (BH). However, BH cannot be applied during long scans. PURPOSE To examine whether interleaved acquisition during calibration scanning could improve pTx repeatability and image homogeneity. STUDY TYPE Prospective. SUBJECTS Nine healthy subjects. FIELD STRENGTH/SEQUENCE 7T MRI with a two-channel RF transmission system was used. ASSESSMENT Calibration scanning for B0 /B1+ mapping was performed under sequential acquisition/free-breathing (Seq-FB), Seq-BH, and interleaved acquisition/FB (Int-FB) conditions. The B0 map was calculated with two echo times, and the B1+ map was obtained using the Bloch-Siegert method. Actual flip-angle imaging (AFI) and gradient echo (GRE) imaging were performed using pTx and quadrature-Tx (qTx). All scans were acquired in five sessions. Repeatability was evaluated using intersession standard deviation (SD) or coefficient of variance (CV), and in-plane homogeneity was evaluated using in-plane CV. STATISTICAL TESTS A paired t-test with Bonferroni correction for multiple comparisons was used. RESULTS The intersession CV/SDs for the B0 /B1+ maps were significantly smaller in Int-FB than in Seq-FB (Bonferroni-corrected P < 0.05 for all). The intersession CVs for the AFI and GRE images were also significantly smaller in Int-FB, Seq-BH, and qTx than in Seq-FB (Bonferroni-corrected P < 0.05 for all). The in-plane CVs for the AFI and GRE images in Seq-FB, Int-FB, and Seq-BH were significantly smaller than in qTx (Bonferroni-corrected P < 0.01 for all). DATA CONCLUSION Using interleaved acquisition during calibration scans of pTx for 7T brain MRI improved the repeatability of B0 /B1+ mapping, AFI, and GRE images, without BH. LEVEL OF EVIDENCE 1 Technical Efficacy Stage 1 J. Magn. Reson. Imaging 2017.
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Affiliation(s)
- Hiroyuki Kameda
- Department of Radiation Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan.,Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Yahaba, Iwate, Japan
| | - Kohsuke Kudo
- Department of Diagnostic and Interventional Radiology, Hokkaido University Hospital, Sapporo, Hokkaido, Japan.,Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan
| | - Tsuyoshi Matsuda
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Yahaba, Iwate, Japan
| | - Taisuke Harada
- Department of Diagnostic and Interventional Radiology, Hokkaido University Hospital, Sapporo, Hokkaido, Japan
| | - Yuji Iwadate
- Global MR Applications and Workflow, GE Healthcare, Hino, Japan
| | - Ikuko Uwano
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Yahaba, Iwate, Japan
| | - Fumio Yamashita
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Yahaba, Iwate, Japan
| | - Kunihiro Yoshioka
- Department of Radiology, School of Medicine, Iwate Medical University, Morioka, Iwate, Japan
| | - Makoto Sasaki
- Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Yahaba, Iwate, Japan
| | - Hiroki Shirato
- Department of Radiation Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan.,Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan
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