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Liu Q, Gagoski B, Shaik IA, Westin CF, Wilde EA, Schneider W, Bilgic B, Grissom W, Nielsen JF, Zaitsev M, Rathi Y, Ning L. Time-division multiplexing (TDM) sequence removes bias in T 2 estimation and relaxation-diffusion measurements. Magn Reson Med 2024; 92:2506-2519. [PMID: 39136245 PMCID: PMC11436305 DOI: 10.1002/mrm.30246] [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: 04/09/2024] [Revised: 07/24/2024] [Accepted: 07/25/2024] [Indexed: 08/21/2024]
Abstract
PURPOSE To compare the performance of multi-echo (ME) and time-division multiplexing (TDM) sequences for accelerated relaxation-diffusion MRI (rdMRI) acquisition and to examine their reliability in estimating accurate rdMRI microstructure measures. METHOD The ME, TDM, and the reference single-echo (SE) sequences with six TEs were implemented using Pulseq with single-band (SB) and multi-band 2 (MB2) acceleration factors. On a diffusion phantom, the image intensities of the three sequences were compared, and the differences were quantified using the normalized RMS error (NRMSE). Shinnar-Le Roux (SLR) pulses were implemented for the SB-ME and SB-SE sequences to investigate the impact of slice profiles on ME sequences. For the in-vivo brain scan, besides the image intensity comparison and T2-estimates, different methods were used to assess sequence-related effects on microstructure estimation, including the relaxation diffusion imaging moment (REDIM) and the maximum-entropy relaxation diffusion distribution (MaxEnt-RDD). RESULTS TDM performance was similar to the gold standard SE acquisition, whereas ME showed greater biases (3-4× larger NRMSEs for phantom, 2× for in-vivo). T2 values obtained from TDM closely matched SE, whereas ME sequences underestimated the T2 relaxation time. TDM provided similar diffusion and relaxation parameters as SE using REDIM, whereas SB-ME exhibited a 60% larger bias in the map and on average 3.5× larger bias in the covariance between relaxation-diffusion coefficients. CONCLUSION Our analysis demonstrates that TDM provides a more accurate estimation of relaxation-diffusion measurements while accelerating the acquisitions by a factor of 2 to 3.
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Affiliation(s)
- Qiang Liu
- Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States
- School of Biomedical Engineering, Southern Medical University, Guangzhou, China
| | - Borjan Gagoski
- Department of Radiology, Harvard Medical School, Boston, MA, United States
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children’s Hospital, Boston, MA, United States
| | - Imam Ahmed Shaik
- Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States
| | - Carl-Fredrik Westin
- Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States
| | - Elisabeth A. Wilde
- Va Salt Lake City Health Care System, Informatics, Decision-Enhancement and Analytic Sciences Center, Salt Lake City, Utah, USA
- Department of Neurology, University of Utah, Salt Lake City, Utah, USA
| | | | - Berkin Bilgic
- Department of Radiology, Harvard Medical School, Boston, MA, United States
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston, MA, United States
- Harvard/MIT Health Sciences and Technology, Cambridge, MA, United States
| | - William Grissom
- Department of Biomedical Engineering, Case School of Medicine, Case Western Reserve University, Cleveland, OH, United States
| | - Jon-Fredrik Nielsen
- Functional MRI Laboratory, Department of Radiology, University of Michigan, Ann Arbor, MI, United States
| | - Maxim Zaitsev
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Yogesh Rathi
- Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States
| | - Lipeng Ning
- Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States
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Liu Q, Gagoski B, Shaik IA, Westin CF, Wilde EA, Schneider W, Bilgic B, Grissom W, Nielsen JF, Zaitsev M, Rathi Y, Ning L. Time-division multiplexing (TDM) sequence removes bias in T2 estimation and relaxation-diffusion measurements. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.06.03.597138. [PMID: 38895252 PMCID: PMC11185580 DOI: 10.1101/2024.06.03.597138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/21/2024]
Abstract
Purpose To compare the performance of multi-echo (ME) and time-division multiplexing (TDM) sequences for accelerated relaxation-diffusion MRI (rdMRI) acquisition and to examine their reliability in estimating accurate rdMRI microstructure measures. Method The ME, TDM, and the reference single-echo (SE) sequences with six echo times (TE) were implemented using Pulseq with single-band (SB-) and multi-band 2 (MB2-) acceleration factors. On a diffusion phantom, the image intensities of the three sequences were compared, and the differences were quantified using the normalized root mean squared error (NRMSE). For the in-vivo brain scan, besides the image intensity comparison and T2-estimates, different methods were used to assess sequence-related effects on microstructure estimation, including the relaxation diffusion imaging moment (REDIM) and the maximum-entropy relaxation diffusion distribution (MaxEnt-RDD). Results TDM performance was similar to the gold standard SE acquisition, whereas ME showed greater biases (3-4× larger NRMSEs for phantom, 2× for in-vivo). T2 values obtained from TDM closely matched SE, whereas ME sequences underestimated the T2 relaxation time. TDM provided similar diffusion and relaxation parameters as SE using REDIM, whereas SB-ME exhibited a 60% larger bias in the map and on average 3.5× larger bias in the covariance between relaxation-diffusion coefficients. Conclusion Our analysis demonstrates that TDM provides a more accurate estimation of relaxation-diffusion measurements while accelerating the acquisitions by a factor of 2 to 3.
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Affiliation(s)
- Qiang Liu
- Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States
- School of Biomedical Engineering, Southern Medical University, Guangzhou, China
| | - Borjan Gagoski
- Department of Radiology, Harvard Medical School, Boston, MA, United States
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children’s Hospital, Boston, MA, United States
| | - Imam Ahmed Shaik
- Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States
| | - Carl-Fredrik Westin
- Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States
| | - Elisabeth A. Wilde
- Va Salt Lake City Health Care System, Informatics, Decision-Enhancement and Analytic Sciences Center, Salt Lake City, Utah, USA
- Department of Neurology, University of Utah, Salt Lake City, Utah, USA
| | | | - Berkin Bilgic
- Department of Radiology, Harvard Medical School, Boston, MA, United States
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston, MA, United States
- Harvard/MIT Health Sciences and Technology, Cambridge, MA, United States
| | - William Grissom
- Department of Biomedical Engineering, Case School of Medicine, Case Western Reserve University, Cleveland, OH, United States
| | - Jon-Fredrik Nielsen
- Functional MRI Laboratory, Department of Radiology, University of Michigan, Ann Arbor, MI, United States
| | - Maxim Zaitsev
- Division of Medical Physics, Department of Diagnostic and Interventional Radiology, University Medical Center Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Yogesh Rathi
- Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States
| | - Lipeng Ning
- Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States
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3
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Abbasi-Rad S, Cloos MA, Jin J, O'Brien K, Barth M. B 1 + inhomogeneity mitigation for diffusion weighted MRI at 7T using TR-FOCI pulses. Magn Reson Med 2024; 91:2508-2518. [PMID: 38321602 DOI: 10.1002/mrm.30024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Revised: 12/14/2023] [Accepted: 01/07/2024] [Indexed: 02/08/2024]
Abstract
PURPOSE The purpose of this study is to improve the image quality of diffusion-weighted images obtained with a single RF transmit channel 7 T MRI setup using time-resampled frequency-offset corrected inversion (TR-FOCI) pulses to refocus the spins in a twice-refocused spin-echo readout scheme. METHODS We replaced the conventional Shinnar-Le Roux-pulses in the twice refocused diffusion sequence with TR-FOCI pulses. The slice profiles were evaluated in simulation and experimentally in phantoms. The image quality was evaluated in vivo comparing the Shinnar-Le Roux and TR-FOCI implementation using a b value of 0 and of 1000 s/mm2. RESULTS The b0 and diffusion-weighted images acquired using the modified sequence improved the image quality across the whole brain. A region of interest-based analysis showed an SNR increase of 113% and 66% for the nondiffusion-weighted (b0) and the diffusion-weighted (b = 1000 s/mm2) images in the temporal lobes, respectively. Investigation of all slices showed that the adiabatic pulses mitigatedB 1 + $$ {B}_1^{+} $$ inhomogeneity globally using a conventional single-channel transmission setup. CONCLUSION The TR-FOCI pulse can be used in a twice-refocused spin-echo diffusion pulse sequence to mitigate the impact ofB 1 + $$ {B}_1^{+} $$ inhomogeneity on the signal intensity across the brain at 7 T. However, further work is needed to address SAR limitations.
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Affiliation(s)
- Shahrokh Abbasi-Rad
- Centre for Advanced Imaging, The University of Queensland, St Lucia, Queensland, Australia
| | - Martijn A Cloos
- Centre for Advanced Imaging, The University of Queensland, St Lucia, Queensland, Australia
- ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, St Lucia, Queensland, Australia
| | - Jin Jin
- ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, St Lucia, Queensland, Australia
- Siemens Healthcare Pty Ltd, Brisbane, Queensland, Australia
| | - Kieran O'Brien
- ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, St Lucia, Queensland, Australia
- Siemens Healthcare Pty Ltd, Brisbane, Queensland, Australia
| | - Markus Barth
- Centre for Advanced Imaging, The University of Queensland, St Lucia, Queensland, Australia
- ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, St Lucia, Queensland, Australia
- School of Electrical Engineering and Computer Science, The University of Queensland, St Lucia, Queensland, Australia
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McCarthy L, Verma G, Hangel G, Neal A, Moffat BA, Stockmann JP, Andronesi OC, Balchandani P, Hadjipanayis CG. Application of 7T MRS to High-Grade Gliomas. AJNR Am J Neuroradiol 2022; 43:1378-1395. [PMID: 35618424 PMCID: PMC9575545 DOI: 10.3174/ajnr.a7502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Accepted: 02/11/2022] [Indexed: 01/26/2023]
Abstract
MRS, including single-voxel spectroscopy and MR spectroscopic imaging, captures metabolites in high-grade gliomas. Emerging evidence indicates that 7T MRS may be more sensitive to aberrant metabolic activity than lower-field strength MRS. However, the literature on the use of 7T MRS to visualize high-grade gliomas has not been summarized. We aimed to identify metabolic information provided by 7T MRS, optimal spectroscopic sequences, and areas for improvement in and new applications for 7T MRS. Literature was found on PubMed using "high-grade glioma," "malignant glioma," "glioblastoma," "anaplastic astrocytoma," "7T," "MR spectroscopy," and "MR spectroscopic imaging." 7T MRS offers higher SNR, modestly improved spatial resolution, and better resolution of overlapping resonances. 7T MRS also yields reduced Cramér-Rao lower bound values. These features help to quantify D-2-hydroxyglutarate in isocitrate dehydrogenase 1 and 2 gliomas and to isolate variable glutamate, increased glutamine, and increased glycine with higher sensitivity and specificity. 7T MRS may better characterize tumor infiltration and treatment effect in high-grade gliomas, though further study is necessary. 7T MRS will benefit from increased sample size; reductions in field inhomogeneity, specific absorption rate, and acquisition time; and advanced editing techniques. These findings suggest that 7T MRS may advance understanding of high-grade glioma metabolism, with reduced Cramér-Rao lower bound values and better measurement of smaller metabolite signals. Nevertheless, 7T is not widely used clinically, and technical improvements are necessary. 7T MRS isolates metabolites that may be valuable therapeutic targets in high-grade gliomas, potentially resulting in wider ranging neuro-oncologic applications.
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Affiliation(s)
- L McCarthy
- From the Department of Neurosurgery (L.M., C.G.H.), Icahn School of Medicine at Mount Sinai, Mount Sinai Health System, New York, New York
| | - G Verma
- BioMedical Engineering and Imaging Institute (G.V., P.B.), Icahn School of Medicine at Mount Sinai, New York, New York
| | - G Hangel
- Department of Neurosurgery (G.H.)
- High-field MR Center (G.H.), Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria
| | - A Neal
- Department of Medicine (A.N.), Royal Melbourne Hospital, University of Melbourne, Melbourne, Australia
- Department of Neurology (A.N.), Royal Melbourne Hospital, Melbourne, Australia
| | - B A Moffat
- The Melbourne Brain Centre Imaging Unit (B.A.M.), Department of Radiology, The University of Melbourne, Melbourne, Australia
| | - J P Stockmann
- A. A. Martinos Center for Biomedical Imaging (J.P.S., O.C.A.), Massachusetts General Hospital, Charlestown, Massachusetts
- Harvard Medical School (J.P.S., O.C.A.), Boston, Massachusetts
| | - O C Andronesi
- A. A. Martinos Center for Biomedical Imaging (J.P.S., O.C.A.), Massachusetts General Hospital, Charlestown, Massachusetts
- Harvard Medical School (J.P.S., O.C.A.), Boston, Massachusetts
| | - P Balchandani
- BioMedical Engineering and Imaging Institute (G.V., P.B.), Icahn School of Medicine at Mount Sinai, New York, New York
| | - C G Hadjipanayis
- From the Department of Neurosurgery (L.M., C.G.H.), Icahn School of Medicine at Mount Sinai, Mount Sinai Health System, New York, New York
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Ordidge R, Blunck Y, Glarin R, Moffat B, Johnston L. Ultrahigh field brain magnetic resonance imaging using semiadiabatic radiofrequency pulses. NMR IN BIOMEDICINE 2022; 35:e4672. [PMID: 34970797 DOI: 10.1002/nbm.4672] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Revised: 11/29/2021] [Accepted: 12/02/2021] [Indexed: 06/14/2023]
Abstract
Great attention is being paid to solving, or mitigating, the technical problems associated with MRI at ultrahigh field strengths of 7 T and higher. This paper explores the use of the semiadiabatic spin-echo (SA-SE) pulse sequence, which uses semiadiabatic radiofrequency (RF) pulses to remove and/or mitigate the effects of the nonuniform B1 excitation field and B0 inhomogeneity associated with the electromagnetic properties of the human brain. A semiadiabatic RF pulse version of the recently published serial transmit excitation pulse (STEP) RF pulse sequence is also presented that now incorporates semiadiabatic pulses, henceforth is called SA-STEP. As demonstrated by computer simulation, and confirmed using head imaging, both techniques can produce multislice SE MR imaging at 7 T. These new methods use relatively low RF power and achieve good coverage of the human brain in a single scan.
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Affiliation(s)
- Roger Ordidge
- Melbourne Brain Centre Imaging Unit, University of Melbourne, Australia
| | - Yasmin Blunck
- Melbourne Brain Centre Imaging Unit, University of Melbourne, Australia
| | - Rebecca Glarin
- Melbourne Brain Centre Imaging Unit, University of Melbourne, Australia
| | - Bradford Moffat
- Melbourne Brain Centre Imaging Unit, University of Melbourne, Australia
| | - Leigh Johnston
- Melbourne Brain Centre Imaging Unit, University of Melbourne, Australia
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Takatsu Y, Yamamura K, Yamatani Y, Takahashi D, Yoshida R, Asahara M, Honda M, Miyati T. Echo-planar imaging is superior to fast spin-echo diffusion-weighted imaging for cranioplasty using titanium mesh in brain magnetic resonance imaging: a phantom study. Radiol Phys Technol 2021; 15:89-99. [PMID: 34855114 DOI: 10.1007/s12194-021-00646-y] [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: 12/19/2020] [Revised: 11/21/2021] [Accepted: 11/22/2021] [Indexed: 12/01/2022]
Abstract
This study aimed to compare the radiofrequency (RF) shielding effects of titanium mesh of echo-planar imaging (EPI) versus fast spin-echo (FSE) diffusion-weighted imaging (DWI) to establish a suitable sequence for patients who undergo cranioplasty and for whom titanium mesh was used in brain magnetic resonance imaging (MRI). A 1.5-T MRI scanner with clinical setting sequences was used. A phantom for the examination constructed using a sucrose solution in a plastic container was used to compare the signal attenuation (SA) ratio, area of RF shielding effect (Area), normalized absolute average deviation (NAAD), and apparent diffusion coefficient (ADC) between EPI and FSE-DWI. EPI provided significantly better SA ratio, Area, and NAAD (P < 0.01). When the number of slices increased, the RF shielding became more negative. There was no significant difference in the ADC. Regardless of the k-trajectory, EPI-DWI had a lower RF shielding effect than FSE-DWI in patients undergoing cranioplasty.
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Affiliation(s)
- Yasuo Takatsu
- Department of System Control Engineering, Graduate School of Engineering, Tokushima Bunri University, 1314-1 Shido, Sanuki-City, Kagawa, 769-2193, Japan. .,Department of Radiological Technology, Faculty of Health and Welfare, Tokushima Bunri University, 1314-1 Shido, Sanuki-City, Kagawa, 769-2193, Japan. .,Division of Health Sciences, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, 920-0942, Japan.
| | - Kenichiro Yamamura
- Department of Radiological Technology, Faculty of Health and Welfare, Tokushima Bunri University, 1314-1 Shido, Sanuki-City, Kagawa, 769-2193, Japan
| | - Yuya Yamatani
- Division of Central Radiology, Nara Medical University Hospital, 840, Shijo-cho, Kashihara, Nara, 634-8522, Japan
| | - Daisuke Takahashi
- Department of Radiological Technology, Iwate Prefectural Central Hospital, 4-1, 1 Cho-me, Ueda, Morioka City, Iwate, 020-0066, Japan
| | - Rei Yoshida
- Department of Radiology, Kurihara Central Hospital, 3-3-1 Miyano cyuou, Tsukidate, Kurihara-City, Miyagi, 987-2205, Japan
| | - Masaki Asahara
- Department of Radiological Technology, Faculty of Health and Welfare, Tokushima Bunri University, 1314-1 Shido, Sanuki-City, Kagawa, 769-2193, Japan
| | - Michitaka Honda
- Department of Radiological Technology, Faculty of Health and Welfare, Tokushima Bunri University, 1314-1 Shido, Sanuki-City, Kagawa, 769-2193, Japan
| | - Tosiaki Miyati
- Division of Health Sciences, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, 920-0942, Japan
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7
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He X, Auerbach EJ, Garwood M, Kobayashi N, Wu X, Metzger GJ. Parallel transmit optimized 3D composite adiabatic spectral-spatial pulse for spectroscopy. Magn Reson Med 2021; 86:17-32. [PMID: 33497006 PMCID: PMC8545499 DOI: 10.1002/mrm.28682] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Revised: 12/22/2020] [Accepted: 12/23/2020] [Indexed: 01/05/2023]
Abstract
PURPOSE To develop a 3D composite adiabatic spectral-spatial pulse for refocusing in spin-echo spectroscopy acquisitions and to compare its performance against standard acquisition methods. METHODS A 3D composite adiabatic pulse was designed by modulating a train of parallel transmit-optimized 2D subpulses with an adiabatic envelope. The spatial and spectral profiles were simulated and validated by experiments to demonstrate the feasibility of the design in both single and double spin-echo spectroscopy acquisitions. Phantom and in vivo studies were performed to evaluate the pulse performance and compared with semi-LASER with respect to localization performance, sequence timing, signal suppression, and specific absorption rate. RESULTS Simultaneous 2D spatial localization with water and lipid suppression was achieved with the designed refocusing pulse, allowing high-quality spectra to be acquired with shorter minimum TE/TR, reduced SAR, as well as adaptation to spatially varying B0 and B 1 + field inhomogeneities in both prostate and brain studies. CONCLUSION The proposed composite pulse can serve as a more SAR efficient alternative to conventional localization methods such as semi-LASER at ultrahigh field for spin echo-based spectroscopy studies. Subpulse parallel-transmit optimization provides the flexibility to manage the tradeoff among multiple design criteria to accommodate different field strengths and applications.
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Affiliation(s)
- Xiaoxuan He
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Edward J. Auerbach
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Michael Garwood
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Naoharu Kobayashi
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Xiaoping Wu
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Gregory J. Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
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8
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Miller JJ, Valkovič L, Kerr M, Timm KN, Watson WD, Lau JYC, Tyler A, Rodgers C, Bottomley PA, Heather LC, Tyler DJ. Rapid, B 1 -insensitive, dual-band quasi-adiabatic saturation transfer with optimal control for complete quantification of myocardial ATP flux. Magn Reson Med 2021; 85:2978-2991. [PMID: 33538063 PMCID: PMC7986077 DOI: 10.1002/mrm.28647] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 10/28/2020] [Accepted: 11/24/2020] [Indexed: 12/16/2022]
Abstract
PURPOSE Phosphorus saturation-transfer experiments can quantify metabolic fluxes noninvasively. Typically, the forward flux through the creatine kinase reaction is investigated by observing the decrease in phosphocreatine (PCr) after saturation of γ-ATP. The quantification of total ATP utilization is currently underexplored, as it requires simultaneous saturation of inorganic phosphate ( P i ) and PCr. This is challenging, as currently available saturation pulses reduce the already-low γ-ATP signal present. METHODS Using a hybrid optimal-control and Shinnar-Le Roux method, a quasi-adiabatic RF pulse was designed for the dual saturation of PCr and P i to enable determination of total ATP utilization. The pulses were evaluated in Bloch equation simulations, compared with a conventional hard-cosine DANTE saturation sequence, before being applied to perfused rat hearts at 11.7 T. RESULTS The quasi-adiabatic pulse was insensitive to a >2.5-fold variation in B 1 , producing equivalent saturation with a 53% reduction in delivered pulse power and a 33-fold reduction in spillover at the minimum effective B 1 . This enabled the complete quantification of the synthesis and degradation fluxes for ATP in 30-45 minutes in the perfused rat heart. While the net synthesis flux (4.24 ± 0.8 mM/s, SEM) was not significantly different from degradation flux (6.88 ± 2 mM/s, P = .06) and both measures are consistent with prior work, nonlinear error analysis highlights uncertainties in the Pi -to-ATP measurement that may explain a trend suggesting a possible imbalance. CONCLUSIONS This work demonstrates a novel quasi-adiabatic dual-saturation RF pulse with significantly improved performance that can be used to measure ATP turnover in the heart in vivo.
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Affiliation(s)
- Jack J Miller
- Department of Physics, University of Oxford, Oxford, UK.,Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK.,Oxford Centre for Clinical Magnetic Resonance Research, John Radcliffe Hospital, Headington, Oxford, UK.,Health, Aarhus University, Aarhus, Denmark
| | - Ladislav Valkovič
- Oxford Centre for Clinical Magnetic Resonance Research, John Radcliffe Hospital, Headington, Oxford, UK.,Department of Imaging Methods, Institute of Measurement Science, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Matthew Kerr
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
| | - Kerstin N Timm
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
| | - William D Watson
- Oxford Centre for Clinical Magnetic Resonance Research, John Radcliffe Hospital, Headington, Oxford, UK
| | - Justin Y C Lau
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK.,Oxford Centre for Clinical Magnetic Resonance Research, John Radcliffe Hospital, Headington, Oxford, UK
| | - Andrew Tyler
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK.,Oxford Centre for Clinical Magnetic Resonance Research, John Radcliffe Hospital, Headington, Oxford, UK
| | - Christopher Rodgers
- Oxford Centre for Clinical Magnetic Resonance Research, John Radcliffe Hospital, Headington, Oxford, UK.,Wolfson Brain Imaging Centre, University of Cambridge, Oxford, UK
| | - Paul A Bottomley
- Oxford Centre for Clinical Magnetic Resonance Research, John Radcliffe Hospital, Headington, Oxford, UK.,Division of MR Research, Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Lisa C Heather
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
| | - Damian J Tyler
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK.,Oxford Centre for Clinical Magnetic Resonance Research, John Radcliffe Hospital, Headington, Oxford, UK
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9
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Abstract
More than one million people in the United States suffer from seizures that are not controlled with antiseizure medications. Targeted interventions such as surgery and deep brain stimulation can confer seizure reduction or even freedom in many of these patients with drug-resistant epilepsy, but success critically depends on identification of epileptogenic zones through MR imaging. Ultrahigh field imaging facilitates improved sensitivity and resolution across many imaging modalities and may facilitate better detection of epileptic markers than is achieved at lower field strengths. The increasing availability and clinical adoption of ultrahigh field scanners play an important role in characterizing drug-resistant epilepsy and planning for its treatment.
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Affiliation(s)
- Gaurav Verma
- Biomedical Engineering and Imaging Institute, The Icahn School of Medicine at Mount Sinai, 1470 Madison Avenue, New York, NY 10029, USA.
| | - Bradley N Delman
- Department of Diagnostic, Molecular and Interventional Radiology, The Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, Box 1234, New York, NY 10029, USA
| | - Priti Balchandani
- Biomedical Engineering and Imaging Institute, The Icahn School of Medicine at Mount Sinai, 1470 Madison Avenue, New York, NY 10029, USA; Department of Diagnostic, Molecular and Interventional Radiology, The Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, Box 1234, New York, NY 10029, USA
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10
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Somai V, Wright AJ, Fala M, Hesse F, Brindle KM. A multi spin echo pulse sequence with optimized excitation pulses and a 3D cone readout for hyperpolarized 13 C imaging. Magn Reson Med 2020; 84:1895-1908. [PMID: 32173908 PMCID: PMC8638674 DOI: 10.1002/mrm.28248] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Revised: 01/23/2020] [Accepted: 02/14/2020] [Indexed: 12/25/2022]
Abstract
PURPOSE Imaging tumor metabolism in vivo using hyperpolarized [1-13 C]pyruvate is a promising technique for detecting disease, monitoring disease progression, and assessing treatment response. However, the transient nature of the hyperpolarization and its depletion following excitation limits the available time for imaging. We describe here a single-shot multi spin echo sequence, which improves on previously reported sequences, with a shorter readout time, isotropic point spread function (PSF), and better signal-to-noise ratio. METHODS The sequence uses numerically optimized spectrally selective excitation pulses set to the resonant frequencies of pyruvate and lactate and a hyperbolic secant adiabatic refocusing pulse, all applied in the absence of slice selection gradients. The excitation pulses were designed to be resistant to the effects of B0 and B1 field inhomogeneity. The gradient readout uses a 3D cone trajectory composed of 13 cones, all fully refocused and distributed among 7 spin echoes. The maximal gradient amplitude and slew rate were set to 4 G/cm and 20 G/cm/ms, respectively, to demonstrate the feasibility of clinical translation. RESULTS The pulse sequence gave an isotropic PSF of 2.8 mm. The excitation profiles of the optimized pulses closely matched simulations and a 46.10 ± 0.04% gain in image SNR was observed compared to a conventional Shinnar-Le Roux excitation pulse. The sequence was demonstrated with dynamic imaging of hyperpolarized [1-13 C]pyruvate and [1-13 C]lactate in vivo. CONCLUSION The pulse sequence was capable of dynamic imaging of hyperpolarized 13 C labeled metabolites in vivo with relatively high spatial and temporal resolution and immunity to system imperfections.
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Affiliation(s)
- Vencel Somai
- Cancer Research UK Cambridge InstituteUniversity of CambridgeCambridgeUnited Kingdom
- Department of Radiology, School of Clinical MedicineUniversity of CambridgeCambridgeUnited Kingdom
| | - Alan J. Wright
- Cancer Research UK Cambridge InstituteUniversity of CambridgeCambridgeUnited Kingdom
| | - Maria Fala
- Cancer Research UK Cambridge InstituteUniversity of CambridgeCambridgeUnited Kingdom
| | - Friederike Hesse
- Cancer Research UK Cambridge InstituteUniversity of CambridgeCambridgeUnited Kingdom
| | - Kevin M. Brindle
- Cancer Research UK Cambridge InstituteUniversity of CambridgeCambridgeUnited Kingdom
- Department of BiochemistryUniversity of CambridgeCambridgeUnited Kingdom
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11
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Delgado PR, Kuehne A, Periquito JS, Millward JM, Pohlmann A, Waiczies S, Niendorf T. B 1 inhomogeneity correction of RARE MRI with transceive surface radiofrequency probes. Magn Reson Med 2020; 84:2684-2701. [PMID: 32447779 DOI: 10.1002/mrm.28307] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Revised: 03/27/2020] [Accepted: 04/13/2020] [Indexed: 12/17/2022]
Abstract
PURPOSE The use of surface radiofrequency (RF) coils is common practice to boost sensitivity in (pre)clinical MRI. The number of transceive surface RF coils is rapidly growing due to the surge in cryogenically cooled RF technology and ultrahigh-field MRI. Consequently, there is an increasing need for effective correction of the excitation field ( B 1 + ) inhomogeneity inherent in these coils. Retrospective B1 correction permits quantitative MRI, but this usually requires a pulse sequence-specific analytical signal intensity (SI) equation. Such an equation is not available for fast spin-echo (Rapid Acquisition with Relaxation Enhancement, RARE) MRI. Here we present, test, and validate retrospective B1 correction methods for RARE. METHODS We implemented the commonly used sensitivity correction and developed an empirical model-based method and a hybrid combination of both. Tests and validations were performed with a cryogenically cooled RF probe and a single-loop RF coil. Accuracy of SI quantification and T1 contrast were evaluated after correction. RESULTS The three described correction methods achieved dramatic improvements in B1 homogeneity and significantly improved SI quantification and T1 contrast, with mean SI errors reduced from >40% to >10% following correction in all cases. Upon correction, images of phantoms and mouse heads demonstrated homogeneity comparable to that of images acquired with a volume resonator. This was quantified by SI profile, SI ratio (error < 10%), and percentage of integral uniformity (PIU > 80% in vivo and ex vivo compared to PIU > 87% with the reference RF coil). CONCLUSION This work demonstrates the efficacy of three B1 correction methods tailored for transceive surface RF probes and RARE MRI. The corrected images are suitable for quantification and show comparable results between the three methods, opening the way for T1 measurements and X-nuclei quantification using surface transceiver RF coils. This approach is applicable to other MR techniques for which no analytical SI exists.
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Affiliation(s)
- Paula Ramos Delgado
- Berlin Ultrahigh Field Facility (B.U.F.F), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.,Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | | | - João S Periquito
- Berlin Ultrahigh Field Facility (B.U.F.F), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.,Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | - Jason M Millward
- Berlin Ultrahigh Field Facility (B.U.F.F), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | - Andreas Pohlmann
- Berlin Ultrahigh Field Facility (B.U.F.F), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | - Sonia Waiczies
- Berlin Ultrahigh Field Facility (B.U.F.F), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (B.U.F.F), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.,Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.,MRI.TOOLS GmbH, Berlin, Germany
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12
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Green EM, Blunck Y, Tahayori B, Farrell PM, Korte JC, Johnston LA. Spin Lock Adiabatic Correction (SLAC) for B 1-insensitive pulse design at 7T. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 308:106595. [PMID: 31542447 DOI: 10.1016/j.jmr.2019.106595] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 08/09/2019] [Accepted: 09/08/2019] [Indexed: 06/10/2023]
Abstract
A new framework for B1 insensitive adiabatic pulse design is proposed, denoted Spin Lock Adiabatic Correction (SLAC), which counteracts deviations from ideal behaviour through inclusion of an additional correction component during pulse design. SLAC pulses are theoretically derived, then applied to the design of enhanced BIR-4 and hyperbolic secant pulses to demonstrate practical utility of the new pulses. At 7T, SLAC pulses are shown to improve the flip angle homogeneity compared to a standard adiabatic pulse with validation in both simulations and phantom experiments, under SAR equivalent experimental conditions. The SLAC framework can be applied to any arbitrary adiabatic pulse to deliver excitation with increased B1 insensitivity.
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Affiliation(s)
- Edward M Green
- Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, VIC, Australia; Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia.
| | - Yasmin Blunck
- Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, VIC, Australia; Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia.
| | - Bahman Tahayori
- Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia; Department of Medical Physics and Biomedical Engineering, Shiraz University of Medical Sciences, Shiraz, Iran; Center for Neuromodulation and Pain, Shiraz, Iran.
| | - Peter M Farrell
- Department of Electrical and Electronic Engineering, The University of Melbourne, Melbourne, VIC, Australia.
| | - James C Korte
- Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia; Department of Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia.
| | - Leigh A Johnston
- Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, VIC, Australia; Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia.
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13
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Affiliation(s)
- Gaurav Verma
- Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, NY
| | - Priti Balchandani
- Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, NY
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14
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Downes DP, Collins JHP, Lama B, Zeng H, Nguyen T, Keller G, Febo M, Long JR. Characterization of Brain Metabolism by Nuclear Magnetic Resonance. Chemphyschem 2019; 20:216-230. [PMID: 30536696 PMCID: PMC6501841 DOI: 10.1002/cphc.201800917] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Revised: 11/26/2018] [Indexed: 12/15/2022]
Abstract
The noninvasive, quantitative ability of nuclear magnetic resonance (NMR) spectroscopy to characterize small molecule metabolites has long been recognized as a major strength of its application in biology. Numerous techniques exist for characterizing metabolism in living, excised, or extracted tissue, with a particular focus on 1 H-based methods due to the high sensitivity and natural abundance of protons. With the increasing use of high magnetic fields, the utility of in vivo 1 H magnetic resonance spectroscopy (MRS) has markedly improved for measuring specific metabolite concentrations in biological tissues. Higher fields, coupled with recent developments in hyperpolarization, also enable techniques for complimenting 1 H measurements with spectroscopy of other nuclei, such as 31 P and 13 C, and for combining measurements of metabolite pools with metabolic flux measurements. We compare ex vivo and in vivo methods for studying metabolism in the brain using NMR and highlight insights gained through using higher magnetic fields, the advent of dissolution dynamic nuclear polarization, and combining in vivo MRS and ex vivo NMR approaches.
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Affiliation(s)
- Daniel P Downes
- Department of Biochemistry and Molecular Biology and McKnight Brain Institute, University of Florida, Box 100245, Gainesville, FL, 32610-0245, United States
| | - James H P Collins
- National High Magnetic Field Laboratory and Biology and McKnight Brain Institute, University of Florida, Box 100015, Gainesville, FL, 32610-0015, United States
| | - Bimala Lama
- Department of Chemistry and Biochemistry, University of Colorado Boulder, 215 UCB, Boulder, CO, 80309-0215, United States
| | - Huadong Zeng
- National High Magnetic Field Laboratory and Biology and McKnight Brain Institute, University of Florida, Box 100015, Gainesville, FL, 32610-0015, United States
| | - Tan Nguyen
- Department of Biochemistry and Molecular Biology and McKnight Brain Institute, University of Florida, Box 100245, Gainesville, FL, 32610-0245, United States
| | - Gabrielle Keller
- Department of Biochemistry and Molecular Biology and McKnight Brain Institute, University of Florida, Box 100245, Gainesville, FL, 32610-0245, United States
| | - Marcelo Febo
- Department of Psychiatry, University of Florida, Box 100256, Gainesville, FL, 32610-0256, United States
| | - Joanna R Long
- Department of Biochemistry and Molecular Biology and McKnight Brain Institute, University of Florida, Box 100245, Gainesville, FL, 32610-0245, United States
- National High Magnetic Field Laboratory and Biology and McKnight Brain Institute, University of Florida, Box 100015, Gainesville, FL, 32610-0015, United States
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15
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Garwood M, Uğurbil K. RF pulse methods for use with surface coils: Frequency-modulated pulses and parallel transmission. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 291:84-93. [PMID: 29705035 PMCID: PMC5943143 DOI: 10.1016/j.jmr.2018.01.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 01/24/2018] [Indexed: 06/08/2023]
Abstract
The first use of a surface coil to obtain a 31P NMR spectrum from an intact rat by Ackerman and colleagues initiated a revolution in magnetic resonance imaging (MRI) and spectroscopy (MRS). Today, we take it for granted that one can detect signals in regions external to an RF coil; at the time, however, this concept was most unusual. In the approximately four decade long period since its introduction, this simple idea gave birth to an increasing number of innovations that has led to transformative changes in the way we collect data in an in vivo magnetic resonance experiment, particularly with MRI of humans. These innovations include spatial localization and/or encoding based on the non-uniform B1 field generated by the surface coil, leading to new spectroscopic localization methods, image acceleration, and unique RF pulses that deal with B1 inhomogeneities and even reduce power deposition. Without the surface coil, many of the major technological advances that define the extraordinary success of MRI in clinical diagnosis and in biomedical research, as exemplified by projects like the Human Connectome Project, would not have been possible.
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Affiliation(s)
- Michael Garwood
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN 55455 USA.
| | - Kamil Uğurbil
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN 55455 USA
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16
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How to choose the right MR sequence for your research question at 7 T and above? Neuroimage 2018; 168:119-140. [DOI: 10.1016/j.neuroimage.2017.04.044] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Revised: 04/18/2017] [Accepted: 04/19/2017] [Indexed: 12/29/2022] Open
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17
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Wu FH, Wu EL, Tung YH, Cheng PW, Chiueh TD, Chen JH. A specific absorption rate reduction method for simultaneous multislice magnetic resonance imaging. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2017; 88:043701. [PMID: 28456274 DOI: 10.1063/1.4979861] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
This study proposes a modified Shinnar-Le Roux method to synthesize the excitation radio frequency (RF) pulse for a 2D gradient echo (GRE) based simultaneous multi-slice (SMS) magnetic resonance imaging (MRI) with features of low specific absorption rate (SAR) and small out-of-slice ripple. This synthesis method for SMS RF pulses employs thinner slice bandwidth and lower multislice offset frequencies to reduce SAR values and adopts a weighted Parks-McClellan algorithm to reduce sidelobes. Formulas for estimating relative SAR values of the SMS pulses are also introduced. Relative SAR values and out-of-slice ripples of the proposed and typical RF pulses with different parameters are presented. In simultaneous 5-slice phantom and 3-slice human brain imaging, SMS pulses synthesized with the proposed method achieve 32% and 28% SAR values of standard pulses while providing similar image qualities. Typical RF pulses such as sinc x cos can also take advantage of the proposed method and offer lower SAR values for SMS imaging. The RF pulse synthesized using the proposed method features low SAR, small sidelobes, and consistent image quality for 2D GRE-based SMS MRI. This method is applicable to the synthesis of typical SMS RF pulses for significant SAR reduction.
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Affiliation(s)
- Fu-Hsing Wu
- Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Edzer L Wu
- Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Yi-Hang Tung
- Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Po-Wei Cheng
- Interdisciplinary MRI/MRS Lab, Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei 10617, Taiwan
| | - Tzi-Dar Chiueh
- MicroSystem Research Lab, Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Jyh-Horng Chen
- Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
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18
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Farkash G, Dumez JN, Frydman L. Sculpting 3D spatial selectivity with pairs of 2D pulses: A comparison of methods. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 273:9-18. [PMID: 27718460 DOI: 10.1016/j.jmr.2016.09.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 09/02/2016] [Accepted: 09/03/2016] [Indexed: 06/06/2023]
Abstract
Enhancing the specificity of the spins' excitation can improve the capabilities of magnetic resonance. Exciting voxels with tailored 3D shapes reduces partial volume effects and enhances contrast, particularly in cases where cubic voxels or other simple geometries do not provide an optimal localization. Spatial excitation profiles of arbitrary shapes can be implemented using so-called multidimensional RF pulses, which are often limited in practice to 2D implementations owing to their sensitivity to field inhomogeneities. Recent work has shown the potential of spatio-temporally encoded (SPEN) pulses towards alleviating these constraints. In particular, 2D pulses operating in a so-called hybrid scheme where the "low-bandwidth" spatial dimension is sculpted by a SPEN strategy while an orthogonal axis is shaped by regular k-space encoding, have been shown resilient to chemical shift and B0 field inhomogeneities. In this work we explore the use of pairs of 2D pulses, with one of these addressing geometries in the x-y plane and the other in the x-z dimension, to sculpt complex 3D volumes in phantoms and in vivo. To overcome limitations caused by the RF discretization demanded by these 2D pulses, a number of "unfolding" techniques yielding images from the centerband RF excitation while deleting sideband contributions - even in cases where center- and side-bands severely overlap - were developed. Thus it was possible to increase the gradient strengths applied along the low bandwidth dimensions, significantly improving the robustness of this kind of 3D sculpting pulses. Comparisons against conventional pulses designed on the basis of pure k-space trajectories, are presented.
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Affiliation(s)
- Gil Farkash
- Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Jean-Nicolas Dumez
- Institut de Chimie des Substances Naturelles, CNRS, 91190 Gif-sur-Yvette, France
| | - Lucio Frydman
- Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot, Israel.
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19
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Aigner CS, Clason C, Rund A, Stollberger R. Efficient high-resolution RF pulse design applied to simultaneous multi-slice excitation. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 263:33-44. [PMID: 26773524 DOI: 10.1016/j.jmr.2015.11.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2015] [Revised: 11/23/2015] [Accepted: 11/25/2015] [Indexed: 06/05/2023]
Abstract
RF pulse design via optimal control is typically based on gradient and quasi-Newton approaches and therefore suffers from slow convergence. We present a flexible and highly efficient method that uses exact second-order information within a globally convergent trust-region CG-Newton method to yield an improved convergence rate. The approach is applied to the design of RF pulses for single- and simultaneous multi-slice (SMS) excitation and validated using phantom and in vivo experiments on a 3T scanner using a modified gradient echo sequence.
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Affiliation(s)
- Christoph Stefan Aigner
- Institute of Medical Engineering, Graz University of Technology, Stremayrgasse 16, 8010 Graz, Austria; BioTechMed Graz, 8010 Graz, Austria.
| | - Christian Clason
- Faculty of Mathematics, University of Duisburg-Essen, 45117 Essen, Germany
| | - Armin Rund
- Institute for Mathematics and Scientific Computing, University of Graz, Heinrichstrasse 36, 8010 Graz, Austria
| | - Rudolf Stollberger
- Institute of Medical Engineering, Graz University of Technology, Stremayrgasse 16, 8010 Graz, Austria; BioTechMed Graz, 8010 Graz, Austria
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20
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Dyvorne H, Balchandani P. Slice-selective adiabatic magnetization T 2 -preparation (SAMPA) for efficient T 2 -weighted imaging at ultrahigh field strengths. Magn Reson Med 2015; 76:1741-1749. [PMID: 26619960 DOI: 10.1002/mrm.26067] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Revised: 10/27/2015] [Accepted: 10/31/2015] [Indexed: 12/29/2022]
Abstract
PURPOSE At high field, T2 -weighted (T2 w) imaging is limited by transmit field inhomogeneity and increased radiofrequency power deposition. In this work, we introduce SAMPA (Slice-selective Adiabatic Magnetization T2 PrepAration) and demonstrate its use for efficient brain T2 w imaging at 7 Tesla (T). METHODS SAMPA was designed by subsampling an optimized B1 insensitive rotation (BIR4) waveform with small tip angle linear subpulses. To perform T2 w imaging, SAMPA was inserted before a fast gradient echo acquisition. The off-resonance behavior, B1 robustness, and slice selectivity of the novel T2 preparation module were analyzed using Bloch simulations. The performance of SAMPA for T2 w imaging was demonstrated in phantom experiments as well as in the brains of healthy volunteers at 7T. RESULTS Based on simulations, the proposed design operates at peak B1 of 15 μT and higher, within a 400 Hz bandwidth. T2 values were in strong agreement with spin echo-based T2 mapping in phantom experiments. Whole brain, interleaved multislab three-dimensional imaging could be acquired with 0.8 mm3 isotropic resolution in 5:36 min per T2 weighting. CONCLUSION Compared with previous adiabatic T2 preparation techniques, SAMPA allows for slice-selectivity, which can lead to efficient and robust acquisitions for T2 w imaging at high field. Magn Reson Med 76:1741-1749, 2016. © 2015 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Hadrien Dyvorne
- Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Priti Balchandani
- Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, New York, USA
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21
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Feldman RE, Balchandani P. A semiadiabatic spectral-spatial spectroscopic imaging (SASSI) sequence for improved high-field MR spectroscopic imaging. Magn Reson Med 2015; 76:1071-82. [PMID: 26519948 DOI: 10.1002/mrm.26025] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Revised: 09/08/2015] [Accepted: 10/02/2015] [Indexed: 12/27/2022]
Abstract
PURPOSE MR spectroscopic imaging (MRSI) benefits from operation at 7T due to increased signal-to-noise ratio (SNR) and spectral separation. The 180° radiofrequency (RF) pulses used in the conventional MRSI sequences are particularly susceptible to the variation in the transmitted RF (B1 ) field and severe chemical shift localization errors at 7T. RF power deposition, as measured by specific absorption rate (SAR), also increases with field strength. Adiabatic 180° RF pulses may mitigate the effects of B1 variation. We designed and implemented a semiadiabatic spectral-spatial spectroscopic imaging (SASSI) pulse sequence to provide more uniform spectral data at 7T with reduced SAR. METHODS The adiabatic Shinnar-Le Roux algorithm was used to generate a high bandwidth 180° adiabatic spectral-spatial (SPSP) pulse that captured a spectral range containing the main metabolites of interest. A pair of 180° SPSP pulses was used to refocus the signal excited by a 90° SPSP pulse in order to select a 3D volume of interest in the SASSI sequence. RESULTS The SASSI pulse sequence produced spectra with more uniform brain metabolite SNR when compared with the conventional nonadiabatic MRSI sequence. CONCLUSION SASSI achieved comparable SNR to the current adiabatic alternative, semi-LASER, but with 1/3 of the SAR. Magn Reson Med 76:1071-1082, 2016. © 2015 Wiley Periodicals, Inc.
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Affiliation(s)
- Rebecca E Feldman
- Translational and Molecular Imaging Institution, Icahn School of Medicine at Mount Sinai, New York, New York, USA.
| | - Priti Balchandani
- Translational and Molecular Imaging Institution, Icahn School of Medicine at Mount Sinai, New York, New York, USA
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22
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Dyvorne H, O'Halloran R, Balchandani P. Ultrahigh field single-refocused diffusion weighted imaging using a matched-phase adiabatic spin echo (MASE). Magn Reson Med 2015; 75:1949-57. [PMID: 26041650 DOI: 10.1002/mrm.25790] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Revised: 04/27/2015] [Accepted: 04/30/2015] [Indexed: 12/24/2022]
Abstract
PURPOSE To improve ultrahigh field diffusion-weighted imaging (DWI) in the presence of inhomogeneous transmit B1 field by designing a novel semi-adiabatic single-refocused DWI technique. METHODS A 180° slice-selective, adiabatic radiofrequency (RF) pulse of 4 ms duration was designed using the adiabatic Shinnar-Le Roux algorithm. A matched-phase slice-selective 90° RF pulse of 8 ms duration was designed to compensate the nonlinear phase of the adiabatic 180° RF pulse. The resulting RF pulse combination, matched-phase adiabatic spin echo (MASE), was integrated into a single-shot echo planar DWI sequence. The performance of this sequence was compared with single-refocused Stejskal-Tanner (ST), twice-refocused spin echo (TRSE) and twice-refocused adiabatic spin echo (TRASE) in simulations, phantoms, and healthy volunteers at 7 Tesla (T). RESULTS In regions with inhomogeneous B1 , MASE resulted in increased signal intensity compared with ST (up to 64%). Moderate increase in specific absorption rate (35-39%) was observed for adiabatic RF pulses. MASE resulted in higher signal homogeneity at 7T, leading to improved visualization of measures derived from diffusion-weighted images such as white matter tractography and track density images. CONCLUSION Efficient adiabatic SLR pulses can be adapted to single-refocused DWI, leading to substantially improved signal uniformity when compared with conventional acquisitions.
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Affiliation(s)
- Hadrien Dyvorne
- Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Rafael O'Halloran
- Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Priti Balchandani
- Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, New York, USA
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23
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Feldman RE, Islam HM, Xu J, Balchandani P. A SEmi-Adiabatic matched-phase spin echo (SEAMS) PINS pulse-pair for B1 -insensitive simultaneous multislice imaging. Magn Reson Med 2015; 75:709-17. [PMID: 25753055 DOI: 10.1002/mrm.25654] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2014] [Revised: 01/13/2015] [Accepted: 01/21/2015] [Indexed: 12/24/2022]
Abstract
PURPOSE Simultaneous multislice (SMS) imaging is a powerful technique that can reduce image acquisition time for anatomical, functional, and diffusion weighted magnetic resonance imaging. At higher magnetic fields, such as 7 Tesla, increased radiofrequency (RF) field inhomogeneity, power deposition, and changes in relaxation parameters make SMS spin echo imaging challenging. We designed an adiabatic 180° Power Independent of Number of Slices (PINS) pulse and a matched-phase 90° PINS pulse to generate a SEmi-Adiabatic Matched-phase Spin echo (SEAMS) PINS sequence to address these issues. METHODS We used the adiabatic Shinnar Le-Roux (SLR) algorithm to generate a 180° pulse. The SLR polynomials for the 180° pulse were then used to create a matched-phase 90° pulse. The pulses were sub-sampled to produce a SEAMS PINS pulse-pair and the performance of this pulse-pair was validated in phantoms and in vivo. RESULTS Simulations as well as phantom and in vivo results, demonstrate multislice capability and improved B1 -insensitivity of the SEAMS PINS pulse-pair when operating at RF amplitudes of up to 40% above adiabatic threshold. CONCLUSION The SEAMS PINS approach presented here achieves multislice spin echo profiles with improved B1 -insensitivity when compared with a conventional spin echo.
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Affiliation(s)
- Rebecca E Feldman
- Translational and Molecular Imaging Institution, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Haisam M Islam
- Bioengineering Department, Stanford University, Stanford, California, USA
| | - Junqian Xu
- Translational and Molecular Imaging Institution, Icahn School of Medicine at Mount Sinai, New York, New York, USA.,Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Priti Balchandani
- Translational and Molecular Imaging Institution, Icahn School of Medicine at Mount Sinai, New York, New York, USA
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24
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Ma C, Liang ZP. Design of multidimensional Shinnar-Le Roux radiofrequency pulses. Magn Reson Med 2015; 73:633-45. [PMID: 24578212 PMCID: PMC4147023 DOI: 10.1002/mrm.25179] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2013] [Revised: 01/21/2014] [Accepted: 01/22/2014] [Indexed: 11/06/2022]
Abstract
PURPOSE To generalize the conventional Shinnar-Le Roux method for the design of multidimensional radiofrequency pulses. METHODS Using echo-planar gradients, the multidimensional radiofrequency pulse design problem was converted into a series of one-dimensional polynomial design problems. Each of the one-dimensional polynomial design problems was solved efficiently. B0 inhomogeneity compensation and design of spatial-spectral pulses were also considered. RESULTS The proposed method was used to design two-dimensional excitation and refocusing pulses. The results were validated through Bloch equation simulation and experiments on a 3.0 T scanner. Large-tip-angle, equiripple-error, multidimensional excitation was achieved with ripple levels closely matching the design specifications. CONCLUSION The conventional Shinnar-Le Roux method can be extended to design multidimensional radiofrequency pulses. The proposed method achieves almost equiripple excitation errors, allows easy control of the tradeoff among design parameters, and is computationally efficient.
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Affiliation(s)
- Chao Ma
- Department of Electrical and Computer Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
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25
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Araujo ECA, Fromes Y, Carlier PG. New insights on human skeletal muscle tissue compartments revealed by in vivo t2 NMR relaxometry. Biophys J 2014; 106:2267-74. [PMID: 24853755 DOI: 10.1016/j.bpj.2014.04.010] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Revised: 03/06/2014] [Accepted: 04/09/2014] [Indexed: 12/29/2022] Open
Abstract
The spin-spin (T2) relaxation of (1)H-NMR signals in human skeletal muscle has been previously hypothesized to reveal information about myowater compartmentation. Although experimental support has been provided, no consensus has yet emerged concerning the attribution of specific anatomical compartments to the observed T2 components. Potential application of a noninvasive tool that might offer such information urges the quest for a definitive answer to this question. The purpose of this work was to obtain new information that might help elucidate the mechanism of T2 distribution in muscle. To do so, in vivo T2 relaxation data was acquired from the soleus of eight healthy volunteers using a localized Carr-Purcell-Meiboom-Gill technique. Each acquisition contained 1000 echoes with an interecho spacing of 1 ms. Data were acquired from each subject under different vascular filling preparations expected to change exclusively the extracellular water fraction. Two exponential components were systematically observed: an intermediate component (T2 ~ 32 ms) and a long component (100 < T2 < 210 ms). The relative fraction and T2 value characterizing the long component systematically increased after progressive augmentation of extracellular water volume. Characteristic relaxation behavior for each vascular filling condition was analyzed with a two-site exchange model and a three-site two-exchange model. We show that a two-site exchange model can only predict the observations for small exchange rates, much more representative of transendothelial than transcytolemmal exchange regimes. The three-site two-exchange model representing the intracellular, interstitial, and vascular spaces was capable of precisely predicting the observations for realistic transcytolemmal and transendothelial exchange rates. The estimated intrinsic relative fractions of each of these compartments corroborate with estimations from previous works and strongly suggest that the T2 relaxation from water within the intracellular and interstitial spaces is described by the intermediate component, whereas the long component represents water within the vascular space.
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Affiliation(s)
- Ericky C A Araujo
- Institute of Myology, Paris, France; University Paris-Sud (Paris 11), Orsay, France.
| | - Yves Fromes
- University Pierre and Marie Curie (Paris 06), Paris, France
| | - Pierre G Carlier
- Institute of Myology, Paris, France; University Pierre and Marie Curie (Paris 06), Paris, France; Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Institut d'Imagerie Biomédicale, Molecular Imaging Research Center, IdM Nuclear Magnetic Resonance Laboratory, Paris, France.
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Abstract
At ultra-high magnetic fields, such as 7T, MR imaging can noninvasively visualize the brain in unprecedented detail and through enhanced contrast mechanisms. The increased SNR and enhanced contrast available at 7T enable higher resolution anatomic and vascular imaging. Greater spectral separation improves detection and characterization of metabolites in spectroscopic imaging. Enhanced blood oxygen level-dependent contrast affords higher resolution functional MR imaging. Ultra-high-field MR imaging also facilitates imaging of nonproton nuclei such as sodium and phosphorus. These improved imaging methods may be applied to detect subtle anatomic, functional, and metabolic abnormalities associated with a wide range of neurologic disorders, including epilepsy, brain tumors, multiple sclerosis, Alzheimer disease, and psychiatric conditions. At 7T, however, physical and hardware limitations cause conventional MR imaging pulse sequences to generate artifacts, requiring specialized pulse sequences and new hardware solutions to maximize the high-field gain in signal and contrast. Practical considerations for ultra-high-field MR imaging include cost, siting, and patient experience.
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Affiliation(s)
- P Balchandani
- From the Translational and Molecular Imaging Institute (P.B.) Department of Radiology (P.B., T.P.N.), Icahn School of Medicine at Mount Sinai, New York, New York.
| | - T P Naidich
- Department of Radiology (P.B., T.P.N.), Icahn School of Medicine at Mount Sinai, New York, New York
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Balchandani P, Qiu D. Semi-adiabatic Shinnar-Le Roux pulses and their application to diffusion tensor imaging of humans at 7T. Magn Reson Imaging 2014; 32:804-12. [PMID: 24928300 PMCID: PMC4099418 DOI: 10.1016/j.mri.2014.04.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Revised: 02/11/2014] [Accepted: 04/04/2014] [Indexed: 10/25/2022]
Abstract
The adiabatic Shinnar-Le Roux (SLR) algorithm for radiofrequency (RF) pulse design enables systematic control of pulse parameters such as bandwidth, RF energy distribution and duration. Some applications, such as diffusion-weighted imaging (DWI) at high magnetic fields, would benefit from RF pulses that can provide greater B1 insensitivity while adhering to echo time and specific absorption rate (SAR) limits. In this study, the adiabatic SLR algorithm was employed to generate 6-ms and 4-ms 180° semi-adiabatic RF pulses which were used to replace the refocusing pulses in a twice-refocused spin echo (TRSE) diffusion-weighted echo planar imaging (DW-EPI) sequence to create two versions of a twice-refocused adiabatic spin echo (TRASE) sequence. The two versions were designed for different trade-offs between adiabaticity and echo time. Since a pair of identical refocusing pulses is applied, the quadratic phase imposed by the first is unwound by the second, preserving the linear phase created by the excitation pulse. In vivo images of the human brain obtained at 7Testa (7T) demonstrate that both versions of the TRASE sequence developed in this study achieve more homogeneous signal in the diffusion-weighted images than the conventional TRSE sequence. Semi-adiabatic SLR pulses offer a more B1-insensitive solution for diffusion preparation at 7T, while operating within SAR constraints. This method may be coupled with any EPI readout trajectory and parallel imaging scheme to provide more uniform coverage for diffusion tensor imaging at 7T and 3T.
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Affiliation(s)
- Priti Balchandani
- Department of Radiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA; Department of Radiology, Stanford University, Stanford, CA, USA.
| | - Deqiang Qiu
- Department of Radiology, Stanford University, Stanford, CA, USA; Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, GA, USA
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28
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Zhu H, Arlinghaus LR, Whisenant JG, Li M, Gore JC, Yankeelov TE. Sequence design and evaluation of the reproducibility of water-selective diffusion-weighted imaging of the breast at 3 T. NMR IN BIOMEDICINE 2014; 27:1030-1036. [PMID: 24986756 PMCID: PMC4134406 DOI: 10.1002/nbm.3146] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Revised: 05/02/2014] [Accepted: 05/08/2014] [Indexed: 06/03/2023]
Abstract
Diffusion measurements derived from breast MRI can be adversely affected by unwanted signals from abundant fatty tissues if they are not suppressed adequately. To minimize this undesired contribution, we designed and optimized a water-selective diffusion-weighted imaging (DWI) sequence, which relies on spectrally selective excitation on the water resonance, obviating the need for fat suppression. As this method is more complex than standard DWI methods, we also report a test-retest study to evaluate its reproducibility. In this study, a spectrally selective Gaussian pulse on water resonance was combined with a pair of slice-selective adiabatic refocusing pulses for water-only DWI. Field map-based shimming and manual determination of the center frequency were used for water selection. The selectivity of the excitation pulse was optimized by a spectrally selective spectroscopy sequence based on the same principles. A test-retest study of 10 volunteers in two separate visits was used to evaluate its reproducibility. Our results from all subjects showed high-quality diffusion-weighted images of the breast without fat contamination. Mean apparent diffusion coefficients for b = 0, 600 s/mm(2) and b = 50, 600 s/mm(2) all showed good reproducibility, as 95% confidence intervals of the apparent diffusion coefficients were 4 × 10(-5) mm(2) /s and 5 × 10(-5) mm(2) /s and repeatability values were 1.09 × 10(-4) and 1.31 × 10(-4) , respectively. In conclusion, water-selective DWI is a feasible alternative to standard methods of DWI based on fat suppression. The added complexity of the method does not compromise the reproducibility of diffusion measurements in the breast.
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Affiliation(s)
- He Zhu
- Vanderbilt University Institute of Imaging Science, Tennessee 37232
- Radiology and Radiological Sciences, Vanderbilt University Nashville, Tennessee 37232
| | - Lori R. Arlinghaus
- Vanderbilt University Institute of Imaging Science, Tennessee 37232
- Radiology and Radiological Sciences, Vanderbilt University Nashville, Tennessee 37232
| | - Jennifer G. Whisenant
- Vanderbilt University Institute of Imaging Science, Tennessee 37232
- Radiology and Radiological Sciences, Vanderbilt University Nashville, Tennessee 37232
| | - Ming Li
- Department of Biostatistics Vanderbilt University Nashville, Tennessee 37232
| | - John C. Gore
- Vanderbilt University Institute of Imaging Science, Tennessee 37232
- Radiology and Radiological Sciences, Vanderbilt University Nashville, Tennessee 37232
- Department of Physics, Vanderbilt University Nashville, Tennessee 37232
- Department of Biomedical Engineering, Vanderbilt University Nashville, Tennessee 37232
- Department of Molecular Physiology and Biophysics, Vanderbilt University Nashville, Tennessee 37232
| | - Thomas E. Yankeelov
- Vanderbilt University Institute of Imaging Science, Tennessee 37232
- Radiology and Radiological Sciences, Vanderbilt University Nashville, Tennessee 37232
- Department of Physics, Vanderbilt University Nashville, Tennessee 37232
- Department of Biomedical Engineering, Vanderbilt University Nashville, Tennessee 37232
- Department of Cancer Biology, Vanderbilt University Nashville, Tennessee 37232
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29
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Wu EL, Chiueh TD, Chen JH. Multiple-frequency excitation wideband MRI (ME-WMRI). Med Phys 2014; 41:092304. [DOI: 10.1118/1.4893502] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Dumez JN, Schmidt R, Frydman L. Simultaneous spatial and spectral selectivity by spatiotemporal encoding. Magn Reson Med 2013; 71:746-55. [DOI: 10.1002/mrm.24718] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Jean-Nicolas Dumez
- Department of Chemical Physics; Weizmann Institute of Science; Rehovot 76100 Israel
| | - Rita Schmidt
- Department of Chemical Physics; Weizmann Institute of Science; Rehovot 76100 Israel
| | - Lucio Frydman
- Department of Chemical Physics; Weizmann Institute of Science; Rehovot 76100 Israel
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Balchandani P, Glover G, Pauly J, Spielman D. Improved slice-selective adiabatic excitation. Magn Reson Med 2013; 71:75-82. [PMID: 23401184 DOI: 10.1002/mrm.24630] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2012] [Revised: 11/17/2012] [Accepted: 12/16/2012] [Indexed: 11/06/2022]
Abstract
PURPOSE The purpose of this work is to design an improved Slice-selective Tunable-flip AdiaBatic Low peak-power Excitation (STABLE) pulse with shorter duration and increased off-resonance immunity to make it suitable for use in a greater range of applications and at higher field strengths. An additional aim is to design a variant of this pulse to achieve B1 -insensitive, fat-suppressed excitation. METHODS The adiabatic SLR algorithm was used to generate a more uniform spectral pulse envelope for this improved radiofrequency pulse for adiabatic slice-selective excitation, called STABLE-2. Pulse parameters were adjusted to design a version of STABLE-2 with a spectral null centered on lipids. RESULTS In vivo images obtained of the human brain at 3 and 7 T demonstrate that STABLE-2 provides robust, uniform, slice-selective excitation over a range of B1 values. Phantom and in vivo knee images obtained at 3 T demonstrate the effectiveness of STABLE-2 for fat suppression. CONCLUSIONS STABLE-2 achieves B1 -insensitive slice-selective excitation while providing greater off-resonance immunity and a shorter pulse duration, when compared to the original STABLE pulse. In particular, the 9.8-ms STABLE-2 pulse provides slice selectivity over 120 Hz whereas the 21-ms STABLE pulse is limited to 80 Hz off-resonance. B1 -Insensitive fat-suppressed excitation may also be achieved by using a variant of this pulse.
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Affiliation(s)
- Priti Balchandani
- Department of Radiology, Stanford University, Stanford, California, USA
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32
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Moore J, Jankiewicz M, Anderson AW, Gore JC. Slice-selective excitation with B₁⁺-insensitive composite pulses. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 214:200-211. [PMID: 22177383 PMCID: PMC3257413 DOI: 10.1016/j.jmr.2011.11.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Revised: 11/08/2011] [Accepted: 11/09/2011] [Indexed: 05/31/2023]
Abstract
Spatially selective excitation pulses have been designed to produce uniform flip angles in the presence of the RF and static field inhomogeneities typically encountered in MRI studies of the human brain at 7 T. Pulse designs are based upon non-selective, composite pulses numerically optimized for the desired performance over prescribed ranges of field inhomogeneities. The non-selective pulses are subsequently transformed into spatially selective pulses with the same field-insensitive properties through modification of the spectral composition of the individual sub-pulses which are then executed in conjunction with an oscillating gradient waveform. An in-depth analysis of the performance of these RF pulses is presented in terms of total pulse durations, slice profiles, linearity of in-slice magnetization phase, sensitivity to RF and static field variations, and signal loss due to T(2) effects. Both simulations and measurements in phantoms and in the human brain are used to evaluate pulses with nominal flip angles of 45° and 90°. Target slice thickness in all cases is 2mm. Results indicate that the described class of field-insensitive RF pulses is capable of improving flip-angle uniformity in 7 T human brain imaging. There appears to be a subset of pulses with durations ≲10 ms for which non-linearities in the magnetization phase are minimal and signal loss due to T(2) decay is not prohibitive. Such pulses represent practical solutions for achieving uniform flip angles in the presence of the large field inhomogeneities common to high-field human imaging and help to better establish the performance limits of high-field imaging systems with single-channel transmission.
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Affiliation(s)
- Jay Moore
- Vanderbilt University Institute of Imaging Science, 1161 21st Ave. South, MCN AA-1105, Nashville, TN 37232-2310, USA.
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Grissom WA, McKinnon GC, Vogel MW. Nonuniform and multidimensional Shinnar-Le Roux RF pulse design method. Magn Reson Med 2011; 68:690-702. [PMID: 22161690 DOI: 10.1002/mrm.23269] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Revised: 09/02/2011] [Accepted: 10/03/2011] [Indexed: 01/01/2023]
Abstract
The Shinnar-Le Roux (SLR) radiofrequency (RF) pulse design algorithm is widely used for designing slice-selective RF pulses due to its intuitiveness, optimality, and speed. SLR is limited, however, in that it is only capable of designing one-dimensional pulses played along constant gradients. We present a nonuniform SLR RF pulse design framework that extends most of the capabilities of classical SLR to nonuniform gradient trajectories and multiple dimensions. Specifically, like classical SLR, the new method is a hard pulse approximation-based technique that uses filter design relationships to produce the lowest power RF pulse that satisfies target magnetization ripple levels. The new method is validated and compared with methods conventionally used for nonuniform and multidimensional large-tip-angle RF pulse design.
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Affiliation(s)
- William A Grissom
- Imaging Technologies Laboratory, GE Global Research, Munich, Germany.
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Balchandani P, Khalighi MM, Glover G, Pauly J, Spielman D. Self-refocused adiabatic pulse for spin echo imaging at 7 T. Magn Reson Med 2011; 67:1077-85. [PMID: 21954048 DOI: 10.1002/mrm.23089] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2011] [Revised: 05/26/2011] [Accepted: 06/16/2011] [Indexed: 11/06/2022]
Abstract
Spin echo pulse sequences are used to produce clinically important T(2) contrast. However, conventional 180° radiofrequency pulses required to generate a spin echo are highly susceptible to the B(1) inhomogeneity at high magnetic fields such as 7 Tesla (7 T), resulting in varying signal and contrast over the region of interest. Adiabatic 180° pulses may be used to replace conventional 180° pulses in spin echo sequences to provide greater immunity to the inhomogeneous B(1) field at 7 T. However, because the spectral profile of an adiabatic 180° pulse has nonlinear phase, pairs of these pulses are needed for proper refocusing, resulting in increased radiofrequency power deposition and long minimum echo times. We used the adiabatic Shinnar Le-Roux method to generate a matched-phase adiabatic 90°-180° pulse pair to obviate the need for a second adiabatic 180° pulse for phase refocusing. The pulse pair was then reformulated into a single self-refocused pulse to minimize the echo time, and phantom and in vivo experiments were performed to validate pulse performance. The self-refocused adiabatic pulse produced transmit profiles that were substantially more uniform than those achieved using a conventional spin echo sequence.
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