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Effectiveness of fat suppression using a water-selective binomial-pulse excitation in chemical exchange saturation transfer (CEST) magnetic resonance imaging. MAGMA (NEW YORK, N.Y.) 2020; 33:809-818. [PMID: 32462557 DOI: 10.1007/s10334-020-00851-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2020] [Revised: 04/24/2020] [Accepted: 05/12/2020] [Indexed: 10/24/2022]
Abstract
PURPOSE The purpose of this study was to characterize the individual contribution of multiple fat peaks to the measured chemical exchange saturation transfer (CEST) signal when using water-selective binomial-pulse excitation and to determine the effects of multiple fat peaks in the presence of B0 inhomogeneity. METHODS The excitation profiles of multiple binomial pulses were simulated. A CEST sequence with binomial-pulse excitation and modified point-resolved spectroscopy localization was then applied to the in vivo lumbar spinal vertebrae to determine the signal contributions of three distinct groups of lipid resonances. These confounding signal contributions were measured as a function of the irradiation frequency offset to determine the effect of the multi-peak nature of the fat signal on CEST imaging of exchange sites (at 1.0, 2.0 and 3.5 ppm) and robustness in the presence of B0 inhomogeneity. RESULTS Numerical simulations and in vivo experiments showed that water excitation (WE) using a 1-3-3-1 (WE-4) pulse provided the broadest signal suppression, which provided partial robustness against B0 inhomogeneity effects. Confounding fat signal contributions to the CEST contrasts at 1.0, 2.0 and 3.5 ppm were unavoidable due to the multi-peak nature of the fat signal. However, these CEST sites only suffer from small lipid artifacts with ∆B0 spanning roughly from - 50 to 50 Hz. Especially for the CEST site at 3.5 ppm, the lipid artifacts are smaller than 1% with ∆B0 in this range. CONCLUSION In WE-4-based CEST magnetic resonance imaging, B0 inhomogeneity is the limiting factor for fat suppression. The CEST sites at 1.0, 2.0 ppm and 3.5 ppm unavoidably suffer from lipid artifacts. However, when the ∆B0 is confined to a limited range, these CEST sites are only affected by small lipid artifacts, which may be ignorable in some cases of clinical applications.
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Zhao Y, Yan X, Zhang Z, Zhao W, Liu Z, Li J. Self-adapting multi-peak water-fat reconstruction for the removal of lipid artifacts in chemical exchange saturation transfer (CEST) imaging. Magn Reson Med 2019; 82:1700-1712. [PMID: 31241219 DOI: 10.1002/mrm.27859] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 04/23/2019] [Accepted: 05/21/2019] [Indexed: 12/26/2022]
Abstract
PURPOSE Artifacts caused by strong lipid signals pose challenges in body chemical exchange saturation transfer (CEST) imaging. This study aimed to develop an accurate water-fat reconstruction method based on the multi-echo Dixon technique to remove lipid artifacts in CEST imaging. THEORY AND METHODS It is well known that fat has multiple spectral peaks. Furthermore, RF pulses in CEST preparation saturate each fat peak at different levels, complicating fat modeling. Therefore, a self-adapting multi-peak model (SMPM) is proposed to update relative amplitudes of fat peaks using numerical calculation. With the SMPM-based updating, nonlinear least-squares fitting combined with IDEAL (Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation) algorithms was used for water-fat reconstruction and B0 mapping. The proposed method was compared with the reported 3-point Dixon method and the fixed multi-peak model in a phantom study using a fat-free Z-spectrum obtained from MR spectroscopy acquisition as the ground truth. This method was also validated by in vivo experiments on human breast. RESULTS In the phantom experiments, the Z-spectrum from the SMPM-based method agreed well with the fat-free Z-spectrum from CEST-PRESS (point-resolved spectroscopy), validating the effective removal of lipid artifacts, while a decrease or a rise that appeared at -3.5 ppm was observed in the Z-spectrum from the 3-point method and the FMPM-based method, respectively. In the in vivo experiments, no lipid artifacts were observed in the Z-spectrum or the amide CEST map from the SMPM-based method in the fibro-glandular region of the breast with high fat fractions. CONCLUSION The SMPM-based method successfully removes lipid artifacts and significantly improves the accuracy of CEST contrast.
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Affiliation(s)
- Yu Zhao
- Shanghai Key Laboratory of Magnetic Resonance, School of Physics and Materials Science, East China Normal University, Shanghai, China
| | - Xu Yan
- MR Collaboration NE Asia, Siemens Healthcare, Shanghai, China
| | | | - Weiwei Zhao
- Shanghai Key Laboratory of Magnetic Resonance, School of Physics and Materials Science, East China Normal University, Shanghai, China
| | - Zhenzhi Liu
- Molecular Imaging Program at Stanford, Department of Radiology, Stanford University, Stanford, California
| | - Jianqi Li
- Shanghai Key Laboratory of Magnetic Resonance, School of Physics and Materials Science, East China Normal University, Shanghai, China
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Kraus MS, Notohamiprodjo M, Partovi S, Sobieh A, Baur-Melnyk A, Hausdorf J, Grosse U. MR arthrography of the hip: diagnostic performance and image quality of 3D-steady state free precession versus 2D turbo spin echo sequences. Skeletal Radiol 2018; 47:811-819. [PMID: 29330619 DOI: 10.1007/s00256-017-2865-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Revised: 11/24/2017] [Accepted: 12/27/2017] [Indexed: 02/02/2023]
Abstract
OBJECTIVE To retrospectively compare the diagnostic performance of isotropic 3D steady-state free precession (3D-SSFP) sequences with 2D turbo spin-echo proton density-weighted fat-saturated (2D-TSE-PD fs) images in hip magnetic resonance arthrography; arthroscopy was a standard of reference. METHODS Eighty-one patients with suspected labral tears who underwent hip MR arthrography (3-T scanner) were included. 2D-TSE-PD fs sequences were acquired in three planes and a singular sagittal 3D-SSFP. Labral tears, cartilage pathology and bone marrow were independently assessed by two blinded radiologists using a 5-point Likert scale. Accuracy was determined in 39 patients using invasive arthroscopy. RESULTS Diagnostic confidence of labral and cartilaginous pathologies based on image quality was rated higher for 3D-SSFP (4.5 ± 0.8; 4.35 ± 0.7; p < 0.0001), but inferior for bone marrow pathology (3.9 ± 0.7; 4.0 ± 0.7; p < 0.0001). In the arthroscopy patients, similar sensitivity (85.9%) but higher specificity (74.4vs.42.9%) and higher positive and negative predictive values were found in 3D-SSFP of labral and cartilage pathologies. CONCLUSIONS 3D-SSFP in hip magnetic resonance arthrography offers increased accuracy in detecting labral and cartilage pathologies compared with 2D-TSE-PD, while reducing the acquisition time. A drawback of 3D-SSFP was the inferior diagnostic confidence for bone marrow evaluation; thus, 3D-SSFP should be combined with conventional 2D-TSE sequences.
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Affiliation(s)
- Mareen Sarah Kraus
- Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Hoppe-Seyler-Strasse 3, 72076, Tuebingen, Germany.
| | - Mike Notohamiprodjo
- Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Hoppe-Seyler-Strasse 3, 72076, Tuebingen, Germany
| | - Sasan Partovi
- Department of Radiology, University Hospitals Case Medical Center, Case Western Reserve University, 11100 Euclid Avenue, Cleveland, OH, 44106, USA
| | - Ahmed Sobieh
- Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Hoppe-Seyler-Strasse 3, 72076, Tuebingen, Germany
| | - Andrea Baur-Melnyk
- Department of Clinical Radiology, University Hospital Munich, Marchioninistrasse 15, 81377, Munich, Germany
| | - Joerg Hausdorf
- Department of Orthopedics, University Hospital Munich, Marchioninistrasse 15, 81377, Munich, Germany
| | - Ulrich Grosse
- Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Hoppe-Seyler-Strasse 3, 72076, Tuebingen, Germany
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Bastiaansen JA, Stuber M. Flexible water excitation for fat-free MRI at 3T using lipid insensitive binomial off-resonant RF excitation (LIBRE) pulses. Magn Reson Med 2017; 79:3007-3017. [DOI: 10.1002/mrm.26965] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Revised: 09/11/2017] [Accepted: 09/21/2017] [Indexed: 11/06/2022]
Affiliation(s)
- Jessica A.M. Bastiaansen
- Department of Radiology; University Hospital (CHUV) and University of Lausanne (UNIL); Lausanne Switzerland
| | - Matthias Stuber
- Department of Radiology; University Hospital (CHUV) and University of Lausanne (UNIL); Lausanne Switzerland
- Center for Biomedical Imaging; Lausanne Switzerland
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Jin N, da Silveira JS, Jolly MP, Firmin DN, Mathew G, Lamba N, Subramanian S, Pennell DJ, Raman SV, Simonetti OP. Free-breathing myocardial T2* mapping using GRE-EPI and automatic non-rigid motion correction. J Cardiovasc Magn Reson 2015; 17:113. [PMID: 26699850 PMCID: PMC4690363 DOI: 10.1186/s12968-015-0216-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 12/09/2015] [Indexed: 02/11/2023] Open
Abstract
BACKGROUND Measurement of myocardial T2* is becoming widely used in the assessment of patients at risk for cardiac iron overload. The conventional breath-hold, ECG-triggered, segmented, multi-echo gradient echo (MGRE) sequence used for myocardial T2* quantification is very sensitive to respiratory motion and may not be feasible in patients who are unable to breath-hold. We propose a free-breathing myocardial T2* mapping approach that combines a single-shot gradient-echo echo-planar imaging (GRE-EPI) sequence for T2*-weighted image acquisition with automatic non-rigid motion correction (MOCO) of respiratory motion between single-shot images. METHODS ECG-triggered T2*-weighted images at different echo times were acquired by a black-blood, single-shot GRE-EPI sequence during free-breathing. A single image at a single TE is acquired in each heartbeat. Automatic non-rigid MOCO was applied to correct for in-plane respiratory motion before pixel-wise T2* mapping. In a total of 117 patients referred for clinical cardiac magnetic resonance exams, the free-breathing MOCO GRE-EPI sequence was compared to the breath-hold segmented MGRE approach. Image quality was scored independently by 2 experienced observers blinded to the particular image acquisition strategy. T2* measurements in the interventricular septum and in the liver were compared for the two methods in all cases with adequate image quality. RESULTS T2* maps were acquired in all 117 patients using the breath-hold MGRE and the free-breathing MOCO GRE-EPI approaches, including 8 patients with myocardial iron overload and 25 patients with hepatic iron overload. The mean image quality of the free-breathing MOCO GRE-EPI images was scored significantly higher than that of the breath-hold MGRE images by both reviewers. Out of the 117 studies, 21 breath-hold MGRE studies (17.9% of all the patients) were scored to be less than adequate or very poor by both reviewers, while only 2 free-breathing MOCO GRE-EPI studies were scored to be less than adequate image quality. In a comparative evaluation of the images with at least adequate quality, the intra-class correlation coefficients for myocardial and liver T2* were 0.868 and 0.986 respectively (p < 0.001), indicating that the T2* measured by breath-hold MGRE and free-breathing MOCO GRE-EPI were in close agreement. The coefficient of variation between the breath-hold and free-breathing approaches for myocardial and liver T2* were 9.88% and 9.38% respectively. Bland-Altman plots demonstrated good absolute agreement of T2* in the interventricular septum and the liver from the free-breathing and breath-hold approaches (mean differences -0.03 and 0.16 ms, respectively). CONCLUSION The free-breathing approach described for T2* mapping using MOCO GRE-EPI enables accurate myocardial and liver T2* measurements and is insensitive to respiratory motion.
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Affiliation(s)
- Ning Jin
- Siemens Medical Solutions USA, Inc, 460 West 12th Ave, Room 311, OH 43210, Columbus, OH, USA.
| | | | - Marie-Pierre Jolly
- Imaging & Computer Vision, Siemens Corporation, Corporate Technology, Princeton, NJ, USA.
| | - David N Firmin
- NIHR Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield NHS Trust, London, UK.
- National Heart and Lung Institute, Imperial College, London, UK.
| | - George Mathew
- NIHR Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield NHS Trust, London, UK.
| | - Nathan Lamba
- Davis Heart & Lung Research Institute, The Ohio State University, Columbus, OH, USA.
| | - Sharath Subramanian
- Department of Internal Medicine - Division of Cardiovascular Medicine, The Ohio State University, Columbus, OH, USA.
| | - Dudley J Pennell
- NIHR Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield NHS Trust, London, UK.
- National Heart and Lung Institute, Imperial College, London, UK.
| | - Subha V Raman
- Davis Heart & Lung Research Institute, The Ohio State University, Columbus, OH, USA.
- Department of Internal Medicine - Division of Cardiovascular Medicine, The Ohio State University, Columbus, OH, USA.
| | - Orlando P Simonetti
- Davis Heart & Lung Research Institute, The Ohio State University, Columbus, OH, USA.
- Department of Internal Medicine - Division of Cardiovascular Medicine, The Ohio State University, Columbus, OH, USA.
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA.
- Department of Radiology, The Ohio State University, Columbus, OH, USA.
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Çukur T. Spectrally selective imaging with wideband balanced steady-state free precession MRI. Magn Reson Med 2015; 75:1132-41. [PMID: 25846631 DOI: 10.1002/mrm.25700] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Revised: 01/26/2015] [Accepted: 02/25/2015] [Indexed: 11/10/2022]
Abstract
PURPOSE Unwanted, bright fat signals in balanced steady-state free precession sequences are commonly suppressed using spectral shaping. Here, a new spectral-shaping method is proposed to significantly improve the uniformity of stopband suppression without compromising the level of passband signals. METHODS The proposed method combines binomial-pattern excitation pulses with a wideband balanced steady-state free precession sequence kernel. It thereby increases the frequency separation between the centers of pass and stopbands by π radians, enabling improved water-fat contrast. Simulations were performed to find the optimal flip angles and subpulse spacing for the binomial pulses that maximize contrast and signal efficiency. RESULTS Comparisons with a conventional binomial balanced steady-state free precession sequence were performed in simulations as well as phantom and in vivo experiments at 1.5 T and 3 T. Enhanced fat suppression is demonstrated in vivo with an average improvement of 58% in blood-fat and 68% in muscle-fat contrast (P < 0.001, Wilcoxon signed-rank test). CONCLUSION The proposed binomial wideband balanced steady-state free precession method is a promising candidate for spectrally selective imaging with enhanced reliability against field inhomogeneities.
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Affiliation(s)
- Tolga Çukur
- Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey.,National Magnetic Resonance Research Center, Bilkent University, Ankara, Turkey
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Ingle RR, Santos JM, Overall WR, McConnell MV, Hu BS, Nishimura DG. Self-gated fat-suppressed cardiac cine MRI. Magn Reson Med 2014; 73:1764-74. [PMID: 24806049 DOI: 10.1002/mrm.25291] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Revised: 04/15/2014] [Accepted: 04/23/2014] [Indexed: 11/08/2022]
Abstract
PURPOSE To develop a self-gated alternating repetition time balanced steady-state free precession (ATR-SSFP) pulse sequence for fat-suppressed cardiac cine imaging. METHODS Cardiac gating is computed retrospectively using acquired magnetic resonance self-gating data, enabling cine imaging without the need for electrocardiogram (ECG) gating. Modification of the slice-select rephasing gradients of an ATR-SSFP sequence enables the acquisition of a one-dimensional self-gating readout during the unused short repetition time (TR). Self-gating readouts are acquired during every TR of segmented, breath-held cardiac scans. A template-matching algorithm is designed to compute cardiac trigger points from the self-gating signals, and these trigger points are used for retrospective cine reconstruction. The proposed approach is compared with ECG-gated ATR-SSFP and balanced steady-state free precession in 10 volunteers and five patients. RESULTS The difference of ECG and self-gating trigger times has a variability of 13 ± 11 ms (mean ± SD). Qualitative reviewer scoring and ranking indicate no statistically significant differences (P > 0.05) between self-gated and ECG-gated ATR-SSFP images. Quantitative blood-myocardial border sharpness is not significantly different among self-gated ATR-SSFP ( 0.61±0.15 mm -1), ECG-gated ATR-SSFP ( 0.61±0.15 mm -1), or conventional ECG-gated balanced steady-state free precession cine MRI ( 0.59±0.15 mm -1). CONCLUSION The proposed self-gated ATR-SSFP sequence enables fat-suppressed cardiac cine imaging at 1.5 T without the need for ECG gating and without decreasing the imaging efficiency of ATR-SSFP.
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Affiliation(s)
- R Reeve Ingle
- Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA
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8
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Deligianni X, Bär P, Scheffler K, Trattnig S, Bieri O. Water-selective excitation of short T2
species with binomial pulses. Magn Reson Med 2013; 72:800-5. [DOI: 10.1002/mrm.24978] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Revised: 09/05/2013] [Accepted: 09/11/2013] [Indexed: 12/19/2022]
Affiliation(s)
- Xeni Deligianni
- Department of Radiology; Division of Radiological Physics, University of Basel Hospital; Basel Switzerland
| | - Peter Bär
- MR Center of Excellence, Department of Radiology; Medical University Vienna; Vienna Austria
| | - Klaus Scheffler
- High-Field Magnetic Resonance Center; Max-Planck Institute for Biological Cybernetics; Tübingen Germany
- Department of Biomedical Magnetic Resonance; University Hospital Tübingen; Tübingen Germany
| | - Siegfried Trattnig
- MR Center of Excellence, Department of Radiology; Medical University Vienna; Vienna Austria
| | - Oliver Bieri
- Department of Radiology; Division of Radiological Physics, University of Basel Hospital; Basel Switzerland
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Bender JA, Ahmad R, Simonetti OP. The Importance of k-Space Trajectory on Off-Resonance Artifact in Segmented Echo-Planar Imaging. CONCEPTS IN MAGNETIC RESONANCE. PART A, BRIDGING EDUCATION AND RESEARCH 2013; 42A:10.1002/cmr.a.21255. [PMID: 24358026 PMCID: PMC3864862 DOI: 10.1002/cmr.a.21255] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Segmented interleaved echo planar imaging (EPI) is a highly efficient data acquisition technique; however, EPI is sensitive to artifacts from off-resonance spins. The choice of k-space trajectories is important in determining how off-resonance spins contribute to image artifacts. Top-down and center-out trajectories are theoretically analyzed, simulated, implemented, and tested in phantom and volunteer experiments. Theoretical results show off-resonance artifact manifests as a simple positional shift for the top-down trajectory, while for the center-out trajectory off-resonance artifact manifests as a splitting of the object, which entails both shift and blurring. These results were validated using simulation and phantom scan data where a frequency-offset was introduced ranging from -300 Hz to +300 Hz. As predicted by the theoretical results, inferior image quality was observed for the center-out trajectory in a single volunteer. Off-resonance produces more severe and complex artifacts with the center-out trajectory than the top-down trajectory.
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Affiliation(s)
- Jacob A Bender
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH ; Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH
| | - Rizwan Ahmad
- Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH ; Department of Electrical and Computer Engineering, The Ohio State University, Columbus, OH
| | - Orlando P Simonetti
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH ; Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH ; Department of Internal Medicine, Division of Cardiovascular Medicine, The Ohio State University, Columbus, OH ; Department of Radiology, The Ohio State University, Columbus, OH
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Lin HY, Bender JA, Ding Y, Chung YC, Hinton AM, Pennell ML, Whitehead KK, Raman SV, Simonetti OP. Shared velocity encoding: a method to improve the temporal resolution of phase-contrast velocity measurements. Magn Reson Med 2011; 68:703-10. [PMID: 22139889 DOI: 10.1002/mrm.23273] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Revised: 10/04/2011] [Accepted: 10/05/2011] [Indexed: 11/09/2022]
Abstract
Phase-contrast magnetic resonance imaging (PC-MRI) is used routinely to measure fluid and tissue velocity with a variety of clinical applications. Phase-contrast magnetic resonance imaging methods require acquisition of additional data to enable phase difference reconstruction, making real-time imaging problematic. Shared Velocity Encoding (SVE), a method devised to improve the effective temporal resolution of phase-contrast magnetic resonance imaging, was implemented in a real-time pulse sequence with segmented echo planar readout. The effect of SVE on peak velocity measurement was investigated in computer simulation, and peak velocities and total flow were measured in a flow phantom and in volunteers and compared with a conventional ECG-triggered, segmented k-space phase-contrast sequence as a reference standard. Computer simulation showed a 36% reduction in peak velocity error from 8.8 to 5.6% with SVE. A similar reduction of 40% in peak velocity error was shown in a pulsatile flow phantom. In the phantom and volunteers, volume flow did not differ significantly when measured with or without SVE. Peak velocity measurements made in the volunteers using SVE showed a higher concordance correlation (0.96) with the reference standard than non-SVE (0.87). The improvement in effective temporal resolution with SVE reconstruction has a positive impact on the precision and accuracy of real-time phase-contrast magnetic resonance imaging peak velocity measurements.
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Affiliation(s)
- Hung-Yu Lin
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA
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Qin Y, Zhang J, Li P, Wang Y. 3D double-echo steady-state with water excitation MR imaging of the intraparotid facial nerve at 1.5T: a pilot study. AJNR Am J Neuroradiol 2011; 32:1167-72. [PMID: 21566007 DOI: 10.3174/ajnr.a2480] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND AND PURPOSE The intraparotid facial nerve is difficult to delineate using conventional MR sequence. Our aim was to assess the value of 3D DESSWE MR imaging in depicting the normal anatomy of the intraparotid facial nerve. MATERIALS AND METHODS A 3D-DESSWE sequence was performed with optimum parameters in 18 healthy volunteers on a 1.5T MR imaging unit. The data obtained were reconstructed in relation to the course of the facial nerve by using the MPR and thin-section MIP programs. Images acquired were analyzed by 2 neuroradiologists. They made the initial evaluations independently but resolved inconsistencies by collaborative review and consensus agreement. The certainty of identifying the intraparotid facial nerve was scored and recorded on an arbitrary scale of 0-2. The lengths of the facial nerves were measured; CNRs of the facial nerves and parotid ducts were calculated. Statistical evaluation of the results was achieved by the 2-tailed Wilcoxon test, ANOVA, and a paired t test. RESULTS In all subjects, 3D DESSWE images provided a reliable definition of the normal facial nerve anatomy bilaterally. There were no significant differences between scores, lengths, and CNRs of bilateral facial nerves (P > .05). The intraparotid facial nerve, parotid ducts, and retromandibular vein showed high signal intensity while the surrounding soft tissue showed relatively low signal intensity. The signal intensity between the facial nerves and parotid ducts was significantly different (P < .01); but no differences could be obtained for the CNRs between the 2 structures (P > .05). CONCLUSIONS The 3D DESSWE sequence can display the intraparotid course of the normal facial nerve, including the relationship between the facial nerve and the parotid duct.
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Affiliation(s)
- Y Qin
- Department of Radiology, First Affiliated Hospital, Tianjin University of Traditional Chinese Medicine, Tianjin, China
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Malik SJ, Larkman DJ, O'Regan DP, Hajnal JV. Subject-specific water-selective imaging using parallel transmission. Magn Reson Med 2010; 63:988-97. [PMID: 20146394 DOI: 10.1002/mrm.22260] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Spectral-spatial excitation pulses are an efficient means of achieving water- or fat-only imaging and can be used in conjunction with a variety of pulse sequences. However, the approach lacks reliability since its performance is dependent on the homogeneity of the static magnetic field. Sensitivity to static magnetic field variation can be reduced by designing pulses with wider frequency stop bands, but these require longer pulse durations. In the proposed method, spectral-spatial pulses are optimized on a subject-dependent basis to take into account measured subject-specific static magnetic field variation. Extra control of the radiofrequency (RF) field from multichannel transmission is used to achieve this without increasing the length of the pulses. The method characterizes RF pulses using relatively few parameters and has been applied to abdominal imaging at 3 T with an eight-channel system. In a comparison of standard and subject-specific pulses on five healthy volunteers, the latter improved fat suppression in all subjects, with a reduction in RF power of 13% +/- 6%. A forward model suggests that the mean flip angle in fat was reduced from 0.72 degrees +/- 0.55 degrees to 0.12 degrees +/- 0.04 degrees for a 20 degrees excitation; uniformity of water excitation also improved, with the standard deviation divided by mean reduced from 0.26 +/- 0.05 to 0.16 +/- 0.05.
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Affiliation(s)
- Shaihan J Malik
- Robert Steiner MRI Unit, Imaging Sciences Department, Hammersmith Hospital Campus, Imperial College London, London, UK.
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Cukur T, Yamada M, Overall WR, Yang P, Nishimura DG. Positive contrast with alternating repetition time SSFP (PARTS): a fast imaging technique for SPIO-labeled cells. Magn Reson Med 2010; 63:427-37. [PMID: 20099331 DOI: 10.1002/mrm.22241] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
There has been recent interest in positive-contrast MRI methods for noninvasive tracking of cells labeled with superparamagnetic iron-oxide nanoparticles. Low-tip-angle balanced steady-state free precession sequences have been used for fast, high-resolution, and flow-insensitive positive-contrast imaging; however, the contrast can be compromised by the limited suppression of the on-resonant and fat signals. In this work, a new technique that produces positive contrast with alternating repetition time steady-state free precession is proposed to achieve robust background suppression for a broad range of tissue parameters. In vitro and in vivo experiments demonstrate the reliability of the generated positive contrast. The results indicate that the proposed method can enhance the suppression level by up to 18 dB compared with conventional balanced steady-state free precession.
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Affiliation(s)
- Tolga Cukur
- Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
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Cukur T, Nishimura DG. Multiple repetition time balanced steady-state free precession imaging. Magn Reson Med 2009; 62:193-204. [PMID: 19449384 DOI: 10.1002/mrm.21990] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Although balanced steady-state free precession (bSSFP) imaging yields high signal-to-noise ratio (SNR) efficiency, the bright lipid signal is often undesirable. The bSSFP spectrum can be shaped to suppress the fat signal with scan-efficient alternating repetition time (ATR) bSSFP. However, the level of suppression is limited, and the pass-band is narrow due to its nonuniform shape. A multiple repetition time (TR) bSSFP scheme is proposed that creates a broad stop-band with a scan efficiency comparable with ATR-SSFP. Furthermore, the pass-band signal uniformity is improved, resulting in fewer shading/banding artifacts. When data acquisition occurs in more than a single TR within the multiple-TR period, the echoes can be combined to significantly improve the level of suppression. The signal characteristics of the proposed technique were compared with bSSFP and ATR-SSFP. The multiple-TR method generates identical contrast to bSSFP, and achieves up to an order of magnitude higher stop-band suppression than ATR-SSFP. In vivo studies at 1.5 T and 3 T demonstrate the superior fat-suppression performance of multiple-TR bSSFP.
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Affiliation(s)
- Tolga Cukur
- Department of Electrical Engineering, Stanford University, Stanford, CA 94305-9510, USA.
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