1
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Li G, Ma X, Li S, Ye X, Börnert P, Zhou XJ, Guo H. Comparison of uniform-density, variable-density, and dual-density spiral samplings for multi-shot DWI. Magn Reson Med 2023; 90:133-149. [PMID: 36883748 DOI: 10.1002/mrm.29633] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2022] [Revised: 02/17/2023] [Accepted: 02/21/2023] [Indexed: 03/09/2023]
Abstract
PURPOSE To compare the performances of uniform-density spiral (UDS), variable-density spiral (VDS), and dual-density spiral (DDS) samplings in multi-shot diffusion imaging, and determine a sampling strategy that balances reliability of shot navigator and overall DWI image quality. THEORY AND METHODS UDS, VDS, and DDS trajectories were implemented to achieve four-shot diffusion-weighted spiral imaging. First, the static B0 off-resonance effects in UDS, VDS, and DDS acquisitions were analyzed based on a signal model. Then, in vivo experiments were performed to verify the theoretical analyses, and fractional anisotropy (FA) fitting residuals were used to quantitatively assess the quality of spiral diffusion data for tensor estimation. Finally, the SNR performances and g-factor behavior of the three spiral samplings were evaluated using a Monte Carlo-based pseudo multiple replica method. RESULTS Among the three spiral trajectories with the same readout duration, UDS sampling exhibited the least off-resonance artifacts. This was most evident when the static B0 off-resonance effect was severe. The UDS diffusion images had higher anatomical fidelity and lower FA fitting residuals than the other two counterparts. Furthermore, the four-shot UDS acquisition achieved the best SNR performance in diffusion imaging with 12.11% and 40.85% improvements over the VDS and DDS acquisitions with the same readout duration, respectively. CONCLUSION UDS sampling is an efficient spiral acquisition scheme for high-resolution diffusion imaging with reliable navigator information. It provides superior off-resonance performance and SNR efficiency over the VDS and DDS samplings for the tested scenarios.
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Affiliation(s)
- Guangqi Li
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, Tsinghua University, Beijing, China
| | - Xiaodong Ma
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, Utah, USA
| | - Sisi Li
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, Tsinghua University, Beijing, China
| | - Xinyu Ye
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, Tsinghua University, Beijing, China
| | - Peter Börnert
- Radiology, C.J. Gorter Center for High-Field MRI, Leiden University Medical Center, Leiden, The Netherlands.,Philips Research, Hamburg, Germany
| | - Xiaohong Joe Zhou
- Center for MR Research and Departments of Radiology, Neurosurgery, and Biomedical Engineering, University of Illinois College of Medicine at Chicago, Chicago, Illinois, USA
| | - Hua Guo
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, Tsinghua University, Beijing, China
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2
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McIlvain G, McGarry MDJ, Johnson CL. Quantitative effects of off-resonance related distortion on brain mechanical property estimation with magnetic resonance elastography. NMR Biomed 2022; 35:e4616. [PMID: 34542196 PMCID: PMC8688217 DOI: 10.1002/nbm.4616] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 07/01/2021] [Accepted: 08/25/2021] [Indexed: 06/13/2023]
Abstract
Off-resonance related geometric distortion can impact quantitative MRI techniques, such as magnetic resonance elastography (MRE), and result in errors to these otherwise sensitive metrics of brain health. MRE is a phase contrast technique to determine the mechanical properties of tissue by imaging shear wave displacements and estimating tissue stiffness through inverse solution of Navier's equation. In this study, we systematically examined the quantitative effects of distortion and corresponding correction approaches on MRE measurements through a series of simulations, phantom models, and in vivo brain experiments. We studied two different k-space trajectories, echo-planar imaging and spiral, and we determined that readout time, off-resonance gradient strength, and the combination of readout direction and off-resonance gradient direction, impact the estimated mechanical properties. Images were also processed through traditional distortion correction pipelines, and we found that each of the correction mechanisms works well for reducing stiffness errors, but are limited in cases of very large distortion. The ability of MRE to detect subtle changes to neural tissue health relies on accurate, artifact-free imaging, and thus off-resonance related geometric distortion must be considered when designing sequences and protocols by limiting readout time and applying correction where appropriate.
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Affiliation(s)
- Grace McIlvain
- Department of Biomedical Engineering, University of Delaware; Newark, DE
| | | | - Curtis L Johnson
- Department of Biomedical Engineering, University of Delaware; Newark, DE
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3
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Peng X, Sui Y, Trzasko JD, Glaser KJ, Huston J, Ehman RL, Pipe JG. Fast 3D MR elastography of the whole brain using spiral staircase: Data acquisition, image reconstruction, and joint deblurring. Magn Reson Med 2021; 86:2011-2024. [PMID: 34096097 PMCID: PMC8498799 DOI: 10.1002/mrm.28855] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Revised: 04/06/2021] [Accepted: 05/04/2021] [Indexed: 02/06/2023]
Abstract
PURPOSE To address the need for a method to acquire 3D data for MR elastography (MRE) of the whole brain with substantially improved spatial resolution, high SNR, and reduced acquisition time compared with conventional methods. METHODS We combined a novel 3D spiral staircase data-acquisition method with a spoiled gradient-echo pulse sequence and MRE motion-encoding gradients (MEGs). The spiral-out acquisition permitted use of longer-duration motion-encoding gradients (ie, over two full oscillatory cycles) to enhance displacement SNR, while still maintaining a reasonably short TE for good phase-SNR. Through-plane parallel imaging with low noise penalties was implemented to accelerate acquisition along the slice direction. Shared anatomical information was exploited in the deblurring procedure to further boost SNR for stiffness inversion. RESULTS In vivo and phantom experiments demonstrated the feasibility of the proposed method in producing brain MRE results comparable to the spin-echo-based approaches, both qualitatively and quantitatively. High-resolution (2-mm isotropic) brain MRE data were acquired in 5 minutes using our method with good SNR. Joint deblurring with shared anatomical information produced SNR-enhanced images, leading to upward stiffness estimation. CONCLUSION A novel 3D gradient-echo-based approach has been designed and implemented, and shown to have promising potential for fast and high-resolution in vivo MRE of the whole brain.
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Affiliation(s)
- Xi Peng
- Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
| | - Yi Sui
- Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
| | | | - Kevin J Glaser
- Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
| | - John Huston
- Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
| | - Richard L Ehman
- Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
| | - James G Pipe
- Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
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4
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Michael Gach H, Curcuru AN, Kim T, Yang D. Technical Note: Effects of rotating gantry on magnetic field and eddy currents in 0.35 T MRI-guided radiotherapy (MR-IGRT) system. Med Phys 2021; 48:7228-7235. [PMID: 34520081 DOI: 10.1002/mp.15226] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Revised: 07/19/2021] [Accepted: 09/04/2021] [Indexed: 01/03/2023] Open
Abstract
PURPOSE The purpose of this study was to identify the cause of severe image artifacts that occurred during gantry rotation in a 0.35 T MRI-Linac by comparing measurements of eddy currents, center frequency, and field inhomogeneities made with the gantry in motion and stationary. METHODS Gradient and B0 eddy currents were calculated from the free induction decays (FIDs) resulting from selective excitation at a temporal resolution of 200 ms/measurement. B0 eddy currents were also calculated from FIDs acquired with nonselective excitation at a temporal resolution of 100 ms/measurement. Center frequencies and B0 inhomogeneities were measured by acquiring FIDs with a repetition time (TR) of 290 ms. Cartesian and radial 2D true fast imaging with steady-state precession (TrueFISP) pulse sequences used in real-time MRI-guided radiation therapy (MR-IGRT) were acquired. To assess artifact severity, the normalized root mean square error (nRMSE) was calculated between a reference MRI (static gantry) and MRIs acquired during gantry rotation for each serial acquisition. Image artifacts were qualitatively graded as nominal, minor, or severe. Measurements were conducted while the gantry was rotated through its entire range for both clockwise and counterclockwise. Measurements during gantry rotation were compared to measurements with a stationary gantry (every 30°). RESULTS Severe image artifacts were observed 22-35% of the time while the gantry was rotating. Short time constant eddy currents were not affected by gantry rotation. The peak to peak center frequency and FWHM rose by factors of 13.2-14.5 and 1.1-1.6, respectively, for the rotating versus stationary gantry. The magnitude of the center frequency offset and field inhomogeneities depended on the direction of the gantry rotation. CONCLUSIONS Image artifacts during gantry rotation were primarily caused by center frequency variations and field inhomogeneities. Therefore, dynamic B0 compensation techniques should be able to reduce artifacts during gantry rotation.
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Affiliation(s)
- H Michael Gach
- Departments of Radiation Oncology, Radiology, and Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Austen N Curcuru
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Taeho Kim
- Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Deshan Yang
- Departments of Radiation Oncology and Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
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5
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Willmering MM, Cleveland ZI, Walkup LL, Woods JC. Removal of off-resonance xenon gas artifacts in pulmonary gas-transfer MRI. Magn Reson Med 2021; 86:907-915. [PMID: 33665905 DOI: 10.1002/mrm.28737] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Revised: 01/25/2021] [Accepted: 01/26/2021] [Indexed: 12/23/2022]
Abstract
PURPOSE Hyperpolarized xenon (129 Xe) gas-transfer imaging allows different components of pulmonary gas transfer-alveolar air space, lung interstitium/blood plasma (barrier), and red blood cells (RBCs)-to be assessed separately in a single breath. However, quantitative analysis is challenging because dissolved-phase 129 Xe images are often contaminated by off-resonant gas-phase signal generated via imperfectly selective excitation. Although previous methods required additional data for gas-phase removal, the method reported here requires no/minimal sequence modifications/data acquisitions, allowing many previously acquired images to be corrected retroactively. METHODS 129 Xe imaging was implemented at 3.0T via an interleaved three-dimensional radial acquisition of the gaseous and dissolved phases (using one-point Dixon reconstruction for the dissolved phase) in 46 human subjects and a phantom. Gas-phase contamination (9.5% ± 4.8%) was removed from gas-transfer data using a modified gas-phase image. The signal-to-noise ratio (SNR) and signal distributions were compared before and after contamination removal. Additionally, theoretical gaseous contaminations were simulated at different magnetic field strengths for comparison. RESULTS Gas-phase contamination at 3.0T was more diffuse and located predominantly outside the lungs, relative to simulated 1.5T contamination caused by the larger frequency offset. Phantom experiments illustrated a 91% removal efficiency. In human subjects, contamination removal produced significant changes in dissolved signal SNR (+7.8%), mean (-1.4%), and standard deviation (-2.3%) despite low contamination. Repeat measurements showed reduced variance (dissolved mean, -1.0%; standard deviation, -8.4%). CONCLUSION Off-resonance gas-phase contamination can be removed robustly with no/minimal sequence modifications. Contamination removal permits more accurate quantification, reduces radiofrequency stringency requirements, and increases data consistency, providing improved sensitivity needed for multicenter trials.
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Affiliation(s)
- Matthew M Willmering
- Center for Pulmonary Imaging Research, Division of Pulmonary Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Zackary I Cleveland
- Center for Pulmonary Imaging Research, Division of Pulmonary Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.,Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA.,Department of Biomedical Engineering, University of Cincinnati, Cincinnati, OH, USA
| | - Laura L Walkup
- Center for Pulmonary Imaging Research, Division of Pulmonary Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.,Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA
| | - Jason C Woods
- Center for Pulmonary Imaging Research, Division of Pulmonary Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.,Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA.,Department of Physics, University of Cincinnati, Cincinnati, OH, USA.,Department of Radiology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
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6
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Lim Y, Bliesener Y, Narayanan S, Nayak KS. Deblurring for spiral real-time MRI using convolutional neural networks. Magn Reson Med 2020; 84:3438-3452. [PMID: 32710516 PMCID: PMC7722023 DOI: 10.1002/mrm.28393] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2020] [Revised: 05/06/2020] [Accepted: 06/01/2020] [Indexed: 12/20/2022]
Abstract
PURPOSE To develop and evaluate a fast and effective method for deblurring spiral real-time MRI (RT-MRI) using convolutional neural networks. METHODS We demonstrate a 3-layer residual convolutional neural networks to correct image domain off-resonance artifacts in speech production spiral RT-MRI without the knowledge of field maps. The architecture is motivated by the traditional deblurring approaches. Spatially varying off-resonance blur is synthetically generated by using discrete object approximation and field maps with data augmentation from a large database of 2D human speech production RT-MRI. The effect of off-resonance range, shift-invariance of blur, and readout durations on deblurring performance are investigated. The proposed method is validated using synthetic and real data with longer readouts, quantitatively using image quality metrics and qualitatively via visual inspection, and with a comparison to conventional deblurring methods. RESULTS Deblurring performance was found superior to a current autocalibrated method for in vivo data and only slightly worse than an ideal reconstruction with perfect knowledge of the field map for synthetic test data. Convolutional neural networks deblurring made it possible to visualize articulator boundaries with readouts up to 8 ms at 1.5 T, which is 3-fold longer than the current standard practice. The computation time was 12.3 ± 2.2 ms per frame, enabling low-latency processing for RT-MRI applications. CONCLUSION Convolutional neural networks deblurring is a practical, efficient, and field map-free approach for the deblurring of spiral RT-MRI. In the context of speech production imaging, this can enable 1.7-fold improvement in scan efficiency and the use of spiral readouts at higher field strengths such as 3 T.
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Affiliation(s)
- Yongwan Lim
- Ming Hsieh Department of Electrical and Computer Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California, USA
| | - Yannick Bliesener
- Ming Hsieh Department of Electrical and Computer Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California, USA
| | - Shrikanth Narayanan
- Ming Hsieh Department of Electrical and Computer Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California, USA
| | - Krishna S. Nayak
- Ming Hsieh Department of Electrical and Computer Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California, USA
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7
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Liu W, Guo X, Xing S, Yao H, Wang Y, Bai L, Wang Q, Zhang L, Wu D, Zhang Y, Wang X, Yi Y. Off-Resonant Absorption Enhancement in Single Nanowires via Graded Dual-Shell Design. Nanomaterials (Basel) 2020; 10:nano10091740. [PMID: 32887500 PMCID: PMC7559431 DOI: 10.3390/nano10091740] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/08/2020] [Revised: 08/30/2020] [Accepted: 09/01/2020] [Indexed: 01/04/2023]
Abstract
Single nanowires (NWs) are of great importance for optoelectronic applications, especially solar cells serving as powering nanoscale devices. However, weak off-resonant absorption can limit its light-harvesting capability. Here, we propose a single NW coated with the graded-index dual shells (DSNW). We demonstrate that, with appropriate thickness and refractive index of the inner shell, the DSNW exhibits significantly enhanced light trapping compared with the bare NW (BNW) and the NW only coated with the outer shell (OSNW) and the inner shell (ISNW), which can be attributed to the optimal off-resonant absorption mode profiles due to the improved coupling between the reemitted light of the transition modes of the leak mode resonances of the Si core and the nanofocusing light from the dual shells with the graded refractive index. We found that the light absorption can be engineered via tuning the thickness and the refractive index of the inner shell, the photocurrent density is significantly enhanced by 134% (56%, 12%) in comparison with that of the BNW (OSNW, ISNW). This work advances our understanding of how to improve off-resonant absorption by applying graded dual-shell design and provides a new choice for designing high-efficiency single NW photovoltaic devices.
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Affiliation(s)
- Wenfu Liu
- School of Mechanical and Energy Engineering, Huanghuai University, Zhumadian 463000, Henan, China; (X.G.); (S.X.); (H.Y.); (Y.W.); (L.B.); (Q.W.); (L.Z.)
- Integrated Nano Optoelectronics Laboratory, University of Michigan, Dearborn, MI 48128, USA; (D.W.); (Y.Z.); (X.W.)
- Correspondence: (W.L.); (Y.Y.)
| | - Xiaolei Guo
- School of Mechanical and Energy Engineering, Huanghuai University, Zhumadian 463000, Henan, China; (X.G.); (S.X.); (H.Y.); (Y.W.); (L.B.); (Q.W.); (L.Z.)
| | - Shule Xing
- School of Mechanical and Energy Engineering, Huanghuai University, Zhumadian 463000, Henan, China; (X.G.); (S.X.); (H.Y.); (Y.W.); (L.B.); (Q.W.); (L.Z.)
| | - Haizi Yao
- School of Mechanical and Energy Engineering, Huanghuai University, Zhumadian 463000, Henan, China; (X.G.); (S.X.); (H.Y.); (Y.W.); (L.B.); (Q.W.); (L.Z.)
| | - Yinling Wang
- School of Mechanical and Energy Engineering, Huanghuai University, Zhumadian 463000, Henan, China; (X.G.); (S.X.); (H.Y.); (Y.W.); (L.B.); (Q.W.); (L.Z.)
| | - Liuyang Bai
- School of Mechanical and Energy Engineering, Huanghuai University, Zhumadian 463000, Henan, China; (X.G.); (S.X.); (H.Y.); (Y.W.); (L.B.); (Q.W.); (L.Z.)
| | - Qi Wang
- School of Mechanical and Energy Engineering, Huanghuai University, Zhumadian 463000, Henan, China; (X.G.); (S.X.); (H.Y.); (Y.W.); (L.B.); (Q.W.); (L.Z.)
| | - Liang Zhang
- School of Mechanical and Energy Engineering, Huanghuai University, Zhumadian 463000, Henan, China; (X.G.); (S.X.); (H.Y.); (Y.W.); (L.B.); (Q.W.); (L.Z.)
| | - Dachuan Wu
- Integrated Nano Optoelectronics Laboratory, University of Michigan, Dearborn, MI 48128, USA; (D.W.); (Y.Z.); (X.W.)
| | - Yuxiao Zhang
- Integrated Nano Optoelectronics Laboratory, University of Michigan, Dearborn, MI 48128, USA; (D.W.); (Y.Z.); (X.W.)
| | - Xiao Wang
- Integrated Nano Optoelectronics Laboratory, University of Michigan, Dearborn, MI 48128, USA; (D.W.); (Y.Z.); (X.W.)
| | - Yasha Yi
- Integrated Nano Optoelectronics Laboratory, University of Michigan, Dearborn, MI 48128, USA; (D.W.); (Y.Z.); (X.W.)
- Energy Institute, University of Michigan, Ann Arbor, MI 48109, USA
- Correspondence: (W.L.); (Y.Y.)
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Ostenson J, Smith DS, Does MD, Damon BM. Slice-selective extended phase graphs in gradient-crushed, transient-state free precession sequences: An application to MR fingerprinting. Magn Reson Med 2020; 84:3409-3422. [PMID: 32697869 DOI: 10.1002/mrm.28381] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 05/08/2020] [Accepted: 05/24/2020] [Indexed: 12/18/2022]
Abstract
PURPOSE Slice-selective, gradient-crushed, transient-state sequences such as those used in MR fingerprinting (MRF) relaxometry are sensitive to slice profile effects. Whereas balanced steady-state free precession MRF profile effects have been studied, less attention has been given to gradient-crushed MRF forms. Extensions of the extended phase graph (EPG) formalism, called slice-selective EPG (ssEPG), are proposed that model slice profile effects. THEORY AND METHODS The hard-pulse approximation to slice-selective excitation in the spatial domain is reformulated in k-space. Excitation is modeled by standard EPG shift and transition operators. This ssEPG modeling is validated against Bloch simulations and phantom slice profile measurements. ssEPG relaxometry accuracy and variability are compared with other EPG methods in phantoms and human leg in vivo. The role of ∆B0 interactions with slice profile and gradient crushers is investigated. RESULTS Simulations and slice profile measurements show that ssEPG can model highly dynamic slice profile effects of gradient-crushed sequences. The MRF ssEPG T2 estimates over 0 < T2 < 100 ms improve accuracy by > 10 ms at some values relative to other modeling approaches. Small deviations in B0 can produce substantial bias in T2 estimations from a range of MRF sequence types, and these effects can be modeled and understood by ssEPG. CONCLUSION Transient-state, gradient-crushed sequences such as those used in MRF are sensitive to slice profile effects, and these effects depend on RF pulse choice, gradient crusher strength, and ∆B0 . It was found ssEPG was the most accurate EPG-based means to model these effects.
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Affiliation(s)
- Jason Ostenson
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA.,Chemical and Physical Biology Program, Vanderbilt University, Nashville, TN, USA.,Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
| | - David S Smith
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA.,Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Mark D Does
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA.,Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA.,Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA.,Department of Electrical Engineering, Vanderbilt University, Nashville, TN, USA
| | - Bruce M Damon
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA.,Chemical and Physical Biology Program, Vanderbilt University, Nashville, TN, USA.,Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA.,Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA.,Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
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9
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Macdonald EB, Barton GP, Cox BL, Johnson KM, Strigel RM, Fain SB. Improved reconstruction stability for chemical shift encoded hyperpolarized 13 C magnetic resonance spectroscopic imaging using k-t spiral acquisitions. Magn Reson Med 2019; 84:25-38. [PMID: 31814173 DOI: 10.1002/mrm.28122] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Revised: 11/17/2019] [Accepted: 11/19/2019] [Indexed: 12/30/2022]
Abstract
PURPOSE A multiecho, field of view (FOV)-oversampled k-t spiral acquisition and direct iterative decomposition of water and fat with echo asymmetry and least-squares estimation reconstruction is demonstrated to improve the stability of hyperpolarized 13 C magnetic resonance spectroscopic imaging (MRSI) in the presence of signal ambiguities attributed to low-SNR (signal-to-noise-ratio) species, local uncertainties in metabolite peaks, and echo-to-echo signal inconsistencies. THEORY k-t spiral acquisitions redistribute readout points to be more densely spaced radially in k-space by acquiring an FOV and matrix that are oversampled by η. These more densely spaced spiral turns constitute effective intraspiral echoes and can supplement conventional interspiral echoes to improve spectral separation and reduce spectral cross-talk to better resolve 13 C-labeled species for spectroscopic imaging. METHODS Digital simulations and imaging phantom experiments were performed for a range of interspiral echo spacings and η using multiecho, k-t spiral acquisitions. Image spectral cross-talk artifacts were evaluated both qualitatively and quantitatively as the percent error in measured metabolite ratios. In vivo murine experiments evaluated the feasibility of multiecho, k-t spiral [1-13 C]pyruvate MRSI to reduce spectral cross-talk for 3 scenarios of different expected reconstruction stability. RESULTS Digital simulations and imaging phantom experiments both demonstrated reduced or comparable image spectral cross-talk and percent errors in measured metabolite ratios with increasing η and better choices of echo spacings. In vivo images displayed markedly reduced spectral cross-talk in lactate images acquired with η = 7 versus η = 1. CONCLUSION The precision of hyperpolarized 13 C metabolic imaging and quantification in the presence of low-SNR species, local uncertainties in metabolite resonances, and echo-to-echo signal inconsistencies can be improved with the use of FOV-oversampled k-t spiral acquisitions.
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Affiliation(s)
- Erin B Macdonald
- Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin
| | - Gregory P Barton
- Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin
| | - Benjamin L Cox
- Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin.,Morgridge Institute for Research, University of Wisconsin-Madison, Madison, Wisconsin.,Laboratory for Optical and Computational Instrumentation, University of Wisconsin-Madison, Madison, Wisconsin
| | - Kevin M Johnson
- Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin.,Department of Radiology, University of Wisconsin-Madison, Madison, Wisconsin
| | - Roberta M Strigel
- Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin.,Department of Radiology, University of Wisconsin-Madison, Madison, Wisconsin.,Carbone Cancer Center, University of Wisconsin-Madison, Madison, Wisconsin
| | - Sean B Fain
- Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin.,Department of Radiology, University of Wisconsin-Madison, Madison, Wisconsin.,Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin
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10
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Serés Roig E, Xin L, Gallichan D, Mlynarik V, Gruetter R. Improved off-resonance phase behavior using a phase-inverted adiabatic half-passage pulse for 13 C MRS in humans at 7 T. NMR Biomed 2019; 32:e4171. [PMID: 31517419 DOI: 10.1002/nbm.4171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 07/23/2019] [Accepted: 08/03/2019] [Indexed: 06/10/2023]
Abstract
In vivo 13 C MRS at high field benefits from an improved SNR and spectral resolution especially when using surface coils in combination with adiabatic pulses, such as the adiabatic half-passage (AHP) pulse for 13 C excitation. However, the excitation profile of the AHP pulse is asymmetric relative to the carrier frequency, which could lead to asymmetric excitation of the spectral lines relative to the center of the spectrum. In this study, a pulse-acquire sequence was designed for adiabatic 13 C excitation with a symmetric bandwidth, utilizing a combination of two AHP pulses with inverted phases in alternate scans. Magnetization and phase behavior as a function of frequency offset and RF amplitude of the B1 field, as well as the steady-state transverse magnetization response to off-resonance, were simulated. Excitation properties of the combined pulse sequence were studied by 23 Na imaging and 13 C spectroscopy in vitro on a phantom and in vivo on the human calf at 7 T. Simulations demonstrated symmetric transverse magnetization and phase with respect to positive and negative frequency offsets when using two AHP pulses with inverted phases in alternate scans, thereby minimizing baseline distortion and achieving symmetric T1 weighting, as confirmed by in vitro measurements. The intensities of the lipid peaks at 15, 30, 62, 73, and 130 ppm were in agreement with those theoretically predicted using two AHP pulses with inverted phases in alternate scans. We conclude that using two phase-inverted AHP pulses improves the symmetry of the 13 C excitation profile and phase response to off-resonance effects at 7 T in comparison with using a single AHP pulse.
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Affiliation(s)
- Eulalia Serés Roig
- Laboratory of Functional and Metabolic Imaging (LIFMET), Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland
| | - Lijing Xin
- Centre d'Imagerie Biomédicale-Animal and Imaging Technology (CIBM-AIT), Lausanne, Switzerland
| | - Daniel Gallichan
- Centre d'Imagerie Biomédicale-Animal and Imaging Technology (CIBM-AIT), Lausanne, Switzerland
| | - Vladimir Mlynarik
- High Field MR Center, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria
| | - Rolf Gruetter
- Laboratory of Functional and Metabolic Imaging (LIFMET), Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland
- Centre d'Imagerie Biomédicale-Animal and Imaging Technology (CIBM-AIT), Lausanne, Switzerland
- Department of Radiology, University of Lausanne (UNIL), Switzerland
- Department of Radiology, University of Geneva (UNIGE), Switzerland
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11
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Schollenberger J, Figueroa CA, Nielsen JF, Hernandez-Garcia L. Practical considerations for territorial perfusion mapping in the cerebral circulation using super-selective pseudo-continuous arterial spin labeling. Magn Reson Med 2019; 83:492-504. [PMID: 31418475 DOI: 10.1002/mrm.27936] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Revised: 06/18/2019] [Accepted: 07/17/2019] [Indexed: 12/29/2022]
Abstract
PURPOSE This paper discusses several challenges faced by super-selective pseudo-continuous arterial spin labeling, which is used to quantify territorial perfusion in the cerebral circulation. The effects of off-resonance, pulsatility, vessel movement, and label rotation scheme are investigated, and methods to maximize labeling efficiency and overall image quality are evaluated. A strategy to calculate the territorial perfusion fractions of individual vessels is proposed. METHODS The effects of off-resonance, label rotation scheme, and vessel movement on labeling efficiency were simulated. Two off-resonance compensation strategies (multiphase prescan, field map), cardiac triggering, and vessel movement were studied in vivo in a group of 10 subjects. Subsequently, a territorial perfusion fraction map was acquired in 2 subjects based on the mean vessel labeling efficiency. RESULTS Multiphase calibration provided the highest labeling efficiency (P = .002) followed by the field map compensation (P = .037) compared with the uncompensated acquisition. Cardiac triggering resulted in a qualitative improvement of the image and an increase in signal contrast between the perfusion territory and the surrounding tissue (P = .010) but failed to show a significant change in temporal and spatial SNR. The constant clockwise label rotation scheme yielded the highest labeling efficiency. Significant vessel movement (>2 mm according to simulations) was observed in 50% of subjects. The measured territorial perfusion fractions showed good agreement with anatomical data. CONCLUSION Optimized labeling efficiency resulted in increased image quality and accuracy of territorial perfusion fraction maps. Labeling efficiency depends critically on off-resonance calibration, cardiac triggering, optimal label rotation scheme, and vessel location tracking.
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Affiliation(s)
- Jonas Schollenberger
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan
| | - C Alberto Figueroa
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan.,Department of Surgery, University of Michigan, Ann Arbor, Michigan
| | - Jon-Fredrik Nielsen
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan.,FMRI Laboratory, University of Michigan, Ann Arbor, Michigan
| | - Luis Hernandez-Garcia
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan.,FMRI Laboratory, University of Michigan, Ann Arbor, Michigan
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12
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Bouazizi K, Guillot G. Cross-relaxation parameters in cortical bone assessed with different MR sequences. NMR Biomed 2019; 32:e4098. [PMID: 30986332 DOI: 10.1002/nbm.4098] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Revised: 02/21/2019] [Accepted: 03/05/2019] [Indexed: 06/09/2023]
Abstract
This study aimed to show evidence of MR cross-relaxation effects in cortical bone and to compare different MR sequences for the quantification of cross-relaxation parameters. Measurements were performed on bovine diaphysis samples with spectroscopic methods (inversion-recovery, off-resonance saturation) and with a variable flip angle (VFA) UTE imaging method on a 4.7 T laboratory-assembled scanner. Cross-relaxation parameter assessment was carried out via a two-pool model simulation with a matrix algebra approach. A proton signal amplitude of 28 Mol/L was observed (equivalent water fraction of 25%). It was attributed to collagen-bound water, with T2* values of ~ 0.3 ms, a "long-T2 " proton pool, in exchange with protons from the collagen macromolecules ( T2* of 10-20 μs). Magnetization transfer (MT) effects were detected with all sequences. The best precision of model parameters was obtained with off-resonance saturation; the fraction of collagen methylene protons was found in the range of 22-28% and the transverse relaxation time for collagen methylene protons was 11 μs (1% precision). The model parameters obtained were compatible with VFA-UTE results but could not be assessed with acceptable accuracy and precision using this method. In vivo MT quantification using off-resonance saturation with a single B1 amplitude and offset frequency may provide information about the relative amount of collagen per unit volume in cortical bone.
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Affiliation(s)
- Khaoula Bouazizi
- Imagerie par Résonance Magnétique Médicale et Multi-Modalités (UMR8081), CNRS, Université Paris-Saclay, Orsay, France
| | - Geneviève Guillot
- Imagerie par Résonance Magnétique Médicale et Multi-Modalités (UMR8081), CNRS, Université Paris-Saclay, Orsay, France
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13
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Tan Z, Voit D, Kollmeier JM, Uecker M, Frahm J. Dynamic water/fat separation and B 0 inhomogeneity mapping-joint estimation using undersampled triple-echo multi-spoke radial FLASH. Magn Reson Med 2019; 82:1000-1011. [PMID: 31033051 DOI: 10.1002/mrm.27795] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Revised: 03/26/2019] [Accepted: 04/10/2019] [Indexed: 11/05/2022]
Abstract
PURPOSE To achieve dynamic water/fat separation and B 0 field inhomogeneity mapping via model-based reconstructions of undersampled triple-echo multi-spoke radial FLASH acquisitions. METHODS This work introduces an undersampled triple-echo multi-spoke radial FLASH sequence, which uses (i) complementary radial spokes per echo train for faster spatial encoding, (ii) asymmetric echoes for flexible and nonuniform echo spacing, and (iii) a golden angle increment across frames for optimal k-space coverage. Joint estimation of water, fat, B 0 inhomogeneity, and coil sensitivity maps from undersampled triple-echo data poses a nonlinear and non-convex inverse problem which is solved by a model-based reconstruction with suitable regularization. The developed methods are validated using phantom experiments with different degrees of undersampling. Real-time MRI studies of the knee, liver, and heart are conducted without prospective gating or retrospective data sorting at temporal resolutions of 70, 158, and 40 ms, respectively. RESULTS Up to 18-fold undersampling is achieved in this work. Even in the presence of rapid physiological motion, large B 0 field inhomogeneities, and phase wrapping, the model-based reconstruction yields reliably separated water/fat maps in conjunction with spatially smooth inhomogeneity maps. CONCLUSIONS The combination of a triple-echo acquisition and joint reconstruction technique provides a practical solution to time-resolved and motion robust water/fat separation at high spatial and temporal resolution.
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Affiliation(s)
- Zhengguo Tan
- Biomedizinische NMR, Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany.,Institute for Diagnostic and Interventional Radiology, University Medical Center Göttingen, Göttingen, Germany
| | - Dirk Voit
- Biomedizinische NMR, Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany
| | - Jost M Kollmeier
- Biomedizinische NMR, Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany
| | - Martin Uecker
- Institute for Diagnostic and Interventional Radiology, University Medical Center Göttingen, Göttingen, Germany.,German Center for Cardiovascular Research (DZHK), partner site Göttingen, Göttingen, Germany
| | - Jens Frahm
- Biomedizinische NMR, Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany.,German Center for Cardiovascular Research (DZHK), partner site Göttingen, Göttingen, Germany
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14
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van Rijssel MJ, Zijlstra F, Seevinck PR, Luijten PR, Gilhuijs KGA, Klomp DWJ, Pluim JPW. Reducing distortions in echo-planar breast imaging at ultrahigh field with high-resolution off-resonance maps. Magn Reson Med 2019; 82:425-435. [PMID: 30825245 PMCID: PMC6593992 DOI: 10.1002/mrm.27701] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Accepted: 01/30/2019] [Indexed: 11/11/2022]
Abstract
PURPOSE DWI is a promising modality in breast MRI, but its clinical acceptance is slow. Analysis of DWI is hampered by geometric distortion artifacts, which are caused by off-resonant spins in combination with the low phase-encoding bandwidth of the EPI sequence used. Existing correction methods assume smooth off-resonance fields, which we show to be invalid in the human breast, where high discontinuities arise at tissue interfaces. METHODS We developed a distortion correction method that incorporates high-resolution off-resonance maps to better solve for severe distortions at tissue interfaces. The method was evaluated quantitatively both ex vivo in a porcine tissue phantom and in vivo in 5 healthy volunteers. The added value of high-resolution off-resonance maps was tested using a Wilcoxon signed rank test comparing the quantitative results obtained with a low-resolution off-resonance map with those obtained with a high-resolution map. RESULTS Distortion correction using low-resolution off-resonance maps corrected most of the distortions, as expected. Still, all quantitative comparison metrics showed increased conformity between the corrected EPI images and a high-bandwidth reference scan for both the ex vivo and in vivo experiments. All metrics showed a significant improvement when a high-resolution off-resonance map was used (P < 0.05), in particular at tissue boundaries. CONCLUSION The use of off-resonance maps of a resolution higher than EPI scans significantly improves upon existing distortion correction techniques, specifically by superior correction at glandular tissue boundaries.
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Affiliation(s)
| | - Frank Zijlstra
- Center for Image Sciences, UMC Utrecht, Utrecht, The Netherlands
| | - Peter R Seevinck
- Center for Image Sciences, UMC Utrecht, Utrecht, The Netherlands
| | - Peter R Luijten
- Center for Image Sciences, UMC Utrecht, Utrecht, The Netherlands
| | | | - Dennis W J Klomp
- Center for Image Sciences, UMC Utrecht, Utrecht, The Netherlands
| | - Josien P W Pluim
- Center for Image Sciences, UMC Utrecht, Utrecht, The Netherlands.,Department of Biomedical Engineering, Technische Universiteit Eindhoven, Eindhoven, The Netherlands
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15
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Mozes FE, Tunnicliffe EM, Moolla A, Marjot T, Levick CK, Pavlides M, Robson MD. Mapping tissue water T 1 in the liver using the MOLLI T 1 method in the presence of fat, iron and B 0 inhomogeneity. NMR Biomed 2019; 32:e4030. [PMID: 30462873 PMCID: PMC6492199 DOI: 10.1002/nbm.4030] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Revised: 09/11/2018] [Accepted: 09/20/2018] [Indexed: 05/11/2023]
Abstract
Modified Look-Locker inversion recovery (MOLLI) T1 mapping sequences can be useful in cardiac and liver tissue characterization, but determining underlying water T1 is confounded by iron, fat and frequency offsets. This article proposes an algorithm that provides an independent water MOLLI T1 (referred to as on-resonance water T1 ) that would have been measured if a subject had no fat and normal iron, and imaging had been done on resonance. Fifteen NiCl2 -doped agar phantoms with different peanut oil concentrations and 30 adults with various liver diseases, nineteen (63.3%) with liver steatosis, were scanned at 3 T using the shortened MOLLI (shMOLLI) T1 mapping, multiple-echo spoiled gradient-recalled echo and 1 H MR spectroscopy sequences. An algorithm based on Bloch equations was built in MATLAB, and water shMOLLI T1 values of both phantoms and human participants were determined. The quality of the algorithm's result was assessed by Pearson's correlation coefficient between shMOLLI T1 values and spectroscopically determined T1 values of the water, and by linear regression analysis. Correlation between shMOLLI and spectroscopy-based T1 values increased, from r = 0.910 (P < 0.001) to r = 0.998 (P < 0.001) in phantoms and from r = 0.493 (for iron-only correction; P = 0.005) to r = 0.771 (for iron, fat and off-resonance correction; P < 0.001) in patients. Linear regression analysis revealed that the determined water shMOLLI T1 values in patients were independent of fat and iron. It can be concluded that determination of on-resonance water (sh)MOLLI T1 independent of fat, iron and macroscopic field inhomogeneities was possible in phantoms and human subjects.
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Affiliation(s)
- Ferenc E. Mozes
- The University of Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, John Radcliffe HospitalOxfordUK
| | - Elizabeth M. Tunnicliffe
- The University of Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, John Radcliffe HospitalOxfordUK
| | - Ahmad Moolla
- The University of Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, John Radcliffe HospitalOxfordUK
- Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM)University of Oxford, Churchill HospitalOxfordUK
| | - Thomas Marjot
- Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM)University of Oxford, Churchill HospitalOxfordUK
| | - Christina K. Levick
- The University of Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, John Radcliffe HospitalOxfordUK
- Translational Gastroenterology UnitUniversity of Oxford, John Radcliffe HospitalOxfordUK
| | - Michael Pavlides
- The University of Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, John Radcliffe HospitalOxfordUK
- Translational Gastroenterology UnitUniversity of Oxford, John Radcliffe HospitalOxfordUK
- Oxford NIHR Biomedical Research CentreOxfordUK
| | - Matthew D. Robson
- The University of Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, John Radcliffe HospitalOxfordUK
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16
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Lau JYC, Geraghty BJ, Chen AP, Cunningham CH. Improved tolerance to off-resonance in spectral-spatial EPI of hyperpolarized [1- 13 C]pyruvate and metabolites. Magn Reson Med 2018; 80:925-934. [PMID: 29380423 DOI: 10.1002/mrm.27086] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2017] [Revised: 11/28/2017] [Accepted: 12/24/2017] [Indexed: 12/16/2022]
Affiliation(s)
- Justin Y C Lau
- Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada.,Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
| | - Benjamin J Geraghty
- Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada.,Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
| | | | - Charles H Cunningham
- Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada.,Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
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17
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Zhao L, Vidorreta M, Soman S, Detre JA, Alsop DC. Improving the robustness of pseudo-continuous arterial spin labeling to off-resonance and pulsatile flow velocity. Magn Reson Med 2017; 78:1342-1351. [PMID: 27774656 PMCID: PMC5848499 DOI: 10.1002/mrm.26513] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Revised: 09/01/2016] [Accepted: 09/26/2016] [Indexed: 01/22/2023]
Abstract
PURPOSE To improve pseudo-continuous arterial spin labeling (PCASL) robustness to off-resonance and pulsatile blood flow velocity. METHODS Bloch equations were solved to evaluate the effect of labeling parameters in a pulsatile flow model for a range of off-resonance. Experimental confirmation was achieved in volunteers using linear phase increase between labeling pulses to approximate off-resonance errors. We first assessed the location of the labeling plane in four volunteers. Next, we explored a range of parameters-including balanced and unbalanced gradients-in five more volunteers at an optimal labeling plane location. RESULTS Simulations demonstrated that 1) high velocities are vulnerable to off-resonance, 2) unbalanced PCASL outperforms balanced PCASL, 3) increased B1 and low average gradient improve the labeling efficiency for high-velocity flow, and 4) a low ratio of selective to average gradient improves off-resonance robustness. A good agreement between theory and experiment was observed. CONCLUSION The robustness of PCASL can be increased by selecting an unbalanced scheme with a low average gradient (0.5 mT/m), a low ratio (7×) of selective to average gradients, and the highest feasible B1 (1.8 μT). Placing the labeling plane above the carotid bifurcation and below the V3 segment, usually between the second and third vertebrae, yielded robust results. Magn Reson Med 78:1342-1351, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Li Zhao
- Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA
| | - Marta Vidorreta
- Department of Radiology, University of Pennsylvania, Philadelphia, PA
- Department of Neurology, University of Pennsylvania, Philadelphia, PA
| | - Salil Soman
- Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA
| | - John A. Detre
- Department of Radiology, University of Pennsylvania, Philadelphia, PA
- Department of Neurology, University of Pennsylvania, Philadelphia, PA
| | - David C. Alsop
- Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA
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18
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Shcherbakova Y, van den Berg CAT, Moonen CTW, Bartels LW. PLANET: An ellipse fitting approach for simultaneous T 1 and T 2 mapping using phase-cycled balanced steady-state free precession. Magn Reson Med 2017; 79:711-722. [PMID: 28543430 PMCID: PMC5811804 DOI: 10.1002/mrm.26717] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Revised: 03/23/2017] [Accepted: 03/26/2017] [Indexed: 11/09/2022]
Abstract
Purpose To demonstrate the feasibility of a novel, ellipse fitting approach, named PLANET, for simultaneous estimation of relaxation times T1 and T2 from a single 3D phase‐cycled balanced steady‐state free precession (bSSFP) sequence. Methods A method is presented in which the elliptical signal model is used to describe the phase‐cycled bSSFP steady‐state signal. The fitting of the model to the acquired data is reformulated into a linear convex problem, which is solved directly by a linear least squares method, specific to ellipses. Subsequently, the relaxation times T1 and T2, the banding free magnitude, and the off‐resonance are calculated from the fitting results. Results Maps of T1 and T2, as well as an off‐resonance and a banding free magnitude can be simultaneously, quickly, and robustly estimated from a single 3D phase‐cycled bSSFP sequence. The feasibility of the method was demonstrated in a phantom and in the brain of healthy volunteers on a clinical MR scanner. The results were in good agreement for the phantom, but a systematic underestimation of T1 was observed in the brain. Conclusion The presented method allows for accurate mapping of relaxation times and off‐resonance, and for the reconstruction of banding free magnitude images at realistic signal‐to‐noise ratios. Magn Reson Med 79:711–722, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.
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Affiliation(s)
- Yulia Shcherbakova
- Center for Image Sciences, Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Cornelis A T van den Berg
- Department of Radiotherapy, Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Chrit T W Moonen
- Center for Image Sciences, Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Lambertus W Bartels
- Center for Image Sciences, Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands
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19
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Wiens CN, Artz NS, Jang H, McMillan AB, Reeder SB. Externally calibrated parallel imaging for 3D multispectral imaging near metallic implants using broadband ultrashort echo time imaging. Magn Reson Med 2016; 77:2303-2309. [PMID: 27403613 DOI: 10.1002/mrm.26327] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2016] [Revised: 06/07/2016] [Accepted: 06/09/2016] [Indexed: 01/23/2023]
Abstract
PURPOSE To develop an externally calibrated parallel imaging technique for three-dimensional multispectral imaging (3D-MSI) in the presence of metallic implants. THEORY AND METHODS A fast, ultrashort echo time (UTE) calibration acquisition is proposed to enable externally calibrated parallel imaging techniques near metallic implants. The proposed calibration acquisition uses a broadband radiofrequency (RF) pulse to excite the off-resonance induced by the metallic implant, fully phase-encoded imaging to prevent in-plane distortions, and UTE to capture rapidly decaying signal. The performance of the externally calibrated parallel imaging reconstructions was assessed using phantoms and in vivo examples. RESULTS Phantom and in vivo comparisons to self-calibrated parallel imaging acquisitions show that significant reductions in acquisition times can be achieved using externally calibrated parallel imaging with comparable image quality. Acquisition time reductions are particularly large for fully phase-encoded methods such as spectrally resolved fully phase-encoded three-dimensional (3D) fast spin-echo (SR-FPE), in which scan time reductions of up to 8 min were obtained. CONCLUSION A fully phase-encoded acquisition with broadband excitation and UTE enabled externally calibrated parallel imaging for 3D-MSI, eliminating the need for repeated calibration regions at each frequency offset. Significant reductions in acquisition time can be achieved, particularly for fully phase-encoded methods like SR-FPE. Magn Reson Med 77:2303-2309, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Curtis N Wiens
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA
| | - Nathan S Artz
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.,Department of Diagnostic Imaging, St. Jude Children's St. Jude Children's Research Hospital, Memphis, Tennessee, USA
| | - Hyungseok Jang
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.,Department of Electrical and Computer Engineering, University of Wisconsin, Madison, Wisconsin, USA
| | - Alan B McMillan
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA
| | - Scott B Reeder
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.,Department of Medical Physics, University of Wisconsin, Madison, Wisconsin, USA.,Department of Biomedical Engineering, University of Wisconsin, Madison, Wisconsin, USA.,Department of Medicine, University of Wisconsin, Madison, Wisconsin, USA.,Dept. of Emergency Medicine, University of Wisconsin, Madison, Wisconsin, USA
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20
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Bano W, Feliciano H, Coristine AJ, Stuber M, van Heeswijk RB. On the accuracy and precision of cardiac magnetic resonance T 2 mapping: A high-resolution radial study using adiabatic T 2 preparation at 3 T. Magn Reson Med 2016; 77:159-169. [PMID: 26762815 DOI: 10.1002/mrm.26107] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Revised: 12/02/2015] [Accepted: 12/03/2015] [Indexed: 11/07/2022]
Abstract
PURPOSE The goal of this study was to characterize the accuracy and precision of cardiac T2 mapping as a function of different factors including low signal-to-noise ratio (SNR), imaging in systole, and off-resonance frequencies. METHODS Bloch equation and Monte Carlo simulations were used to determine the influence of SNR and the choice of T2 preparation echo time (TET2prep ) increments on the accuracy and precision of high-resolution radial cardiac T2 mapping at 3.0 T. Healthy volunteers were scanned to establish the difference in precision and inter- and intraobserver variability between T2 mapping in diastole and systole, as well as the effect of SNR and off-resonance frequencies on the accuracy of T2 maps. RESULTS The simulations demonstrated that a TET2prep increment of ∼0.75 times the T2 value of interest optimally increases the precision of the T2 fit. Systolic T2 maps were found to have a higher precision (P = 0.002), but similar inter- and intraobserver variability compared with diastolic T2 maps, whereas off-resonance frequencies beyond ± 100 Hz cause a significant decrease in both accuracy and precision (P < 0.05). CONCLUSION This evaluation of the accuracy and precision of cardiac T2 mapping characterizes the major vulnerabilities of the technique and will help guide protocol definition of studies that include T2 mapping. Magn Reson Med 77:159-169, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Wajiha Bano
- Cardiovascular Magnetic Resonance Research Center, Department of Radiology, University Hospital and University of Lausanne, Lausanne, Switzerland
| | - Hélène Feliciano
- Cardiovascular Magnetic Resonance Research Center, Department of Radiology, University Hospital and University of Lausanne, Lausanne, Switzerland
| | - Andrew J Coristine
- Cardiovascular Magnetic Resonance Research Center, Department of Radiology, University Hospital and University of Lausanne, Lausanne, Switzerland
| | - Matthias Stuber
- Cardiovascular Magnetic Resonance Research Center, Department of Radiology, University Hospital and University of Lausanne, Lausanne, Switzerland
| | - Ruud B van Heeswijk
- Cardiovascular Magnetic Resonance Research Center, Department of Radiology, University Hospital and University of Lausanne, Lausanne, Switzerland
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21
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Abstract
Image blurring due to off-resonance and fast T 2* signal decay is a common issue in radial ultrashort echo time MRI sequences. One solution is to use a higher readout bandwidth, but this may be impractical for some techniques like pointwise encoding time reduction with radial acquisition (PETRA), which is a hybrid method of zero echo time and single point imaging techniques. Specifically, PETRA has severe specific absorption rate (SAR) and radiofrequency (RF) pulse peak power limitations when using higher bandwidths in human measurements. In this study, we introduce gradient modulation (GM) to PETRA to reduce image blurring artifacts while keeping SAR and RF peak power low. Tolerance of GM-PETRA to image blurring was evaluated in simulations and experiments by comparing with the conventional PETRA technique. We performed inner ear imaging of a healthy subject at 7T. GM-PETRA showed significantly less image blurring due to off-resonance and fast T2* signal decay compared to PETRA. In in vivo imaging, GM-PETRA nicely captured complex structures of the inner ear such as the cochlea and semicircular canals. Gradient modulation can improve the PETRA image quality and mitigate SAR and RF peak power limitations without special hardware modification in clinical scanners.
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Affiliation(s)
- Naoharu Kobayashi
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, MN, USA
| | - Ute Goerke
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, MN, USA
| | - Luning Wang
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, MN, USA
| | - Jutta Ellermann
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, MN, USA
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, MN, USA
| | - Michael Garwood
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, MN, USA
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22
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Smith MR, Artz NS, Wiens C, Hernando D, Reeder SB. Characterizing the limits of MRI near metallic prostheses. Magn Reson Med 2014; 74:1564-73. [PMID: 25483410 DOI: 10.1002/mrm.25540] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Revised: 10/22/2014] [Accepted: 10/27/2014] [Indexed: 12/11/2022]
Abstract
PURPOSE To characterize the fundamental limits of MRI near metallic implants on RF excitation, frequency encoding, and chemical shift-encoding water-fat separation. METHODS Multicomponent three-dimensional (3D) digital models of a total hip and a total knee replacement were used to construct material-specific susceptibility maps. The fundamental limits and spatial relationship of imaging near metallic prostheses were investigated as a function of distance from the prosthetic surface by calculating 3D field map perturbations using a well-validated k-space based dipole kernel. RESULTS Regions limited by the bandwidth of RF excitation overlap substantially with those fundamentally limited by frequency encoding. Rapid breakdown of water-fat separation occurs once the intravoxel off-resonance exceeds ∼6 ppm over a full range of fat fractions (0%-100%) and SNR (5-100). CONCLUSION Current 3D multispectral imaging methods would not benefit greatly from exciting spins beyond ±12 kHz despite the presence of signal that lies outside of this range from tissue directly adjacent to the metallic implants. Methods such as phase encoding in all three spatial dimensions are necessary to spatially resolve spins beyond an excitation bandwidth of ±12 kHz. The approach described in this study provides a benchmark for the capabilities of current imaging techniques to guide development of new MRI methods for imaging near metal.
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Affiliation(s)
- Matthew R Smith
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA
| | - Nathan S Artz
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA
| | - Curtis Wiens
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA
| | - Diego Hernando
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA
| | - Scott B Reeder
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.,Department of Medical Physics, University of Wisconsin, Madison, Wisconsin, USA.,Department of Biomedical Engineering, University of Wisconsin, Madison, Wisconsin, USA.,Department of Medicine, University of Wisconsin, Madison, Wisconsin, USA.,Department of Emergency Medicine, University of Wisconsin, Madison, Wisconsin, USA
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Smith MR, Artz NS, Koch KM, Samsonov A, Reeder SB. Accelerating sequences in the presence of metal by exploiting the spatial distribution of off-resonance. Magn Reson Med 2014; 72:1658-67. [PMID: 24431210 DOI: 10.1002/mrm.25087] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2013] [Revised: 11/26/2013] [Accepted: 11/26/2013] [Indexed: 11/08/2022]
Abstract
PURPOSE To demonstrate feasibility of exploiting the spatial distribution of off-resonance surrounding metallic implants for accelerating multispectral imaging techniques. THEORY AND METHODS Multispectral imaging (MSI) techniques perform time-consuming independent three-dimensional acquisitions with varying radio frequency offsets to address the extreme off-resonance from metallic implants. Each off-resonance bin provides a unique spatial sensitivity that is analogous to the sensitivity of a receiver coil and, therefore, provides a unique opportunity for acceleration. Fully sampled MSI was performed to demonstrate retrospective acceleration. A uniform sampling pattern across off-resonance bins was compared with several adaptive sampling strategies using a total hip replacement phantom. Monte Carlo simulations were performed to compare noise propagation of two of these strategies. With a total knee replacement phantom, positive and negative off-resonance bins were strategically sampled with respect to the B0 field to minimize aliasing. Reconstructions were performed with a parallel imaging framework to demonstrate retrospective acceleration. RESULTS An adaptive sampling scheme dramatically improved reconstruction quality, which was supported by the noise propagation analysis. Independent acceleration of negative and positive off-resonance bins demonstrated reduced overlapping of aliased signal to improve the reconstruction. CONCLUSION This work presents the feasibility of acceleration in the presence of metal by exploiting the spatial sensitivities of off-resonance bins.
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Affiliation(s)
- Matthew R Smith
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA
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Abstract
The longitudinal relaxation time constant (T1) of the myocardium is altered in various disease states due to increased water content or other changes to the local molecular environment. Changes in both native T1 and T1 following administration of gadolinium (Gd) based contrast agents are considered important biomarkers and multiple methods have been suggested for quantifying myocardial T1 in vivo. Characterization of the native T1 of myocardial tissue may be used to detect and assess various cardiomyopathies while measurement of T1 with extracellular Gd based contrast agents provides additional information about the extracellular volume (ECV) fraction. The latter is particularly valuable for more diffuse diseases that are more challenging to detect using conventional late gadolinium enhancement (LGE). Both T1 and ECV measures have been shown to have important prognostic significance. T1-mapping has the potential to detect and quantify diffuse fibrosis at an early stage provided that the measurements have adequate reproducibility. Inversion recovery methods such as MOLLI have excellent precision and are highly reproducible when using tightly controlled protocols. The MOLLI method is widely available and is relatively mature. The accuracy of inversion recovery techniques is affected significantly by magnetization transfer (MT). Despite this, the estimate of apparent T1 using inversion recovery is a sensitive measure, which has been demonstrated to be a useful tool in characterizing tissue and discriminating disease. Saturation recovery methods have the potential to provide a more accurate measurement of T1 that is less sensitive to MT as well as other factors. Saturation recovery techniques are, however, noisier and somewhat more artifact prone and have not demonstrated the same level of reproducibility at this point in time.This review article focuses on the technical aspects of key T1-mapping methods and imaging protocols and describes their limitations including the factors that influence their accuracy, precision, and reproducibility.
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Affiliation(s)
- Peter Kellman
- National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Michael S Hansen
- National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
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Björk M, Ingle RR, Gudmundson E, Stoica P, Nishimura DG, Barral JK. Parameter estimation approach to banding artifact reduction in balanced steady-state free precession. Magn Reson Med 2013; 72:880-92. [PMID: 24166591 DOI: 10.1002/mrm.24986] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Revised: 08/13/2013] [Accepted: 09/02/2013] [Indexed: 11/11/2022]
Abstract
PURPOSE The balanced steady-state free precession (bSSFP) pulse sequence has shown to be of great interest due to its high signal-to-noise ratio efficiency. However, bSSFP images often suffer from banding artifacts due to off-resonance effects, which we aim to minimize in this article. METHODS We present a general and fast two-step algorithm for 1) estimating the unknowns in the bSSFP signal model from multiple phase-cycled acquisitions, and 2) reconstructing band-free images. The first step, linearization for off-resonance estimation (LORE), solves the nonlinear problem approximately by a robust linear approach. The second step applies a Gauss-Newton algorithm, initialized by LORE, to minimize the nonlinear least squares criterion. We name the full algorithm LORE-GN. RESULTS We derive the Cramér-Rao bound, a theoretical lower bound of the variance for any unbiased estimator, and show that LORE-GN is statistically efficient. Furthermore, we show that simultaneous estimation of T1 and T2 from phase-cycled bSSFP is difficult, since the Cramér-Rao bound is high at common signal-to-noise ratio. Using simulated, phantom, and in vivo data, we illustrate the band-reduction capabilities of LORE-GN compared to other techniques, such as sum-of-squares. CONCLUSION Using LORE-GN we can successfully minimize banding artifacts in bSSFP.
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Affiliation(s)
- Marcus Björk
- Department of Information Technology, Uppsala University, Uppsala, Sweden
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Kellman P, Herzka DA, Arai AE, Hansen MS. Influence of Off-resonance in myocardial T1-mapping using SSFP based MOLLI method. J Cardiovasc Magn Reson 2013; 15:63. [PMID: 23875774 PMCID: PMC3733653 DOI: 10.1186/1532-429x-15-63] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Accepted: 07/07/2013] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND Myocardial T1-mapping methods such as MOLLI use SSFP readout and are prone to frequency-dependent error in T1-measurement. A significant error in T1 may result at relatively small off-resonance frequencies that are well within the region without banding artifacts. METHODS The sensitivity of T1-estimates based on the SSFP based MOLLI sequence to errors in center frequency are calculated by means of a Bloch simulation and validated by phantom measurements. Typical off-resonance errors following local cardiac shimming are determined by field mapping at both 1.5 and 3.0T. In vivo examples demonstrate the artifactual appearance of T1-maps in the presence of off-resonance variation. RESULTS Off-resonance varied 61.8 ± 15.5 Hz (mean ± SD, n = 18) across the heart at 1.5T and 125.0 ± 40.6 Hz (mean ± SD, n = 18) at 3.0T. For T1 = 1000 ms, the variation in T1 due to off-resonance variation was approximately 20 ms at 62 Hz, and > 50 ms at 125 Hz. CONCLUSIONS Regional variations due to the inability to completely shim the B0-field variation around the heart appear as regional variation in T1, which is artifactual.
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Affiliation(s)
- Peter Kellman
- National Heart, Lung, and Blood Institute, National Institutes of Health, DHHS, 10 Center Drive MSC-1061, Bethesda, MD 20892, USA
| | - Daniel A Herzka
- Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Andrew E Arai
- National Heart, Lung, and Blood Institute, National Institutes of Health, DHHS, 10 Center Drive MSC-1061, Bethesda, MD 20892, USA
| | - Michael Schacht Hansen
- National Heart, Lung, and Blood Institute, National Institutes of Health, DHHS, 10 Center Drive MSC-1061, Bethesda, MD 20892, USA
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Schneider R, Ritter D, Haueisen J, Pfeuffer J. B0-informed variable density trajectory design for enhanced correction of off-resonance effects in parallel transmission. Magn Reson Med 2013; 71:1381-93. [PMID: 23716347 DOI: 10.1002/mrm.24780] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2012] [Revised: 02/18/2013] [Accepted: 03/30/2013] [Indexed: 11/06/2022]
Abstract
PURPOSE To improve B1 and B0 inhomogeneity mitigation performance of spatially selective radio-frequency (RF) pulses in parallel transmission while decreasing RF pulse power. Further enhancement of off-resonance correction for rectilinear spoke-trajectory-based RF pulses with known residual geometric distortions after optimization. METHODS The appropriate definition of the target magnetization pattern is discussed regarding the maximum physical excitation resolution. Furthermore, a novel variable-density trajectory design is introduced, which subsamples accrued B0 phase error elevations in k-space. A simulation study (echo-planar and spiral 2DRF) at different off-resonance levels and pulse acceleration factors was pursued using data from a whole-body 2-channel parallel transmit 3T MRI system. The new trajectory design for echo-planar 2DRF was validated in human in-vivo experiments. RESULTS Proper target pattern definition can require spatial filtering, such that RF pulse optimization is prevented from lower excitation performance with significant higher RF power level. The new trajectory design proposed can considerably improve off-resonance compensation, while further reducing the RF power, e.g., 43% less RMSE with 79% less RF power for spoke based pulses. CONCLUSION The proposed methods offer significant improvements of the excitation performance (homogeneity and acceleration), while significantly decreasing the RF power. Furthermore, single-channel transmit RF pulse performance can be similarly improved.
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Affiliation(s)
- Rainer Schneider
- MR Application Development, Siemens Healthcare, Erlangen, Germany; Institute of Biomedical Engineering and Informatics, Ilmenau University of Technology, Ilmenau, Germany
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Iñarrea J. Off-resonance magnetoresistance spike in irradiated ultraclean 2D electron systems. Nanoscale Res Lett 2013; 8:241. [PMID: 23680117 PMCID: PMC3664069 DOI: 10.1186/1556-276x-8-241] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2012] [Accepted: 04/06/2013] [Indexed: 06/02/2023]
Abstract
: We report on the theoretical studies of a recently discovered strong radiation-induced magnetoresistance spike obtained in ultraclean two-dimensional electron systems at low temperatures. The most striking feature of this spike is that it shows up on the second harmonic of the cyclotron resonance. We apply the radiation-driven electron orbits model in the ultraclean scenario. Accordingly, we calculate the new average advanced distance by the electron in a scattering event which will define the unexpected resonance spike position. Calculated results are in good agreement with experiments.
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Affiliation(s)
- Jesus Iñarrea
- Escuela Politécnica Superior, Universidad Carlos III, Leganes, Madrid, 28911, Spain.
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Reyhan M, Natsuaki Y, Ennis DB. Off-resonance insensitive complementary SPAtial Modulation of Magnetization (ORI-CSPAMM) for quantification of left ventricular twist. J Magn Reson Imaging 2013; 39:339-45. [PMID: 23625854 DOI: 10.1002/jmri.24154] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2012] [Accepted: 03/05/2013] [Indexed: 12/31/2022] Open
Abstract
PURPOSE To evaluate Off Resonance Insensitive Complementary SPAtial Modulation of Magnetization (ORI-CSPAMM) and Fourier Analysis of STimulated echoes (FAST) for the quantification of left ventricular (LV) systolic and diastolic function and compare it with the previously validated FAST+SPAMM technique. MATERIALS AND METHODS LV short-axis tagged images were acquired with ORI-CSPAMM and SPAMM in healthy volunteers (n = 13). The FAST method was used to automatically estimate LV systolic and diastolic twist parameters from rotation of the stimulated echo and stimulated anti-echo about the middle of k-space subsequent to ∼3 min of user interaction. RESULTS There was no significant difference between measures obtained for FAST+ORI-CSPAMM and FAST+SPAMM for mean peak twist (12.9 ± 3.4° versus 11.9 ± 4.0°; P = 0.4), torsion (3.3 ± 0.9°/cm versus 2.9 ± 1.0°/cm, P = 0.3), circumferential-longitudinal shear angle (9.1 ± 3.0° versus 8.2 ± 3.4°, P = 0.3), twisting rate (79.6 ± 20.2°/s versus 68.2 ± 23.4°/s, P = 0.1), untwisting rate (-117.5 ± 31.4°/s versus -106.6 ± 32.4°/s, P = 0.3), normalized untwisting rate (-9.3 ± 2.0/s versus -9.9 ± 4.4/s, P = 0.7), and time of peak twist (281 ± 18 ms versus 293 ± 25 ms, P = 0.04). FAST+ORI-CSPAMM also provided measures of duration of untwisting (148 ± 21 ms) and the ratio of rapid untwisting to peak twist (0.9 ± 0.3). Bland-Altman analysis of FAST+ORI-CSPAMM and FAST+SPAMM twist data demonstrates excellent agreement with a bias of -0.1° and 95% confidence intervals of (-1.0°, 3.2°). CONCLUSION FAST+ORI-CSPAMM is a semi-automated method that provides a quick and quantitative assessment of LV systolic and diastolic twist and torsion. ORI-CSPAMM corrects off-resonance accrued during tagging preparation and readout and visibly removes chemical shift from the tagging pattern, which confers greater robustness to the derived quantitative measures.
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Affiliation(s)
- Meral Reyhan
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, California, USA; Biomedical Physics Interdepartmental Program, University of California, Los Angeles, California, USA
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Ye Y, Hu J, Haacke EM. Robust selective signal suppression using binomial off-resonant rectangular (BORR) pulses. J Magn Reson Imaging 2013; 39:195-202. [PMID: 23589344 DOI: 10.1002/jmri.24149] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2012] [Accepted: 03/01/2013] [Indexed: 12/13/2022] Open
Abstract
PURPOSE To study the selective signal suppression capability of a binomial off-resonant rectangular (BORR) radiofrequency pulse method. MATERIALS AND METHODS The BORR pulse consists of two consecutive rectangular pulses with a phase difference of π. The exact solution of the Bloch equations was used to simulate its frequency response. The BORR pulse was implemented in a gradient echo sequence and tested on phantoms, the knee, and the breast. RESULTS The frequency response of the BORR pulse acquired on the phantom confirmed the theory. Broad suppression bands ensured high suppression efficiency and robustness in both in vitro and in vivo scans compared with other saturation pulses. CONCLUSION The BORR pulse method provides a simple, efficient, and robust selective signal suppression alternative for three-dimensional short TR (repetition time) imaging.
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Affiliation(s)
- Yongquan Ye
- Department of Radiology, Wayne State University, Detroit, Michigan, USA
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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 Magn Reson Part A Bridg Educ Res 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] [What about the content of this article? (0)] [Affiliation(s)] [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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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] [What about the content of this article? (0)] [Affiliation(s)] [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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Lee D, Santos JM, Hu BS, Pauly JM, Kerr AB. Reducing artifacts in one-dimensional Fourier velocity encoding for fast and pulsatile flow. Magn Reson Med 2012; 68:1876-85. [PMID: 22457248 PMCID: PMC3499673 DOI: 10.1002/mrm.24212] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2011] [Revised: 12/27/2011] [Accepted: 01/20/2012] [Indexed: 11/08/2022]
Abstract
When evaluating the severity of valvular stenosis, the peak velocity of the blood flow is routinely used to estimate the transvalvular pressure gradient. One-dimensional Fourier velocity encoding effectively detects the peak velocity with an ungated time series of spatially resolved velocity spectra in real time. However, measurement accuracy can be degraded by the pulsatile and turbulent nature of stenotic flow and the existence of spatially varying off-resonance. In this work, we investigate the feasibility of improving the peak velocity detection capability of one-dimensional Fourier velocity encoding for stenotic flow using a novel echo-shifted interleaved readout combined with a variable-density circular k-space trajectory. The shorter echo and readout times of the echo-shifted interleaved acquisitions are designed to reduce sensitivity to off-resonance. Preliminary results from limited phantom and in vivo results also indicate that some artifacts from pulsatile flow appear to be suppressed when using this trajectory compared to conventional single-shot readouts, suggesting that peak velocity detection may be improved. The efficiency of the new trajectory improves the temporal and spatial resolutions. To realize the proposed readout, a novel multipoint-traversing algorithm is introduced for flexible and automated gradient-waveform design.
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Affiliation(s)
- Daeho Lee
- Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
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Lee CY, Li Z, Pipe JG, Debbins JP. Turboprop+: enhanced Turboprop diffusion-weighted imaging with a new phase correction. Magn Reson Med 2012; 70:497-503. [PMID: 23023533 DOI: 10.1002/mrm.24481] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Revised: 08/13/2012] [Accepted: 08/13/2012] [Indexed: 01/01/2023]
Abstract
Faster periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) diffusion-weighted imaging acquisitions, such as Turboprop and X-prop, remain subject to phase errors inherent to a gradient echo readout, which ultimately limits the applied turbo factor (number of gradient echoes between each pair of radiofrequency refocusing pulses) and, thus, scan time reductions. This study introduces a new phase correction to Turboprop, called Turboprop+. This technique employs calibration blades, which generate 2-D phase error maps and are rotated in accordance with the data blades, to correct phase errors arising from off-resonance and system imperfections. The results demonstrate that with a small increase in scan time for collecting calibration blades, Turboprop+ had a superior immunity to the off-resonance-related artifacts when compared to standard Turboprop and recently proposed X-prop with the high turbo factor (turbo factor = 7). Thus, low specific absorption rate and short scan time can be achieved in Turboprop+ using a high turbo factor, whereas off-resonance related artifacts are minimized.
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Affiliation(s)
- Chu-Yu Lee
- School of Electrical, Computer, and Energy Engineering, Ira A, Fulton School of Engineering, Arizona State University, Tempe, Arizona, USA
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