1
|
Ipek TD, Han V, Maravilla JA, Lustig M, Liu C. Multiphoton simultaneous multislice imaging. Magn Reson Med 2024; 92:1584-1599. [PMID: 38899346 DOI: 10.1002/mrm.30148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Revised: 03/20/2024] [Accepted: 04/22/2024] [Indexed: 06/21/2024]
Abstract
PURPOSE To develop multiphoton excitation techniques for simultaneous multislice (SMS) imaging and evaluate their performance and specific absorption rate (SAR) benefit. To improve multiphoton SMS reconstruction quality with a novel CAIPIRINHA (controlled aliasing in parallel imaging results in higher acceleration) design. THEORY AND METHODS When a conventional single-slice RF field is applied together with an oscillating gradient field, the two can combine to generate multiphoton excitation at multiple discrete spatial locations. Because the conventional RF is reused at multiple spatial locations, multiphoton excitation offers reduced SAR for SMS applications. CAIPIRINHA shifts are often used to improve parallel-imaging acceleration. Interestingly, CAIPIRINHA-type shifts can be obtained for multiphoton SMS by updating the oscillating gradient phase at every phase encode. In this work, both a gradient-echo and a spin-echo sequence with multiphoton CAIPIRINHA-SMS excitation pulses are implemented for in vivo human imaging at 3 T. RESULTS For three slices, multiphoton SMS provides a 51% reduction in SAR compared with conventional superposition SMS, whereas for five slices, SAR is reduced by 66%. Multiphoton SMS outperforms PINS (power independent of number of slices) and MultiPINS in terms of SAR reduction especially when the pulse duration is short, slices are thin, and/or the slice spacing is large. A custom CAIPIRINHA phase-encoding design for multiphoton SMS significantly improves reconstruction quality. CONCLUSION Multiphoton SMS excitation can be obtained by combining conventional single-slice RF pulses with an oscillating gradient and offers significant SAR benefits compared with conventional superposition SMS. A novel CAIPIRINHA design allows higher multiband factors for multiphoton SMS imaging.
Collapse
Affiliation(s)
- Tanya Deniz Ipek
- Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, California, USA
| | - Victor Han
- Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, California, USA
| | - Julian Adolfo Maravilla
- Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, California, USA
| | - Michael Lustig
- Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, California, USA
| | - Chunlei Liu
- Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, California, USA
- Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, California, USA
| |
Collapse
|
2
|
Zhang Y, Ye Z, Xia C, Tan Y, Zhang M, Lv X, Tang J, Li Z. Clinical Applications and Recent Updates of Simultaneous Multi-slice Technique in Accelerated MRI. Acad Radiol 2024; 31:1976-1988. [PMID: 38220568 DOI: 10.1016/j.acra.2023.12.032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2023] [Revised: 12/15/2023] [Accepted: 12/19/2023] [Indexed: 01/16/2024]
Abstract
Simultaneous multi-slice (SMS) is a magnetic resonance imaging (MRI) acceleration technique that utilizes multi-band radio-frequency pulses to simultaneously excite and encode multiple slices. Currently, SMS has been widely studied and applied in the MRI examination to reduce acquisition time, which can significantly improve the examination efficiency and patient throughput. Moreover, SMS technique can improve spatial resolution, which is of great value in disease diagnosis, treatment response monitoring, and prognosis prediction. This review will briefly introduce the technical principles of SMS, and summarize its current clinical applications. More importantly, we will discuss the recent technical progress and future research direction of SMS, hoping to highlight the clinical value and scientific potential of this technique.
Collapse
Affiliation(s)
- Yiteng Zhang
- Department of Radiology, West China Hospital of Sichuan University, No. 37 Guoxue Alley, Chengdu, 610041, Sichuan, China
| | - Zheng Ye
- Department of Radiology, West China Hospital of Sichuan University, No. 37 Guoxue Alley, Chengdu, 610041, Sichuan, China
| | - Chunchao Xia
- Department of Radiology, West China Hospital of Sichuan University, No. 37 Guoxue Alley, Chengdu, 610041, Sichuan, China
| | - Yuqi Tan
- Department of Radiology, West China Hospital of Sichuan University, No. 37 Guoxue Alley, Chengdu, 610041, Sichuan, China
| | - Meng Zhang
- Department of Radiology, West China Hospital of Sichuan University, No. 37 Guoxue Alley, Chengdu, 610041, Sichuan, China
| | - Xinyang Lv
- Department of Radiology, West China Hospital of Sichuan University, No. 37 Guoxue Alley, Chengdu, 610041, Sichuan, China
| | - Jing Tang
- Department of Radiology, West China Hospital of Sichuan University, No. 37 Guoxue Alley, Chengdu, 610041, Sichuan, China
| | - Zhenlin Li
- Department of Radiology, West China Hospital of Sichuan University, No. 37 Guoxue Alley, Chengdu, 610041, Sichuan, China.
| |
Collapse
|
3
|
Ji Y, Hoge WS, Gagoski B, Westin CF, Rathi Y, Ning L. Accelerating joint relaxation-diffusion MRI by integrating time division multiplexing and simultaneous multi-slice (TDM-SMS) strategies. Magn Reson Med 2022; 87:2697-2709. [PMID: 35092081 DOI: 10.1002/mrm.29160] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Revised: 12/01/2021] [Accepted: 12/27/2021] [Indexed: 12/12/2022]
Abstract
PURPOSE To accelerate the acquisition of relaxation-diffusion imaging by integrating time-division multiplexing (TDM) with simultaneous multi-slice (SMS) for EPI and evaluate imaging quality and diffusion measures. METHODS The time-division multiplexing (TDM) technique and SMS method were integrated to achieve a high slice-acceleration (e.g., 6×) factor for acquiring relaxation-diffusion MRI. Two variants of the sequence, referred to as TDM3e-SMS and TDM2s-SMS, were developed to simultaneously acquire slice groups with three distinct TEs and two slice groups with the same TE, respectively. Both sequences were evaluated on a 3T scanner with in vivo human brains and compared with standard single-band (SB) -EPI and SMS-EPI using diffusion measures and tractography results. RESULTS Experimental results showed that the TDM3e-SMS sequence with total slice acceleration of 6 (multiplexing factor (MP) = 3 × multi-band factor (MB) = 2) provided similar image intensity and microstructure measures compared to standard SMS-EPI with MB = 2, and yielded less bias in intensity compared to standard SMS-EPI with MB = 4. The three sequences showed a similar positive correlation between TE and mean kurtosis (MK) and a negative correlation between TE and mean diffusivity (MD) in white matter. Multi-fiber tractography also shows consistency of results in TE-dependent measures between different sequences. The TDM2s-SMS sequence (MP = 2, MB = 2) also provided imaging measures similar to standard SMS-EPI sequences (MB = 2) for single-TE diffusion imaging. CONCLUSIONS The TDM-SMS sequence can provide additional 2× to 3× acceleration to SMS without degrading imaging quality. With the significant reduction in scan time, TDM-SMS makes joint relaxation-diffusion MRI a feasible technique in neuroimaging research to investigate new markers of brain disorders.
Collapse
Affiliation(s)
- Yang Ji
- Department of Psychiatry, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.,Wellcome Centre for Integrative Neuroimaging, FMRIB Division, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
| | - W Scott Hoge
- Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Borjan Gagoski
- Fetal-Neonatal Neuroimaging and Developmental Science Center, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Carl-Fredrik Westin
- Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Yogesh Rathi
- Department of Psychiatry, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.,Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Lipeng Ning
- Department of Psychiatry, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| |
Collapse
|
4
|
Lim EJ, Sohn CH, Shin T, Park J. FID-calibrated simultaneous multi-slice fast spin echo with long trains of hard pulses. Phys Med Biol 2022; 67. [PMID: 35008082 DOI: 10.1088/1361-6560/ac499a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Accepted: 01/10/2022] [Indexed: 11/12/2022]
Abstract
Objective. To develop a novel, free-induction-decay (FID)-calibrated single-shot simultaneous multi-slice fast spin echo (SMS-FSE) with very long hard pulse trains for high encoding efficiency and low energy deposition.Approach. The proposed single-shot SMS-FSE employs a mixed pulse configuration in which a long excitation pulse that is spatially multi-band (MB) selective is used in conjunction with short spatially nonselective refocusing pulses. To alleviate energy deposition to tissues while reducing signal modulation along the echo train, variable low flip angles with signal prescription are utilized in the refocusing pulse train. A time-efficient FID calibration and correction method is introduced before aliased voxels in the slice direction are resolved. Simulations and experiments are performed to demonstrate the feasibility of the proposed method as an alternative to conventional HASTE for generatingT2-weighted images.Main results. Compared with conventional HASTE, the proposed method enhances imaging speed effectively by an MB factor up to 5 without apparent loss of image contrast while successfully eliminating FID artifacts.Significance. We successfully demonstrated the feasibility of the proposed method as an encoding- and energy-efficient alternative to conventional HASTE for generation ofT2-weighted contrast.
Collapse
Affiliation(s)
- Eun Ji Lim
- Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Republic of Korea
| | - Chul-Ho Sohn
- Department of Radiology, Seoul National University Hospital, Seoul, Republic of Korea
| | - Taehoon Shin
- Division of Mechanical and Biomedical Engineering, Ewha Womans University, Seoul, Republic of Korea
| | - Jaeseok Park
- Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Republic of Korea.,Department for Intelligent Precision Healthcare Convergence, Sungkyunkwan University, Suwon, Republic of Korea
| |
Collapse
|
5
|
Mani M, Yang B, Bathla G, Magnotta V, Jacob M. Multi-band- and in-plane-accelerated diffusion MRI enabled by model-based deep learning in q-space and its extension to learning in the spherical harmonic domain. Magn Reson Med 2021; 87:1799-1815. [PMID: 34825729 DOI: 10.1002/mrm.29095] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Revised: 10/13/2021] [Accepted: 11/03/2021] [Indexed: 12/13/2022]
Abstract
PURPOSE To propose a new method for the recovery of combined in-plane- and multi-band (MB)-accelerated diffusion MRI data. METHODS Combining MB acceleration with in-plane acceleration is crucial to improve the time efficiency of high (angular and spatial) resolution diffusion scans. However, as the MB factor and in-plane acceleration increase, the reconstruction becomes challenging due to the heavy aliasing. The new reconstruction utilizes an additional q-space prior to constrain the recovery, which is derived from the previously proposed qModeL framework. Specifically, the qModeL prior provides a pre-learned representation of the diffusion signal space to which the measured data belongs. We show that the pre-learned q-space prior along with a model-based iterative reconstruction that accommodate multi-band unaliasing, can efficiently reconstruct the in-plane- and MB-accelerated data. The power of joint reconstruction is maximally utilized by using an incoherent under-sampling pattern in the k-q domain. We tested the proposed method on single- and multi-shell data, with high/low angular resolution, high/low spatial resolution, healthy/abnormal tissues, and 3T/7T field strengths. Furthermore, the learning is extended to the spherical harmonic basis, to provide a rotational invariant learning framework. RESULTS The qModeL joint reconstruction is shown to simultaneously unalias and jointly recover DWIs with reasonable accuracy in all the cases studied. The reconstruction error from 18-fold accelerated multi-shell datasets was <3%. The microstructural maps derived from the accelerated acquisitions also exhibit reasonable accuracy for both healthy and abnormal tissues. The deep learning (DL)-enabled reconstructions are comparable to those derived using traditional methods. CONCLUSION qModeL enables the joint recovery of combined in-plane- and MB-accelerated dMRI utilizing DL.
Collapse
Affiliation(s)
- Merry Mani
- Department of Radiology, University of Iowa, Iowa City, Iowa, USA.,Department of Biomedical Engineering, University of Iowa, Iowa City, Iowa, USA
| | | | - Girish Bathla
- Department of Radiology, University of Iowa, Iowa City, Iowa, USA
| | - Vincent Magnotta
- Department of Radiology, University of Iowa, Iowa City, Iowa, USA.,Department of Biomedical Engineering, University of Iowa, Iowa City, Iowa, USA.,Department of Psychiatry, University of Iowa, Iowa City, Iowa, USA
| | - Mathews Jacob
- Department of Electrical and Computer Engineering, University of Iowa, Iowa City, Iowa, USA
| |
Collapse
|
6
|
Han S, Eun S, Cho H, Uludaǧ K, Kim SG. Improvement of sensitivity and specificity for laminar BOLD fMRI with double spin-echo EPI in humans at 7 T. Neuroimage 2021; 241:118435. [PMID: 34324976 DOI: 10.1016/j.neuroimage.2021.118435] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2021] [Accepted: 07/26/2021] [Indexed: 12/19/2022] Open
Abstract
Mapping mesoscopic cortical functional units such as columns or laminae is increasingly pursued by ultra-high field (UHF) functional magnetic resonance imaging (fMRI). The most popular approach for high-resolution fMRI is currently gradient-echo (GE) blood oxygenation level-dependent (BOLD) fMRI. However, its spatial accuracy is reduced due to its sensitivity to draining vessels, including pial veins, whereas spin-echo (SE) BOLD signal is expected to have higher spatial accuracy, albeit with lower sensitivity than the GE-BOLD signal. Here, we introduce a new double spin-echo (dSE) echo-planar imaging (EPI) method to improve the sensitivity of SE-BOLD contrast by averaging two spin-echoes using three radiofrequency pulses. Human fMRI experiments were performed with slices perpendicular to the central sulcus between motor and sensory cortices at 7 T during fist-clenching with touching. First, we evaluated the feasibility of single-shot dSE-EPI for BOLD fMRI with 1.5 mm isotropic resolution and found that dSE-BOLD fMRI has higher signal-to-noise ratio (SNR), temporal SNR (tSNR), and higher functional sensitivity than conventional SE-BOLD fMRI. Second, to investigate the laminar specificity of dSE-BOLD fMRI, we implemented a multi-shot approach to achieve 0.8-mm isotropic resolution with sliding-window reconstruction. Unlike GE-BOLD fMRI, the cortical profile of dSE-BOLD fMRI peaked at ~ 1.0 mm from the surface of the primary motor and sensory cortices, demonstrating an improvement of laminar specificity in humans over GE-BOLD fMRI. The proposed multi-shot dSE-EPI method is viable for high spatial resolution UHF-fMRI studies in the pursuit of resolving mesoscopic functional units.
Collapse
Affiliation(s)
- SoHyun Han
- Center for Neuroscience Imaging Research, Institute for Basic Science (IBS), Suwon, Republic of Korea; Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Republic of Korea.
| | - Seulgi Eun
- Center for Neuroscience Imaging Research, Institute for Basic Science (IBS), Suwon, Republic of Korea; Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Republic of Korea
| | - HyungJoon Cho
- Department of Biomedical Engineering, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea
| | - Kâmil Uludaǧ
- Center for Neuroscience Imaging Research, Institute for Basic Science (IBS), Suwon, Republic of Korea; Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Republic of Korea; Techna Institute & Koerner Scientist in MR Imaging, University Health Network, Toronto, Canada
| | - Seong-Gi Kim
- Center for Neuroscience Imaging Research, Institute for Basic Science (IBS), Suwon, Republic of Korea; Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Republic of Korea; Department of Intelligent Precision Healthcare Convergence, Sungkyunkwan University, Suwon, Republic of Korea.
| |
Collapse
|
7
|
Fritz FJ, Poser BA, Roebroeck A. MESMERISED: Super-accelerating T 1 relaxometry and diffusion MRI with STEAM at 7 T for quantitative multi-contrast and diffusion imaging. Neuroimage 2021; 239:118285. [PMID: 34147632 DOI: 10.1016/j.neuroimage.2021.118285] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Revised: 06/14/2021] [Accepted: 06/16/2021] [Indexed: 12/17/2022] Open
Abstract
There is an increasing interest in quantitative imaging of T1, T2 and diffusion contrast in the brain due to greater robustness against bias fields and artifacts, as well as better biophysical interpretability in terms of microstructure. However, acquisition time constraints are a challenge, particularly when multiple quantitative contrasts are desired and when extensive sampling of diffusion directions, high b-values or long diffusion times are needed for multi-compartment microstructure modeling. Although ultra-high fields of 7 T and above have desirable properties for many MR modalities, the shortening T2 and the high specific absorption rate (SAR) of inversion and refocusing pulses bring great challenges to quantitative T1, T2 and diffusion imaging. Here, we present the MESMERISED sequence (Multiplexed Echo Shifted Multiband Excited and Recalled Imaging of STEAM Encoded Diffusion). MESMERISED removes the dead time in Stimulated Echo Acquisition Mode (STEAM) imaging by an echo-shifting mechanism. The echo-shift (ES) factor is independent of multiband (MB) acceleration and allows for very high multiplicative (ESxMB) acceleration factors, particularly under moderate and long mixing times. This results in super-acceleration and high time efficiency at 7 T for quantitative T1 and diffusion imaging, while also retaining the capacity to perform quantitative T2 and B1 mapping. We demonstrate the super-acceleration of MESMERISED for whole-brain T1 relaxometry with total acceleration factors up to 36 at 1.8 mm isotropic resolution, and up to 54 at 1.25 mm resolution qT1 imaging, corresponding to a 6x and 9x speedup, respectively, compared to MB-only accelerated acquisitions. We then demonstrate highly efficient diffusion MRI with high b-values and long diffusion times in two separate cases. First, we show that super-accelerated multi-shell diffusion acquisitions with 370 whole-brain diffusion volumes over 8 b-value shells up to b = 7000 s/mm2 can be generated at 2 mm isotropic in under 8 minutes, a data rate of almost a volume per second, or at 1.8 mm isotropic in under 11 minutes, achieving up to 3.4x speedup compared to MB-only. A comparison of b = 7000 s/mm2 MESMERISED against standard MB pulsed gradient spin echo (PGSE) diffusion imaging shows 70% higher SNR efficiency and greater effectiveness in supporting complex diffusion signal modeling. Second, we demonstrate time-efficient sampling of different diffusion times with 1.8 mm isotropic diffusion data acquired at four diffusion times up to 290 ms, which supports both Diffusion Tensor Imaging (DTI) and Diffusion Kurtosis Imaging (DKI) at each diffusion time. Finally, we demonstrate how adding quantitative T2 and B1+ mapping to super-accelerated qT1 and diffusion imaging enables efficient quantitative multi-contrast mapping with the same MESMERISED sequence and the same readout train. MESMERISED extends possibilities to efficiently probe T1, T2 and diffusion contrast for multi-component modeling of tissue microstructure.
Collapse
Affiliation(s)
- F J Fritz
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands; Institut für Systemische Neurowissenschaften, Zentrum für Experimentelle Medizin, Universitätklinikum Hamburg-Eppendorf (UKE), Hamburg, Deutschland
| | - B A Poser
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands
| | - A Roebroeck
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands.
| |
Collapse
|
8
|
Middione MJ, Loecher M, Moulin K, Ennis DB. Optimization methods for magnetic resonance imaging gradient waveform design. NMR IN BIOMEDICINE 2020; 33:e4308. [PMID: 32342560 PMCID: PMC7606655 DOI: 10.1002/nbm.4308] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Revised: 02/07/2020] [Accepted: 03/13/2020] [Indexed: 06/11/2023]
Abstract
The development and implementation of novel MRI pulse sequences remains challenging and laborious. Gradient waveforms are typically designed using a combination of analytical and ad hoc methods to construct each gradient waveform axis independently. This strategy makes coding the pulse sequence complicated, in addition to being time inefficient. As a consequence, nearly all commercial MRI pulse sequences fail to maximize use of the available gradient hardware or efficiently mitigate physiological effects. This results in expensive MRI systems that underperform relative to their inherent hardware capabilities. To address this problem, a software solution is proposed that incorporates numerical optimization methods into MRI pulse sequence programming. Examples are shown for rotational variant vs. invariant waveform designs, acceleration nulled velocity encoding gradients, and mitigation of peripheral nerve stimulation for diffusion encoding. The application of optimization methods to MRI pulse sequence design incorporates gradient hardware limits and the prescribed MRI protocol parameters (e.g. field-of-view, resolution, gradient moments, and/or b-value) to simultaneously construct time-optimal gradient waveforms. In many cases, the resulting constrained gradient waveform design problem is convex and can be solved on-the-fly on the MRI scanner. The result is a set of multi-axis time-optimal gradient waveforms that satisfy the design constraints, thereby increasing SNR-efficiency. These optimization methods can also be used to mitigate imaging artifacts (e.g. eddy currents) or account for peripheral nerve stimulation. The result of the optimization method is to enable easier pulse sequence gradient waveform design and permit on-the-fly implementation for a range of MRI pulse sequences.
Collapse
Affiliation(s)
| | - Michael Loecher
- Department of Radiology, Stanford University, Stanford, CA, USA
| | - Kévin Moulin
- Department of Radiology, Stanford University, Stanford, CA, USA
| | - Daniel B. Ennis
- Department of Radiology, Stanford University, Stanford, CA, USA
- Department of Radiology, Veterans Affairs Palo Alto Health Care System, Palo Alto, CA, USA
| |
Collapse
|
9
|
Ma YJ, Jang H, Wei Z, Cai Z, Xue Y, Lee RR, Chang EY, Bydder GM, Corey-Bloom J, Du J. Myelin Imaging in Human Brain Using a Short Repetition Time Adiabatic Inversion Recovery Prepared Ultrashort Echo Time (STAIR-UTE) MRI Sequence in Multiple Sclerosis. Radiology 2020; 297:392-404. [PMID: 32779970 DOI: 10.1148/radiol.2020200425] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Background Water signal contamination is a major challenge for direct ultrashort echo time (UTE) imaging of myelin in vivo because water contributes most of the signals detected in white matter. Purpose To validate a new short repetition time (TR) adiabatic inversion recovery (STAIR) prepared UTE (STAIR-UTE) sequence designed to suppress water signals and to allow imaging of ultrashort T2 protons of myelin in white matter using a clinical 3-T scanner. Materials and Methods In this prospective study, an optimization framework was used to obtain the optimal inversion time for nulling water signals using STAIR-UTE imaging at different TRs. Numeric simulation and phantom studies were performed. Healthy volunteers and participants with multiple sclerosis (MS) underwent MRI between November 2018 and October 2019 to compare STAIR-UTE and a clinical T2-weighted fluid-attenuated inversion recovery sequence for assessment of MS lesions. UTE measures of myelin were also performed to allow comparison of signals in lesions and with those in normal-appearing white matter (NAWM) in patients with MS and in normal white matter (NWM) in healthy volunteers. Results Simulation and phantom studies both suggest that the proposed STAIR-UTE technique can effectively suppress long T2 tissues with a broad range of T1s. Ten healthy volunteers (mean age, 33 years ± 8 [standard deviation]; six women) and 10 patients with MS (mean age, 51 years ± 16; seven women) were evaluated. The three-dimensional STAIR-UTE sequence effectively suppressed water components in white matter and selectively imaged myelin, which had a measured T2* value of 0.21 msec ± 0.04 in the volunteer study. A much lower mean UTE measure of myelin proton density was found in MS lesions (3.8 mol/L ± 1.5), and a slightly lower mean UTE measure was found in NAWM (7.2 mol/L ± 0.8) compared with that in NWM (8.0 mol/L ± 0.8) in the healthy volunteers (P < .001 for both comparisons). Conclusion The short repetition time adiabatic inversion recovery-prepared ultrashort echo time sequence provided efficient water signal suppression for volumetric imaging of myelin in the brain and showed excellent myelin signal contrast as well as marked ultrashort echo time signal reduction in multiple sclerosis lesions and a smaller reduction in normal-appearing white matter compared with normal white matter in volunteers. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Messina and Port in this issue.
Collapse
Affiliation(s)
- Ya-Jun Ma
- From the Departments of Radiology (Y.J.M., H.J., Z.W., Z.C., Y.X., R.R.L., E.Y.C., G.M.B., J.D.) and Neurosciences (J.C.B.) University of California San Diego, 9452 Medical Center Dr, La Jolla, CA 92037; and Radiology Service, Veterans Affairs San Diego Healthcare System, San Diego, Calif (E.Y.C.)
| | - Hyungseok Jang
- From the Departments of Radiology (Y.J.M., H.J., Z.W., Z.C., Y.X., R.R.L., E.Y.C., G.M.B., J.D.) and Neurosciences (J.C.B.) University of California San Diego, 9452 Medical Center Dr, La Jolla, CA 92037; and Radiology Service, Veterans Affairs San Diego Healthcare System, San Diego, Calif (E.Y.C.)
| | - Zhao Wei
- From the Departments of Radiology (Y.J.M., H.J., Z.W., Z.C., Y.X., R.R.L., E.Y.C., G.M.B., J.D.) and Neurosciences (J.C.B.) University of California San Diego, 9452 Medical Center Dr, La Jolla, CA 92037; and Radiology Service, Veterans Affairs San Diego Healthcare System, San Diego, Calif (E.Y.C.)
| | - Zhenyu Cai
- From the Departments of Radiology (Y.J.M., H.J., Z.W., Z.C., Y.X., R.R.L., E.Y.C., G.M.B., J.D.) and Neurosciences (J.C.B.) University of California San Diego, 9452 Medical Center Dr, La Jolla, CA 92037; and Radiology Service, Veterans Affairs San Diego Healthcare System, San Diego, Calif (E.Y.C.)
| | - Yanping Xue
- From the Departments of Radiology (Y.J.M., H.J., Z.W., Z.C., Y.X., R.R.L., E.Y.C., G.M.B., J.D.) and Neurosciences (J.C.B.) University of California San Diego, 9452 Medical Center Dr, La Jolla, CA 92037; and Radiology Service, Veterans Affairs San Diego Healthcare System, San Diego, Calif (E.Y.C.)
| | - Roland R Lee
- From the Departments of Radiology (Y.J.M., H.J., Z.W., Z.C., Y.X., R.R.L., E.Y.C., G.M.B., J.D.) and Neurosciences (J.C.B.) University of California San Diego, 9452 Medical Center Dr, La Jolla, CA 92037; and Radiology Service, Veterans Affairs San Diego Healthcare System, San Diego, Calif (E.Y.C.)
| | - Eric Y Chang
- From the Departments of Radiology (Y.J.M., H.J., Z.W., Z.C., Y.X., R.R.L., E.Y.C., G.M.B., J.D.) and Neurosciences (J.C.B.) University of California San Diego, 9452 Medical Center Dr, La Jolla, CA 92037; and Radiology Service, Veterans Affairs San Diego Healthcare System, San Diego, Calif (E.Y.C.)
| | - Graeme M Bydder
- From the Departments of Radiology (Y.J.M., H.J., Z.W., Z.C., Y.X., R.R.L., E.Y.C., G.M.B., J.D.) and Neurosciences (J.C.B.) University of California San Diego, 9452 Medical Center Dr, La Jolla, CA 92037; and Radiology Service, Veterans Affairs San Diego Healthcare System, San Diego, Calif (E.Y.C.)
| | - Jody Corey-Bloom
- From the Departments of Radiology (Y.J.M., H.J., Z.W., Z.C., Y.X., R.R.L., E.Y.C., G.M.B., J.D.) and Neurosciences (J.C.B.) University of California San Diego, 9452 Medical Center Dr, La Jolla, CA 92037; and Radiology Service, Veterans Affairs San Diego Healthcare System, San Diego, Calif (E.Y.C.)
| | - Jiang Du
- From the Departments of Radiology (Y.J.M., H.J., Z.W., Z.C., Y.X., R.R.L., E.Y.C., G.M.B., J.D.) and Neurosciences (J.C.B.) University of California San Diego, 9452 Medical Center Dr, La Jolla, CA 92037; and Radiology Service, Veterans Affairs San Diego Healthcare System, San Diego, Calif (E.Y.C.)
| |
Collapse
|
10
|
Han S, Liao C, Manhard MK, Park DJ, Bilgic B, Fair MJ, Wang F, Blazejewska AI, Grissom WA, Polimeni JR, Setsompop K. Accelerated spin-echo functional MRI using multisection excitation by simultaneous spin-echo interleaving (MESSI) with complex-encoded generalized slice dithered enhanced resolution (cgSlider) simultaneous multislice echo-planar imaging. Magn Reson Med 2020; 84:206-220. [PMID: 31840295 PMCID: PMC7083698 DOI: 10.1002/mrm.28108] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Revised: 10/29/2019] [Accepted: 11/14/2019] [Indexed: 12/14/2022]
Abstract
PURPOSE Spin-echo functional MRI (SE-fMRI) has the potential to improve spatial specificity when compared with gradient-echo fMRI. However, high spatiotemporal resolution SE-fMRI with large slice-coverage is challenging as SE-fMRI requires a long echo time to generate blood oxygenation level-dependent (BOLD) contrast, leading to long repetition times. The aim of this work is to develop an acquisition method that enhances the slice-coverage of SE-fMRI at high spatiotemporal resolution. THEORY AND METHODS An acquisition scheme was developed entitled multisection excitation by simultaneous spin-echo interleaving (MESSI) with complex-encoded generalized slice dithered enhanced resolution (cgSlider). MESSI uses the dead-time during the long echo time by interleaving the excitation and readout of 2 slices to enable 2× slice-acceleration, while cgSlider uses the stable temporal background phase in SE-fMRI to encode/decode 2 adjacent slices simultaneously with a "phase-constrained" reconstruction method. The proposed cgSlider-MESSI was also combined with simultaneous multislice (SMS) to achieve further slice-acceleration. This combined approach was used to achieve 1.5-mm isotropic whole-brain SE-fMRI with a temporal resolution of 1.5 s and was evaluated using sensory stimulation and breath-hold tasks at 3T. RESULTS Compared with conventional SE-SMS, cgSlider-MESSI-SMS provides 4-fold increase in slice-coverage for the same repetition time, with comparable temporal signal-to-noise ratio. Corresponding fMRI activation from cgSlider-MESSI-SMS for both fMRI tasks were consistent with those from conventional SE-SMS. Overall, cgSlider-MESSI-SMS achieved a 32× encoding-acceleration by combining Rinplane × MB × cgSlider × MESSI = 4 × 2 × 2 × 2. CONCLUSION High-quality, high-resolution whole-brain SE-fMRI was acquired at a short repetition time using cgSlider-MESSI-SMS. This method should be beneficial for high spatiotemporal resolution SE-fMRI studies requiring whole-brain coverage.
Collapse
Affiliation(s)
- SoHyun Han
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
| | - Congyu Liao
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
| | - Mary Kate Manhard
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
| | - Daniel Joseph Park
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
| | - Berkin Bilgic
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
| | - Merlin J. Fair
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
| | - Fuyixue Wang
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Medical Engineering & Medical Physics, Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts
| | - Anna I. Blazejewska
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
| | - William A. Grissom
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA
| | - Jonathan R. Polimeni
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
- Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts
| | - Kawin Setsompop
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
- Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts
| |
Collapse
|
11
|
Image Artifact Management for Clinical Magnetic Resonance Imaging on a 7 T Scanner Using Single-Channel Radiofrequency Transmit Mode. Invest Radiol 2020; 54:781-791. [PMID: 31503079 DOI: 10.1097/rli.0000000000000598] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
OBJECTIVES The aim of this work was to devise mitigation strategies for addressing a range of image artifacts on a clinical 7 T magnetic resonance imaging scanner using the regulatory-approved single-channel radiofrequency transmit mode and vendor-supplied radiofrequency coils to facilitate clinical scanning within reasonable scan times. MATERIALS AND METHODS Optimized imaging sequence protocols were developed for routine musculoskeletal knee and neurological imaging. Sources of severe image nonuniformities were identified, and mitigation strategies were devised. A range of custom-made high permittivity dielectric pads were used to compensate for B1 and B1 inhomogeneities, and also for magnetic susceptibility-induced signal dropouts particularly in the basal regions of the temporal lobes and in the cerebellum. RESULTS Significant improvements in image uniformity were obtained using dielectric pads in the knee and brain. A combination of small voxels, reduced field of view B0 shimming, and high in-plane parallel imaging factors helped to minimize signal loss in areas of high susceptibility-induced field distortions. The high inherent signal-to-noise ratio at 7 T allowed for high receiver bandwidths and thin slices to minimize chemical shift artifacts. Intermittent artifacts due to radiofrequency inversion pulse limitations (power, bandwidth) were minimized with dielectric pads. A patient with 2 implanted metallic cranial fixation devices located within the radiofrequency transmit field was successfully imaged, with minimal image geometric distortions. CONCLUSIONS Challenges relating to severe image artifacts at 7 T using single-channel radiofrequency transmit functionality in the knee and brain were overcome using the approaches described in this article. The resultant high diagnostic image quality paves the way for incorporation of this technology into the routine clinical workflow. Further developmental efforts are required to expand the range of applications to other anatomical areas, and to expand the evidence- and knowledge-base relating to the safety of scanning patients with implanted metallic devices.
Collapse
|
12
|
Aigner CS, Rund A, Abo Seada S, Price AN, Hajnal JV, Malik SJ, Kunisch K, Stollberger R. Time optimal control-based RF pulse design under gradient imperfections. Magn Reson Med 2019; 83:561-574. [PMID: 31441536 PMCID: PMC6899978 DOI: 10.1002/mrm.27955] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Revised: 07/25/2019] [Accepted: 07/29/2019] [Indexed: 12/15/2022]
Abstract
Purpose This study incorporates a gradient system imperfection model into an optimal control framework for radio frequency (RF) pulse design. Theory and Methods The joint design of minimum‐time RF and slice selective gradient shapes is posed as an optimal control problem. Hardware limitations such as maximal amplitudes for RF and slice selective gradient or its slew rate are included as hard constraints to assure practical applicability of the optimized waveforms. In order to guarantee the performance of the optimized waveform with possible gradient system disturbances such as limited system bandwidth and eddy currents, a measured gradient impulse response function (GIRF) for a specific system is integrated into the optimization. Results The method generates optimized RF and pre‐distorted slice selective gradient shapes for refocusing that are able to fully compensate the modeled imperfections of the gradient system under investigation. The results nearly regenerate the optimal results of an idealized gradient system. The numerical Bloch simulations are validated by phantom and in‐vivo experiments on 2 3T scanners. Conclusions The presented design approach demonstrates the successful correction of gradient system imperfections within an optimal control framework for RF pulse design.
Collapse
Affiliation(s)
- Christoph S Aigner
- Institute of Medical Engineering, Graz University of Technology, Graz, Austria
| | - Armin Rund
- Institute for Mathematics and Scientific Computing, University of Graz, Graz, Austria
| | - Samy Abo Seada
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Anthony N Price
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Joseph V Hajnal
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Shaihan J Malik
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Karl Kunisch
- Institute for Mathematics and Scientific Computing, University of Graz, Graz, Austria.,Johann Radon Institute for Computational and Applied Mathematics (RICAM), Austrian Academy of Sciences, Linz, Austria.,BioTechMed-Graz, Graz, Austria
| | - Rudolf Stollberger
- Institute of Medical Engineering, Graz University of Technology, Graz, Austria.,BioTechMed-Graz, Graz, Austria
| |
Collapse
|
13
|
Zhang K, Yun SD, Triphan SMF, Sturm VJ, Buschle LR, Hahn A, Heiland S, Bendszus M, Schlemmer HP, Shah NJ, Ziener CH, Kurz FT. Vessel architecture imaging using multiband gradient-echo/spin-echo EPI. PLoS One 2019; 14:e0220939. [PMID: 31398234 PMCID: PMC6688807 DOI: 10.1371/journal.pone.0220939] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Accepted: 07/26/2019] [Indexed: 12/04/2022] Open
Abstract
Objectives To apply the MB (multiband) excitation and blipped-CAIPI (blipped-controlled aliasing in parallel imaging) techniques in a spin and gradient-echo (SAGE) EPI sequence to improve the slice coverage for vessel architecture imaging (VAI). Materials and methods Both MB excitation and blipped-CAIPI with in-plane parallel imaging were incorporated into a gradient-echo (GE)/spin-echo (SE) EPI sequence for simultaneous tracking of the dynamic MR signal changes in both GE and SE contrasts after the injection of contrast agent. MB and singleband (SB) excitation were compared using a 20-channel head coil at 3 Tesla, and high-resolution MB VAI could be performed in 32 glioma patients. Results Whole-brain covered high resolution VAI can be achieved after applying multiband excitation with a factor of 2 and in-plane parallel imaging with a factor of 3. The quality of the images resulting from MB acceleration was comparable to those from the SB method: images were reconstructed without any loss of spatial resolution or severe distortions. In addition, MB and SB signal-to-noise ratios (SNR) were similar. A relative low g-factor induced from the MB acceleration method was achieved after using a blipped-CAIPI technique (1.35 for GE and 1.33 for SE imaging). Performing quantitative VAI, we found that, among all VAI parametric maps, microvessel type indicator (MTI), distance map (I) and vascular-induced bolus peak-time shift (VIPS) were highly correlated. Likewise, VAI parametric maps of slope, slope length and short axis were highly correlated. Conclusions Multiband accelerated SAGE successfully doubles the number of readout slices in the same measurement time when compared to conventional readout sequences. The corresponding VAI parametric maps provide insights into the complexity and heterogeneity of vascular changes in glioma.
Collapse
Affiliation(s)
- Ke Zhang
- Department of Radiology, German Cancer Research Center, Heidelberg, Germany.,Department of Neuroradiology, Heidelberg University Hospital, Heidelberg, Germany
| | - Seong Dae Yun
- Institute of Neuroscience and Medicine- 4, Medical Imaging Physics, Forschungszentrum Jülich, Germany
| | - Simon M F Triphan
- Department of Diagnostic & Interventional Radiology, Heidelberg University Hospital, Heidelberg, Germany
| | - Volker J Sturm
- Department of Radiology, German Cancer Research Center, Heidelberg, Germany.,Department of Neuroradiology, Heidelberg University Hospital, Heidelberg, Germany
| | - Lukas R Buschle
- Department of Radiology, German Cancer Research Center, Heidelberg, Germany.,Department of Neuroradiology, Heidelberg University Hospital, Heidelberg, Germany
| | - Artur Hahn
- Department of Neuroradiology, Heidelberg University Hospital, Heidelberg, Germany.,Department of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany
| | - Sabine Heiland
- Department of Neuroradiology, Heidelberg University Hospital, Heidelberg, Germany
| | - Martin Bendszus
- Department of Neuroradiology, Heidelberg University Hospital, Heidelberg, Germany
| | | | - N Jon Shah
- Institute of Neuroscience and Medicine- 4, Medical Imaging Physics, Forschungszentrum Jülich, Germany.,Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany
| | - Christian H Ziener
- Department of Radiology, German Cancer Research Center, Heidelberg, Germany.,Department of Neuroradiology, Heidelberg University Hospital, Heidelberg, Germany
| | - Felix T Kurz
- Department of Radiology, German Cancer Research Center, Heidelberg, Germany.,Department of Neuroradiology, Heidelberg University Hospital, Heidelberg, Germany
| |
Collapse
|
14
|
Hoff MN, McKinney A, Shellock FG, Rassner U, Gilk T, Watson RE, Greenberg TD, Froelich J, Kanal E. Safety Considerations of 7-T MRI in Clinical Practice. Radiology 2019; 292:509-518. [PMID: 31310177 DOI: 10.1148/radiol.2019182742] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Although 7-T MRI has recently received approval for use in clinical patient care, there are distinct safety issues associated with this relatively high magnetic field. Forces on metallic implants and radiofrequency power deposition and heating are safety considerations at 7 T. Patient bioeffects such as vertigo, dizziness, false feelings of motion, nausea, nystagmus, magnetophosphenes, and electrogustatory effects are more common and potentially more pronounced at 7 T than at lower field strengths. Herein the authors review safety issues associated with 7-T MRI. The rationale for safety concerns at this field strength are discussed as well as potential approaches to mitigate risk to patients and health care professionals.
Collapse
Affiliation(s)
- Michael N Hoff
- From the Department of Radiology, University of Washington, 1959 NE Pacific St, Seattle, WA 98195-7117 (M.N.H.); Department of Radiology, University of Minnesota, Minneapolis, Minn (A.M., J.F.); Department of Clinical Physical Therapy, University of Southern California, Los Angeles, Calif (F.G.S.); Department of Radiology, University of Utah Health Sciences Center, Salt Lake City, Utah (U.R.); RADIOLOGY-Planning, Kansas City, Mo (T.G.); Department of Radiology, Mayo Clinic, Rochester, Minn (R.E.W.); G3 Global Group, Boulder, Colo, Mo (T.D.G.); and Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, Pa (E.K.)
| | - Alexander McKinney
- From the Department of Radiology, University of Washington, 1959 NE Pacific St, Seattle, WA 98195-7117 (M.N.H.); Department of Radiology, University of Minnesota, Minneapolis, Minn (A.M., J.F.); Department of Clinical Physical Therapy, University of Southern California, Los Angeles, Calif (F.G.S.); Department of Radiology, University of Utah Health Sciences Center, Salt Lake City, Utah (U.R.); RADIOLOGY-Planning, Kansas City, Mo (T.G.); Department of Radiology, Mayo Clinic, Rochester, Minn (R.E.W.); G3 Global Group, Boulder, Colo, Mo (T.D.G.); and Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, Pa (E.K.)
| | - Frank G Shellock
- From the Department of Radiology, University of Washington, 1959 NE Pacific St, Seattle, WA 98195-7117 (M.N.H.); Department of Radiology, University of Minnesota, Minneapolis, Minn (A.M., J.F.); Department of Clinical Physical Therapy, University of Southern California, Los Angeles, Calif (F.G.S.); Department of Radiology, University of Utah Health Sciences Center, Salt Lake City, Utah (U.R.); RADIOLOGY-Planning, Kansas City, Mo (T.G.); Department of Radiology, Mayo Clinic, Rochester, Minn (R.E.W.); G3 Global Group, Boulder, Colo, Mo (T.D.G.); and Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, Pa (E.K.)
| | - Ulrich Rassner
- From the Department of Radiology, University of Washington, 1959 NE Pacific St, Seattle, WA 98195-7117 (M.N.H.); Department of Radiology, University of Minnesota, Minneapolis, Minn (A.M., J.F.); Department of Clinical Physical Therapy, University of Southern California, Los Angeles, Calif (F.G.S.); Department of Radiology, University of Utah Health Sciences Center, Salt Lake City, Utah (U.R.); RADIOLOGY-Planning, Kansas City, Mo (T.G.); Department of Radiology, Mayo Clinic, Rochester, Minn (R.E.W.); G3 Global Group, Boulder, Colo, Mo (T.D.G.); and Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, Pa (E.K.)
| | - Tobias Gilk
- From the Department of Radiology, University of Washington, 1959 NE Pacific St, Seattle, WA 98195-7117 (M.N.H.); Department of Radiology, University of Minnesota, Minneapolis, Minn (A.M., J.F.); Department of Clinical Physical Therapy, University of Southern California, Los Angeles, Calif (F.G.S.); Department of Radiology, University of Utah Health Sciences Center, Salt Lake City, Utah (U.R.); RADIOLOGY-Planning, Kansas City, Mo (T.G.); Department of Radiology, Mayo Clinic, Rochester, Minn (R.E.W.); G3 Global Group, Boulder, Colo, Mo (T.D.G.); and Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, Pa (E.K.)
| | - Robert E Watson
- From the Department of Radiology, University of Washington, 1959 NE Pacific St, Seattle, WA 98195-7117 (M.N.H.); Department of Radiology, University of Minnesota, Minneapolis, Minn (A.M., J.F.); Department of Clinical Physical Therapy, University of Southern California, Los Angeles, Calif (F.G.S.); Department of Radiology, University of Utah Health Sciences Center, Salt Lake City, Utah (U.R.); RADIOLOGY-Planning, Kansas City, Mo (T.G.); Department of Radiology, Mayo Clinic, Rochester, Minn (R.E.W.); G3 Global Group, Boulder, Colo, Mo (T.D.G.); and Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, Pa (E.K.)
| | - Todd D Greenberg
- From the Department of Radiology, University of Washington, 1959 NE Pacific St, Seattle, WA 98195-7117 (M.N.H.); Department of Radiology, University of Minnesota, Minneapolis, Minn (A.M., J.F.); Department of Clinical Physical Therapy, University of Southern California, Los Angeles, Calif (F.G.S.); Department of Radiology, University of Utah Health Sciences Center, Salt Lake City, Utah (U.R.); RADIOLOGY-Planning, Kansas City, Mo (T.G.); Department of Radiology, Mayo Clinic, Rochester, Minn (R.E.W.); G3 Global Group, Boulder, Colo, Mo (T.D.G.); and Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, Pa (E.K.)
| | - Jerry Froelich
- From the Department of Radiology, University of Washington, 1959 NE Pacific St, Seattle, WA 98195-7117 (M.N.H.); Department of Radiology, University of Minnesota, Minneapolis, Minn (A.M., J.F.); Department of Clinical Physical Therapy, University of Southern California, Los Angeles, Calif (F.G.S.); Department of Radiology, University of Utah Health Sciences Center, Salt Lake City, Utah (U.R.); RADIOLOGY-Planning, Kansas City, Mo (T.G.); Department of Radiology, Mayo Clinic, Rochester, Minn (R.E.W.); G3 Global Group, Boulder, Colo, Mo (T.D.G.); and Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, Pa (E.K.)
| | - Emanuel Kanal
- From the Department of Radiology, University of Washington, 1959 NE Pacific St, Seattle, WA 98195-7117 (M.N.H.); Department of Radiology, University of Minnesota, Minneapolis, Minn (A.M., J.F.); Department of Clinical Physical Therapy, University of Southern California, Los Angeles, Calif (F.G.S.); Department of Radiology, University of Utah Health Sciences Center, Salt Lake City, Utah (U.R.); RADIOLOGY-Planning, Kansas City, Mo (T.G.); Department of Radiology, Mayo Clinic, Rochester, Minn (R.E.W.); G3 Global Group, Boulder, Colo, Mo (T.D.G.); and Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, Pa (E.K.)
| |
Collapse
|
15
|
Hilbert T, Schulz J, Marques JP, Thiran J, Krueger G, Norris DG, Kober T. Fast model‐based T
2
mapping using SAR‐reduced simultaneous multislice excitation. Magn Reson Med 2019; 82:2090-2103. [DOI: 10.1002/mrm.27890] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 05/23/2019] [Accepted: 06/13/2019] [Indexed: 12/14/2022]
Affiliation(s)
- Tom Hilbert
- Advanced Clinical Imaging Technology Siemens Healthcare Lausanne Switzerland
- Department of Radiology Lausanne University Hospital Lausanne Switzerland
- Signal Processing Laboratory 5 École Polytechnique Fédérale de Lausanne Lausanne Switzerland
| | - Jenni Schulz
- Donders Institute for Brain, Cognition and Behavior Radboud University Nijmegen Nijmegen Netherlands
| | - José P. Marques
- Donders Institute for Brain, Cognition and Behavior Radboud University Nijmegen Nijmegen Netherlands
| | - Jean‐Philippe Thiran
- Department of Radiology Lausanne University Hospital Lausanne Switzerland
- Signal Processing Laboratory 5 École Polytechnique Fédérale de Lausanne Lausanne Switzerland
| | - Gunnar Krueger
- Technology and Innovation EMEA, Siemens Healthcare Lausanne Switzerland
| | - David G. Norris
- Donders Institute for Brain, Cognition and Behavior Radboud University Nijmegen Nijmegen Netherlands
| | - Tobias Kober
- Advanced Clinical Imaging Technology Siemens Healthcare Lausanne Switzerland
- Department of Radiology Lausanne University Hospital Lausanne Switzerland
- Signal Processing Laboratory 5 École Polytechnique Fédérale de Lausanne Lausanne Switzerland
| |
Collapse
|
16
|
Abo Seada S, Price AN, Schneider T, Hajnal JV, Malik SJ. Multiband RF pulse design for realistic gradient performance. Magn Reson Med 2019; 81:362-376. [PMID: 30277267 PMCID: PMC6334175 DOI: 10.1002/mrm.27411] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Revised: 05/29/2018] [Accepted: 05/29/2018] [Indexed: 11/07/2022]
Abstract
PURPOSE Simultaneous multi-slice techniques are reliant on multiband RF pulses, for which conventional design strategies result in long pulse durations, lengthening echo-times so lowering SNR for spin-echo imaging, and lengthening repetition times for gradient echo sequences. Pulse durations can be reduced with advanced RF pulse design methods that use time-variable selection gradients. However, the ability of gradient systems to reproduce fast switching pulses is often limited and can lead to image artifacts when ignored. We propose a time-efficient pulse design method that inherently produces gradient waveforms with lower temporal bandwidth. METHODS Efficient multiband RF pulses with time-variable gradients were designed using time-optimal VERSE. Using VERSE directly on multiband pulses leads to gradient waveforms with high temporal bandwidth, whereas VERSE applied first to singleband RF pulses and then modulated to make them multiband, significantly reduces this. The relative performance of these approaches was compared using simulation and experimental measurements. RESULTS Applying VERSE before multiband modulation was successful at removing out-of-band slice distortion. This effectively removes the need for high frequency modulation in the gradient waveform while preserving the benefit of time-efficiency inherited from VERSE. CONCLUSION We propose a time-efficient RF pulse design that produces gradient pulses with lower temporal bandwidth, reducing image artifacts associated with finite temporal bandwidth of gradient systems.
Collapse
Affiliation(s)
- Samy Abo Seada
- School of Biomedical Engineering & Imaging SciencesKing’s College London, King’s Health Partners, St Thomas’ HospitalLondonSE1 7EH
| | - Anthony N. Price
- School of Biomedical Engineering & Imaging SciencesKing’s College London, King’s Health Partners, St Thomas’ HospitalLondonSE1 7EH
| | | | - Joseph V. Hajnal
- School of Biomedical Engineering & Imaging SciencesKing’s College London, King’s Health Partners, St Thomas’ HospitalLondonSE1 7EH
| | - Shaihan J. Malik
- School of Biomedical Engineering & Imaging SciencesKing’s College London, King’s Health Partners, St Thomas’ HospitalLondonSE1 7EH
| |
Collapse
|
17
|
Ladd ME, Bachert P, Meyerspeer M, Moser E, Nagel AM, Norris DG, Schmitter S, Speck O, Straub S, Zaiss M. Pros and cons of ultra-high-field MRI/MRS for human application. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2018; 109:1-50. [PMID: 30527132 DOI: 10.1016/j.pnmrs.2018.06.001] [Citation(s) in RCA: 267] [Impact Index Per Article: 44.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 06/06/2018] [Accepted: 06/07/2018] [Indexed: 05/08/2023]
Abstract
Magnetic resonance imaging and spectroscopic techniques are widely used in humans both for clinical diagnostic applications and in basic research areas such as cognitive neuroimaging. In recent years, new human MR systems have become available operating at static magnetic fields of 7 T or higher (≥300 MHz proton frequency). Imaging human-sized objects at such high frequencies presents several challenges including non-uniform radiofrequency fields, enhanced susceptibility artifacts, and higher radiofrequency energy deposition in the tissue. On the other side of the scale are gains in signal-to-noise or contrast-to-noise ratio that allow finer structures to be visualized and smaller physiological effects to be detected. This review presents an overview of some of the latest methodological developments in human ultra-high field MRI/MRS as well as associated clinical and scientific applications. Emphasis is given to techniques that particularly benefit from the changing physical characteristics at high magnetic fields, including susceptibility-weighted imaging and phase-contrast techniques, imaging with X-nuclei, MR spectroscopy, CEST imaging, as well as functional MRI. In addition, more general methodological developments such as parallel transmission and motion correction will be discussed that are required to leverage the full potential of higher magnetic fields, and an overview of relevant physiological considerations of human high magnetic field exposure is provided.
Collapse
Affiliation(s)
- Mark E Ladd
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; Faculty of Medicine, University of Heidelberg, Heidelberg, Germany; Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany; Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany.
| | - Peter Bachert
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany.
| | - Martin Meyerspeer
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; MR Center of Excellence, Medical University of Vienna, Vienna, Austria.
| | - Ewald Moser
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; MR Center of Excellence, Medical University of Vienna, Vienna, Austria.
| | - Armin M Nagel
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
| | - David G Norris
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, Netherlands; Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany.
| | - Sebastian Schmitter
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany.
| | - Oliver Speck
- Department of Biomedical Magnetic Resonance, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany; German Center for Neurodegenerative Diseases, Magdeburg, Germany; Center for Behavioural Brain Sciences, Magdeburg, Germany; Leibniz Institute for Neurobiology, Magdeburg, Germany.
| | - Sina Straub
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
| | - Moritz Zaiss
- High-Field Magnetic Resonance Center, Max-Planck-Institute for Biological Cybernetics, Tübingen, Germany.
| |
Collapse
|
18
|
Wu X, Auerbach EJ, Vu AT, Moeller S, Lenglet C, Schmitter S, Van de Moortele PF, Yacoub E, Uğurbil K. High-resolution whole-brain diffusion MRI at 7T using radiofrequency parallel transmission. Magn Reson Med 2018; 80:1857-1870. [PMID: 29603381 DOI: 10.1002/mrm.27189] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2017] [Revised: 02/20/2018] [Accepted: 03/02/2018] [Indexed: 12/21/2022]
Abstract
PURPOSE Investigating the utility of RF parallel transmission (pTx) for Human Connectome Project (HCP)-style whole-brain diffusion MRI (dMRI) data at 7 Tesla (7T). METHODS Healthy subjects were scanned in pTx and single-transmit (1Tx) modes. Multiband (MB), single-spoke pTx pulses were designed to image sagittal slices. HCP-style dMRI data (i.e., 1.05-mm resolutions, MB2, b-values = 1000/2000 s/mm2 , 286 images and 40-min scan) and data with higher accelerations (MB3 and MB4) were acquired with pTx. RESULTS pTx significantly improved flip-angle detected signal uniformity across the brain, yielding ∼19% increase in temporal SNR (tSNR) averaged over the brain relative to 1Tx. This allowed significantly enhanced estimation of multiple fiber orientations (with ∼21% decrease in dispersion) in HCP-style 7T dMRI datasets. Additionally, pTx pulses achieved substantially lower power deposition, permitting higher accelerations, enabling collection of the same data in 2/3 and 1/2 the scan time or of more data in the same scan time. CONCLUSION pTx provides a solution to two major limitations for slice-accelerated high-resolution whole-brain dMRI at 7T; it improves flip-angle uniformity, and enables higher slice acceleration relative to current state-of-the-art. As such, pTx provides significant advantages for rapid acquisition of high-quality, high-resolution truly whole-brain dMRI data.
Collapse
Affiliation(s)
- Xiaoping Wu
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota
| | - Edward J Auerbach
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota
| | - An T Vu
- Center for Imaging of Neurodegenerative Diseases, VA Healthcare System, San Francisco, California
| | - Steen Moeller
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota
| | - Christophe Lenglet
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota
| | - Sebastian Schmitter
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota.,Physikalisch-Technische Bundesanstalt, Berlin, Germany
| | | | - Essa Yacoub
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota
| | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota
| |
Collapse
|
19
|
Poser BA, Setsompop K. Pulse sequences and parallel imaging for high spatiotemporal resolution MRI at ultra-high field. Neuroimage 2018; 168:101-118. [PMID: 28392492 PMCID: PMC5630499 DOI: 10.1016/j.neuroimage.2017.04.006] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 04/01/2017] [Accepted: 04/03/2017] [Indexed: 12/18/2022] Open
Abstract
The SNR and CNR benefits of ultra-high field (UHF) have helped push the envelope of achievable spatial resolution in MRI. For applications based on susceptibility contrast where there is a large CNR gain, high quality sub-millimeter resolution imaging is now being routinely performed, particularly in fMRI and phase imaging/QSM. This has enabled the study of structure and function of very fine-scale structures in the brain. UHF has also helped push the spatial resolution of many other MRI applications as will be outlined in this review. However, this push in resolution comes at a cost of a large encoding burden leading to very lengthy scans. Developments in parallel imaging with controlled aliasing and the move away from 2D slice-by-slice imaging to much more SNR-efficient simultaneous multi-slice (SMS) and 3D acquisitions have helped address this issue. In particular, these developments have revolutionized the efficiency of UHF MRI to enable high spatiotemporal resolution imaging at an order of magnitude faster acquisition. In addition to describing the main approaches to these techniques, this review will also outline important key practical considerations in using these methods in practice. Furthermore, new RF pulse design to tackle the B1+ and SAR issues of UHF and the increased SAR and power requirement of SMS RF pulses will also be touched upon. Finally, an outlook into new developments of smart encoding in more dimensions, particularly through using better temporal/across-contrast encoding and reconstruction will be described. Just as controlled aliasing fully exploits spatial encoding in parallel imaging to provide large multiplicative gains in accelerations, the complimentary use of these new approaches in temporal and across-contrast encoding are expected to provide exciting opportunities for further large gains in efficiency to further push the spatiotemporal resolution of MRI.
Collapse
Affiliation(s)
- Benedikt A Poser
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands.
| | - Kawin Setsompop
- Department of Radiology, Harvard Medical School, Boston, MA, USA; Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA
| |
Collapse
|
20
|
Obusez EC, Lowe M, Oh SH, Wang I, Jennifer Bullen, Ruggieri P, Hill V, Lockwood D, Emch T, Moon D, Loy G, Lee J, Kiczek M, Manoj Massand, Statsevych V, Stultz T, Jones SE. 7T MR of intracranial pathology: Preliminary observations and comparisons to 3T and 1.5T. Neuroimage 2018; 168:459-476. [DOI: 10.1016/j.neuroimage.2016.11.030] [Citation(s) in RCA: 56] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2016] [Revised: 10/26/2016] [Accepted: 11/12/2016] [Indexed: 12/12/2022] Open
|
21
|
How to choose the right MR sequence for your research question at 7 T and above? Neuroimage 2018; 168:119-140. [DOI: 10.1016/j.neuroimage.2017.04.044] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Revised: 04/18/2017] [Accepted: 04/19/2017] [Indexed: 12/29/2022] Open
|
22
|
Uğurbil K. Imaging at ultrahigh magnetic fields: History, challenges, and solutions. Neuroimage 2018; 168:7-32. [PMID: 28698108 PMCID: PMC5758441 DOI: 10.1016/j.neuroimage.2017.07.007] [Citation(s) in RCA: 86] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 07/05/2017] [Accepted: 07/07/2017] [Indexed: 01/06/2023] Open
Abstract
Following early efforts in applying nuclear magnetic resonance (NMR) spectroscopy to study biological processes in intact systems, and particularly since the introduction of 4 T human scanners circa 1990, rapid progress was made in imaging and spectroscopy studies of humans at 4 T and animal models at 9.4 T, leading to the introduction of 7 T and higher magnetic fields for human investigation at about the turn of the century. Work conducted on these platforms has provided numerous technological solutions to challenges posed at these ultrahigh fields, and demonstrated the existence of significant advantages in signal-to-noise ratio and biological information content. Primary difference from lower fields is the deviation from the near field regime at the radiofrequencies (RF) corresponding to hydrogen resonance conditions. At such ultrahigh fields, the RF is characterized by attenuated traveling waves in the human body, which leads to image non-uniformities for a given sample-coil configuration because of destructive and constructive interferences. These non-uniformities were initially considered detrimental to progress of imaging at high field strengths. However, they are advantageous for parallel imaging in signal reception and transmission, two critical technologies that account, to a large extend, for the success of ultrahigh fields. With these technologies and improvements in instrumentation and imaging methods, today ultrahigh fields have provided unprecedented gains in imaging of brain function and anatomy, and started to make inroads into investigation of the human torso and extremities. As extensive as they are, these gains still constitute a prelude to what is to come given the increasingly larger effort committed to ultrahigh field research and development of ever better instrumentation and techniques.
Collapse
Affiliation(s)
- Kamil Uğurbil
- Center for Magnetic Resonance Research (CMRR), University of Minnesota Medical School, Minneapolis, MN 55455, USA.
| |
Collapse
|
23
|
Rund A, Aigner CS, Kunisch K, Stollberger R. Simultaneous multislice refocusing via time optimal control. Magn Reson Med 2018; 80:1416-1428. [DOI: 10.1002/mrm.27124] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Revised: 01/17/2018] [Accepted: 01/17/2018] [Indexed: 12/26/2022]
Affiliation(s)
- Armin Rund
- Institute for Mathematics and Scientific Computing, University of Graz; Graz Austria
- BioTechMed-Graz; Graz Austria
| | | | - Karl Kunisch
- Institute for Mathematics and Scientific Computing, University of Graz; Graz Austria
- BioTechMed-Graz; Graz Austria
- Johann Radon Institute for Computational and Applied Mathematics (RICAM), Austrian Academy of Sciences; Linz Austria
| | - Rudolf Stollberger
- BioTechMed-Graz; Graz Austria
- Institute of Medical Engineering, Graz University of Technology; Graz Austria
| |
Collapse
|
24
|
Rund A, Aigner CS, Kunisch K, Stollberger R. Magnetic Resonance RF Pulse Design by Optimal Control With Physical Constraints. IEEE TRANSACTIONS ON MEDICAL IMAGING 2018; 37:461-472. [PMID: 28981407 DOI: 10.1109/tmi.2017.2758391] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Optimal control approaches have proved useful in designing RF pulses for large tip-angle applications. A typical challenge for optimal control design is the inclusion of constraints resulting from physiological or technical limitations that assure the realizability of the optimized pulses. In this paper, we show how to treat such inequality constraints, in particular, amplitude constraints on the B1 field, the slice-selective gradient, and its slew rate, as well as constraints on the slice profile accuracy. For the latter, a pointwise profile error and additional phase constraints are prescribed. Here, a penalization method is introduced that corresponds to a higher order tracking instead of the common quadratic tracking. The order is driven to infinity in the course of the optimization. We jointly optimize for the RF and slice-selective gradient waveform. The amplitude constraints on these control variables are treated efficiently by semismooth Newton or quasi-Newton methods. The method is flexible, adapting to many optimization goals. As an application, we reduce the power of refocusing pulses, which is important for spin echo-based applications with a short echo spacing. Here, the optimization method is tested in numerical experiments for reducing the pulse power of simultaneous multislice refocusing pulses. The results are validated by phantom and in-vivo experiments.
Collapse
|
25
|
Norbeck O, Avventi E, Engström M, Rydén H, Skare S. Simultaneous multi-slice combined with PROPELLER. Magn Reson Med 2017; 80:496-506. [DOI: 10.1002/mrm.27041] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2017] [Revised: 11/14/2017] [Accepted: 11/17/2017] [Indexed: 11/10/2022]
Affiliation(s)
- Ola Norbeck
- Department of Neuroradiology; Karolinska University Hospital; Stockholm Sweden
- Department of Clinical Neuroscience; Karolinska Institutet; Stockholm Sweden
| | - Enrico Avventi
- Department of Neuroradiology; Karolinska University Hospital; Stockholm Sweden
- Department of Clinical Neuroscience; Karolinska Institutet; Stockholm Sweden
| | - Mathias Engström
- MR Applied Science Laboratory Europe, GE Healthcare; Stockholm Sweden
| | - Henric Rydén
- Department of Neuroradiology; Karolinska University Hospital; Stockholm Sweden
- Department of Clinical Neuroscience; Karolinska Institutet; Stockholm Sweden
| | - Stefan Skare
- Department of Neuroradiology; Karolinska University Hospital; Stockholm Sweden
- Department of Clinical Neuroscience; Karolinska Institutet; Stockholm Sweden
| |
Collapse
|
26
|
Ertan K, Taraghinia S, Sadeghi A, Atalar E. A z-gradient array for simultaneous multi-slice excitation with a single-band RF pulse. Magn Reson Med 2017; 80:400-412. [PMID: 29205480 DOI: 10.1002/mrm.27031] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 11/13/2017] [Accepted: 11/13/2017] [Indexed: 12/25/2022]
Abstract
PURPOSE Multi-slice radiofrequency (RF) pulses have higher specific absorption rates, more peak RF power, and longer pulse durations than single-slice RF pulses. Gradient field design techniques using a z-gradient array are investigated for exciting multiple slices with a single-band RF pulse. THEORY AND METHODS Two different field design methods are formulated to solve for the required current values of the gradient array elements for the given slice locations. The method requirements are specified, optimization problems are formulated for the minimum current norm and an analytical solution is provided. A 9-channel z-gradient coil array driven by independent, custom-designed gradient amplifiers is used to validate the theory. RESULTS Performance measures such as normalized slice thickness error, gradient strength per unit norm current, power dissipation, and maximum amplitude of the magnetic field are provided for various slice locations and numbers of slices. Two and 3 slices are excited by a single-band RF pulse in simulations and phantom experiments. CONCLUSION The possibility of multi-slice excitation with a single-band RF pulse using a z-gradient array is validated in simulations and phantom experiments. Magn Reson Med 80:400-412, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Koray Ertan
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Bilkent, Ankara, Turkey.,Department of Electrical and Electronics Engineering, Bilkent University, Bilkent, Ankara, Turkey
| | - Soheil Taraghinia
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Bilkent, Ankara, Turkey.,Department of Electrical and Electronics Engineering, Bilkent University, Bilkent, Ankara, Turkey
| | - Alireza Sadeghi
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Bilkent, Ankara, Turkey.,Department of Electrical and Electronics Engineering, Bilkent University, Bilkent, Ankara, Turkey
| | - Ergin Atalar
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Bilkent, Ankara, Turkey.,Department of Electrical and Electronics Engineering, Bilkent University, Bilkent, Ankara, Turkey
| |
Collapse
|
27
|
Schulz J, P Marques J, Ter Telgte A, van Dorst A, de Leeuw FE, Meijer FJA, Norris DG. Clinical application of Half Fourier Acquisition Single Shot Turbo Spin Echo (HASTE) imaging accelerated by simultaneous multi-slice acquisition. Eur J Radiol 2017; 98:200-206. [PMID: 29279164 DOI: 10.1016/j.ejrad.2017.11.022] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Revised: 10/09/2017] [Accepted: 11/29/2017] [Indexed: 02/06/2023]
Abstract
PURPOSE As a single-shot sequence with a long train of refocusing pulses, Half-Fourier Acquisition Single-Shot Turbo-Spin-Echo (HASTE) suffers from high power deposition limiting use at high resolutions and high field strengths, particularly if combined with acceleration techniques such as simultaneous multi-slice (SMS) imaging. Using a combination of multiband (MB)-excitation and PINS-refocusing pulses will effectively accelerate the acquisition time while staying within the SAR limitations. In particular, uncooperative and young patients will profit from the speed of the MB-PINS HASTE sequence, as clinical diagnosis can be possible without sedation. Materials and MethodsMB-excitation and PINS-refocusing pulses were incorporated into a HASTE-sequence with blipped CAIPIRINHA and TRAPS including an internal FLASH reference scan for online reconstruction. Whole brain MB-PINS HASTE data were acquired on a Siemens 3T-Prisma system from 10 individuals and compared to a clinical HASTE protocol. ResultsThe proposed MB-PINS HASTE protocol accelerates the acquisition by about a factor 2 compared to the clinical HASTE. The diagnostic image quality proved to be comparable for both sequences for the evaluation of the overall aspect of the brain, the detection of white matter changes and areas of tissue loss, and for the evaluation of the CSF spaces although artifacts were more frequently encountered with MB-PINS HASTE. ConclusionsMB-PINS HASTE enables acquisition of slice accelerated highly T2-weighted images and provides good diagnostic image quality while reducing acquisition time.
Collapse
Affiliation(s)
- Jenni Schulz
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, The Netherlands.
| | - José P Marques
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, The Netherlands
| | - Annemieke Ter Telgte
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, The Netherlands; Department of Neurology, Radboud University Medical Centre Nijmegen, The Netherlands
| | - Anouk van Dorst
- Department of Radiology and Nuclear Medicine, Jeroen Bosch Hospital, 's Hertogenbosch, The Netherlands
| | - Frank-Erik de Leeuw
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, The Netherlands; Department of Neurology, Radboud University Medical Centre Nijmegen, The Netherlands
| | - Frederick J A Meijer
- Department of Radiology and Nuclear Medicine, Radboud University Medical Centre Nijmegen, The Netherlands
| | - David G Norris
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, The Netherlands; Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
| |
Collapse
|
28
|
Grissom WA, Setsompop K, Hurley SA, Tsao J, Velikina JV, Samsonov AA. Advancing RF pulse design using an open-competition format: Report from the 2015 ISMRM challenge. Magn Reson Med 2017; 78:1352-1361. [PMID: 27790754 PMCID: PMC5408273 DOI: 10.1002/mrm.26512] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Revised: 09/26/2016] [Accepted: 09/27/2016] [Indexed: 02/03/2023]
Abstract
PURPOSE To advance the best solutions to two important RF pulse design problems with an open head-to-head competition. METHODS Two sub-challenges were formulated in which contestants competed to design the shortest simultaneous multislice (SMS) refocusing pulses and slice-selective parallel transmission (pTx) excitation pulses, subject to realistic hardware and safety constraints. Short refocusing pulses are needed for spin echo SMS imaging at high multiband factors, and short slice-selective pTx pulses are needed for multislice imaging in ultra-high field MRI. Each sub-challenge comprised two phases, in which the first phase posed problems with a low barrier of entry, and the second phase encouraged solutions that performed well in general. The Challenge ran from October 2015 to May 2016. RESULTS The pTx Challenge winners developed a spokes pulse design method that combined variable-rate selective excitation with an efficient method to enforce SAR constraints, which achieved 10.6 times shorter pulse durations than conventional approaches. The SMS Challenge winners developed a time-optimal control multiband pulse design algorithm that achieved 5.1 times shorter pulse durations than conventional approaches. CONCLUSION The Challenge led to rapid step improvements in solutions to significant problems in RF excitation for SMS imaging and ultra-high field MRI. Magn Reson Med 78:1352-1361, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- William A. Grissom
- Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA
- Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
| | - Kawin Setsompop
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | | | | | - Julia V. Velikina
- Department of Medical Physics, University of Wisconsin, Madison, USA
| | | |
Collapse
|
29
|
Wu W, Miller KL. Image formation in diffusion MRI: A review of recent technical developments. J Magn Reson Imaging 2017; 46:646-662. [PMID: 28194821 PMCID: PMC5574024 DOI: 10.1002/jmri.25664] [Citation(s) in RCA: 84] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Accepted: 01/25/2017] [Indexed: 12/13/2022] Open
Abstract
Diffusion magnetic resonance imaging (MRI) is a standard imaging tool in clinical neurology, and is becoming increasingly important for neuroscience studies due to its ability to depict complex neuroanatomy (eg, white matter connectivity). Single-shot echo-planar imaging is currently the predominant formation method for diffusion MRI, but suffers from blurring, distortion, and low spatial resolution. A number of methods have been proposed to address these limitations and improve diffusion MRI acquisition. Here, the recent technical developments for image formation in diffusion MRI are reviewed. We discuss three areas of advance in diffusion MRI: improving image fidelity, accelerating acquisition, and increasing the signal-to-noise ratio. LEVEL OF EVIDENCE 5 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:646-662.
Collapse
Affiliation(s)
- Wenchuan Wu
- FMRIB Centre, Nuffield Department of Clinical NeurosciencesUniversity of OxfordOxfordUK
| | - Karla L. Miller
- FMRIB Centre, Nuffield Department of Clinical NeurosciencesUniversity of OxfordOxfordUK
| |
Collapse
|
30
|
Hamilton J, Franson D, Seiberlich N. Recent advances in parallel imaging for MRI. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2017; 101:71-95. [PMID: 28844222 PMCID: PMC5927614 DOI: 10.1016/j.pnmrs.2017.04.002] [Citation(s) in RCA: 106] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 04/09/2017] [Accepted: 04/17/2017] [Indexed: 05/22/2023]
Abstract
Magnetic Resonance Imaging (MRI) is an essential technology in modern medicine. However, one of its main drawbacks is the long scan time needed to localize the MR signal in space to generate an image. This review article summarizes some basic principles and recent developments in parallel imaging, a class of image reconstruction techniques for shortening scan time. First, the fundamentals of MRI data acquisition are covered, including the concepts of k-space, undersampling, and aliasing. It is demonstrated that scan time can be reduced by sampling a smaller number of phase encoding lines in k-space; however, without further processing, the resulting images will be degraded by aliasing artifacts. Nearly all modern clinical scanners acquire data from multiple independent receiver coil arrays. Parallel imaging methods exploit properties of these coil arrays to separate aliased pixels in the image domain or to estimate missing k-space data using knowledge of nearby acquired k-space points. Three parallel imaging methods-SENSE, GRAPPA, and SPIRiT-are described in detail, since they are employed clinically and form the foundation for more advanced methods. These techniques can be extended to non-Cartesian sampling patterns, where the collected k-space points do not fall on a rectangular grid. Non-Cartesian acquisitions have several beneficial properties, the most important being the appearance of incoherent aliasing artifacts. Recent advances in simultaneous multi-slice imaging are presented next, which use parallel imaging to disentangle images of several slices that have been acquired at once. Parallel imaging can also be employed to accelerate 3D MRI, in which a contiguous volume is scanned rather than sequential slices. Another class of phase-constrained parallel imaging methods takes advantage of both image magnitude and phase to achieve better reconstruction performance. Finally, some applications are presented of parallel imaging being used to accelerate MR Spectroscopic Imaging.
Collapse
Affiliation(s)
- Jesse Hamilton
- Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA.
| | - Dominique Franson
- Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA.
| | - Nicole Seiberlich
- Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA; Radiology, University Hospitals Cleveland Medical Center, Cleveland, OH, USA.
| |
Collapse
|
31
|
Kraff O, Quick HH. 7T: Physics, safety, and potential clinical applications. J Magn Reson Imaging 2017; 46:1573-1589. [DOI: 10.1002/jmri.25723] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Accepted: 03/17/2017] [Indexed: 12/19/2022] Open
Affiliation(s)
- Oliver Kraff
- Erwin L. Hahn Institute for MR Imaging; University of Duisburg-Essen; Essen Germany
| | - Harald H. Quick
- Erwin L. Hahn Institute for MR Imaging; University of Duisburg-Essen; Essen Germany
- High Field and Hybrid MR Imaging; University Hospital Essen; Essen Germany
| |
Collapse
|
32
|
Wu FH, Wu EL, Tung YH, Cheng PW, Chiueh TD, Chen JH. A specific absorption rate reduction method for simultaneous multislice magnetic resonance imaging. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2017; 88:043701. [PMID: 28456274 DOI: 10.1063/1.4979861] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
This study proposes a modified Shinnar-Le Roux method to synthesize the excitation radio frequency (RF) pulse for a 2D gradient echo (GRE) based simultaneous multi-slice (SMS) magnetic resonance imaging (MRI) with features of low specific absorption rate (SAR) and small out-of-slice ripple. This synthesis method for SMS RF pulses employs thinner slice bandwidth and lower multislice offset frequencies to reduce SAR values and adopts a weighted Parks-McClellan algorithm to reduce sidelobes. Formulas for estimating relative SAR values of the SMS pulses are also introduced. Relative SAR values and out-of-slice ripples of the proposed and typical RF pulses with different parameters are presented. In simultaneous 5-slice phantom and 3-slice human brain imaging, SMS pulses synthesized with the proposed method achieve 32% and 28% SAR values of standard pulses while providing similar image qualities. Typical RF pulses such as sinc x cos can also take advantage of the proposed method and offer lower SAR values for SMS imaging. The RF pulse synthesized using the proposed method features low SAR, small sidelobes, and consistent image quality for 2D GRE-based SMS MRI. This method is applicable to the synthesis of typical SMS RF pulses for significant SAR reduction.
Collapse
Affiliation(s)
- Fu-Hsing Wu
- Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Edzer L Wu
- Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Yi-Hang Tung
- Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Po-Wei Cheng
- Interdisciplinary MRI/MRS Lab, Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei 10617, Taiwan
| | - Tzi-Dar Chiueh
- MicroSystem Research Lab, Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Jyh-Horng Chen
- Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
| |
Collapse
|
33
|
Schmitter S, Moeller S, Wu X, Auerbach EJ, Metzger GJ, Van de Moortele PF, Uğurbil K. Simultaneous multislice imaging in dynamic cardiac MRI at 7T using parallel transmission. Magn Reson Med 2017; 77:1010-1020. [PMID: 26949107 DOI: 10.1002/mrm.26180] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Revised: 01/08/2016] [Accepted: 02/03/2016] [Indexed: 12/25/2022]
Abstract
PURPOSE Cardiac MRI at 7T suffers from contrast heterogeneity that can be mitigated with parallel transmission (pTX) and, when performed during breath-hold, from a limited number of slices that can be multiplied with multiband (MB) radiofrequency pulses by simultaneous excitation of multiple slices (SMS). The goal of this study was to apply both approaches simultaneously. METHODS Using a 16-channel transmit/receive body coil, pTX SMS was applied with/without CAIPIRINHA with a modified gradient echo cine sequence. Different calibration schemes were investigated for the slice-GRAPPA reconstruction kernels as a function of the cardiac cycle. RESULTS Excellent slice separation for MB = 2 was achieved with CAIPIRINHA, with slice leakage values below 3% for 99% of all voxels. A critical finding of this study was the variation of the MB leakage factor in the heart by as much as 30% throughout the cardiac cycle, which was reduced greatly when reconstruction kernels were calibrated on multiple cardiac phases. Acceptable results were still obtained when applying further acceleration with MB = 3 in combination with in-plane GRAPPA. In one case, two-spoke pulses were compared with one-spoke pulses, resulting as expected in improved homogeneity. CONCLUSION pTX SMS imaging at 7T can address contrast heterogeneity while allowing larger slice coverage in cardiac MRI performed under breath-hold. Magn Reson Med 77:1010-1020, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Sebastian Schmitter
- University of Minnesota, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Steen Moeller
- University of Minnesota, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Xiaoping Wu
- University of Minnesota, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Edward J Auerbach
- University of Minnesota, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Gregory J Metzger
- University of Minnesota, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | | | - Kâmil Uğurbil
- University of Minnesota, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| |
Collapse
|
34
|
Weiss J, Martirosian P, Taron J, Othman AE, Kuestner T, Erb M, Bedke J, Bamberg F, Nikolaou K, Notohamiprodjo M. Feasibility of accelerated simultaneous multislice diffusion-weighted MRI of the prostate. J Magn Reson Imaging 2017; 46:1507-1515. [DOI: 10.1002/jmri.25665] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Accepted: 01/25/2017] [Indexed: 01/22/2023] Open
Affiliation(s)
- Jakob Weiss
- Department of Diagnostic and Interventional Radiology; Eberhard Karls University Tuebingen; Germany
| | - Petros Martirosian
- Section on Experimental Radiology; Eberhard Karls University Tuebingen; Germany
| | - Jana Taron
- Department of Diagnostic and Interventional Radiology; Eberhard Karls University Tuebingen; Germany
| | - Ahmed E. Othman
- Department of Diagnostic and Interventional Radiology; Eberhard Karls University Tuebingen; Germany
| | - Thomas Kuestner
- Institute of Signal Processing and System Theory; University of Stuttgart; Germany
| | - Michael Erb
- Department of Biomedical Magnetic Resonance; Eberhard Karls University Tuebingen; Germany
| | - Jens Bedke
- Department of Urology; Eberhard Karls University Tuebingen; Germany
| | - Fabian Bamberg
- Department of Diagnostic and Interventional Radiology; Eberhard Karls University Tuebingen; Germany
| | - Konstantin Nikolaou
- Department of Diagnostic and Interventional Radiology; Eberhard Karls University Tuebingen; Germany
| | - Mike Notohamiprodjo
- Department of Diagnostic and Interventional Radiology; Eberhard Karls University Tuebingen; Germany
| |
Collapse
|
35
|
Setsompop K, Feinberg DA, Polimeni JR. Rapid brain MRI acquisition techniques at ultra-high fields. NMR IN BIOMEDICINE 2016; 29:1198-221. [PMID: 26835884 PMCID: PMC5245168 DOI: 10.1002/nbm.3478] [Citation(s) in RCA: 78] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Revised: 11/28/2015] [Accepted: 12/02/2015] [Indexed: 05/04/2023]
Abstract
Ultra-high-field MRI provides large increases in signal-to-noise ratio (SNR) as well as enhancement of several contrast mechanisms in both structural and functional imaging. Combined, these gains result in a substantial boost in contrast-to-noise ratio that can be exploited for higher-spatial-resolution imaging to extract finer-scale information about the brain. With increased spatial resolution, however, there is a concurrent increased image-encoding burden that can cause unacceptably long scan times for structural imaging and slow temporal sampling of the hemodynamic response in functional MRI - particularly when whole-brain imaging is desired. To address this issue, new directions of imaging technology development - such as the move from conventional 2D slice-by-slice imaging to more efficient simultaneous multislice (SMS) or multiband imaging (which can be viewed as "pseudo-3D" encoding) as well as full 3D imaging - have provided dramatic improvements in acquisition speed. Such imaging paradigms provide higher SNR efficiency as well as improved encoding efficiency. Moreover, SMS and 3D imaging can make better use of coil sensitivity information in multichannel receiver arrays used for parallel imaging acquisitions through controlled aliasing in multiple spatial directions. This has enabled unprecedented acceleration factors of an order of magnitude or higher in these imaging acquisition schemes, with low image artifact levels and high SNR. Here we review the latest developments of SMS and 3D imaging methods and related technologies at ultra-high field for rapid high-resolution functional and structural imaging of the brain. Copyright © 2016 John Wiley & Sons, Ltd.
Collapse
Affiliation(s)
- Kawin Setsompop
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA
- Department of Radiology, Harvard Medical School, Boston, MA, USA
| | - David A. Feinberg
- Helen Wills Institute for Neuroscience, University of California, Berkeley, CA, USA
- Advanced MRI Technologies, Sebastopol, CA, USA
| | - Jonathan R. Polimeni
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA
- Department of Radiology, Harvard Medical School, Boston, MA, USA
| |
Collapse
|
36
|
Wu X, Tian J, Schmitter S, Vaughan JT, Uğurbil K, Van de Moortele PF. Distributing coil elements in three dimensions enhances parallel transmission multiband RF performance: A simulation study in the human brain at 7 Tesla. Magn Reson Med 2016; 75:2464-72. [PMID: 26997332 PMCID: PMC6014621 DOI: 10.1002/mrm.26194] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Revised: 01/18/2016] [Accepted: 02/10/2016] [Indexed: 12/26/2022]
Abstract
PURPOSE We explore the advantages of using a double-ring radiofrequency (RF) array and slice orientation to design parallel transmission (pTx) multiband (MB) pulses for simultaneous multislice (SMS) imaging with whole-brain coverage at 7 Tesla (T). METHODS A double-ring head array with 16 elements split evenly in two rings stacked in the z-direction was modeled and compared with two single-ring arrays consisting of 8 or 16 elements. The array performance was evaluated by designing band-specific pTx MB pulses with local specific absorption rate (SAR) control. The impact of slice orientations was also investigated. RESULTS The double-ring array consistently and significantly outperformed the other two single-ring arrays, with peak local SAR reduced by up to 40% at a fixed excitation error of 0.024. For all three arrays, exciting sagittal or coronal slices yielded better RF performance than exciting axial or oblique slices. CONCLUSIONS A double-ring RF array can be used to drastically improve SAR versus excitation fidelity tradeoff for pTx MB pulse design for brain imaging at 7 T; therefore, it is preferable against single-ring RF array designs when pursuing various biomedical applications of pTx SMS imaging. In comparing the stripline arrays, coronal and sagittal slices are more advantageous than axial and oblique slices for pTx MB pulses. Magn Reson Med 75:2464-2472, 2016. © 2016 Wiley Periodicals, Inc.
Collapse
Affiliation(s)
- Xiaoping Wu
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN
| | - Jinfeng Tian
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN
| | - Sebastian Schmitter
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN
| | - J Tommy Vaughan
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN
| | - Kâmil Uğurbil
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN
| | | |
Collapse
|
37
|
Artz NS, Wiens CN, Smith MR, Hernando D, Samsonov A, Reeder SB. Accelerating fully phase-encoded MRI near metal using multiband radiofrequency excitation. Magn Reson Med 2016; 77:1223-1230. [PMID: 27052204 DOI: 10.1002/mrm.26209] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2015] [Revised: 02/18/2016] [Accepted: 02/18/2016] [Indexed: 11/10/2022]
Abstract
PURPOSE To develop a multiband radiofrequency (RF) excitation strategy for simultaneous excitation of multiple RF offsets to accelerate fully phase-encoded imaging near metallic prostheses. METHODS Multiband RF excitation was designed and incorporated into a spectrally resolved fully phase-encoded (SR-FPE) imaging scheme. A triband (-6, 0, 6 kHz) acquisition was compared with three separate single-band acquisitions at the corresponding RF offsets with a phantom containing the head of a hip prosthesis. In vivo multiband data with continuous spectral coverage were acquired in the knee of a healthy volunteer with the head of a hip prosthesis placed posteriorly and in a volunteer with a total knee prosthetic implant. RESULTS Phantom images acquired with triband excitation were essentially identical to the composite of three single-band excitations, but with an acceleration factor of three. In vivo multiband images of the healthy knee with adjacent metal demonstrated very good depiction of knee anatomy. In vivo images of the total knee replacement were successfully acquired, allowing visualization of native tissue with far less signal dropout than 2D-FSE. CONCLUSIONS FPE imaging with multiband excitation is feasible in the presence of extreme off-resonance. This approach can reduce scan time and/or increase off-resonance coverage, enabling in vivo FPE imaging near metallic prostheses over a broad off-resonance spectrum. Magn Reson Med 77:1223-1230, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Nathan S Artz
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.,Department of Diagnostic Imaging, St. Jude Children's Research Hospital, Memphis, Tennessee, USA
| | - Curtis N Wiens
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA
| | - Matthew R Smith
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA
| | - Diego Hernando
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA
| | - Alexey Samsonov
- 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
| |
Collapse
|
38
|
Aigner CS, Clason C, Rund A, Stollberger R. Efficient high-resolution RF pulse design applied to simultaneous multi-slice excitation. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 263:33-44. [PMID: 26773524 DOI: 10.1016/j.jmr.2015.11.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2015] [Revised: 11/23/2015] [Accepted: 11/25/2015] [Indexed: 06/05/2023]
Abstract
RF pulse design via optimal control is typically based on gradient and quasi-Newton approaches and therefore suffers from slow convergence. We present a flexible and highly efficient method that uses exact second-order information within a globally convergent trust-region CG-Newton method to yield an improved convergence rate. The approach is applied to the design of RF pulses for single- and simultaneous multi-slice (SMS) excitation and validated using phantom and in vivo experiments on a 3T scanner using a modified gradient echo sequence.
Collapse
Affiliation(s)
- Christoph Stefan Aigner
- Institute of Medical Engineering, Graz University of Technology, Stremayrgasse 16, 8010 Graz, Austria; BioTechMed Graz, 8010 Graz, Austria.
| | - Christian Clason
- Faculty of Mathematics, University of Duisburg-Essen, 45117 Essen, Germany
| | - Armin Rund
- Institute for Mathematics and Scientific Computing, University of Graz, Heinrichstrasse 36, 8010 Graz, Austria
| | - Rudolf Stollberger
- Institute of Medical Engineering, Graz University of Technology, Stremayrgasse 16, 8010 Graz, Austria; BioTechMed Graz, 8010 Graz, Austria
| |
Collapse
|
39
|
Bilgic B, Xie L, Dibb R, Langkammer C, Mutluay A, Ye H, Polimeni JR, Augustinack J, Liu C, Wald LL, Setsompop K. Rapid multi-orientation quantitative susceptibility mapping. Neuroimage 2016; 125:1131-1141. [PMID: 26277773 PMCID: PMC4691433 DOI: 10.1016/j.neuroimage.2015.08.015] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Revised: 08/02/2015] [Accepted: 08/04/2015] [Indexed: 01/10/2023] Open
Abstract
Three-dimensional gradient echo (GRE) is the main workhorse sequence used for susceptibility weighted imaging (SWI), quantitative susceptibility mapping (QSM), and susceptibility tensor imaging (STI). Achieving optimal phase signal-to-noise ratio requires late echo times, thus necessitating a long repetition time (TR). Combined with the large encoding burden of whole-brain coverage with high resolution, this leads to increased scan time. Further, the dipole kernel relating the tissue phase to the underlying susceptibility distribution undersamples the frequency content of the susceptibility map. Scans at multiple head orientations along with calculation of susceptibility through multi-orientation sampling (COSMOS) are one way to effectively mitigate this issue. Additionally, STI requires a minimum of 6 head orientations to solve for the independent tensor elements in each voxel. The requirements of high-resolution imaging with long TR at multiple orientations substantially lengthen the acquisition of COSMOS and STI. The goal of this work is to dramatically speed up susceptibility mapping at multiple head orientations. We demonstrate highly efficient acquisition using 3D-GRE with Wave-CAIPI and dramatically reduce the acquisition time of these protocols. Using R=15-fold acceleration with Wave-CAIPI permits acquisition per head orientation in 90s at 1.1mm isotropic resolution, and 5:35min at 0.5mm isotropic resolution. Since Wave-CAIPI fully harnesses the 3D spatial encoding capability of receive arrays, the maximum g-factor noise amplification remains below 1.30 at 3T and 1.12 at 7T. This allows a 30-min exam for STI with 12 orientations, thus paving the way to its clinical application.
Collapse
Affiliation(s)
- Berkin Bilgic
- Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA.
| | - Luke Xie
- Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC, USA
| | - Russell Dibb
- Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC, USA; Brain Imaging and Analysis Center, Duke University Medical Center, Durham, NC, USA
| | - Christian Langkammer
- Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; Department of Neurology, Medical University of Graz, Graz, Austria; Department of Radiology, Harvard Medical School, Boston, MA, USA
| | | | - Huihui Ye
- Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA
| | - Jonathan R Polimeni
- Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA
| | - Jean Augustinack
- Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA
| | - Chunlei Liu
- Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC, USA; Brain Imaging and Analysis Center, Duke University Medical Center, Durham, NC, USA
| | - Lawrence L Wald
- Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA; Harvard-MIT Health Sciences and Technology, MIT, Cambridge, MA, USA
| | - Kawin Setsompop
- Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA
| |
Collapse
|
40
|
Huettner AM, Mickevicius NJ, Ersoz A, Koch KM, Muftuler LT, Nencka AS. Wavelet Domain Radiofrequency Pulse Design Applied to Magnetic Resonance Imaging. PLoS One 2015; 10:e0141151. [PMID: 26517262 PMCID: PMC4627821 DOI: 10.1371/journal.pone.0141151] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2015] [Accepted: 10/04/2015] [Indexed: 11/18/2022] Open
Abstract
A new method for designing radiofrequency (RF) pulses with numerical optimization in the wavelet domain is presented. Numerical optimization may yield solutions that might otherwise have not been discovered with analytic techniques alone. Further, processing in the wavelet domain reduces the number of unknowns through compression properties inherent in wavelet transforms, providing a more tractable optimization problem. This algorithm is demonstrated with simultaneous multi-slice (SMS) spin echo refocusing pulses because reduced peak RF power is necessary for SMS diffusion imaging with high acceleration factors. An iterative, nonlinear, constrained numerical minimization algorithm was developed to generate an optimized RF pulse waveform. Wavelet domain coefficients were modulated while iteratively running a Bloch equation simulator to generate the intermediate slice profile of the net magnetization. The algorithm minimizes the L2-norm of the slice profile with additional terms to penalize rejection band ripple and maximize the net transverse magnetization across each slice. Simulations and human brain imaging were used to demonstrate a new RF pulse design that yields an optimized slice profile and reduced peak energy deposition when applied to a multiband single-shot echo planar diffusion acquisition. This method may be used to optimize factors such as magnitude and phase spectral profiles and peak RF pulse power for multiband simultaneous multi-slice (SMS) acquisitions. Wavelet-based RF pulse optimization provides a useful design method to achieve a pulse waveform with beneficial amplitude reduction while preserving appropriate magnetization response for magnetic resonance imaging.
Collapse
Affiliation(s)
- Andrew M. Huettner
- Department of Biophysics, The Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Nikolai J. Mickevicius
- Department of Radiation Oncology, The Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Ali Ersoz
- Department of Neurosurgery, The Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Kevin M. Koch
- Department of Biophysics, The Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
- Department of Radiology, The Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - L. Tugan Muftuler
- Department of Neurosurgery, The Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
| | - Andrew S. Nencka
- Department of Biophysics, The Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
- Department of Radiology, The Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America
- * E-mail:
| |
Collapse
|
41
|
Barth M, Breuer F, Koopmans PJ, Norris DG, Poser BA. Simultaneous multislice (SMS) imaging techniques. Magn Reson Med 2015; 75:63-81. [PMID: 26308571 PMCID: PMC4915494 DOI: 10.1002/mrm.25897] [Citation(s) in RCA: 357] [Impact Index Per Article: 39.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 07/25/2015] [Accepted: 07/27/2015] [Indexed: 12/25/2022]
Abstract
Simultaneous multislice imaging (SMS) using parallel image reconstruction has rapidly advanced to become a major imaging technique. The primary benefit is an acceleration in data acquisition that is equal to the number of simultaneously excited slices. Unlike in‐plane parallel imaging this can have only a marginal intrinsic signal‐to‐noise ratio penalty, and the full acceleration is attainable at fixed echo time, as is required for many echo planar imaging applications. Furthermore, for some implementations SMS techniques can reduce radiofrequency (RF) power deposition. In this review the current state of the art of SMS imaging is presented. In the Introduction, a historical overview is given of the history of SMS excitation in MRI. The following section on RF pulses gives both the theoretical background and practical application. The section on encoding and reconstruction shows how the collapsed multislice images can be disentangled by means of the transmitter pulse phase, gradient pulses, and most importantly using multichannel receiver coils. The relationship between classic parallel imaging techniques and SMS reconstruction methods is explored. The subsequent section describes the practical implementation, including the acquisition of reference data, and slice cross‐talk. Published applications of SMS imaging are then reviewed, and the article concludes with an outlook and perspective of SMS imaging. Magn Reson Med 75:63–81, 2016. © 2015 The Authors. Magnetic Resonance in Medicine Published by Wiley Periodicals, Inc. on behalf of International Society of Medicine in Resonance.
Collapse
Affiliation(s)
- Markus Barth
- Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia.,Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands
| | - Felix Breuer
- Research Center Magnetic Resonance Bavaria (MRB), Würzburg, Germany
| | - Peter J Koopmans
- Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands.,FMRIB Centre, University of Oxford, Oxford, United Kingdom
| | - David G Norris
- Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands.,Erwin L. Hahn Institute for Magnetic Resonance Imaging, UNESCO-Weltkulturerbe Zollverein, Leitstand Kokerei Zollverein, Essen, Germany.,MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands
| | - Benedikt A Poser
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.,Maastricht Brain Imaging Center (M-BIC), Maastricht University, Maastricht, The Netherlands
| |
Collapse
|
42
|
Vu AT, Auerbach E, Lenglet C, Moeller S, Sotiropoulos SN, Jbabdi S, Andersson J, Yacoub E, Ugurbil K. High resolution whole brain diffusion imaging at 7T for the Human Connectome Project. Neuroimage 2015; 122:318-31. [PMID: 26260428 DOI: 10.1016/j.neuroimage.2015.08.004] [Citation(s) in RCA: 137] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2015] [Revised: 07/31/2015] [Accepted: 08/01/2015] [Indexed: 11/16/2022] Open
Abstract
Mapping structural connectivity in healthy adults for the Human Connectome Project (HCP) benefits from high quality, high resolution, multiband (MB)-accelerated whole brain diffusion MRI (dMRI). Acquiring such data at ultrahigh fields (7T and above) can improve intrinsic signal-to-noise ratio (SNR), but suffers from shorter T2 and T2(⁎) relaxation times, increased B1(+) inhomogeneity (resulting in signal loss in cerebellar and temporal lobe regions), and increased power deposition (i.e. specific absorption rate (SAR)), thereby limiting our ability to reduce the repetition time (TR). Here, we present recent developments and optimizations in 7T image acquisitions for the HCP that allow us to efficiently obtain high quality, high resolution whole brain in-vivo dMRI data at 7T. These data show spatial details typically seen only in ex-vivo studies and complement already very high quality 3T HCP data in the same subjects. The advances are the result of intensive pilot studies aimed at mitigating the limitations of dMRI at 7T. The data quality and methods described here are representative of the datasets that will be made freely available to the community in 2015.
Collapse
Affiliation(s)
- A T Vu
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA.
| | - E Auerbach
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA
| | - C Lenglet
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA
| | - S Moeller
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA
| | - S N Sotiropoulos
- Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB), University of Oxford, UK
| | - S Jbabdi
- Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB), University of Oxford, UK
| | - J Andersson
- Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB), University of Oxford, UK
| | - E Yacoub
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA
| | - K Ugurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA
| |
Collapse
|
43
|
Eichner C, Cauley SF, Cohen-Adad J, Möller HE, Turner R, Setsompop K, Wald LL. Real diffusion-weighted MRI enabling true signal averaging and increased diffusion contrast. Neuroimage 2015; 122:373-84. [PMID: 26241680 DOI: 10.1016/j.neuroimage.2015.07.074] [Citation(s) in RCA: 78] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Revised: 07/01/2015] [Accepted: 07/24/2015] [Indexed: 11/16/2022] Open
Abstract
This project aims to characterize the impact of underlying noise distributions on diffusion-weighted imaging. The noise floor is a well-known problem for traditional magnitude-based diffusion-weighted MRI (dMRI) data, leading to biased diffusion model fits and inaccurate signal averaging. Here, we introduce a total-variation-based algorithm to eliminate shot-to-shot phase variations of complex-valued diffusion data with the intention to extract real-valued dMRI datasets. The obtained real-valued diffusion data are no longer superimposed by a noise floor but instead by a zero-mean Gaussian noise distribution, yielding dMRI data without signal bias. We acquired high-resolution dMRI data with strong diffusion weighting and, thus, low signal-to-noise ratio. Both the extracted real-valued and traditional magnitude data were compared regarding signal averaging, diffusion model fitting and accuracy in resolving crossing fibers. Our results clearly indicate that real-valued diffusion data enables idealized conditions for signal averaging. Furthermore, the proposed method enables unbiased use of widely employed linear least squares estimators for model fitting and demonstrates an increased sensitivity to detect secondary fiber directions with reduced angular error. The use of phase-corrected, real-valued data for dMRI will therefore help to clear the way for more detailed and accurate studies of white matter microstructure and structural connectivity on a fine scale.
Collapse
Affiliation(s)
- Cornelius Eichner
- Martinos Center for Biomedical Imaging, Harvard Medical School, Boston, MA, USA; Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
| | - Stephen F Cauley
- Martinos Center for Biomedical Imaging, Harvard Medical School, Boston, MA, USA
| | | | - Harald E Möller
- Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Robert Turner
- Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Kawin Setsompop
- Martinos Center for Biomedical Imaging, Harvard Medical School, Boston, MA, USA.
| | - Lawrence L Wald
- Martinos Center for Biomedical Imaging, Harvard Medical School, Boston, MA, USA
| |
Collapse
|
44
|
Sharma A, Lustig M, Grissom WA. Root-flipped multiband refocusing pulses. Magn Reson Med 2015; 75:227-37. [PMID: 25704154 DOI: 10.1002/mrm.25629] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Revised: 12/11/2014] [Accepted: 01/03/2015] [Indexed: 12/24/2022]
Abstract
PURPOSE To design low peak power multiband refocusing radiofrequency pulses, with application to simultaneous multislice spin echo MRI. THEORY AND METHODS Multiband Shinnar-Le Roux β polynomials were designed using convex optimization. A Monte Carlo algorithm was used to determine patterns of β polynomial root flips that minimized the peak power of the resulting refocusing pulses. Phase-matched multiband excitation pulses were also designed to obtain linear-phase spin echoes. Simulations compared the performance of the root-flipped pulses with time-shifted and phase-optimized pulses. Phantom and in vivo experiments at 7T validated the function of the root-flipped pulses and compared them to time-shifted spin echo signal profiles. RESULTS Averaged across number of slices, time-bandwidth product, and slice separation, the root-flipped pulses have 46% shorter durations than time-shifted pulses with the same peak radiofrequency amplitude. Unlike time-shifted and phase-optimized pulses, the root-flipped pulses' excitation errors do not increase with decreasing band separation. Experiments showed that the root-flipped pulses excited the desired slices at the target locations, and that for equivalent slice characteristics, the shorter root-flipped pulses allowed shorter echo times, resulting in higher signal than time-shifted pulses. CONCLUSION The proposed root-flipped multiband radiofrequency pulse design method produces low peak power pulses for simultaneous multislice spin echo MRI.
Collapse
Affiliation(s)
- Anuj Sharma
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA.,Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
| | - Michael Lustig
- Department of Electrical Engineering and Computer Science, University of California Berkeley, Berkeley, California, USA
| | - William A Grissom
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA.,Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.,Department of Radiology, Vanderbilt University, Nashville, Tennessee, USA.,Department of Electrical Engineering, Vanderbilt University, Nashville, Tennessee, USA
| |
Collapse
|
45
|
Gagoski BA, Bilgic B, Eichner C, Bhat H, Grant PE, Wald LL, Setsompop K. RARE/turbo spin echo imaging with Simultaneous Multislice Wave-CAIPI. Magn Reson Med 2015; 73:929-938. [PMID: 25640187 DOI: 10.1002/mrm.25615] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Revised: 12/21/2014] [Accepted: 12/22/2014] [Indexed: 02/04/2023]
Abstract
PURPOSE To enable highly accelerated RARE/Turbo Spin Echo (TSE) imaging using Simultaneous MultiSlice (SMS) Wave-CAIPI acquisition with reduced g-factor penalty. METHODS SMS Wave-CAIPI incurs slice shifts across simultaneously excited slices while playing sinusoidal gradient waveforms during the readout of each encoding line. This results in an efficient k-space coverage that spreads aliasing in all three dimensions to fully harness the encoding power of coil sensitivities. The novel MultiPINS radiofrequency (RF) pulses dramatically reduce the power deposition of multiband (MB) refocusing pulse, thus allowing high MB factors within the Specific Absorption Rate (SAR) limit. RESULTS Wave-CAIPI acquisition with MultiPINS permits whole brain coverage with 1 mm isotropic resolution in 70 s at effective MB factor 13, with maximum and average g-factor penalties of gmax = 1.34 and gavg = 1.12, and without √R penalty. With blipped-CAIPI, the g-factor performance was degraded to gmax = 3.24 and gavg = 1.42; a 2.4-fold increase in gmax relative to Wave-CAIPI. At this MB factor, the SAR of the MultiBand and PINS pulses are 4.2 and 1.9 times that of the MultiPINS pulse, while the peak RF power are 19.4 and 3.9 times higher. CONCLUSION Combination of the two technologies, Wave-CAIPI and MultiPINS pulse, enables highly accelerated RARE/TSE imaging with low SNR penalty at reduced SAR.
Collapse
Affiliation(s)
- Borjan A Gagoski
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Boston, MA, USA.,Department of Radiology, Harvard Medical School, Boston, MA, USA
| | - Berkin Bilgic
- Department of Radiology, Harvard Medical School, Boston, MA, USA.,Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA
| | - Cornelius Eichner
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA.,Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Himanshu Bhat
- Siemens Medical Solutions USA Inc., Charlestown, MA, USA
| | - P Ellen Grant
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Boston, MA, USA.,Department of Radiology, Harvard Medical School, Boston, MA, USA
| | - Lawrence L Wald
- Department of Radiology, Harvard Medical School, Boston, MA, USA.,Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA.,Harvard-MIT Health Sciences and Technology, Cambridge, MA, USA
| | - Kawin Setsompop
- Department of Radiology, Harvard Medical School, Boston, MA, USA.,Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA
| |
Collapse
|