1
|
Shang Y, Simegn GL, Gillen K, Yang HJ, Han H. Advancements in MR hardware systems and magnetic field control: B 0 shimming, RF coils, and gradient techniques for enhancing magnetic resonance imaging and spectroscopy. PSYCHORADIOLOGY 2024; 4:kkae013. [PMID: 39258223 PMCID: PMC11384915 DOI: 10.1093/psyrad/kkae013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2024] [Revised: 07/02/2024] [Accepted: 08/12/2024] [Indexed: 09/12/2024]
Abstract
High magnetic field homogeneity is critical for magnetic resonance imaging (MRI), functional MRI, and magnetic resonance spectroscopy (MRS) applications. B0 inhomogeneity during MR scans is a long-standing problem resulting from magnet imperfections and site conditions, with the main issue being the inhomogeneity across the human body caused by differences in magnetic susceptibilities between tissues, resulting in signal loss, image distortion, and poor spectral resolution. Through a combination of passive and active shim techniques, as well as technological advances employing multi-coil techniques, optimal coil design, motion tracking, and real-time modifications, improved field homogeneity and image quality have been achieved in MRI/MRS. The integration of RF and shim coils brings a high shim efficiency due to the proximity of participants. This technique will potentially be applied to high-density RF coils with a high-density shim array for improved B0 homogeneity. Simultaneous shimming and image encoding can be achieved using multi-coil array, which also enables the development of novel encoding methods using advanced magnetic field control. Field monitoring enables the capture and real-time compensation for dynamic field perturbance beyond the static background inhomogeneity. These advancements have the potential to better use the scanner performance to enhance diagnostic capabilities and broaden applications of MRI/MRS in a variety of clinical and research settings. The purpose of this paper is to provide an overview of the latest advances in B0 magnetic field shimming and magnetic field control techniques as well as MR hardware, and to emphasize their significance and potential impact on improving the data quality of MRI/MRS.
Collapse
Affiliation(s)
- Yun Shang
- Department of Radiology, Weill Medical College of Cornell University, New York, NY 10065, United States
| | - Gizeaddis Lamesgin Simegn
- Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, United States
- F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD 21205, United States
| | - Kelly Gillen
- Department of Radiology, Weill Medical College of Cornell University, New York, NY 10065, United States
| | - Hsin-Jung Yang
- Department of Biomedical Sciences, Cedars-Sinai Medical Center, Biomedical Imaging Research Institute, Los Angeles, CA 90048, United States
| | - Hui Han
- Department of Radiology, Weill Medical College of Cornell University, New York, NY 10065, United States
| |
Collapse
|
2
|
Theilenberg S, Shang Y, Ghazouani J, Kumaragamage C, Nixon TW, McIntyre S, Vaughan JT, Parkinson B, Garwood M, de Graaf RA, Juchem C. Design and realization of a multi-coil array for B 0 field control in a compact 1.5T head-only MRI scanner. Magn Reson Med 2023; 90:1228-1241. [PMID: 37145035 PMCID: PMC10330274 DOI: 10.1002/mrm.29692] [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: 12/17/2022] [Revised: 03/27/2023] [Accepted: 04/14/2023] [Indexed: 05/06/2023]
Abstract
PURPOSE To design and implement a multi-coil (MC) array for B0 field generation for image encoding and simultaneous advanced shimming in a novel 1.5T head-only MRI scanner. METHODS A 31-channel MC array was designed following the unique constraints of this scanner design: The vertically oriented magnet is very short, stopping shortly above the shoulders of a sitting subject, and includes a window for the subject to see through. Key characteristics of the MC hardware, the B0 field generation capabilities, and thermal behavior, were optimized in simulations prior to its construction. The unit was characterized via bench testing. B0 field generation capabilities were validated on a human 4T MR scanner by analysis of experimental B0 fields and by comparing images for several MRI sequences acquired with the MC array to those acquired with the system's linear gradients. RESULTS The MC system was designed to produce a multitude of linear and nonlinear magnetic fields including linear gradients of up to 10 kHz/cm (23.5 mT/m) with MC currents of 5 A per channel. With water cooling it can be driven with a duty cycle of up to 74% and ramp times of 500 μs. MR imaging experiments encoded with the developed multi-coil hardware were largely artifact-free; residual imperfections were predictable, and correctable. CONCLUSION The presented compact multi-coil array is capable of generating image encoding fields with amplitudes and quality comparable to clinical systems at very high duty cycles, while additionally enabling high-order B0 shimming capabilities and the potential for nonlinear encoding fields.
Collapse
Affiliation(s)
- Sebastian Theilenberg
- Department of Biomedical Engineering, Columbia University, New York, NY, United States
| | - Yun Shang
- Department of Biomedical Engineering, Columbia University, New York, NY, United States
| | - Jalal Ghazouani
- Department of Biomedical Engineering, Columbia University, New York, NY, United States
| | - Chathura Kumaragamage
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, CT, United States
| | - Terence W. Nixon
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, CT, United States
| | - Scott McIntyre
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, CT, United States
| | - J. Thomas Vaughan
- Department of Biomedical Engineering, Columbia University, New York, NY, United States
- Department of Radiology, Columbia University Medical Center, New York, NY, United States
| | - Ben Parkinson
- Robinson Research Institute, Victoria University of Wellington, Wellington, New Zealand
| | - Mike Garwood
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, United States
| | - Robin A. de Graaf
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, CT, United States
| | - Christoph Juchem
- Department of Biomedical Engineering, Columbia University, New York, NY, United States
- Department of Radiology, Columbia University Medical Center, New York, NY, United States
| |
Collapse
|
3
|
Gutierrez A, Mullen M, Xiao D, Jang A, Froelich T, Garwood M, Haupt J. Reducing the Complexity of Model-Based MRI Reconstructions via Sparsification. IEEE TRANSACTIONS ON MEDICAL IMAGING 2021; 40:2477-2486. [PMID: 33999816 PMCID: PMC8569912 DOI: 10.1109/tmi.2021.3081013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Model-based reconstruction methods have emerged as a powerful alternative to classical Fourier-based MRI techniques, largely because of their ability to explicitly model (and therefore, potentially overcome) moderate field inhomogeneities, streamline reconstruction from non-Cartesian sampling, and even allow for the use of custom designed non-Fourier encoding methods. Their application in such scenarios, however, often comes with a substantial increase in computational cost, owing to the fact that the corresponding forward model in such settings no longer possesses a direct Fourier Transform based implementation. This paper introduces an algorithmic framework designed to reduce the computational burden associated with model-based MRI reconstruction tasks. The key innovation is the strategic sparsification of the corresponding forward operators for these models, giving rise to approximations of the forward models (and their adjoints) that admit low computational complexity application. This enables overall a reduced computational complexity application of popular iterative first-order reconstruction methods for these reconstruction tasks. Computational results obtained on both synthetic and experimental data illustrate the viability and efficiency of the approach.
Collapse
|
4
|
Froelich T, Mullen M, Garwood M. MRI exploiting frequency-modulated pulses and their nonlinear phase. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 318:106779. [PMID: 32917297 DOI: 10.1016/j.jmr.2020.106779] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Revised: 06/15/2020] [Accepted: 06/24/2020] [Indexed: 06/11/2023]
Abstract
Frequency-modulated (FM) pulses can provide several advantages over conventional amplitude-modulated pulses in the field of MRI; however, the manner in which spins are manipulated imprints a quadratic phase on the resulting magnetization. Historically this was considered a hindrance and slowed the widespread adoption of FM pulses. This article seeks to provide a historical perspective of the different techniques that researchers have used to exploit the benefits of FM pulses and to compensate for the nonlinear phase created by this class of pulses in MRI. Expanding on existing techniques, a new method of phase compensation is presented that utilizes nonlinear gradients to mitigate the undesirable phase imparted by this class of pulses.
Collapse
Affiliation(s)
- Taylor Froelich
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN, USA.
| | - Michael Mullen
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN, USA.
| | - Michael Garwood
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN, USA.
| |
Collapse
|
5
|
Juchem C, Theilenberg S, Kumaragamage C, Mullen M, DelaBarre L, Adriany G, Brown PB, McIntyre S, Nixon TW, Garwood M, de Graaf RA. Dynamic multicoil technique (DYNAMITE) MRI on human brain. Magn Reson Med 2020; 84:2953-2963. [PMID: 32544274 DOI: 10.1002/mrm.28323] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2020] [Revised: 04/23/2020] [Accepted: 04/23/2020] [Indexed: 12/14/2022]
Abstract
PURPOSE Spatial encoding for MRI is generally based on linear x, y, and z magnetic field gradients generated by a set of dedicated gradient coils. We recently introduced the dynamic multicoil technique (DYNAMITE) for B0 field control and demonstrated DYNAMITE MRI in a preclinical MR environment. In this study, we report the first realization of DYNAMITE MRI of the in vivo human head. METHODS Gradient fields for DYNAMITE MRI were generated with a 28-channel multicoil hardware arranged in 4 rows of 7 coils on a cylindrical surface (length 359 mm, diameter 344 mm, maximum 5 A per coil). DYNAMITE MRIs of a resolution phantom and in vivo human heads were acquired with multislice gradient-echo, multislice spin-echo, and 3D gradient-echo sequences. The resultant image fidelity was compared to that obtained with conventional gradient coil technology. RESULTS DYNAMITE field control enabled the realization of all imaging sequences with average gradient errors ≤ 1%. DYNAMITE MRI provided image quality and sensitivity comparable to conventional gradient technology without any obvious artifacts. Some minor geometric deformations were noticed primarily in the image periphery as the result of regional field imperfections. The imperfections can be readily approximated theoretically through numerical integration of the Biot-Savart law and removed through image distortion correction. CONCLUSION The first realization of DYNAMITE MRI of the in vivo human head has been presented. The obtained image fidelity is comparable to MRI with conventional gradient coils, paving the way for full-fledged DYNAMITE MRI and B0 shim systems for human applications.
Collapse
Affiliation(s)
- Christoph Juchem
- Department of Biomedical Engineering, Columbia University, New York, New York, USA.,Department of Radiology, Columbia University, New York, New York, USA
| | | | - Chathura Kumaragamage
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Michael Mullen
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Lance DelaBarre
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Peter B Brown
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Scott McIntyre
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Terence W Nixon
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Michael Garwood
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Robin A de Graaf
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, USA
| |
Collapse
|
6
|
Cousin SF, Liberman G, Solomon E, Otikovs M, Frydman L. A regularized reconstruction pipeline for high‐definition diffusion MRI in challenging regions incorporating a per‐shot image correction. Magn Reson Med 2019; 82:1322-1330. [DOI: 10.1002/mrm.27802] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 04/09/2019] [Accepted: 04/16/2019] [Indexed: 12/20/2022]
Affiliation(s)
- Samuel F. Cousin
- Department of Chemical and Biological Physics Weizmann Institute Rehovot Israel
| | - Gilad Liberman
- Department of Chemical and Biological Physics Weizmann Institute Rehovot Israel
| | - Eddy Solomon
- Department of Chemical and Biological Physics Weizmann Institute Rehovot Israel
| | - Martins Otikovs
- Department of Chemical and Biological Physics Weizmann Institute Rehovot Israel
| | - Lucio Frydman
- Department of Chemical and Biological Physics Weizmann Institute Rehovot Israel
| |
Collapse
|
7
|
Corbin BA, Pollard AC, Allen MJ, Pagel MD. Summary of Imaging in 2020: Visualizing the Future of Healthcare with MR Imaging. Mol Imaging Biol 2019; 21:193-199. [PMID: 30680525 PMCID: PMC6450763 DOI: 10.1007/s11307-019-01315-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The Imaging in 2020 meeting convenes biannually to discuss innovations in medical imaging. The 2018 meeting, titled "Visualizing the Future of Healthcare with MR Imaging," sought to encourage discussions of the future goals of MRI research, feature important discoveries, and foster scientific discourse between scientists from a variety of fields of expertise. Here, we highlight presented research and resulting discussions of the meeting.
Collapse
Affiliation(s)
- Brooke A Corbin
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, MI, USA
| | - Alyssa C Pollard
- Department of Chemistry, Rice University, 6100 S Main Street, Houston, TX, USA
- Department of Cancer Systems Imaging, The University of Texas MD Anderson Cancer Center, 1881 East Road, Houston, TX, USA
| | - Matthew J Allen
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, MI, USA.
| | - Mark D Pagel
- Department of Chemistry, Rice University, 6100 S Main Street, Houston, TX, USA.
- Department of Cancer Systems Imaging, The University of Texas MD Anderson Cancer Center, 1881 East Road, Houston, TX, USA.
| |
Collapse
|
8
|
Umesh Rudrapatna S, Fluerenbrock F, Nixon TW, de Graaf RA, Juchem C. Combined imaging and shimming with the dynamic multi-coil technique. Magn Reson Med 2018; 81:1424-1433. [PMID: 30303553 DOI: 10.1002/mrm.27408] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Revised: 05/01/2018] [Accepted: 05/29/2018] [Indexed: 01/07/2023]
Abstract
PURPOSE Spatial encoding and shimming in MRI have traditionally been performed using dedicated coils that generate orthogonal spherical harmonic fields. The recently introduced multi-coil hardware has proven that MRI-relevant magnetic fields can also be created by a generic set of localized coils producing non-orthogonal fields. As a step towards establishing a purely multi-coil-based MRI field generation system, the feasibility of performing conventional Cartesian k-space encoding and echo-planar imaging (EPI), as well as concurrent encoding and shimming is demonstrated in this study. METHODS We report the use of Dynamic Multi-Coil Technique (DYNAMITE) for combined Cartesian encoding and shimming, and EPI using a 48-channel multi-coil system. Experiments were performed on phantom objects and biological specimens in a 9.4 T pre-clinical scanner. Cartesian Fourier-encoded MRI and EPI were implemented whereby the magnetic fields required for encoding of the three orthogonal spatial dimensions were entirely based on linear combinations of multi-coil fields. Furthermore, DYNAMITE imaging was augmented by concurrent DYNAMITE shimming with the same hardware. RESULTS DYNAMITE-based MR and echo-planar images were indistinguishable from those acquired with the conventional linear imaging gradients provided by the scanner. In experiments with concurrent DYNAMITE shimming and imaging, shim challenges that would result in extreme spatial distortion and signal loss were corrected very effectively with more than 92% signal recovery in case of extreme Z2 shim challenge that resulted in complete signal dephasing in most slices. CONCLUSIONS We demonstrate the first successful implementation of combined DYNAMITE imaging and shimming and show the feasibility of performing EPI with DYNAMITE hardware. Our results substantiate the potential of multi-coil hardware as a full-fledged imaging and shimming system, with additional potential benefits of reduced echo-time and risk of peripheral nerve stimulation while performing EPI.
Collapse
Affiliation(s)
- S Umesh Rudrapatna
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut
| | | | - Terence W Nixon
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut
| | - Robin A de Graaf
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut
| | - Christoph Juchem
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut.,Department of Biomedical Engineering and Radiology, Columbia University in the City of New York, New York, New York.,Department of Neurology, Yale University School of Medicine, New Haven, Connecticut
| |
Collapse
|
9
|
Abstract
Imaging of hard and soft tissue of the oral cavity is important for dentistry. However, medical computed tomography, cone beam computed tomography (CBCT), nor MRI enables soft and hard tissue imaging simultaneously. Some MRI sequences were shown to provide fast soft and hard tissue imaging of hydrogen, which increased the interest in dental MRI. Recently, MRI allowed direct visualization of cancellous bone, intraoral mucosa, and dental pulp despite that cortical bone and dental roots are indirectly visualized. MRI seems to be adequate for many indications that CBCT is currently used for: implant treatment and inflammatory diseases of the tooth.
Collapse
Affiliation(s)
- Husniye Demirturk Kocasarac
- Division of Oral and Maxillofacial Radiology, Department of Comprehensive Dentistry, University of Texas Health San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA.
| | - Hassem Geha
- Division of Oral and Maxillofacial Radiology, Department of Comprehensive Dentistry, University of Texas Health San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA
| | - Laurence R Gaalaas
- Oral and Maxillofacial Radiology, Division of Oral Medicine, Diagnosis and Radiology, Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, 7-536 Moos Tower, 515 Delaware Street Southeast, Minneapolis, MN 55455, USA
| | - Donald R Nixdorf
- Division of TMD and Orofacial Pain, Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, 6-320 Moos Tower, 515 Delaware Street SE, Minneapolis, MN 55455, USA
| |
Collapse
|
10
|
Stockmann JP, Wald LL. In vivo B 0 field shimming methods for MRI at 7T. Neuroimage 2018; 168:71-87. [PMID: 28602943 PMCID: PMC5760477 DOI: 10.1016/j.neuroimage.2017.06.013] [Citation(s) in RCA: 85] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2016] [Revised: 05/19/2017] [Accepted: 06/06/2017] [Indexed: 01/12/2023] Open
Abstract
Functional MRI (fMRI) at 7T and above provides improved Signal-to-Noise Ratio and Contrast-to-Noise Ratio compared to 3T acquisitions. In addition to the beneficial effects on spin polarization and magnetization of deoxyhemoglobin, the increased applied field also further magnetizes air and tissue. While the magnets themselves typically provide a static B0 field with sufficient spatial homogeneity, the diamagnetism of tissue and the paramagnetism of air causes local field deviations inside the human head. These spatially-varying field offsets (ΔB0) cause image artifacts, especially in single shot EPI, including geometric distortion, signal dropout, and blurring. These effects are particularly strong near air-tissue interfaces such as the frontal sinus, and ear canals. Furthermore, if the field offsets are dynamically modulated through physiological processes such as respiration or motion, then the effect on the image time-series can be even more problematic. While post-processing methods have been developed to mitigate these effects, the ideal solution would be to reduce the ΔB0 variations at their source. Typically 7T scanners contain 2nd and some 3rd order spherical harmonic shim coil terms to cancel static ΔB0 variations of low spatial order. In this article, we will motivate the need for improved, higher-order compensation for B0 inhomogeneity and potentially add dynamic control of these fields. We discuss and compare several promising hardware approaches for static and dynamic B0 shimming using either higher-order spherical harmonic shim coils or multi-coil shim arrays as well as passive shimming approaches, and active variants such and adaptive current networks.
Collapse
Affiliation(s)
- Jason P Stockmann
- A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA 02129, United States.
| | - Lawrence L Wald
- A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA 02129, United States; Harvard Medical School, Boston, MA, United States
| |
Collapse
|
11
|
Liberman G, Frydman L. Reducing SAR requirements in multislice volumetric single-shot spatiotemporal MRI by two-dimensional RF pulses. Magn Reson Med 2017; 77:1959-1965. [PMID: 27203401 PMCID: PMC5184845 DOI: 10.1002/mrm.26270] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Revised: 04/17/2016] [Accepted: 04/17/2016] [Indexed: 12/15/2022]
Abstract
PURPOSE Spatiotemporal encoding (SPEN) can deliver single-scan MR images without folding complications and with increased robustness to chemical shift and susceptibility artifacts. Yet, it does so at the expense of relatively high specific absorption rates (SAR) owing to its reliance on frequency-swept pulses. This study describes SPEN implementations aimed at full three-dimensional (3D) multislice imaging, possessing reduced SAR thanks to an implementation based on new 2D radiofrequency (RF) pulses. METHODS Fully refocused spin- and stimulated-echo SPEN sequences incorporating 2D spatial/spatial swept RF pulses were implemented at 3 Tesla and compared to echo planar imaging. The use of effective 90-degree slice-selective excitation pulses enabled the scanning of 3D volumes with a low SAR. RESULTS Experiments validating the theoretical expectations were carried out on phantoms and on human volunteers, including zooming and diffusion measurements. The chosen sequences showed much smaller SARs than EPI, while delivering similar sensitivities when targeting human brain and fewer distortions when targeting human breast. CONCLUSION Two-dimensional RF pulses can exploit SPEN's advantages while fulfilling the SAR and multislice coverage demands required for clinical imaging. Magn Reson Med 77:1959-1965, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Gilad Liberman
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Lucio Frydman
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| |
Collapse
|
12
|
Farkash G, Dumez JN, Frydman L. Sculpting 3D spatial selectivity with pairs of 2D pulses: A comparison of methods. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 273:9-18. [PMID: 27718460 DOI: 10.1016/j.jmr.2016.09.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 09/02/2016] [Accepted: 09/03/2016] [Indexed: 06/06/2023]
Abstract
Enhancing the specificity of the spins' excitation can improve the capabilities of magnetic resonance. Exciting voxels with tailored 3D shapes reduces partial volume effects and enhances contrast, particularly in cases where cubic voxels or other simple geometries do not provide an optimal localization. Spatial excitation profiles of arbitrary shapes can be implemented using so-called multidimensional RF pulses, which are often limited in practice to 2D implementations owing to their sensitivity to field inhomogeneities. Recent work has shown the potential of spatio-temporally encoded (SPEN) pulses towards alleviating these constraints. In particular, 2D pulses operating in a so-called hybrid scheme where the "low-bandwidth" spatial dimension is sculpted by a SPEN strategy while an orthogonal axis is shaped by regular k-space encoding, have been shown resilient to chemical shift and B0 field inhomogeneities. In this work we explore the use of pairs of 2D pulses, with one of these addressing geometries in the x-y plane and the other in the x-z dimension, to sculpt complex 3D volumes in phantoms and in vivo. To overcome limitations caused by the RF discretization demanded by these 2D pulses, a number of "unfolding" techniques yielding images from the centerband RF excitation while deleting sideband contributions - even in cases where center- and side-bands severely overlap - were developed. Thus it was possible to increase the gradient strengths applied along the low bandwidth dimensions, significantly improving the robustness of this kind of 3D sculpting pulses. Comparisons against conventional pulses designed on the basis of pure k-space trajectories, are presented.
Collapse
Affiliation(s)
- Gil Farkash
- Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Jean-Nicolas Dumez
- Institut de Chimie des Substances Naturelles, CNRS, 91190 Gif-sur-Yvette, France
| | - Lucio Frydman
- Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot, Israel.
| |
Collapse
|
13
|
Marhabaie S, Bodenhausen G, Pelupessy P. The effects of molecular diffusion in spatially encoded magnetic resonance imaging. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 273:98-104. [PMID: 27821292 DOI: 10.1016/j.jmr.2016.10.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Revised: 10/10/2016] [Accepted: 10/14/2016] [Indexed: 06/06/2023]
Abstract
In spatially encoded MRI, the signal is acquired sequentially for different coordinates. In particular for single-scan acquisitions in inhomogeneous fields, spatially encoded methods improve the image quality compared to traditional k-space encoding. Previously, much attention has been paid in order to homogenize T2 losses across the sample. In this work, we investigate the effects of diffusion on the image quality in spatially encoded MRI. We show that losses due to diffusion are often not uniform along the spatially encoded dimension, and how to adapt spatially encoded sequences in order to obtain uniformly diffusion-weighted images.
Collapse
Affiliation(s)
- Sina Marhabaie
- Département de Chimie, École Normale Supérieure, PSL Research University, UPMC Univ Paris 06, CNRS, Laboratoire des Biomolecules (LBM), 24 rue Lhomond, 75005 Paris, France; Sorbonne Universités, UPMC Univ. Paris 06, École Normale Supérieure, CNRS, Laboratoire des Biomolecules (LBM), Paris, France
| | - Geoffrey Bodenhausen
- Département de Chimie, École Normale Supérieure, PSL Research University, UPMC Univ Paris 06, CNRS, Laboratoire des Biomolecules (LBM), 24 rue Lhomond, 75005 Paris, France; Sorbonne Universités, UPMC Univ. Paris 06, École Normale Supérieure, CNRS, Laboratoire des Biomolecules (LBM), Paris, France; Institut des Sciences et Ingéniérie Chimiques, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
| | - Philippe Pelupessy
- Département de Chimie, École Normale Supérieure, PSL Research University, UPMC Univ Paris 06, CNRS, Laboratoire des Biomolecules (LBM), 24 rue Lhomond, 75005 Paris, France; Sorbonne Universités, UPMC Univ. Paris 06, École Normale Supérieure, CNRS, Laboratoire des Biomolecules (LBM), Paris, France.
| |
Collapse
|
14
|
Jang A, Kobayashi N, Moeller S, Vaughan JT, Zhang J, Garwood M. 2D Pulses using spatially dependent frequency sweeping. Magn Reson Med 2016; 76:1364-1374. [PMID: 26614693 PMCID: PMC4884179 DOI: 10.1002/mrm.25973] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2015] [Revised: 07/13/2015] [Accepted: 08/17/2015] [Indexed: 11/08/2022]
Abstract
PURPOSE To introduce a method of designing two-dimensional (2D) frequency-modulated pulses that produce phase coherence in a spatiotemporal manner. Uniquely, this class of pulses provides the ability to compensate for field inhomogeneity using a spatiotemporally dependent trajectory of maximum coherence in a single-shot. THEORY AND METHODS A pulse design method based on a k-space description is developed. Bloch simulations and phantom experiments are used to demonstrate sequential spatiotemporal phase coherence and compensation for B1+ and B0 inhomogeneity. RESULTS In the presence of modulated gradients, the 2D frequency-modulated pulses were shown to excite a cylinder in a selective manner. With a surface coil transmitter, compensation of the effect of B1+ inhomogeneity was experimentally verified, in agreement with simulation results. In addition, simulations were used to demonstrate partial compensation for B0 inhomogeneity. CONCLUSION The 2D frequency-modulated pulses are a new class of pulses that generate phase coherence sequentially along a spatial trajectory determined by gradient- and frequency-modulated functions. By exploiting their spatiotemporal nature, 2D frequency-modulated pulses can compensate for spatial variation of the radiofrequency field in a single-shot excitation. Preliminary results shown suggest extensions might also be used to compensate for static field inhomogeneity. Magn Reson Med 76:1364-1374, 2016. © 2015 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Albert Jang
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minnesota, USA
- Department of Electrical and Computer Engineering, University of Minnesota, Minnesota, USA
- Department of Medicine, Cardiovascular Division, University of Minnesota, Minnesota, USA
| | - Naoharu Kobayashi
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minnesota, USA
| | - Steen Moeller
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minnesota, USA
| | - J Thomas Vaughan
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minnesota, USA
- Department of Electrical and Computer Engineering, University of Minnesota, Minnesota, USA
| | - Jianyi Zhang
- Department of Electrical and Computer Engineering, University of Minnesota, Minnesota, USA
- Department of Medicine, Cardiovascular Division, University of Minnesota, Minnesota, USA
| | - Michael Garwood
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minnesota, USA.
| |
Collapse
|
15
|
Chen L, Huang J, Zhang T, Li J, Cai C, Cai S. Variable density sampling and non-Cartesian super-resolved reconstruction for spatiotemporally encoded single-shot MRI. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 272:1-9. [PMID: 27591366 DOI: 10.1016/j.jmr.2016.08.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Revised: 08/14/2016] [Accepted: 08/26/2016] [Indexed: 06/06/2023]
Abstract
Spatiotemporally encoded (SPEN) single-shot MRI is an emerging ultrafast technique, which is capable of spatially selective acquisition and reduced field-of-view imaging. Compared to uniform sampling, variable density sampling has great potential in reducing aliasing artifacts and improving sampling efficiency. In this study, variable density spiral trajectory and non-Cartesian super-resolved (SR) reconstruction method are developed for SPEN MRI. The gradient waveforms design of spiral trajectory is mathematically described as an optimization problem subjected to the limitations of hardware. Non-Cartesian SR reconstruction with specific gridding method is developed to retrieve a resolution enhanced image from raw SPEN data. The robustness and efficiency of the proposed methods are demonstrated by numerical simulation and various experiments. The results indicate that variable density SPEN MRI can provide better spatial resolution and fewer aliasing artifacts compared to Cartesian counterpart. The proposed methods will facilitate the development of variable density SPEN MRI.
Collapse
Affiliation(s)
- Lin Chen
- Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Electronic Science, Xiamen University, Xiamen 361005, China; Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, United States.
| | - Jianpan Huang
- Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Electronic Science, Xiamen University, Xiamen 361005, China.
| | - Ting Zhang
- Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Electronic Science, Xiamen University, Xiamen 361005, China.
| | - Jing Li
- Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Electronic Science, Xiamen University, Xiamen 361005, China.
| | - Congbo Cai
- Department of Communication Engineering, Xiamen University, Xiamen 361005, China.
| | - Shuhui Cai
- Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Electronic Science, Xiamen University, Xiamen 361005, China.
| |
Collapse
|
16
|
Stockmann JP, Cooley CZ, Guerin B, Rosen MS, Wald LL. Transmit Array Spatial Encoding (TRASE) using broadband WURST pulses for RF spatial encoding in inhomogeneous B0 fields. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 268:36-48. [PMID: 27155906 PMCID: PMC4909507 DOI: 10.1016/j.jmr.2016.04.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Revised: 03/17/2016] [Accepted: 04/07/2016] [Indexed: 06/01/2023]
Abstract
Transmit Array Spatial Encoding (TRASE) is a promising new MR encoding method that uses transmit RF (B1(+)) phase gradients over the field-of-view to perform Fourier spatial encoding. Acquisitions use a spin echo train in which the transmit coil phase ramp is modulated to jump from one k-space point to the next. This work extends the capability of TRASE by using swept radiofrequency (RF) pulses and a quadratic phase removal method to enable TRASE where it is arguably most needed: portable imaging systems with inhomogeneous B0 fields. The approach is particularly well-suited for portable MR scanners where (a) inhomogeneous B0 fields are a byproduct of lightweight magnet design, (b) heavy, high power-consumption gradient coil systems are a limitation to siting the system in non-conventional locations and (c) synergy with the use of spin echo trains is required to overcome intra-voxel dephasing (short T2(∗)) in the inhomogeneous field. TRASE does not use a modulation of the B0 field to encode, but it does suffer from secondary effects of the inhomogeneous field. Severe artifacts arise in TRASE images due to off-resonance effects when the RF pulse does not cover the full bandwidth of spin resonances in the imaging FOV. Thus, for highly inhomogeneous B0 fields, the peak RF power needed for high-bandwidth refocusing hard pulses becomes very expensive, in addition to requiring RF coils that can withstand thousands of volts. In this work, we use swept WURST RF pulse echo trains to achieve TRASE imaging in a highly inhomogeneous magnetic field (ΔB0/B0∼0.33% over the sample). By accurately exciting and refocusing the full bandwidth of spins, the WURST pulses eliminate artifacts caused by the limited bandwidth of the hard pulses used in previous realizations of TRASE imaging. We introduce a correction scheme to remove the unwanted quadratic phase modulation caused by the swept pulses. Also, a phase alternation scheme is employed to mitigate artifacts caused by mixture of the even and odd-echo coherence pathways due to defects in the refocusing pulse. In this paper, we describe this needed methodology and demonstrate the ability of TRASE to Fourier encode in an inhomogeneous field (ΔB0/B0∼1% over the full FOV).
Collapse
Affiliation(s)
- Jason P Stockmann
- A.A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA 02129, United States.
| | - Clarissa Z Cooley
- A.A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA 02129, United States
| | - Bastien Guerin
- A.A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA 02129, United States; Harvard Medical School, Boston, MA, United States
| | - Matthew S Rosen
- A.A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA 02129, United States; Department of Physics, Harvard University, Cambridge, MA 02141, United States; Harvard Medical School, Boston, MA, United States
| | - Lawrence L Wald
- A.A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA 02129, United States; Harvard Medical School, Boston, MA, United States
| |
Collapse
|
17
|
Schmidt R, Mishkovsky M, Hyacinthe JN, Kunz N, Gruetter R, Comment A, Frydman L. Correcting surface coil excitation inhomogeneities in single-shot SPEN MRI. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2015; 259:199-206. [PMID: 26363583 PMCID: PMC5035682 DOI: 10.1016/j.jmr.2015.08.018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Revised: 08/25/2015] [Accepted: 08/26/2015] [Indexed: 05/08/2023]
Abstract
Given their high sensitivity and ability to limit the field of view (FOV), surface coils are often used in magnetic resonance spectroscopy (MRS) and imaging (MRI). A major downside of surface coils is their inherent radiofrequency (RF) B1 heterogeneity across the FOV, decreasing with increasing distance from the coil and giving rise to image distortions due to non-uniform spatial responses. A robust way to compensate for B1 inhomogeneities is to employ adiabatic inversion pulses, yet these are not well adapted to all imaging sequences - including to single-shot approaches like echo planar imaging (EPI). Hybrid spatiotemporal encoding (SPEN) sequences relying on frequency-swept pulses provide another ultrafast MRI alternative, that could help solve this problem thanks to their built-in heterogeneous spatial manipulations. This study explores how this intrinsic SPEN-based spatial discrimination, could be used to compensate for the B1 inhomogeneities inherent to surface coils. Experiments carried out in both phantoms and in vivo rat brains demonstrate that, by suitably modulating the amplitude of a SPEN chirp pulse that progressively excites the spins in a direction normal to the coil, it is possible to compensate for the RF transmit inhomogeneities and thus improve sensitivity and image fidelity.
Collapse
Affiliation(s)
- Rita Schmidt
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Mor Mishkovsky
- Laboratory of Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Jean-Noel Hyacinthe
- School of health, University of Applied Sciences and Arts Western Switzerland, Geneva, Switzerland
| | - Nicolas Kunz
- Center of Biomedical Imaging (CIBM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Rolf Gruetter
- Laboratory of Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
- Center of Biomedical Imaging (CIBM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Arnaud Comment
- Institute of the Physics of Biological Systems, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Lucio Frydman
- Department of Chemical Physics, Weizmann Institute of Science, Rehovot, Israel
| |
Collapse
|