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Bhuiyan EH, Dewdney A, Weinreb J, Galiana G. Feasibility of diffusion weighting with a local inside-out nonlinear gradient coil for prostate MRI. Med Phys 2021; 48:5804-5818. [PMID: 34287937 DOI: 10.1002/mp.15100] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Revised: 04/04/2021] [Accepted: 06/23/2021] [Indexed: 11/09/2022] Open
Abstract
PURPOSE Prostate cancer remains the 2nd leading cancer killer of men, yet it is also a disease with a high rate of overtreatment. Diffusion weighted imaging (DWI) has shown promise as a reliable, grade-sensitive imaging method, but it is limited by low image quality. Currently, DWI quality image is directly related to low gradient amplitudes, since weak gradients must be compensated with long echo times. METHODS We propose a new type of MRI accessory, an "inside-out" and nonlinear gradient, whose sole purpose is to deliver diffusion encoding to a region of interest. Performance was simulated in OPERA and the resulting fields were used to simulate DWI with two compartment and kurtosis models. Experiments with a nonlinear head gradient prove the accuracy of DWI and ADC maps diffusion encoded with nonlinear gradients. RESULTS Simulations validated thermal and mechanical safety while showing a 5 to 10-fold increase in gradient strength over prostate. With these strengths, lesion CNR in ADC maps approximately doubled for a range of anatomical positions. Proof-of-principle experiments show that spatially varying b-values can be corrected for accurate DWI and ADC. CONCLUSIONS Dedicated nonlinear diffusion encoding hardware could improve prostate DWI.
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Affiliation(s)
| | | | - Jeffrey Weinreb
- Department of Radiology and Biomedical Imaging, Yale School of Medicine, USA
| | - Gigi Galiana
- Department of Radiology and Biomedical Imaging, Yale School of Medicine, USA
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Wang H, Liang D, Su S, King KF, Chang Y, Liu X, Zheng H, Ying L. Improved gradient-echo 3D magnetic resonance imaging using compressed sensing and Toeplitz encoding with phase-scrambled RF excitation. Med Phys 2020; 47:1579-1589. [PMID: 31872450 DOI: 10.1002/mp.13987] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Revised: 10/28/2019] [Accepted: 12/01/2019] [Indexed: 01/17/2023] Open
Abstract
PURPOSE To develop a novel three-dimensional (3D) hybrid-encoding framework using compressed sensing (CS) and Toeplitz encoding with variable phase-scrambled radio-frequency (RF) excitation, which has the following advantages: low power deposition of RF pulses, reduction of the signal dynamic range, no additional hardware requirement, and signal-to-noise ratio (SNR) improvement. METHODS In light of the actual imaging framework of magnetic resonance imaging (MRI) scanners, we applied specially tailored RF pulses with phase-scrambled RF excitation to implement a 3D hybrid Fourier-Toeplitz encoding method based on 3D gradient-recalled echo pulse (GRASS) sequence. This method exploits Toeplitz encoding along the phase encoding direction, while keeping Fourier encoding along the readout and slice encoding directions. Phantom experiments were conducted to optimize the amplitude of specially tailored RF pulses in the 3D GRASS sequence. In vivo experiments were conducted to validate the feasibility of the proposed method, and simulations were conducted to compare the 3D hybrid-encoding method with Fourier encoding and other non-Fourier encoding methods. RESULTS An optimized low RF amplitude was obtained in the phantom experiments. Using the optimized specially tailored RF pulses, both the watermelon and knee experiments demonstrated that the proposed method was able to preserve more image details than the conventional 3D Fourier-encoded methods at acceleration factors of 3.1 and 2.0. Additionally, SNR was improved because of no additional gradients and 3D volume encoding, when compared with single-slice scanning without 3D encoding. Simulation results demonstrated that the proposed scheme was superior to the conventional Fourier encoding method, and obtained comparative performance with other non-Fourier encoding methods in preserving details. CONCLUSIONS We developed a practical hybrid-encoding method for 3D MRI with specially tailored RF pulses of phase-scrambled RF excitation. The proposed method improves image SNR and detail preservation compared with the conventional Fourier encoding methods. Furthermore, our proposed method exhibits superior performance in terms of detail preservation, compared with the conventional Fourier encoding method.
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Affiliation(s)
- Haifeng Wang
- Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China.,Department of Electrical Engineering and Biomedical Engineering, University at Buffalo, The State University of New York (SUNY), Buffalo, NY, USA
| | - Dong Liang
- Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China
| | - Shi Su
- Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China
| | - Kevin F King
- Global Applied Science Lab, GE Healthcare, Waukesha, WI, USA
| | - Yuchou Chang
- Department of Computer Science and Engineering Technology, University of Houston-Downtown, Houston, TX, USA
| | - Xin Liu
- Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China
| | - Hairong Zheng
- Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China
| | - Leslie Ying
- Department of Electrical Engineering and Biomedical Engineering, University at Buffalo, The State University of New York (SUNY), Buffalo, NY, USA
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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).
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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
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Weber H, Schultz G, Gallichan D, Hennig J, Zaitsev M. Local field of view imaging for alias-free undersampling with nonlinear spatial encoding magnetic fields. Magn Reson Med 2015; 71:1002-14. [PMID: 23649975 DOI: 10.1002/mrm.24754] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
PURPOSE Nonlinear spatial encoding magnetic fields result in an inhomogeneous image resolution. Within this study, this characteristic property of nonlinear encoding is investigated with regard to its potential to accelerate MRI acquisitions. THEORY A dependency between k-space coverage and local resolvability of the image causes k-space samples to have a spatially localized contribution to the reconstruction of the spin density. On the basis of this observation, a concept for alias-free data undersampling is developed, which is referred to as the local field of view concept. METHODS On the basis of this concept, a fast sampling trajectory is developed. It is evaluated with simulations and experiments (both using a phantom and in vivo) for MRI with, as an example, pure quadrupolar encoding fields. To demonstrate that the concept is only applicable to (spatially) nonlinear encoding, a comparison with linear encoding is provided. RESULTS Application of the local field of view concept results in a localized adaptation of the image resolution by undersampling higher frequency k-space samples without introducing aliasing. CONCLUSIONS A new effect of nonlinear spatial encoding magnetic fields was found, which allows more efficient data sampling and at the same time counterbalancing the natural variation in image resolution.
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Affiliation(s)
- Hans Weber
- Department of Radiology-Medical Physics, University Medical Center Freiburg, Freiburg, Germany
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Chen Y, Chen S, Zhong J, Chen Z. Reference-free unwarping of single-shot spatiotemporally encoded MRI using asymmetric self-refocused echoes acquisition. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2015; 254:1-9. [PMID: 25768263 DOI: 10.1016/j.jmr.2015.02.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2014] [Revised: 02/05/2015] [Accepted: 02/09/2015] [Indexed: 06/04/2023]
Abstract
This paper presents a phase evolution rewinding algorithm for correcting the geometric and intensity distortions in single-shot spatiotemporally encoded (SPEN) MRI with acquisition of asymmetric self-refocused echo trains. Using the field map calculated from the phase distribution of the source image, the off-resonance induced phase errors are successfully rewound through deconvolution. The alias-free partial Fourier transform reconstruction helps improve the signal-to-noise ratio of the field maps and the output images. The effectiveness of the proposed algorithm was validated through 7 T MRI experiments on a lemon, a water phantom, and in vivo rat head. SPEN imaging was evaluated using rapid acquisition by sequential excitation and refocusing (RASER) which produces uniform T2 weighting. The results indicate that the new technique can more robustly deal with the cases in which the images obtained with conventional single-shot spin-echo EPI are difficult to be restored due to serious field variations.
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Affiliation(s)
- Ying Chen
- Department of Electronic Science, Fijian Provincial Key Laboratory of Plasma and Magnetic Resonance, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen, China; Center for Brain Imaging Science and Technology, Zhejiang University, Hangzhou, China
| | - Song Chen
- Center for Brain Imaging Science and Technology, Zhejiang University, Hangzhou, China
| | - Jianhui Zhong
- Center for Brain Imaging Science and Technology, Zhejiang University, Hangzhou, China.
| | - Zhong Chen
- Department of Electronic Science, Fijian Provincial Key Laboratory of Plasma and Magnetic Resonance, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen, China.
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Zaitsev M, Schultz G, Hennig J, Gruetter R, Gallichan D. Parallel imaging with phase scrambling. Magn Reson Med 2014; 73:1407-19. [DOI: 10.1002/mrm.25252] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2013] [Revised: 03/20/2014] [Accepted: 03/24/2014] [Indexed: 11/11/2022]
Affiliation(s)
- Maxim Zaitsev
- Medical Physics; Department of Radiology; University Medical Center Freiburg; Freiburg Germany
| | - Gerrit Schultz
- Medical Physics; Department of Radiology; University Medical Center Freiburg; Freiburg Germany
| | - Juergen Hennig
- Medical Physics; Department of Radiology; University Medical Center Freiburg; Freiburg Germany
| | - Rolf Gruetter
- Laboratory for Functional and Metabolic Imaging, EPFL; Lausanne Switzerland
- Department of Radiology; University of Lausanne; Lausanne Switzerland
- Department of Radiology; University of Geneva; Geneva Switzerland
| | - Daniel Gallichan
- Laboratory for Functional and Metabolic Imaging, EPFL; Lausanne Switzerland
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Ben-Eliezer N, Shrot Y, Frydman L, Sodickson DK. Parametric analysis of the spatial resolution and signal-to-noise ratio in super-resolved spatiotemporally encoded (SPEN) MRI. Magn Reson Med 2013; 72:418-29. [DOI: 10.1002/mrm.24954] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 08/18/2013] [Accepted: 08/21/2013] [Indexed: 12/29/2022]
Affiliation(s)
- Noam Ben-Eliezer
- The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York; University School of Medicine; New York New York USA
| | - Yoav Shrot
- Department of Chemical Physics; Weizmann Institute of Science; Rehovot Israel
| | - Lucio Frydman
- Department of Chemical Physics; Weizmann Institute of Science; Rehovot Israel
| | - Daniel K. Sodickson
- The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York; University School of Medicine; New York New York USA
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Cai C, Dong J, Cai S, Li J, Chen Y, Bao L, Chen Z. An efficient de-convolution reconstruction method for spatiotemporal-encoding single-scan 2D MRI. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 228:136-147. [PMID: 23433507 DOI: 10.1016/j.jmr.2012.12.020] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Revised: 12/26/2012] [Accepted: 12/30/2012] [Indexed: 06/01/2023]
Abstract
Spatiotemporal-encoding single-scan MRI method is relatively insensitive to field inhomogeneity compared to EPI method. Conjugate gradient (CG) method has been used to reconstruct super-resolved images from the original blurred ones based on coarse magnitude-calculation. In this article, a new de-convolution reconstruction method is proposed. Through removing the quadratic phase modulation from the signal acquired with spatiotemporal-encoding MRI, the signal can be described as a convolution of desired super-resolved image and a point spread function. The de-convolution method proposed herein not only is simpler than the CG method, but also provides super-resolved images with better quality. This new reconstruction method may make the spatiotemporal-encoding 2D MRI technique more valuable for clinic applications.
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Affiliation(s)
- Congbo Cai
- Department of Communication Engineering, State Key Laboratory for Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen 361005, China
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Puy G, Marques JP, Gruetter R, Thiran JP, Van De Ville D, Vandergheynst P, Wiaux Y. Spread spectrum magnetic resonance imaging. IEEE TRANSACTIONS ON MEDICAL IMAGING 2012; 31:586-598. [PMID: 22042149 DOI: 10.1109/tmi.2011.2173698] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We propose a novel compressed sensing technique to accelerate the magnetic resonance imaging (MRI) acquisition process. The method, coined spread spectrum MRI or simply s(2)MRI, consists of premodulating the signal of interest by a linear chirp before random k-space under-sampling, and then reconstructing the signal with nonlinear algorithms that promote sparsity. The effectiveness of the procedure is theoretically underpinned by the optimization of the coherence between the sparsity and sensing bases. The proposed technique is thoroughly studied by means of numerical simulations, as well as phantom and in vivo experiments on a 7T scanner. Our results suggest that s(2)MRI performs better than state-of-the-art variable density k-space under-sampling approaches.
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Affiliation(s)
- Gilles Puy
- Institute of Electrical Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
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Witschey WRT, Cocosco CA, Gallichan D, Schultz G, Weber H, Welz A, Hennig J, Zaitsev M. Localization by nonlinear phase preparation and k-space trajectory design. Magn Reson Med 2011; 67:1620-32. [PMID: 22127679 DOI: 10.1002/mrm.23146] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Revised: 06/21/2011] [Accepted: 07/20/2011] [Indexed: 11/08/2022]
Abstract
A technique is described to localize MR signals from a target volume using nonlinear pulsed magnetic fields and spatial encoding trajectories designed using local k-space theory. The concept of local k-space is outlined theoretically, and this principle is applied to simulated phantom and cardiac MRI data in the presence of surface and quadrupolar gradient coil phase modulation. Phantom and in vivo human brain images are obtained using a custom, high-performance quadrupolar gradient coil integrated with a whole-body 3-T MRI system to demonstrate target localization using three-dimensional T 2*-weighted spoiled gradient echo, two-dimensional segmented, multiple gradient encoded spin echo, and three-dimensional balanced steady-state free precession acquisitions. This method may provide a practical alternative to selective radiofrequency excitation at ultra-high-field, particularly for steady-state applications where repetition time (TR) must be minimized and when the amount of energy deposited in human tissues is prohibitive. There are several limitations to the approach including the spatial variation in resolution, high frequency aliasing artifacts, and spatial variation in echo times and contrast.
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Parot V, Sing-Long C, Lizama C, Tejos C, Uribe S, Irarrazaval P. Application of the fractional Fourier transform to image reconstruction in MRI. Magn Reson Med 2011; 68:17-29. [PMID: 22006642 DOI: 10.1002/mrm.23190] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2011] [Revised: 07/21/2011] [Accepted: 07/28/2011] [Indexed: 11/08/2022]
Abstract
The classic paradigm for MRI requires a homogeneous B(0) field in combination with linear encoding gradients. Distortions are produced when the B(0) is not homogeneous, and several postprocessing techniques have been developed to correct them. Field homogeneity is difficult to achieve, particularly for short-bore magnets and higher B(0) fields. Nonlinear magnetic components can also arise from concomitant fields, particularly in low-field imaging, or intentionally used for nonlinear encoding. In any of these situations, the second-order component is key, because it constitutes the first step to approximate higher-order fields. We propose to use the fractional Fourier transform for analyzing and reconstructing the object's magnetization under the presence of quadratic fields. The fractional fourier transform provides a precise theoretical framework for this. We show how it can be used for reconstruction and for gaining a better understanding of the quadratic field-induced distortions, including examples of reconstruction for simulated and in vivo data. The obtained images have improved quality compared with standard Fourier reconstructions. The fractional fourier transform opens a new paradigm for understanding the MR signal generated by an object under a quadratic main field or nonlinear encoding.
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Affiliation(s)
- Vicente Parot
- Department of Electrical Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile
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