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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] [What about the content of this article? (0)] [Affiliation(s)] [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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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] [What about the content of this article? (0)] [Affiliation(s)] [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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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. J Magn Reson 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] [What about the content of this article? (0)] [Affiliation(s)] [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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Witschey WR, Littin S, Cocosco CA, Gallichan D, Schultz G, Weber H, Welz A, Hennig J, Zaitsev M. Stages: sub-Fourier dynamic shim updating using nonlinear magnetic field phase preparation. Magn Reson Med 2013; 71:57-66. [PMID: 23440677 DOI: 10.1002/mrm.24625] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2012] [Revised: 11/05/2012] [Accepted: 12/11/2012] [Indexed: 11/09/2022]
Abstract
Heterogeneity of the static magnetic field in magnetic resonance imaging may cause image artifacts and degradation in image quality. The field heterogeneity can be reduced by dynamically adjusting shim fields or dynamic shim updating, in which magnetic field homogeneity is optimized for each tomographic slice to improve image quality. A limitation of this approach is that a new magnetic field can be applied only once for each slice, otherwise image quality would improve somewhere to its detriment elsewhere in the slice. The motivation of this work is to overcome this limitation and develop a technique using nonlinear magnetic fields to dynamically shim the static magnetic field within a single Fourier-encoded volume or slice, called sub-Fourier dynamic shim updating. However, the nonlinear magnetic fields are not used as shim fields; instead, they impart a strong spatial dependence to the acquired MR signal by nonlinear phase preparation, which may be exploited to locally improve magnetic field homogeneity during acquisition. A theoretical description of the method is detailed, simulations and a proof-of-principle experiment are performed using a magnet coil with a known field geometry. The method is shown to remove artifacts associated with magnetic field homogeneity in balanced steady-state free-precession pulse sequences. We anticipate that this method will be useful to improve the quality of magnetic resonance images by removing deleterious artifacts associated with a heterogeneous static magnetic field.
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Affiliation(s)
- Walter Rt Witschey
- University of Pennsylvania, Philadelphia, PA, USA.,University Medical Center Freiburg, Freiburg i. Breisgau, Germany
| | - Sebastian Littin
- University Medical Center Freiburg, Freiburg i. Breisgau, Germany
| | - Chris A Cocosco
- University Medical Center Freiburg, Freiburg i. Breisgau, Germany
| | - Daniel Gallichan
- University Medical Center Freiburg, Freiburg i. Breisgau, Germany
| | - Gerrit Schultz
- University Medical Center Freiburg, Freiburg i. Breisgau, Germany
| | - Hans Weber
- University Medical Center Freiburg, Freiburg i. Breisgau, Germany
| | - Anna Welz
- University Medical Center Freiburg, Freiburg i. Breisgau, Germany
| | - Jürgen Hennig
- University Medical Center Freiburg, Freiburg i. Breisgau, Germany
| | - Maxim Zaitsev
- University Medical Center Freiburg, Freiburg i. Breisgau, Germany
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Lin FH. Multidimensionally encoded magnetic resonance imaging. Magn Reson Med 2012; 70:86-96. [PMID: 22926830 DOI: 10.1002/mrm.24443] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2012] [Revised: 06/25/2012] [Accepted: 07/06/2012] [Indexed: 11/12/2022]
Abstract
Magnetic resonance imaging (MRI) typically achieves spatial encoding by measuring the projection of a q-dimensional object over q-dimensional spatial bases created by linear spatial encoding magnetic fields (SEMs). Recently, imaging strategies using nonlinear SEMs have demonstrated potential advantages for reconstructing images with higher spatiotemporal resolution and reducing peripheral nerve stimulation. In practice, nonlinear SEMs and linear SEMs can be used jointly to further improve the image reconstruction performance. Here, we propose the multidimensionally encoded (MDE) MRI to map a q-dimensional object onto a p-dimensional encoding space where p > q. MDE MRI is a theoretical framework linking imaging strategies using linear and nonlinear SEMs. Using a system of eight surface SEM coils with an eight-channel radiofrequency coil array, we demonstrate the five-dimensional MDE MRI for a two-dimensional object as a further generalization of PatLoc imaging and O-space imaging. We also present a method of optimizing spatial bases in MDE MRI. Results show that MDE MRI with a higher dimensional encoding space can reconstruct images more efficiently and with a smaller reconstruction error when the k-space sampling distribution and the number of samples are controlled.
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Affiliation(s)
- Fa-Hsuan Lin
- Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan.
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Gallichan D, Cocosco CA, Schultz G, Weber H, Welz AM, Hennig J, Zaitsev M. Practical considerations for in vivo MRI with higher dimensional spatial encoding. Magn Reson Mater Phy 2012; 25:419-31. [DOI: 10.1007/s10334-012-0314-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Revised: 03/06/2012] [Accepted: 03/14/2012] [Indexed: 11/29/2022]
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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 Trans Med 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] [What about the content of this article? (0)] [Affiliation(s)] [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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Lee GR, Tkach JA, Griswold MA. Time-efficient slab-selective water excitation for 3D MRI. Magn Reson Med 2012; 67:127-36. [DOI: 10.1002/mrm.22994] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2011] [Revised: 03/22/2011] [Accepted: 04/15/2011] [Indexed: 11/11/2022]
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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] [What about the content of this article? (0)] [Affiliation(s)] [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] [What about the content of this article? (0)] [Affiliation(s)] [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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11
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Gallichan D, Cocosco CA, Dewdney A, Schultz G, Welz A, Hennig J, Zaitsev M. Simultaneously driven linear and nonlinear spatial encoding fields in MRI. Magn Reson Med 2010; 65:702-14. [DOI: 10.1002/mrm.22672] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2010] [Revised: 09/03/2010] [Accepted: 09/14/2010] [Indexed: 11/10/2022]
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12
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Gabr RE, Schär M, Edelstein AD, Kraitchman DL, Bottomley PA, Edelstein WA. MRI dynamic range and its compatibility with signal transmission media. J Magn Reson 2009; 198:137-145. [PMID: 19251444 PMCID: PMC2873084 DOI: 10.1016/j.jmr.2009.01.037] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Revised: 01/10/2009] [Accepted: 01/27/2009] [Indexed: 05/27/2023]
Abstract
As the number of MRI phased array coil elements grows, interactions among cables connecting them to the system receiver become increasingly problematic. Fiber optic or wireless links would reduce electromagnetic interference, but their dynamic range (DR) is generally less than that of coaxial cables. Raw MRI signals, however, have a large DR because of the high signal amplitude near the center of k-space. Here, we study DR in MRI in order to determine the compatibility of MRI multicoil imaging with non-coaxial cable signal transmission. Since raw signal data are routinely discarded, we have developed an improved method for estimating the DR of MRI signals from conventional magnitude images. Our results indicate that the DR of typical surface coil signals at 3T for human subjects is less than 88 dB, even for three-dimensional acquisition protocols. Cardiac and spine coil arrays had a maximum DR of less than 75 dB and head coil arrays less than 88 dB. The DR derived from magnitude images is in good agreement with that measured from raw data. The results suggest that current analog fiber optic links, with a spurious-free DR of 60-70 dB at 500 kHz bandwidth, are not by themselves adequate for transmitting MRI data from volume or array coils with DR approximately 90 dB. However, combining analog links with signal compression might make non-coaxial cable signal transmission viable.
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Affiliation(s)
- Refaat E. Gabr
- Division of MR Research, Department of Radiology, Johns Hopkins School of Medicine, 600 N Wolfe St., Park 328, Baltimore, MD, USA
- Department of Electrical and Computer Engineering, The Johns Hopkins University, Baltimore, MD, USA
| | - Michael Schär
- Division of MR Research, Department of Radiology, Johns Hopkins School of Medicine, 600 N Wolfe St., Park 328, Baltimore, MD, USA
- Philips Healthcare, Cleveland, OH, USA
| | | | - Dara L. Kraitchman
- Division of MR Research, Department of Radiology, Johns Hopkins School of Medicine, 600 N Wolfe St., Park 328, Baltimore, MD, USA
| | - Paul A. Bottomley
- Division of MR Research, Department of Radiology, Johns Hopkins School of Medicine, 600 N Wolfe St., Park 328, Baltimore, MD, USA
- Department of Electrical and Computer Engineering, The Johns Hopkins University, Baltimore, MD, USA
| | - William A. Edelstein
- Division of MR Research, Department of Radiology, Johns Hopkins School of Medicine, 600 N Wolfe St., Park 328, Baltimore, MD, USA
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Ito S, Yamada Y. Alias-free image reconstruction using Fresnel transform in the phase-scrambling Fourier imaging technique. Magn Reson Med 2008; 60:422-30. [DOI: 10.1002/mrm.21672] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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14
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Johnson GA, Ali-Sharief A, Badea A, Brandenburg J, Cofer G, Fubara B, Gewalt S, Hedlund LW, Upchurch L. High-throughput morphologic phenotyping of the mouse brain with magnetic resonance histology. Neuroimage 2007; 37:82-9. [PMID: 17574443 PMCID: PMC1994723 DOI: 10.1016/j.neuroimage.2007.05.013] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2007] [Revised: 04/30/2007] [Accepted: 05/07/2007] [Indexed: 11/19/2022] Open
Abstract
The Mouse Biomedical Informatics Research Network (MBIRN) has been established to integrate imaging studies of the mouse brain ranging from three-dimensional (3D) studies of the whole brain to focused regions at a sub-cellular scale. Magnetic resonance (MR) histology provides the entry point for many morphologic comparisons of the whole brain. We describe a standardized protocol that allows acquisition of 3D MR histology (43-microm resolution) images of the fixed, stained mouse brain with acquisition times <30 min. A higher resolution protocol with isotropic spatial resolution of 21.5 microm can be executed in 2 h. A third acquisition protocol provides an alternative image contrast (at 43-microm isotropic resolution), which is exploited in a statistically driven algorithm that segments 33 of the most critical structures in the brain. The entire process, from specimen perfusion, fixation and staining, image acquisition and reconstruction, post-processing, segmentation, archiving, and analysis, is integrated through a structured workflow. This yields a searchable database for archive and query of the very large (1.2 GB) images acquired with this standardized protocol. These methods have been applied to a collection of both male and female adult murine brains ranging over 4 strains and 6 neurologic knockout models. These collection and acquisition methods are now available to the neuroscience community as a standard web-deliverable service.
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Affiliation(s)
- G Allan Johnson
- Center for In Vivo Microscopy, Box 3302, Duke University Medical Center, Durham, NC 27710, USA.
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Ito S, Yamada Y. Optical on-line running reconstruction of MR-images in the phase-scrambling Fourier-imaging technique. Appl Opt 2002; 41:5527-5537. [PMID: 12224776 DOI: 10.1364/ao.41.005527] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Recently, the use of magnetic-resonance-guided navigation to improve the safety and effectiveness of surgical procedures has shown great promise. The purpose of the present study was to develop and demonstrate an imaging strategy that allows surgeons to continue operating without delays caused by imaging. The phase-scrambling Fourier-imaging technique has two prominent characteristics: localized image reconstruction and holographic image reconstruction. The combination of these characteristics allows images to be observed even during the data-acquisition period, because the acquired signal is converted into a hologram and the image is reconstructed instantly in the coherent optical image-processing system. Experimental studies have shown that the phase-scrambling Fourier-imaging technique enables the motion of objects to be imaged more quickly than the standard fast imaging. The proposed running reconstruction strategy can be easily implemented in the well-established magnetic-resonance imaging equipment that is currently in use.
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Affiliation(s)
- Satoshi Ito
- Utsunomia University, Department of Information Science, Faculty of Engineering, Japan.
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Abstract
The development and optimization of spin-echo-based, single-slab, three-dimensional techniques for magnetic resonance imaging of the whole brain are described. T1-weighted and T2-weighted image sets with a volume resolution of 1 mm(3) and fluid-attenuated inversion-recovery image sets with a volume resolution of 3 mm(3) were obtained in acquisition times of less than 10 minutes per image set.
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Affiliation(s)
- J P Mugler
- Dept of Radiology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
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Elliott MA, Insko EK, Greenman RL, Leigh JS. Improved resolution and signal-to-noise ratio in MRI via enhanced signal digitization. J Magn Reson 1998; 130:300-304. [PMID: 9500903 DOI: 10.1006/jmre.1997.1319] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The high frequency k-space data in magnetic resonance imaging is often poorly reproduced due to the finite dynamic range of an analog-to-digital converter. The magnitude of this digitization error can equal and even exceed the magnitude of the thermal noise. Under such conditions, attempts to increase image signal-to-noise ratio via signal averaging meet with diminishing success. Because the relative size of the digitization error increases at higher spatial frequencies, a reduction in image resolution is incurred as well. By adjusting the level of the analog signal sampled by the analog-to-digital converter during the course of an imaging experiment, the magnitude of the digitization artifact can be greatly reduced. The results of simulations and imaging experiments are presented which demonstrate that this strategy improves both the signal-to-noise ratio and resolution of magnetic resonance images.
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Affiliation(s)
- M A Elliott
- Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6100, USA
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Abstract
An RF excitation technique with which one can improve the effective dynamic range of the receiver and reduce the interference between slices for 3D volume-selective multislice MRI is described. The basic idea of the technique is to use phase scrambling in conjunction with slice encoding through the use of RF pulses. The spins in each slice are encoded by RF pulses which have the scrambled as well as slice-encoded phase components along the slice-selection direction. The scrambled, or randomly distributed, phase reduces the peak signal intensity, thereby reducing the dynamic range of the signal. Since the proposed technique utilizes RF slice encoding together with phase scrambling, interslice image interference is greatly reduced and the dynamic range is improved. In addition, the method has several advantages such as a reduction in the power requirement for the RF pulses and the elimination of the necessity for hardware such as nonlinear gradient coils.
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Affiliation(s)
- C H Oh
- Department of Radiology, Columbia University, New York, New York 10032
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Abstract
In magnetic resonance imaging, if the object of interest is known to be spatially bounded within the image field-of-view, then the high-intensity, low spatial frequencies can be determined by postprocessing. This allows the system receiver gain to be increased, thereby decreasing the quantitation noise from the analog-to-digital converters. No imaging sequence modifications are required.
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Affiliation(s)
- J Jackson
- Magnetic Resonance Systems Research Laboratory, Stanford University, California 94305
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