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Kimberly WT, Sorby-Adams AJ, Webb AG, Wu EX, Beekman R, Bowry R, Schiff SJ, de Havenon A, Shen FX, Sze G, Schaefer P, Iglesias JE, Rosen MS, Sheth KN. Brain imaging with portable low-field MRI. NATURE REVIEWS BIOENGINEERING 2023; 1:617-630. [PMID: 37705717 PMCID: PMC10497072 DOI: 10.1038/s44222-023-00086-w] [Citation(s) in RCA: 16] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 06/06/2023] [Indexed: 09/15/2023]
Abstract
The advent of portable, low-field MRI (LF-MRI) heralds new opportunities in neuroimaging. Low power requirements and transportability have enabled scanning outside the controlled environment of a conventional MRI suite, enhancing access to neuroimaging for indications that are not well suited to existing technologies. Maximizing the information extracted from the reduced signal-to-noise ratio of LF-MRI is crucial to developing clinically useful diagnostic images. Progress in electromagnetic noise cancellation and machine learning reconstruction algorithms from sparse k-space data as well as new approaches to image enhancement have now enabled these advancements. Coupling technological innovation with bedside imaging creates new prospects in visualizing the healthy brain and detecting acute and chronic pathological changes. Ongoing development of hardware, improvements in pulse sequences and image reconstruction, and validation of clinical utility will continue to accelerate this field. As further innovation occurs, portable LF-MRI will facilitate the democratization of MRI and create new applications not previously feasible with conventional systems.
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Affiliation(s)
- W Taylor Kimberly
- Department of Neurology and the Center for Genomic Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
| | - Annabel J Sorby-Adams
- Department of Neurology and the Center for Genomic Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
| | - Andrew G Webb
- Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Ed X Wu
- Laboratory of Biomedical Imaging and Signal Processing, Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China
| | - Rachel Beekman
- Division of Neurocritical Care and Emergency Neurology, Department of Neurology, Yale New Haven Hospital and Yale School of Medicine, Yale Center for Brain & Mind Health, New Haven, CT, USA
| | - Ritvij Bowry
- Departments of Neurosurgery and Neurology, McGovern Medical School, University of Texas Health Neurosciences, Houston, TX, USA
| | - Steven J Schiff
- Department of Neurosurgery, Yale School of Medicine, New Haven, CT, USA
| | - Adam de Havenon
- Division of Vascular Neurology, Department of Neurology, Yale New Haven Hospital and Yale School of Medicine, New Haven, CT, USA
| | - Francis X Shen
- Harvard Medical School Center for Bioethics, Harvard law School, Boston, MA, USA
- Department of Psychiatry, Massachusetts General Hospital, Boston, MA, USA
| | - Gordon Sze
- Department of Radiology, Yale New Haven Hospital and Yale School of Medicine, New Haven, CT, USA
| | - Pamela Schaefer
- Division of Neuroradiology, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
| | - Juan Eugenio Iglesias
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
- Centre for Medical Image Computing, University College London, London, UK
- Computer Science and AI Laboratory, Massachusetts Institute of Technology, Boston, MA, USA
| | - Matthew S Rosen
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
| | - Kevin N Sheth
- Division of Neurocritical Care and Emergency Neurology, Department of Neurology, Yale New Haven Hospital and Yale School of Medicine, Yale Center for Brain & Mind Health, New Haven, CT, USA
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2
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Yu B, Song C, Feng CL, Zhang J, Wang Y, Zhu YM, Zhang L, Ji XM, Tian XF, Cheng GF, Chen WL, Zablotskii V, Wang H, Zhang X. Effects of gradient high-field static magnetic fields on diabetic mice. Zool Res 2023; 44:249-258. [PMID: 36650064 PMCID: PMC10083230 DOI: 10.24272/j.issn.2095-8137.2022.460] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Accepted: 01/11/2023] [Indexed: 01/15/2023] Open
Abstract
Although 9.4 T magnetic resonance imaging (MRI) has been tested in healthy volunteers, its safety in diabetic patients is unclear. Furthermore, the effects of high static magnetic fields (SMFs), especially gradient vs. uniform fields, have not been investigated in diabetics. Here, we investigated the consequences of exposure to 1.0-9.4 T high SMFs of different gradients (>10 T/m vs. 0-10 T/m) on type 1 diabetic (T1D) and type 2 diabetic (T2D) mice. We found that 14 h of prolonged treatment of gradient (as high as 55.5 T/m) high SMFs (1.0-8.6 T) had negative effects on T1D and T2D mice, including spleen, hepatic, and renal tissue impairment and elevated glycosylated serum protein, blood glucose, inflammation, and anxiety, while 9.4 T quasi-uniform SMFs at 0-10 T/m did not induce the same effects. In regular T1D mice (blood glucose ≥16.7 mmol/L), the >10 T/m gradient high SMFs increased malondialdehyde ( P<0.01) and decreased superoxide dismutase ( P<0.05). However, in the severe T1D mice (blood glucose ≥30.0 mmol/L), the >10 T/m gradient high SMFs significantly increased tissue damage and reduced survival rate. In vitro cellular studies showed that gradient high SMFs increased cellular reactive oxygen species and apoptosis and reduced MS-1 cell number and proliferation. Therefore, this study showed that prolonged exposure to high-field (1.0-8.6 T) >10 T/m gradient SMFs (35-1 380 times higher than that of current clinical MRI) can have negative effects on diabetic mice, especially mice with severe T1D, whereas 9.4 T high SMFs at 0-10 T/m did not produce the same effects, providing important information for the future development and clinical application of SMFs, especially high-field MRI.
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Affiliation(s)
- Biao Yu
- High Magnetic Field Laboratory, CAS Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui 230031, China
| | - Chao Song
- High Magnetic Field Laboratory, CAS Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui 230031, China
| | - Chuan-Lin Feng
- High Magnetic Field Laboratory, CAS Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui 230031, China
- Science Island Branch of Graduate School, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Jing Zhang
- High Magnetic Field Laboratory, CAS Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui 230031, China
- Science Island Branch of Graduate School, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Ying Wang
- High Magnetic Field Laboratory, CAS Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui 230031, China
- Science Island Branch of Graduate School, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Yi-Ming Zhu
- Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui, 230601, China
| | - Lei Zhang
- High Magnetic Field Laboratory, CAS Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui 230031, China
| | - Xin-Miao Ji
- High Magnetic Field Laboratory, CAS Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui 230031, China
| | - Xiao-Fei Tian
- Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui, 230601, China
| | - Guo-Feng Cheng
- High Magnetic Field Laboratory, CAS Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui 230031, China
- Science Island Branch of Graduate School, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Wei-Li Chen
- Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui, 230601, China
| | - Vitalii Zablotskii
- Institute of Physics of the Czech Academy of Sciences, Prague, 18221, Czech Republic
- International Magnetobiology Frontier Research Center, Science Island, Hefei, Anhui 230031, China
| | - Hua Wang
- Department of Oncology, First Affiliated Hospital of Anhui Medical University, Hefei, Anhui 230022, China
| | - Xin Zhang
- High Magnetic Field Laboratory, CAS Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui 230031, China
- Science Island Branch of Graduate School, University of Science and Technology of China, Hefei, Anhui 230026, China
- Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui, 230601, China
- International Magnetobiology Frontier Research Center, Science Island, Hefei, Anhui 230031, China. E-mail:
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3
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Kose K. Physical and technical aspects of human magnetic resonance imaging: present status and 50 years historical review. ADVANCES IN PHYSICS: X 2021. [DOI: 10.1080/23746149.2021.1885310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Affiliation(s)
- Katsumi Kose
- MRIsimulations Inc., University of Tsukuba, Tsukuba, Japan
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4
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Tian X, Lv Y, Fan Y, Wang Z, Yu B, Song C, Lu Q, Xi C, Pi L, Zhang X. Safety evaluation of mice exposed to 7.0-33.0 T high-static magnetic fields. J Magn Reson Imaging 2020; 53:1872-1884. [PMID: 33382516 DOI: 10.1002/jmri.27496] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 12/14/2020] [Accepted: 12/16/2020] [Indexed: 01/26/2023] Open
Abstract
Magnetic resonance imaging (MRI) of 7 T and higher can provide superior image resolution and capability. Clinical tests have been performed in 9.4 T MRI, and 21.1 T small-bore-size MRI has also been tested in rodents. Although the safety issue is a prerequisite for their future medical application, there are very few relevant studies for the safety of static magnetic fields (SMFs) of ≧20 T. The aim of this study was to assess the biological effects of 7.0-33.0 T SMFs in healthy adult mice. This was a prospective study, in which 104 healthy adult C57BL/6 mice were divided into control, sham control, and 7.0-33.0 T SMF-exposed groups.The sham control group and SMF group were handled identically, except for the electric current for producing SMF. A separate control group was placed outside the magnet and their data were used as normal range. After 1 h exposure, all mice were routinely fed for another 2 months while their body weight and food/water consumption were monitored. After 2 months, their complete blood count, blood biochemistry, key organ weight, and histomorphology were examined. All data are normally distributed. Differences between the sham and SMF-exposed groups were evaluated by unpaired t test. Most indicators did not show statistically significant changes or were still within the normal ranges, with only a few exceptions. For example, mono % in Group 2 (11.1 T) is 6.03 ± 1.43% while the normal range is 6.60-9.90% (p < 0.05). The cholesterol level in 33 T group is 3.38 ± 0.36 mmol/L while the normal range is 2.48-3.29 mmol/L (p < 0.05). The high-density lipoprotein cholesterol level in 33 T group is 2.54 ± 0.29 mmol/L while the normal reference range is 1.89-2.43 mmol/L (p < 0.01). Exposure to 7.0-33.0 T for 1 h did not have detrimental effects on normal adult mice. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 1.
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Affiliation(s)
- Xiaofei Tian
- High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China.,Institutes of Physical Science and Information Technology, Anhui University, Hefei, China
| | - Yue Lv
- High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China.,Science Island Branch of Graduate School, University of Science and Technology of China, Hefei, China
| | - Yixiang Fan
- High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China.,Science Island Branch of Graduate School, University of Science and Technology of China, Hefei, China
| | - Ze Wang
- High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China.,Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, China
| | - Biao Yu
- High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China.,Science Island Branch of Graduate School, University of Science and Technology of China, Hefei, China
| | - Chao Song
- High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China.,Science Island Branch of Graduate School, University of Science and Technology of China, Hefei, China
| | - Qingyou Lu
- High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China.,Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, China.,Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions, Hefei, China
| | - Chuanying Xi
- High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China
| | - Li Pi
- High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China
| | - Xin Zhang
- High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, China.,Science Island Branch of Graduate School, University of Science and Technology of China, Hefei, China.,Institutes of Physical Science and Information Technology, Anhui University, Hefei, China
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5
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Börnert P, Norris DG. A half-century of innovation in technology-preparing MRI for the 21st century. Br J Radiol 2020; 93:20200113. [PMID: 32496816 DOI: 10.1259/bjr.20200113] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
MRI developed during the last half-century from a very basic concept to an indispensable non-ionising medical imaging technique that has found broad application in diagnostics, therapy control and far beyond. Due to its excellent soft-tissue contrast and the huge variety of accessible tissue- and physiological-parameters, MRI is often preferred to other existing modalities. In the course of its development, MRI underwent many substantial transformations. From the beginning, starting as a proof of concept, much effort was expended to develop the appropriate basic scanning technology and methodology, and to establish the many clinical contrasts (e.g., T1, T2, flow, diffusion, water/fat, etc.) that MRI is famous for today. Beyond that, additional prominent innovations to the field have been parallel imaging and compressed sensing, leading to significant scanning time reductions, and the move towards higher static magnetic field strengths, which led to increased sensitivity and improved image quality. Improvements in workflow and the use of artificial intelligence are among many current trends seen in this field, paving the way for a broad use of MRI. The 125th anniversary of the BJR is a good point to reflect on all these changes and developments and to offer some slightly speculative ideas as to what the future may bring.
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Affiliation(s)
- Peter Börnert
- Philips Research, Hamburg, Germany.,Department of Radiology, LUMC, Leiden, the Netherlands
| | - David G Norris
- Donders Institute for Brain, Cognition and Behaviour, Radboud University, Nijmegen, Netherlands.,Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany.,Magnetic Detection and Imaging, Science and Technology Faculty, University of Twente, Enschede, Netherlands
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6
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Affiliation(s)
- Thomas M Grist
- From the Department of Radiology, University of Wisconsin-Madison, School of Medicine and Public Health, 600 Highland Ave, Madison, WI 53705
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7
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8
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Uğurbil K. Imaging at ultrahigh magnetic fields: History, challenges, and solutions. Neuroimage 2018; 168:7-32. [PMID: 28698108 PMCID: PMC5758441 DOI: 10.1016/j.neuroimage.2017.07.007] [Citation(s) in RCA: 86] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 07/05/2017] [Accepted: 07/07/2017] [Indexed: 01/06/2023] Open
Abstract
Following early efforts in applying nuclear magnetic resonance (NMR) spectroscopy to study biological processes in intact systems, and particularly since the introduction of 4 T human scanners circa 1990, rapid progress was made in imaging and spectroscopy studies of humans at 4 T and animal models at 9.4 T, leading to the introduction of 7 T and higher magnetic fields for human investigation at about the turn of the century. Work conducted on these platforms has provided numerous technological solutions to challenges posed at these ultrahigh fields, and demonstrated the existence of significant advantages in signal-to-noise ratio and biological information content. Primary difference from lower fields is the deviation from the near field regime at the radiofrequencies (RF) corresponding to hydrogen resonance conditions. At such ultrahigh fields, the RF is characterized by attenuated traveling waves in the human body, which leads to image non-uniformities for a given sample-coil configuration because of destructive and constructive interferences. These non-uniformities were initially considered detrimental to progress of imaging at high field strengths. However, they are advantageous for parallel imaging in signal reception and transmission, two critical technologies that account, to a large extend, for the success of ultrahigh fields. With these technologies and improvements in instrumentation and imaging methods, today ultrahigh fields have provided unprecedented gains in imaging of brain function and anatomy, and started to make inroads into investigation of the human torso and extremities. As extensive as they are, these gains still constitute a prelude to what is to come given the increasingly larger effort committed to ultrahigh field research and development of ever better instrumentation and techniques.
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Affiliation(s)
- Kamil Uğurbil
- Center for Magnetic Resonance Research (CMRR), University of Minnesota Medical School, Minneapolis, MN 55455, USA.
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9
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Evaluation of 2D multiband EPI imaging for high-resolution, whole-brain, task-based fMRI studies at 3T: Sensitivity and slice leakage artifacts. Neuroimage 2015; 124:32-42. [PMID: 26341029 PMCID: PMC4655914 DOI: 10.1016/j.neuroimage.2015.08.056] [Citation(s) in RCA: 108] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Revised: 08/13/2015] [Accepted: 08/25/2015] [Indexed: 01/08/2023] Open
Abstract
Functional magnetic resonance imaging (fMRI) studies that require high-resolution whole-brain coverage have long scan times that are primarily driven by the large number of thin slices acquired. Two-dimensional multiband echo-planar imaging (EPI) sequences accelerate the data acquisition along the slice direction and therefore represent an attractive approach to such studies by improving the temporal resolution without sacrificing spatial resolution. In this work, a 2D multiband EPI sequence was optimized for 1.5 mm isotropic whole-brain acquisitions at 3 T with 10 healthy volunteers imaged while performing simultaneous visual and motor tasks. The performance of the sequence was evaluated in terms of BOLD sensitivity and false-positive activation at multiband (MB) factors of 1, 2, 4, and 6, combined with in-plane GRAPPA acceleration of 2 × (GRAPPA 2), and the two reconstruction approaches of Slice-GRAPPA and Split Slice-GRAPPA. Sensitivity results demonstrate significant gains in temporal signal-to-noise ratio (tSNR) and t-score statistics for MB 2, 4, and 6 compared to MB 1. The MB factor for optimal sensitivity varied depending on anatomical location and reconstruction method. When using Slice-GRAPPA reconstruction, evidence of false-positive activation due to signal leakage between simultaneously excited slices was seen in one instance, 35 instances, and 70 instances over the ten volunteers for the respective accelerations of MB 2 × GRAPPA 2, MB 4 × GRAPPA 2, and MB 6 × GRAPPA 2. The use of Split Slice-GRAPPA reconstruction suppressed the prevalence of false positives significantly, to 1 instance, 5 instances, and 5 instances for the same respective acceleration factors. Imaging protocols using an acceleration factor of MB 2 × GRAPPA 2 can be confidently used for high-resolution whole-brain imaging to improve BOLD sensitivity with very low probability for false-positive activation due to slice leakage. Imaging protocols using higher acceleration factors (MB 3 or MB 4 × GRAPPA 2) can likely provide even greater gains in sensitivity but should be carefully optimized to minimize the possibility of false activations. MB factors 1, 2, 4, and 6 and two reconstructions were evaluated for fMRI performance. MB accelerations 2, 4, and 6 improved BOLD sensitivity metrics over MB 1. False-positive activation due to signal leakage was seen at high accelerations. Use of Split Slice-GRAPPA reconstruction significantly reduces false positives.
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10
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A historical overview of magnetic resonance imaging, focusing on technological innovations. Invest Radiol 2013; 47:725-41. [PMID: 23070095 DOI: 10.1097/rli.0b013e318272d29f] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Magnetic resonance imaging (MRI) has now been used clinically for more than 30 years. Today, MRI serves as the primary diagnostic modality for many clinical problems. In this article, historical developments in the field of MRI will be discussed with a focus on technological innovations. Topics include the initial discoveries in nuclear magnetic resonance that allowed for the advent of MRI as well as the development of whole-body, high field strength, and open MRI systems. Dedicated imaging coils, basic pulse sequences, contrast-enhanced, and functional imaging techniques will also be discussed in a historical context. This article describes important technological innovations in the field of MRI, together with their clinical applicability today, providing critical insights into future developments.
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11
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Wadghiri YZ, Hoang DM, Wisniewski T, Sigurdsson EM. In vivo magnetic resonance imaging of amyloid-β plaques in mice. Methods Mol Biol 2012; 849:435-51. [PMID: 22528108 PMCID: PMC3555565 DOI: 10.1007/978-1-61779-551-0_30] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Transgenic mice are used increasingly to model brain amyloidosis, mimicking the pathogenic processes involved in Alzheimer's disease (AD). In this chapter, an in vivo strategy is described that has been successfully used to map amyloid-β deposits in transgenic mouse models of AD with magnetic resonance imaging (MRI), utilizing both the endogenous contrast induced by the plaques attributed to their iron content and by selectively enhancing the signal from amyloid-β plaques using molecular-targeting vectors labeled with MRI contrast agents. To obtain sufficient spatial resolution for effective and sensitive mouse brain imaging, magnetic fields of 7-Tesla (T) or more are required. These are higher than the 1.5-T field strength routinely used for human brain imaging. The higher magnetic fields affect contrast agent efficiency and dictate the choice of pulse sequence parameters for in vivo MRI, all addressed in this chapter. Two-dimensional (2D) multi-slice and three-dimensional (3D) MRI acquisitions are described and their advantages and limitations are discussed. The experimental setup required for mouse brain imaging is explained in detail, including anesthesia, immobilization of the mouse's head to reduce motion artifacts, and anatomical landmarks to use for the slice alignment procedure to improve image co-registration during longitudinal studies and for subsequent matching of MRI with histology.
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Affiliation(s)
- Youssef Zaim Wadghiri
- Department of Radiology, Center for Biomedical Imaging, New York University School of Medicine, New York, NY, USA.
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12
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Tyler DJ, Robson MD, Henkelman RM, Young IR, Bydder GM. Magnetic resonance imaging with ultrashort TE (UTE) PULSE sequences: Technical considerations. J Magn Reson Imaging 2007; 25:279-89. [PMID: 17260388 DOI: 10.1002/jmri.20851] [Citation(s) in RCA: 142] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
It is now possible to detect signals from tissues and tissue components with short T(2)s, such as cortical bone, using ultrashort TE (UTE) pulse sequences. The background to the use of these sequences is reviewed with particular emphasis on MR system issues. Tissue properties are discussed, and tissues are divided into those with a majority and those with a minority of short T(2) components. UTE pulse sequences and their variants are described and clinical applications are illustrated. System design requirements for sequences of this type, including gradient performance, RF switching, and data-processing issues, are outlined.
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Affiliation(s)
- Damian J Tyler
- Oxford University Centre for Clinical Magnetic Resonance Research, MRS Unit, John Radcliffe Hospital, Oxford, United Kingdom
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13
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Abstract
A magnetic resonance imaging (MRI) system requires the highest possible signal fidelity and stability for clinical applications. Quadrature analog receivers have problems with channel matching, dc offset and analog-to-digital linearity. Fixed-point digital receivers (DRs) reduce all of these problems. We have demonstrated that a floating-point DR using large (order 124 to 512) FIR low-pass filters also overcomes these problems, automatically provides long word length and has low latency between signals. A preloaded table of finite impuls response (FIR) filter coefficients provides fast switching between one of 129 different one-stage and two-stage multrate FIR low-pass filters with bandwidths between 4 KHz and 125 KHz. This design has been implemented on a dual channel circuit board for a commercial MRI system.
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Affiliation(s)
- John C Hoenninger
- Toshiba America MRI, Inc, RIL Division, South San Francisco, CA 94080, USA.
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14
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Abstract
A method to encode multiple two-dimensional Fourier transform (2D FT) images within a single echo train is presented. This new method, simultaneous echo refocusing (SER), is a departure from prior echo planar image (EPI) sequences which use repeated single-shot echo trains for multislice imaging. SER simultaneously acquires multiple slices in a single-shot echo train utilizing a shared refocusing process. The SER technique acquires data faster than conventional multislice EPI since it uses fewer gradient switchings and fewer preparation pulses such as diffusion gradients. SER introduces a new capability to simultaneously record multiple spatially separated sources of physiologic information in subsecond image acquisitions, which enables several applications that are dependent on temporal coherence in MRI data including velocity vector field mapping and brain activation mapping.
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Affiliation(s)
- David A Feinberg
- Advanced MRI Technologies, LLC, Sebastopol, California 95472, USA.
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15
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Newhouse JH. Urinary tract imaging by nuclear magnetic resonance. 1982. J Urol 2002; 167:1040-2; discussion 1043. [PMID: 11905874 DOI: 10.1016/s0022-5347(02)80334-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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16
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Moon KL, Genant HK, Davis PL, Chafetz NI, Helms CA, Morris JM, Rodrigo JJ, Jergesen HE, Brasch RC, Bovill EG. Nuclear magnetic resonance imaging in orthopaedics: principles and applications. J Orthop Res 2001; 1:101-14. [PMID: 6679570 DOI: 10.1002/jor.1100010113] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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17
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Abstract
A new method is introduced for increasing the efficiency in multislice single spin-echo MRI. The method interlaces the excitation and measurement of different slices, resulting in an effective use of the echo delay time between RF excitation and reception. Under certain conditions, the method allows for scan time reduction compared to standard single spin-echo MRI, in particular for long echo times. The technique is demonstrated in examples of brain scans, indicating that a substantial increase is scan speed can be achieved without loss in image signal-to-noise ratio or contrast. Potential applications include perfusion imaging using T(2)-contrast agents, as well as BOLD-based functional imaging. Magn Reson Med 43:905-908, 2000. Published 2000 Wiley-Liss, Inc.
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Affiliation(s)
- J H Duyn
- Laboratory of Diagnostic Radiology Research, CC, NIH, Bethesda, Maryland 20892, USA.
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18
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19
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Abstract
A simple theoretical model was developed to compare the sensitivities (i.e., signal-to-noise ratios per unit imaging time) of two-dimensional (2D) multislice and 3D imaging sequences. The model shows that the sensitivities of 3D and 2D multislice MRI sequences are usually similar. Sensitivities are identical in T2-weighted sequences when the T(R)s of the two sequences are the same. In T1-weighted gradient-echo sequences, sensitivities are very similar when Ernst angle excitation is used and the T(R) of the 2D sequence is less than T1. The predictions of the model are confirmed in phantom and animal experiments.
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Affiliation(s)
- G Johnson
- Department of Radiology, New York University Medical Center, New York 10016, USA.
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Magnetic Resonance Imaging: A Historical Introduction. Magn Reson Imaging 1999. [DOI: 10.1007/978-3-662-03800-0_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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21
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Affiliation(s)
- G M Bydder
- The Robert Steiner Magnetic Resonance Unit, Imperial College School of Medicine, Hammersmith Hospital, London, UK
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22
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Abstract
Following Paul Lauterbur's seminal 1973 paper in Nature, considerable work was needed to overcome a number of physical, engineering and technical problems before the new technique of magnetic resonance imaging (MRI) could be applied clinically. Much of that pioneering work was done in the UK. Since the first head and whole-body images were obtained in the late 1970s, MRI has become a widely used clinical imaging modality capable of yielding tomographic images of excellent spatial resolution and tissue contrast. This review outlines the historical development of MRI in the context both of the technical problems which had to be overcome, and of the clinical uses of MRI. Current areas of research, such as the use of MRI to map brain function, the measurement of physiological parameters such as tissue perfusion, and the use of open-access real-time MRI to guide interventional procedures, are briefly discussed.
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Affiliation(s)
- T W Redpath
- Department of Medical Physics, University of Aberdeen, Foresterhill, UK
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23
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Li D, Haacke EM, Tarr RW, Venkatesan R, Lin W, Wielopolski P. Magnetic resonance imaging of the brain with gadopentetate dimeglumine-DTPA: comparison of T1-weighted spin-echo and 3D gradient-echo sequences. J Magn Reson Imaging 1996; 6:415-24. [PMID: 8724406 DOI: 10.1002/jmri.1880060302] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Short TR, short TE, high resolution, 3D gradient-recalled echo (GRE) imaging was evaluated for lesion detection in the brain. High resolution 3D GRE data acquisition was used to reduce partial volume effects and flow artifacts, to better visualize smaller structures, to minimize signal losses caused by field inhomogeneities, and to allow better image reformatting. Spin-echo (SE) and 3D GRE approaches were compared for lesion detection after the administration of an MR contrast agent, gadopentetate dimeglumine. Preliminary clinical studies demonstrated that the signal-to-noise ratio (SNR) in each slice of the GRE scan was worse than that of the SE scan because of the much thicker slices acquired with the SE technique. However, by averaging two adjacent 3D slices, the SNR of the two methods was essentially equivalent. In the averaged GRE slices, large lesions were seen just as well as in the SE images. More importantly, small lesions were better visualized in the thin 3D GRE images than in the thick SE images for the lesions studied in this work and the protocols used. These observations were confirmed by theoretical simulations.
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Affiliation(s)
- D Li
- Mallinckrodt Institute of Radiology, Washington University, St. Louis, MO 63110, USA
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Feinberg DA, Kiefer B, Litt AW. Dual contrast GRASE (gradient-spin echo) imaging using mixed bandwidth. Magn Reson Med 1994; 31:461-4. [PMID: 8208124 DOI: 10.1002/mrm.1910310417] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Equal time spacing of RF pulses in the CPMG sequence imposes a constraint of equal signal read periods in spin-echo train imaging. GRASE imaging differs by using multiple read gradients in each pi-pi time interval, which are not constrained to be equal in number or duration. This additional degree of freedom is developed in dual contrast imaging. Closely spaced read periods are used for the PDW image to reduce T2 decay effects, while fewer low-bandwidth read periods in each of several pi-pi intervals are used to raise the signal-to-noise ratio and avoid signal averaging in the T2-weighted image.
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Affiliation(s)
- D A Feinberg
- Department of Radiology, New York University Medical Center, NY 10016
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26
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Duyn JH, Moonen CT. Fast proton spectroscopic imaging of human brain using multiple spin-echoes. Magn Reson Med 1993; 30:409-14. [PMID: 8255188 DOI: 10.1002/mrm.1910300403] [Citation(s) in RCA: 129] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We introduce a multi-echo multi-slice MR proton spectroscopic imaging method, which allows for a dramatic reduction of the measurement time by acquiring multiple spin-echoes within a single repetition time. In the multi-echo multi-slice experiment discussed in this paper, a threefold reduction in measurement time is obtained by sacrificing some spectral resolution. Signal-to-noise ratio and spatial resolution are preserved. Metabolite images of N-acetyl aspartate, and total choline+total creatine from multiple slices through the human brain are presented and compared with images obtained with a conventional single-echo multi-slice method.
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Affiliation(s)
- J H Duyn
- Laboratory of Diagnostic Radiology Research, National Institutes of Health, Bethesda, Maryland 20892
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27
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Rosenberg TD, Franklin JL, Baldwin GN, Nelson KA. Extensor mechanism function after patellar tendon graft harvest for anterior cruciate ligament reconstruction. Am J Sports Med 1992; 20:519-25; discussion 525-6. [PMID: 1443318 DOI: 10.1177/036354659202000506] [Citation(s) in RCA: 220] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
We evaluated extensor mechanism function in 10 patients after they had arthroscopically assisted ACL reconstruction using the central third of the patellar tendon. The patients were randomly selected 12 to 24 months after reconstruction. All had rehabilitation where range of motion was initiated within the 1st postoperative week. All patients stated that they were satisfied and considered their knee to be stable. The KT-1000 maximum measurements (30 to 40 pounds) averaged an increase of 1.7 mm when compared with the opposite knee. Subjective complaints, such as anterior knee pain, grating, and weakness, were common and only 3 of 10 patients returned to all of their preinjury sports. Persistent radiographic abnormalities were common. Physical examination and functional testing also revealed persistent dysfunction of the extensor mechanism in patients with radiographic abnormalities. Isokinetic testing at 60 deg/sec showed an average quadriceps deficit of 18% compared to the normal extremity. Axial computed tomography scans revealed significant decrease in quadriceps cross-sectional area. Magnetic resonance imaging and computed tomography confirmed persistent defects at the harvest site; there was significant anterior knee scar formation in these patients. Despite achieving ligamentous stability, patients still experienced permanent weakness, functional deficits, patellar chondrosis, and pain after ACL reconstruction using the central one-third of the patellar tendon.
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Affiliation(s)
- T D Rosenberg
- Orthopaedic Specialty Hospital, Salt Lake City, UT 84107
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28
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Abstract
Hybrid imaging techniques have been proposed as a means of decreasing imaging time without the cost and technical constraints of echo planar imaging. With this technique phase encoding measurements acquired at different echo times in more than one multiecho experiment are used to form a single image. This study analyzes the trade-offs which occur in the selection of this technique over more conventional imaging in terms of signal/noise, contrast, resolution, imaging time, and efficiency. Hybrid imaging is shown to be advantageous when raw speed is essential such as in abdominal or pediatric imaging. When coverage rather than time becomes the important factor, hybrid imaging does not offer a significant advantage over conventional methods. T2 decay will also serve as a roll-off filter which will reduce the spatial resolution, but not the noise, for short TE hybrid imaging.
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Affiliation(s)
- D A Ortendahl
- Radiologic Imaging Laboratory, University of California, San Francisco 94080
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29
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Abstract
A new pulse sequence that increases the number of sections that can be acquired with a T2-weighted multisection imaging prescription is presented. The sequence achieves a higher efficiency in section acquisition per unit time by interleaving excitation and data collection for up to three separate sections during the long TE (greater than or equal to 80 msec) of a T2-weighted spin-echo pulse sequence. The necessary modifications of the section-select and readout gradient waveforms for the implementation of TE-interleaved (TEI) sequences, with and without flow compensation, are described. Secondary- and stimulated-echo artifacts are present on some TEI images, but these can be controlled with appropriate spoiler gradients. The signal-to-noise ratio for contiguous sections is slightly reduced compared with that of a standard multisection pulse sequence. These observations indicate that the effects of radio-frequency section interference are enhanced by the TEI sequence.
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Affiliation(s)
- J E Bishop
- Sunnybrook Health Science Centre, North York, Ontario, Canada
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30
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Groch MW, Turner DA, Erwin WD. Respiratory gating in magnetic resonance imaging: improved image quality over non-gated images for equal scan time. Clin Imaging 1991; 15:196-201. [PMID: 1933649 DOI: 10.1016/0899-7071(91)90077-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Magnetic resonance image quality is adversely affected by respiratory (RESP) motion during the scan. Respiratory gating improves magnetic resonance image (MRI) quality and removes artifacts, but has not been widely used, as RESP gating increases scan time. Our RESP-gating device was used to study scan time versus improvement in image quality using various gating modes; with and without combined electrocardiographic (ECG) gating. When RESP scans were acquired for the same time as non-gated scans, by using a wide RESP-gating window bracketing end expiration and a reduced number of pulse sequence repetitions, substantial improvement in image quality (over non-gated scans) resulted, despite the inferior statistical content of the acquisition.
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Affiliation(s)
- M W Groch
- Department of Diagnostic Radiology and Nuclear Medicine, Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612
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32
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Lanzer P, Gross GM, Keller FS, Pohost GM. Sequential 2D inflow venography: initial clinical observations. Magn Reson Med 1991; 19:470-6. [PMID: 1881336 DOI: 10.1002/mrm.1910190240] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Sequential 2D inflow NMR (SDI) venography was employed to define venous anatomy and pathology in five healthy subjects and five patients, mean age 48 +/- 7 years, with documented deep vein thrombosis. SDI images were graded independently by two observers on a scale of 1,2 nondiagnostic and 3,4 diagnostic categories. All iliac and femoropopliteal SDI venograms were diagnostic. In contrast, only one out of nine calf SDI venograms was diagnostic. SDI is a promising new method to assess the proximal peripheral venous system. Improved imaging strategy is needed to produce flow images of the calf veins.
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Affiliation(s)
- P Lanzer
- Department of Medicine, University of Alabama, Birmingham 35294
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33
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Mountz JM, Wilson MW. Brain structure localization in positron emission tomography: comparison of magnetic resonance imaging and a stereotactic method. Comput Med Imaging Graph 1991; 15:17-22. [PMID: 2009493 DOI: 10.1016/0895-6111(91)90102-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
A method commonly used for localization of brain regions on positron emission tomographic (PET) images is direct visualization and designation of structure on the image itself. This technique, however, is limited to portions of the brain having sufficient differential radionuclide uptake to permit the recognition of structure by observers familiar with brain anatomy. Two other methods commonly used instead of direct visualization are magnetic resonance imaging (MRI) and stereotactic methods of localization. This report compares the accuracy of a MRI method versus a stereotactic method of brain structure localization of PET. The three localization methods were analyzed for sixteen different brain regions in 5 different subjects by two independent observers. The results were converted to PET pixel size (1 pixel = .127 cm) for comparison. MRI localization differed from direct visualization by a mean and standard deviation of approximately 2 +/- 1 pixels in both the X and Y dimensions. Stereotactic localization differed from direct visualization by approximately 2 +/- 1 pixels in the X dimension and by approximately 6 +/- 2 pixels in the Y dimension. This larger variation seen with the stereotactic method may be attributed to the questionable assumption of linearity of structure location with respect to size of the inner table of the calvarium.
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Affiliation(s)
- J M Mountz
- Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor
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34
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Kramer DM, Kaufman L, Rothschild P, Hale J, Wummer J, Hake KK. Low-field 3-DFT MRI: conceptual, analytical, and experimental aspects. IEEE TRANSACTIONS ON MEDICAL IMAGING 1991; 10:382-386. [PMID: 18222840 DOI: 10.1109/42.97588] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Three-dimensional Fourier transform (3-DFT) magnetic resonance imaging (MRI) offers advantages in terms of signal-to-noise (S/N) per unit of time for the case where a large number of slices is desired. This advantage is enhanced when the relaxation time, T(1 ), is short. Because time limitations in 3-DFT imaging force the use of short time intervals, TR, between excitations of a slice, lesion contrast is often undesirable at mid-and high-field strength even when the S/N is good. At low fields, where T(1) values are short, high S/N and contrast can both be achieved with 3-DFT MR images. The conceptual and analytical aspects of low-field 3-DFT MRI are presented and demonstrated at 640 G.
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35
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Lanzer P, Gross G, Nanda N, Pohost G. Timing of data acquisition determines image quality in femoropopliteal phase-sensitive MR angiography. Angiology 1990; 41:817-24. [PMID: 2221460 DOI: 10.1177/000331979004101002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
To study the effects of timing of data acquisition on quality of femoropopliteal magnetic resonance (MR) angiograms, the authors studied 16 healthy men, mean age 34.3 +/- 6 years, by color Doppler imaging and by phase-sensitive (PS) MR angiography. PS MR imaging was performed at 1.5T using a flow adjustable gradient (FLAG) pulse sequence. The images were graded in a blinded fashion by two independent observers. Of 16 MR angiograms consisting of 141 angiographic images (AI), 45 (31.9%) were diagnostic. At least 1 diagnostic AI was obtained in each subject, and 38 (84.4%) of the diagnostic images were acquired within the first 120 milli-seconds (ms) of the systolic flow pulse. The highest yield of diagnostic images (90.9%) was obtained in the interval of thirty to sixty ms before the peak flow velocity. In healthy man diagnostic PS MR angiography requires triggering to the femoropopliteal systolic flow pulse. The highest yield of diagnostic images is acquired during the flow pulse acceleration.
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Affiliation(s)
- P Lanzer
- Department of Medicine, University of Alabama, Birmingham
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36
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Lanzer P, Bohning D, Groen J, Gross G, Nanda N, Pohost G. Aortoiliac and femoropopliteal phase-based NMR angiography: a comparison between FLAG and RSE. Magn Reson Med 1990; 15:372-85. [PMID: 2233217 DOI: 10.1002/mrm.1910150304] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
To assess the performance of FLAG and RSE NMR angiography 22 aortoiliac (AI) and 22 femoropopliteal (FP) angiograms in 11 healthy males, mean age 38 +/- 7.6 years, were acquired. The image quality was graded in a blinded fashion by two independent readers. The readers grades were not statistically different (kappa = 0.5696). The representation of diagnostic images was 6/11 FLAG and 8/11 RSE AI as well as 8/11 FLAG and 8/11 RSE FP. On back-to-back comparison six RSE AI and seven RSE FP were graded better than their FLAG counterparts. Although these differences did not achieve a statistical significance RSE NMR angiography provided consistently better images and appears preferable for imaging of the peripheral vascular system in normal subjects.
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Affiliation(s)
- P Lanzer
- University of Alabama, Department of Medicine, Birmingham 35294
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37
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Lanzer P, McKibbin W, Bohning D, Thorn B, Gross G, Cranney G, Nanda N, Pohost G. Aortoiliac imaging by projective phase sensitive MR angiography: effects of triggering and timing of data acquisition on image quality. Magn Reson Imaging 1990; 8:107-16. [PMID: 2338891 DOI: 10.1016/0730-725x(90)90243-u] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
To assess the ability of projective phase sensitive magnetic resonance (MR) angiography to visualize the aortoiliac vascular segment, and to determine the effects of triggering and timing of data acquisition om image quality, we studied 18 healthy volunteers, mean age 33.3 +/- 11 years, by color Doppler imaging and by MR angiography. MR angiography was performed at 1.5 T using a flow-adjustable gradient-echo (FLAG) sequence operated in both ECG-triggered and non-triggered acquisition modes. The images were graded in a blinded fashion by two independent observers. The data were analyzed using Pearson's chi-square analysis. Eighteen triggered time-resolved and 17 non-triggered, time-averaged MR angiograms consisting of 252 and 17 angiographic images, (AI) respectively, were analyzed. In the triggered mode 69 (27.4%) AI and in the non-triggered mode 2 (11.8%) AI were diagnostic. At least one triggered diagnostic AI was obtained in each subject. The image grades were not statistically different between observers (kappa = 0.6686). In the triggered mode diagnostic images were acquired within +/- 90 msec of the peak systolic flow velocity determined by Doppler. The proportion of diagnostic images in the triggered mode was highest (73.3%) within a 30-msec interval before the peak flow. In healthy subjects the aortoiliac segment is reliably visualized by FLAG MR angiography. The optimum results are achieved using the triggered acquisition mode and timing acquisition to the initial 180 msec of the abdominal aortic systolic flow pulse.
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Affiliation(s)
- P Lanzer
- Department of Medicine, University of Alabama at Birmingham 35294
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38
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Tropp J, Derby KA, Hawryszko C, Sugiura S, Yamagata H. Automated shimming of B0 for spectroscopic imaging. ACTA ACUST UNITED AC 1989. [DOI: 10.1016/0022-2364(89)90140-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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39
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Abstract
The principles of Magnetic Resonance Imaging (MRI) evolved during the late 1970s and early years of the following decade. The author was fortunate in being able to visit many of the pioneer research projects in the U.K. and U.S.A. and attend two conferences. This paper briefly describes these projects and their role in the evolution of the present technology, illustrated by photographs obtained from colour slides taken during these visits.
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40
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Germano IM, Pitts LH, Berry I, Moseley M. Magnetic resonance imaging and 31P magnetic resonance spectroscopy for evaluating focal cerebral ischemia. J Neurosurg 1989; 70:612-8. [PMID: 2926502 DOI: 10.3171/jns.1989.70.4.0612] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Recent advances in magnetic resonance (MR) imaging and MR spectroscopy (MRS) allow the noninvasive in vivo study of a variety of anatomical, physiological, and biochemical alterations that may occur in different cerebral pathologies. The authors have investigated the use of MR imaging and MRS to monitor the evolution of experimental focal cerebral ischemia in rats. Permanent focal cerebral ischemia was induced in 36 rats, and 12 normal rats were used as a control group. Changes in high-energy phosphate metabolites were followed in vivo using MRS during the 1st hour and at 3 and 6 hours after ischemic insult. Changes in vivo MR images were evaluated at 1, 3, 6, 12, and 24 hours after ischemic insult. Significant decreases (p less than 0.05) in phosphocreatine/inorganic phosphate ratios and intracellular pH values occurred immediately after the induction of ischemia. The presence of an infarcted area seen on MR images was a constant finding at 3 hours after ischemic insult, and was well defined and localized at 12 and 24 hours. The location of areas of infarction seen on MR images correlated well with areas identified histopathologically. The T1 and T2 MR relaxation times were significantly increased 3 hours after ischemic insult and remained prolonged for at least 24 hours. The results show that MR imaging is a sensitive method to measure cerebral infarction, and that MRS is a sensitive measure of changes that occur in the early phases of ischemia, perhaps when cellular changes may still be reversible. At 3 and 6 hours after the ischemic insult, however, 31P-MRS spectra may appear to be "normal" despite the presence of well-documented areas of infarction.
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Affiliation(s)
- I M Germano
- Department of Neurological Surgery, School of Medicine, University of California, San Francisco
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41
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Abstract
A display method is proposed in which the spin-lattice relaxation time T1, the spin-spin relaxation time T2, and the proton density rho of each pixel in a MR image are simultaneously expressed in color features in a unified way that allows international standardization. MR images were made from a phantom, a healthy volunteer, and patients in such a way that T1 and T2 and proton density images could be derived. T1 and T2 data were compared with accurate relaxation time measurements of the phantom content. Color images were computed from the acquired T1 and T2 images using matrix multiplication on a pixel base. In this way the color combination in each pixel represents the properties of that particular pixel by a unique mixing of the elementary colors red, green, and blue. Color resolution could be modified using different choices of the reference triangle in which the color combinations were defined. This method of representation offers a means for displaying multiple features as T1 and T2 in one directly interpretable image, independent of instrumental settings.
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Affiliation(s)
- R L Kamman
- University of Groningen, Department of Physical Chemistry, The Netherlands
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42
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Gamsu G, Sostman D. Magnetic resonance imaging of the thorax. THE AMERICAN REVIEW OF RESPIRATORY DISEASE 1989; 139:254-74. [PMID: 2643375 DOI: 10.1164/ajrccm/139.1.254] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- G Gamsu
- Department of Radiology, University of California Medical Center, San Francisco 94143-0628
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43
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Affiliation(s)
- G M Bydder
- NMR Unit, Royal Postgraduate Medical School, Hammersmith Hospital, London
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44
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Olofsson PA, Auffermann W, Higgins CB, Rabahie GN, Tavares N, Stoney RJ. Diagnosis of prosthetic aortic graft infection by magnetic resonance imaging. J Vasc Surg 1988. [DOI: 10.1016/0741-5214(88)90394-1] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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45
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Affiliation(s)
- D G Taylor
- Department of Physics, University of Surrey, Guildford, UK
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46
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White RD, Holt WW, Cheitlin MD, Cassidy MM, Ports TA, Lim AD, Botvinick EH, Higgins CB. Estimation of the functional and anatomic extent of myocardial infarction using magnetic resonance imaging. Am Heart J 1988; 115:740-8. [PMID: 3354402 DOI: 10.1016/0002-8703(88)90873-3] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
This study assesses magnetic resonance (MR) imaging for the evaluation of both the functional and anatomic extent of damage to the left ventricle (LV) from myocardial infarction (MI). This was accomplished by blinded region-of-interest analysis of 36 MR examinations (orthogonal-transaxial, electrocardiographically-gated, multiphasic, single spin-echo) for determination of ejection fraction (EF) and relative MI volume (i.e., percent of total LV myocardial volume). Comparison of the results was then made with a measure of global residual LV function (i.e., score quotient or SQ) derived from segmental scoring of LV wall motion on a two-dimensional echocardiogram (Echo) and with an EF value from a left ventriculogram (LVG), both performed relatively concurrently with MR. Significant (p less than 0.01) overall correlations were noted between MR-EF and both Echo-SQ (r = 0.56) and LVG-EF (r = 0.78), and these relationships were relatively stronger when MI was located in the right coronary artery (RCA) than when it was found in the left anterior descending (LAD) distribution (e.g., MR-EF compared with LVG-EF: r = 0.87, p less than 0.05 for RCA; and r = 0.48, p = NS for LAD). The best expression of relative MI volume appeared to be based upon absolute volume of regionally-thinned LV wall multiplied by a correction factor for its residual contractility and then the addition of a volume correcting for the amount of regional wall thinning by necrosis (i.e., "total-Fxn" MI volume).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- R D White
- Department of Radiology, University of California-San Francisco
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47
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48
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Abstract
A fast chemical-shift imaging technique is presented. The method involves saturating all spins outside a plane, selectively exciting individual lines, phase encoding along each line, sampling the FID without gradients, and interleaving interrogation of multiple lines. A 64 X 64 array of spectra with 5 Hz resolution can be obtained in 17 min.
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Affiliation(s)
- G Johnson
- NMR Research Group, Institute of Neurology, London, United Kingdom
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49
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Casamassima F, Villari N, Fargnoli R, Di Lollo S, Cellerini A, Ruggiero C. Magnetic resonance imaging and high-resolution computed tomography in tumors of the lung and the mediastinum. Radiother Oncol 1988; 11:21-9. [PMID: 3344352 DOI: 10.1016/0167-8140(88)90043-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Magnetic resonance (MR) imaging and high resolution computed tomography (CT) have been compared in 37 patients who had expansive processes of the lung and the mediastinum. MR imaging and CT scanning gave identical results in 32 patients; in 5 patients, CT scanning has proved more useful in evaluating the stag e of primary lung tumors. MR imaging often gives more information about the actual size of the tumor, and the involvement of close structures, although it does not modify staging of the tumor. MR imaging has the advantage to differentiate hilar adenopathy from blood vessel structures. Evaluation of T2 relaxing time (that we have performed in the same location of thin-needle biopsy aspiration), however, did not prove to be of diagnostic significance; this indicates that MR imaging at the moment is not suitable for tissue typification.
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Affiliation(s)
- F Casamassima
- Department of Clinical Physiopathology, Service of Oncologic Diagnostic, University of Florence, Italy
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50
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White RD, Cassidy MM, Cheitlin MD, Emilson B, Ports TA, Lim AD, Botvinick EH, Schiller NB, Higgins CB. Segmental evaluation of left ventricular wall motion after myocardial infarction: magnetic resonance imaging versus echocardiography. Am Heart J 1988; 115:166-75. [PMID: 3336970 DOI: 10.1016/0002-8703(88)90533-9] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
To assess relative capabilities of magnetic resonance (MR) imaging and two-dimensional echocardiography (2DE) for evaluating regional contractile dysfunction in the left ventricle after a myocardial infarction, results from 22 concurrent MR (orthogonal-transaxial, ECG-gated, multiphasic, single-spin echo) and 2DE examinations were compared. By means of the same 11-segment LV description, MR and 2DE examinations were independently scored segment by segment for residual wall motion (point scores: 2 = normal, 1 = hypokinesia, 0 = akinesia, and -1 = dyskinesia). Significant correlation between MR and 2DE scoring was found throughout most of the left anterior descending (LAD) distribution, but right coronary artery (RCA) distribution (i.e., middle-posterior segment not well seen) could not be fully evaluated by MR imaging. When cumulative scores for the 10 segments mutually evaluated were used to derive measures of global residual LV function (i.e., score quotient [SQ] = accumulated points divided by 20 total possible points), MR SQ correlated well overall with both 2DE SQ (r = 0.82; p less than 0.05) and ejection fraction (EF) from ventriculography (r = 0.86, p less than 0.05 vs r = 0.88, p less than 0.05 for 2DE SQ compared with EF). MR evaluation of segmental wall motion was relatively stronger in the LAD distribution (MR SQ compared with 2DE SQ: r = 0.86, p less than 0.05; MR SQ compared with EF: r = 0.96, p less than 0.05) than in the RCA distribution (r = 0.06, p greater than or equal to 0.05 and r = 0.62, p greater than or equal to 0.05, respectively). For 2DE, regional variations were not as evident (2DE SQ compared with EF: r = 0.90, p less than 0.05 for LAD and r = 0.81, p less than 0.05 for RCA). For segmental evaluation of wall motion after myocardial infarction, MR imaging (transaxial, multiphasic) appears to be comparable to 2DE overall but superior in LAD distribution and inferior in RCA distribution.
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Affiliation(s)
- R D White
- Department of Radiology, University of California, San Francisco
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