Lightweight, compact, and high‐performance 3 T MR system for imaging the brain and extremities (original) (raw)
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Lightweight, compact, and high-performance 3T MR system for imaging the brain and extremities
Magnetic resonance in medicine, 2018
To build and evaluate a small-footprint, lightweight, high-performance 3T MRI scanner for advanced brain imaging with image quality that is equal to or better than conventional whole-body clinical 3T MRI scanners, while achieving substantial reductions in installation costs. A conduction-cooled magnet was developed that uses less than 12 liters of liquid helium in a gas-charged sealed system, and standard NbTi wire, and weighs approximately 2000 kg. A 42-cm inner-diameter gradient coil with asymmetric transverse axes was developed to provide patient access for head and extremity exams, while minimizing magnet-gradient interactions that adversely affect image quality. The gradient coil was designed to achieve simultaneous operation of 80-mT/m peak gradient amplitude at a slew rate of 700 T/m/s on each gradient axis using readily available 1-MVA gradient drivers. In a comparison of anatomical imaging in 16 patients using T -weighted 3D fluid-attenuated inversion recovery (FLAIR) betwe...
A portable scanner for magnetic resonance imaging of the brain
Nature Biomedical Engineering, 2020
Access to scanners for magnetic resonance imaging (MRI) is typically limited by cost and by infrastructure requirements. Here, we report the design and testing of a portable prototype scanner for brain MRI that uses a compact and lightweight permanent rare-earth magnet with a built-in readout field gradient. The 122-kg low-field (80 mT) magnet has a Halbach cylinder design that results in a minimal stray field and requires neither cryogenics nor external power. The built-in magnetic field gradient reduces the reliance on high-power gradient drivers, lowering the overall requirements for power and cooling, and reducing acoustic noise. Imperfections in the encoding fields are mitigated with a generalized iterative image reconstruction technique that leverages previous characterization of the field patterns. In healthy adult volunteers, the scanner can generate T1-weighted, T2-weighted and proton density-weighted brain images with a spatial resolution of 2.2 × 1.3 × 6.8 mm 3. Future versions of the scanner could improve the accessibility of brain MRI at the point of care, particularly for critically ill patients.
Body MR Imaging at 3.0 T: Understanding the Opportunities and Challenges
RadioGraphics, 2007
The development of high-field-strength magnetic resonance (MR) imaging systems has been driven in part by expected improvements in signal-to-noise ratio, contrast-to-noise ratio, spatial-temporal resolution trade-off, and spectral resolution. However, the transition from 1.5-to 3.0-T MR imaging is not straightforward. Compared with body imaging at lower field strength, body imaging at 3.0 T results in altered relaxation times, augmented and new artifacts, changes in chemical shift effects, and a dramatic increase in power deposition, all of which must be accounted for when developing imaging protocols. Inhomogeneities in the static magnetic field and the radiofrequency field at 3.0 T necessitate alterations in the design of coils and other hardware and new approaches to pulse sequence design. Techniques to reduce total body heating are demanded by the physics governing the specific absorption rate. Furthermore, the siting and maintenance of 3.0-T MR imaging systems are complicated by additional safety hazards unique to high-field-strength magnets. These aspects of 3.0-T body imaging represent current challenges and opportunities for radiology practice.
Body MR Imaging at 3.0 T: Understanding the Opportunities and Challenges1
…, 2007
The development of high-field-strength magnetic resonance (MR) imaging systems has been driven in part by expected improvements in signal-to-noise ratio, contrast-to-noise ratio, spatial-temporal resolution trade-off, and spectral resolution. However, the transition from 1.5-to 3.0-T MR imaging is not straightforward. Compared with body imaging at lower field strength, body imaging at 3.0 T results in altered relaxation times, augmented and new artifacts, changes in chemical shift effects, and a dramatic increase in power deposition, all of which must be accounted for when developing imaging protocols. Inhomogeneities in the static magnetic field and the radiofrequency field at 3.0 T necessitate alterations in the design of coils and other hardware and new approaches to pulse sequence design. Techniques to reduce total body heating are demanded by the physics governing the specific absorption rate. Furthermore, the siting and maintenance of 3.0-T MR imaging systems are complicated by additional safety hazards unique to high-field-strength magnets. These aspects of 3.0-T body imaging represent current challenges and opportunities for radiology practice.
Magnetic Resonance Materials in Physics, Biology and Medicine
Objectives The Iseult MRI is an actively shielded whole-body magnet providing a homogeneous and stable magnetic field of 11.7 T. After nearly 20 years of research and development, the magnet successfully reached its target field strength for the first time in 2019. This article reviews its commissioning status, the gradient–magnet interaction test results and first imaging experience. Materials and methods Vibration, acoustics, power deposition in the He bath, and field monitoring measurements were carried out. Magnet safety system was tested against outer magnetic perturbations, and calibrated to define a safe operation of the gradient coil. First measurements using parallel transmission were also performed on an ex-vivo brain to mitigate the RF field inhomogeneity effect. Results Acoustics measurements show promising results with sound pressure levels slightly above the enforced limits only at certain frequency intervals. Vibrations of the gradient coil revealed a linear trend wit...
Scientific Reports, 2015
Magnetic Resonance Imaging (MRI) is unparalleled in its ability to visualize anatomical structure and function non-invasively with high spatial and temporal resolution. Yet to overcome the low sensitivity inherent in inductive detection of weakly polarized nuclear spins, the vast majority of clinical MRI scanners employ superconducting magnets producing very high magnetic fields. Commonly found at 1.5-3 tesla (T), these powerful magnets are massive and have very strict infrastructure demands that preclude operation in many environments. MRI scanners are costly to purchase, site, and maintain, with the purchase price approaching 1Mpertesla(T)ofmagneticfield.Wepresentherearemarkablysimple,non−cryogenicapproachtohigh−performancehumanMRIatultra−lowmagneticfield,wherebymodernunder−samplingstrategiesarecombinedwithfully−refocuseddynamicspincontrolusingsteady−statefreeprecessiontechniques.At6.5mT(morethan450timeslowerthanclinicalMRIscanners)wedemonstrate(2.5×3.5×8.5)mm3imagingresolutioninthelivinghumanbrainusingasimple,open−geometryelectromagnet,with3Dimageacquisitionovertheentirebrainin6minutes.Wecontendthatthesepracticalultra−lowmagneticfieldimplementationsofMRI(<10mT)willcomplementtraditionalMRI,providingclinicallyrelevantimagesandsettingnewstandardsforaffordable(<1 M per tesla (T) of magnetic field. We present here a remarkably simple, non-cryogenic approach to high-performance human MRI at ultra-low magnetic field, whereby modern under-sampling strategies are combined with fully-refocused dynamic spin control using steady-state free precession techniques. At 6.5 mT (more than 450 times lower than clinical MRI scanners) we demonstrate (2.5 × 3.5 × 8.5) mm 3 imaging resolution in the living human brain using a simple, open-geometry electromagnet, with 3D image acquisition over the entire brain in 6 minutes. We contend that these practical ultra-low magnetic field implementations of MRI (<10 mT) will complement traditional MRI, providing clinically relevant images and setting new standards for affordable (<1Mpertesla(T)ofmagneticfield.Wepresentherearemarkablysimple,non−cryogenicapproachtohigh−performancehumanMRIatultra−lowmagneticfield,wherebymodernunder−samplingstrategiesarecombinedwithfully−refocuseddynamicspincontrolusingsteady−statefreeprecessiontechniques.At6.5mT(morethan450timeslowerthanclinicalMRIscanners)wedemonstrate(2.5×3.5×8.5)mm3imagingresolutioninthelivinghumanbrainusingasimple,open−geometryelectromagnet,with3Dimageacquisitionovertheentirebrainin6minutes.Wecontendthatthesepracticalultra−lowmagneticfieldimplementationsofMRI(<10mT)willcomplementtraditionalMRI,providingclinicallyrelevantimagesandsettingnewstandardsforaffordable(<50,000) and robust portable devices.
A Portable Brain MRI Scanner for Underserved Settings and Point-Of-Care Imaging
arXiv: Image and Video Processing, 2020
Access to and availability of MRI scanners is typically limited by their cost, siting and infrastructure requirements. This precludes MRI diagnostics, the reference standard for neurological assessment, in patients who cannot be transported to specialized scanner suites. This includes patients who are critically ill and unstable, and patients located in low-resource settings. The scanner design presented here aims to extend the reach of MRI by substantially reducing these limitations. Our goal is to shift the cost-benefit calculation for MRI toward more frequent and varied use, including improved accessibility worldwide and point of care operation. Here, we describe a portable brain MRI scanner using a compact, lightweight permanent magnet, with a built-in readout field gradient. Our low-field (80 mT) Halbach cylinder design of rare-earth permanent magnets results in a 122 kg magnet with minimal stray-field, requiring neither cryogenics nor external power. The built-in magnetic fiel...
Routine clinical brain MRI sequences for use at 3.0 Tesla
Journal of Magnetic Resonance Imaging, 2005
Purpose: To establish image parameters for some routine clinical brain MRI pulse sequences at 3.0 T with the goal of maintaining, as much as possible, the well-characterized 1.5-T image contrast characteristics for daily clinical diagnosis, while benefiting from the increased signal to noise at higher field. Materials and Methods: A total of 10 healthy subjects were scanned on 1.5-T and 3.0-T systems for T 1 and T 2 relaxation time measurements of major gray and white matter structures. The relaxation times were subsequently used to determine 3.0-T acquisition parameters for spin-echo (SE), T 1-weighted, fast spin echo (FSE) or turbo spin echo (TSE), T 2-weighted, and fluid-attenuated inversion recovery (FLAIR) pulse sequences that give image characteristics comparable to 1.5 T, to facilitate routine clinical diagnostics. Application of the routine clinical sequences was performed in 10 subjects, five normal subjects and five patients with various pathologies. Results: T 1 and T 2 relaxation times were, respectively, 14% to 30% longer and 12% to 19% shorter at 3.0 T when compared to the values at 1.5 T, depending on the region evaluated. When using appropriate parameters, routine clinical images acquired at 3.0 T showed similar image characteristics to those obtained at 1.5 T, but with higher signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), which can be used to reduce the number of averages and scan times. Recommended imaging parameters for these sequences are provided. Conclusion: When parameters are adjusted for changes in relaxation rates, routine clinical scans at 3.0 T can provide similar image appearance as 1.5 T, but with superior image quality and/or increased speed.
3.0 T magnetic resonance in neuroradiology
European Journal of Radiology, 2003
Ever since the introduction of magnetic resonance (MR), imaging with 1.5 T has been considered the gold standard for the study of all body areas. Until not long ago, higher-field MR equipment was exclusively employed for research, not for clinical use. More recently, the introduction of 3.0 T MR machines for new and more sophisticated clinical applications has yielded in important benefits, especially in neuroradiology. Indeed, their high gradient power and field intensity allow adjunctive and more advanced diagnostic methodologies to be applied with excellent resolution in a fraction of the time of acquisition compared with earlier machines. The numerous advantages of these machines in terms of higher signal, increased spatial resolution and greater sensitivity, and their few limitations, which can be overcome and anyway do not adversely affect diagnostic efficacy, will make 3.0 T MR systems the gold standard for morphological and functional studies of the brain.