Low-Field MRI: How Low Can We Go? A Fresh View on an Old Debate

Sarracanie, Mathieu; Salameh, Najat

doi:10.3389/fphy.2020.00172

Cited by 122 publications

(132 citation statements)

References 67 publications

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“…These scanners find potential applications in stroke diagnosis, neurological, and musculoskeletal disorders. 154 Low-field scanners further offer flexibility in designing open-bore MR systems, thereby helping claustrophobic, children, and obese adult patients. 155 More importantly, such an open configurations offers intraoperative assistance and permits quick access for interventions such as anesthesia or intravenous thrombolysis in the case of stroke.…”

Section: Discussionmentioning

confidence: 99%

Low‐Field MRI of Stroke: Challenges and Opportunities

Bhat

Fernandes

Poojar

et al. 2020

Magnetic Resonance Imaging

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Stroke is a leading cause of death and disability worldwide. The reasons for increased stroke burden in developing countries are inadequately controlled risk factors resulting from poor public awareness and inadequate infrastructure. Computed tomography and MRI are common neuroimaging modalities used to assess stroke with diffusion-weighted MRI, in particular, being the recommended choice for acute stroke imaging. However, access to these imaging modalities is primarily restricted to major cities and high-income groups. In the case of stroke, the time-window of treatment to limit the damage is of a few hours and needs a point-of-care diagnosis. A low-cost MR system typically achieved at the ultra-lowand very-low-field would meet the need for a geographically accessible and portable solution. We review studies focused on accessible stroke imaging and recent developments in MR methodologies, including hardware, to image at low fields. We hypothesize that in the absence of a formal, rapid stroke triaging system, the value of timely on-site delivery of the scanner to the stroke patient can be significant. To this end, we discuss multiple recent hardware and methods developments in the low-field regime. Our review suggests a compelling need to explore further the trade-offs between high signal, contrast, and accessibility at low fields in low-income communities.

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Section: Discussionmentioning

confidence: 99%

Low‐Field MRI of Stroke: Challenges and Opportunities

Bhat

Fernandes

Poojar

et al. 2020

Magnetic Resonance Imaging

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“…This story can be changed by the adoption of LF MRI technologies. A recent review by Sarracanie and Salameh [23] cites several examples of LF MRI systems with magnetic field strengths from less the 1 mT to 199 mT that have given quality of images for clinical diagnosis.…”

Section: Motivation For Use Of Lf Mrimentioning

confidence: 99%

Approaches in cooling of resistive coil-based low-field Magnetic Resonance Imaging (MRI) systems for application in low resource settings

2021

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Magnetic Resonance Imaging (MRI), a non-invasive method for the diagnosis of diverse health conditions has experienced growing popularity over other imaging modalities like ultrasound and Computer Tomography. Initially, proof-of-concept and earlier MRI systems were based on resistive and permanent magnet technology. However, superconducting magnets have long held monopoly of the market for MRI systems with their high-field (HF) strength capability, although they present high construction, installation, and siting requirements. Such stringent prerequisites restrict their availability and use in low-middle income countries. Resistive coil-based magnet, albeit low-field (LF) in capacity, represent a plausible boost for the availability and use of MRI systems in resource constrained settings. These systems are characterized by low costs coupled with substantial image quality for diagnosis of some conditions such as hydrocephalus common is such regions. However, the nature of resistive coils causes them to heat up during operation, thus necessitating a dedicated cooling system to improve image quality and enhance system longevity. This paper explores a range of cooling methods as have been applied to resistive magnets, citing their pros and cons and areas for improvement.

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“…One disadvantage of MRI as a clinical imaging modality is the expense of system, both in terms of purchase cost and continued maintenance. The magnet must be housed in an RF shielded room, and its operation requires highly-trained technicians [3][4][5]. These factors limit its use to late in the healthcare cycle, and its siting to major hospitals.…”

Section: Introductionmentioning

confidence: 99%

Characterization of displacement forces and image artifacts in the presence of passive medical implants in low-field (<100 mT) permanent magnet-based MRI systems, and comparisons with clinical MRI systems

et al. 2021

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To investigate the displacement forces and image artifacts associated with passive medical implants for recently-developed low-field (<100 mT) MRI systems, and to compare these with values from higher field strengths used for clinical diagnosis. Methods: Setups were constructed to measure displacement forces in a permanent magnet-based Halbach array used for in vivo MRI at 50 mT, and results compared with measurements at 7 T. Image artifacts were assessed using turbo (fast) spin echo imaging sequences for four different passive medical implants: a septal occluder, iliac stent, pedicle screw and (ferromagnetic) endoscopic clip. Comparisons were made with artifacts produced at 1.5, 3 and 7 T. Finally, specific absorption rate (SAR) simulations were performed to determine under what operating conditions the limits might be approached at low-field. Results: Displacement forces at 50 mT on all but the ferromagnetic implant were between 1 and 10 mN. Image artifacts at 50 mT were much less than at clinical field strengths for all passive devices, and with the exception of the ferromagnetic clip. SAR simulations show that very long echo train (>128) turbo spin echo sequences can be run with short inter-pulse times (5-10 ms) within SAR limits. Conclusions: This work presents the first evaluation of the effects of passive implants at field strengths less than 100 mT in terms of displacement forces, image artifacts and SAR. The results support previous claims that such systems can be used safely and usefully in challenging enviroments such as the intensive care unit.

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Low-Field MRI: How Low Can We Go? A Fresh View on an Old Debate

Cited by 122 publications

References 67 publications

Low‐Field MRI of Stroke: Challenges and Opportunities

Low‐Field MRI of Stroke: Challenges and Opportunities

Approaches in cooling of resistive coil-based low-field Magnetic Resonance Imaging (MRI) systems for application in low resource settings

Characterization of displacement forces and image artifacts in the presence of passive medical implants in low-field (<100 mT) permanent magnet-based MRI systems, and comparisons with clinical MRI systems

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