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 uses has a Halbach-cylinder design that results in 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 prior characterization of the field patterns. In healthy adult volunteers, the scanner can generate T 1 -weighted, T 2 -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.
Research in MRI technology has traditionally expanded diagnostic benefit by developing acquisition techniques and instrumentation to enable MRI scanners to "see more." This typically focuses on improving MRI's sensitivity and spatiotemporal resolution, or expanding its range of biological contrasts and targets. In complement to the clear benefits achieved in this direction, extending the reach of MRI by reducing its cost, siting, and operational burdens also directly benefits healthcare by increasing the number of patients with access to MRI examinations and tilting its cost–benefit equation to allow more frequent and varied use. The introduction of low‐cost, and/or truly portable scanners, could also enable new point‐of‐care and monitoring applications not feasible for today's scanners in centralized settings. While cost and accessibility have always been considered, we have seen tremendous advances in the speed and spatial‐temporal capabilities of general‐purpose MRI scanners and quantum leaps in patient comfort (such as magnet length and bore diameter), but only modest success in the reduction of cost and siting constraints. The introduction of specialty scanners (eg, extremity, brain‐only, or breast‐only scanners) have not been commercially successful enough to tilt the balance away from the prevailing model: a general‐purpose scanner in a centralized healthcare location. Portable MRI scanners equivalent to their counterparts in ultrasound or even computed tomography have not emerged and MR monitoring devices exist only in research laboratories. Nonetheless, recent advances in hardware and computational technology as well as burgeoning markets for MRI in the developing world has created a resurgence of interest in the topic of low‐cost and accessible MRI. This review examines the technical forces and trade‐offs that might facilitate a large step forward in the push to "jail‐break" MRI from its centralized location in healthcare and allow it to reach larger patient populations and achieve new uses.Level of Evidence: 5Technical Efficacy Stage: 6J. Magn. Reson. Imaging 2019. J. Magn. Reson. Imaging 2020;52:686–696.
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