Magnetic Resonance Imaging (MRI) has been the undisputed standard of care for the detection and diagnosis of neurological disorders and injuries since its inception over 3 decades ago. The cost, weight, size, and maintenance needs of MRI scanners, however, typically precludes their use in some locations with perhaps the greatest need - including Emergency Departments, Neurological Intensive Care Units (ICUs), surgical suites, sports fields, battlefields, rural healthcare sites, and ambulances. Indeed, no truly portable, """"""""point-of-care"""""""" MRI system currently exists, despite attempts by several groups to miniaturize and simplify MRI scanner components. A new approach is needed to create such a truly portable, affordable brain scanner, referred to here as the """"""""Portable Brain Scanner"""""""" (PBS). The problem, however, with rendering conventional scanners portable is not only the requirement for a large, highly homogeneous magnetic field (necessitating the use of multi ton magnets and cryogenic apparatus), but also, the weight and power consumption requirements of switchable gradient encoding fields (an additional ton of weight and up to 2 MW of peak power). In this work, we refine our proof-of-concept prototype PBS and, in pilot clinical testing, validate it as a low cost, point-of-care MRI scanner that can be sited almost anywhere. We employ an approach whereby the magnet's field homogeneity requirements are relaxed approximately 1000 fold. This allows a lightweight, permanent magnet design with no cryogens or power consumption. Our prototype brain magnet weighs just 45kg. We achieve image encoding and eliminate the heavy, power consuming gradient coil, by rotating this inhomogeneous field around the head using the magnet's field inhomogeneity to spatially modulate the signal in a generalized fashion compared to what is done with conventional imaging gradients. Specifically, the field inhomogeneities of the main magnet serve as the encoding field, and the image is reconstructed as an iterative inverse problem. This design """"""""kills two birds with one stone"""""""", in that it both simplifies the magnet and eliminates the gradient coil - resulting in a truly """"""""point-of-care"""""""" brain MRI scanner. We further refine this design by adding truly parallel reception, to improve spatial encoding, as well as by adding TRASE encoding for the third dimension. Preliminary clinical evaluation of this prototype will be performed on a cohort of patients with mild-to-moderate hemorrhagic brain injury in the Emergency Department, and in stable peri-operative patients with structural lesions in the Neurological Intensive Care Unit.
Although MRI scanners are exceedingly effective at evaluating brain disease and injury, their large size, specialized siting constraints, and high cos limit their impact by precluding them from most emergency medicine and acute care situations, including Intensive Care Units (ICUs), ambulances, and most hospital Emergency Departments. Our goal is to address this with a novel, simplified brain MRI scanner whose entire weight is less than 150kg. We will validate the clinical potential of this device through pilot testing of patient in the Emergency Department and Neurological Intensive Care Unit.
|Stockmann, Jason P; Cooley, Clarissa Z; Guerin, Bastien et al. (2016) Transmit Array Spatial Encoding (TRASE) using broadband WURST pulses for RF spatial encoding in inhomogeneous B0 fields. J Magn Reson 268:36-48|