A scoping review of portable ultra-low-field MRI studies in patients with acquired brain injury: Past, present, and future.

Acquired Brain Injury (ABI) refers to any post-birth damage to the brain, commonly resulting from traumatic events (traumatic brain injury) or non-traumatic events (such as stroke, brain disease, or infection). In Australia, ABI places a substantial economic burden on society. Assessment using high-field (HF) MRI is critical after sustaining an ABI however its usage is impeded by scanner availability and stringent safety requirements. Portable ultra-low-field (ULF MRI) may address these challenges. This review summarises literature on portable ULF MRI use in ABI patients, and outlines its safety and efficacy in detecting structural abnormalities and assessing extent of damage. A systematic search using four databases yielded 20 studies: six studies in stroke, one in traumatic brain injury (TBI), three in brain tumours, three in multiple sclerosis, and eight in other neurological disorders. The findings suggest that portable ULF MRI has been used primarily in critical care and found it was safe for use in the presence of ferromagnetic material and with patients on mechanical aids (e.g. ventilator). Most studies also reported high sensitivity and specificity in detecting various lesions (e.g. ischemic stroke, TBI), particularly those that utilised deep learning to generate a synthetic scan. Strong volumetric correlations between portable ULF MRI and traditional neuroimaging were also reported. Portable ULF MRI usage in ABI patients is encouraging, however lack of diverse ABI samples and quantitative analyses limit its generalisability. Studies in a research context, carried out under controlled conditions, with larger samples (and across multiple centres) are necessary to ascertain portable ULF MRI's validity and reliability vis-à-vis conventional HF MRI.