Detecting Acute Ischemic Lesions Using Mobile, Low-Field MRI in TIA and minor stroke in the Emergency Room

Background: Using mobile low-field MRI in the emergency department to detect cerebral infarction(s) in patients with minor ischemic stroke (MIS) and transient ischemic attack (TIA) has not yet been thoroughly reported. Aim: We aimed to evaluate the performance of mobile low-field (0.23T) MRI in detecting acute ischemic infarction in MIS or TIA patients within 72 hours of symptom onset and compare it to CT in those scanned within 24 hours. We also aimed to analyse predictors of DWI positive lesions on mobile MRI. Methods: This prospective observational cohort consecutively included patients with MIS (National Institutes of Health Stroke Scale (NIHSS) ≤5) or TIA who underwent mobile low-field MRI within 72 hours of symptom onset in the emergency department of a tertiary general hospital. The MRI protocol included localizer, axial T1-weighted fluid-attenuated inversion recovery (FLAIR), axial T2-weighted FLAIR, axial T2-weighted fast spin-echo, hematoma-enhanced inversion recovery (HEIR), and diffusion-weighted imaging (DWI) with apparent diffusion coefficient sequences. The total acquisition time is 10 minutes 28 seconds. Two raters, blinded to clinical information and CT findings, interpreted the MRI images for acute infarction. Multivariable logistic regression identified predictors of DWI positivity. The primary outcome was restricted diffusion (acute infarction) on the brain low field MRI scan. We analyzed patients who underwent head CT scan within 24 hours of low-field MRI to compare the detection rates of acute infarction between low-field MRI and head CT. Results: A total of 974 patients (564 men and 410 women; mean [standard deviation, SD] age, 61.3 [14.9]) were enrolled. New ischemic lesions were detected by low-field MRI on the DWI sequence in 37.4% (338 in 974) of patients. Among them, 304 underwent head CT within 24 hours of the low-field MRI scan; CT identified new ischemic lesions in only 122 (40.1%) of these. Higher NIHSS score (hazard ratio, 1.36 [95% CI, 1.21-1.54]; P<0.01), longer onset to imaging time (hazard ratio, 1.33 [95%CI, 1.10-1.63]; P<0.01), aphasia (hazard ratio, 2.24 [95%CI, 1.36-3.71]; P<0.01), and hemiplegia (hazard ratio, 2.50 [95%CI, 1.76-3.55]; P<0.01) were independently associated with DWI positivity on mobile low-field MRI. Female sex (hazard ratio, 0.57 [95%CI, 0.42-0.79]; P<0.01) and non-focal symptoms were negatively associated with DWI positivity. Conclusions: Mobile low-field MRI provides a safe, efficient, and accessible imaging solution for MIS and TIA evaluation in emergency settings and detects more acute infarctions than non-contrast head CT. Higher NIHSS score, longer onset to imaging time and focal clinical features were independently associated with DWI positivity.