Diffusion‐Weighted Imaging Fluid‐Attenuated Inversion Recovery Mismatch on Portable, Low‐Field Magnetic Resonance Imaging Among Acute Stroke Patients

Objective For stroke patients with unknown time of onset, mismatch between diffusion‐weighted imaging (DWI) and fluid‐attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) can guide thrombolytic intervention. However, access to MRI for hyperacute stroke is limited. Here, we sought to evaluate whether a portable, low‐field (LF)‐MRI scanner can identify DWI‐FLAIR mismatch in acute ischemic stroke. Methods Eligible patients with a diagnosis of acute ischemic stroke underwent LF‐MRI acquisition on a 0.064‐T scanner within 24 h of last known well. Qualitative and quantitative metrics were evaluated. Two trained assessors determined the visibility of stroke lesions on LF‐FLAIR. An image coregistration pipeline was developed, and the LF‐FLAIR signal intensity ratio (SIR) was derived. Results The study included 71 patients aged 71 ± 14 years and a National Institutes of Health Stroke Scale of 6 (interquartile range 3–14). The interobserver agreement for identifying visible FLAIR hyperintensities was high ( κ = 0.85, 95% CI 0.70–0.99). Visual DWI‐FLAIR mismatch had a 60% sensitivity and 82% specificity for stroke patients <4.5 h, with a negative predictive value of 93%. LF‐FLAIR SIR had a mean value of 1.18 ± 0.18 <4.5 h, 1.24 ± 0.39 4.5–6 h, and 1.40 ± 0.23 >6 h of stroke onset. The optimal cut‐point for LF‐FLAIR SIR was 1.15, with 85% sensitivity and 70% specificity. A cut‐point of 6.6 h was established for a FLAIR SIR <1.15, with an 89% sensitivity and 62% specificity. Interpretation A 0.064‐T portable LF‐MRI can identify DWI‐FLAIR mismatch among patients with acute ischemic stroke. Future research is needed to prospectively validate thresholds and evaluate a role of LF‐MRI in guiding thrombolysis among stroke patients with uncertain time of onset. ANN NEUROL 2024;96:321–331