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Updated: Jun 26, 2025
A Magnetic Resonance Imaging Protocol for Stroke Onset Time Estimation in Permanent Cerebral Ischemia
Published on: September 16, 2017
Diffusion-Weighted Imaging Fluid-Attenuated Inversion Recovery Mismatch on Portable, Low-Field Magnetic Resonance
Annabel Sorby-Adams1, Jennifer Guo1, Adam de Havenon2
1Department of Neurology and the Center for Genomic Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
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.
Insights
A portable, low-field MRI scanner effectively identifies diffusion-weighted imaging (DWI) and fluid-attenuated inversion recovery (FLAIR) mismatch in acute ischemic stroke patients. This technology shows promise for guiding thrombolytic treatment in stroke cases with unknown onset times.
Area of Science:
- Neurology
- Radiology
- Medical Imaging
Background:
- Diffusion-weighted imaging (DWI) and fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) are crucial for identifying DWI-FLAIR mismatch in acute ischemic stroke patients with unknown onset times, guiding thrombolytic therapy.
- Limited access to MRI for hyperacute stroke hinders timely intervention.
Purpose of the Study:
- To evaluate the capability of a portable, low-field (LF)-MRI scanner in identifying DWI-FLAIR mismatch in acute ischemic stroke.
- To assess the diagnostic performance of LF-MRI in detecting stroke lesions and guiding treatment decisions.
Main Methods:
- Acquisition of LF-MRI (0.064-T) in 71 acute ischemic stroke patients within 24 hours of last known well.
- Qualitative assessment of lesion visibility on LF-FLAIR by two trained assessors.
- Quantitative analysis using an image coregistration pipeline to derive LF-FLAIR signal intensity ratio (SIR).
Main Results:
- High interobserver agreement (κ=0.85) for identifying visible FLAIR hyperintensities.
- Visual DWI-FLAIR mismatch demonstrated 60% sensitivity and 82% specificity for stroke onset <4.5 hours.
- LF-FLAIR SIR thresholds were established, with an optimal cut-point of 1.15 (85% sensitivity, 70% specificity) for identifying mismatch and a cut-point of 6.6 hours for FLAIR SIR <1.15.
Conclusions:
- A 0.064-T portable LF-MRI scanner can successfully identify DWI-FLAIR mismatch in acute ischemic stroke patients.
- Further prospective validation of thresholds and evaluation of LF-MRI's role in guiding thrombolysis for stroke patients with uncertain onset are warranted.
