MR Imaging Helps Predict Time from Symptom Onset in Patients with Acute Stroke: Implications for Patients with Unknown Onset Time
Abstract
At 1.5 T, the use of quantitative signal intensity changes at fluid-attenuated inversion recovery (FLAIR) imaging or the visual assessment of FLAIR and/or diffusion-weighted images as a surrogate marker of stroke age could help identify patients with unknown stroke onset time who may potentially be eligible for thrombolysis.
Purpose
To assess the value of magnetic resonance (MR) imaging parameters as surrogate markers of stroke duration.
Materials and Methods
The study was approved by the Ethics Committee of Ile de France III and was found to conform to generally accepted scientific principles and ethical standards. The authors studied 130 patients with acute stroke of known onset time who underwent 1.5-T MR imaging within 12 hours of the onset of stroke symptoms. Fluid-attenuated inversion recovery (FLAIR), diffusion-weighted (DW) imaging, and apparent diffusion coefficient (ADC) ratios were computed by using three-dimensional regions of interest to outline signal intensity changes on DW images and then projecting them onto the contralateral hemisphere. Imaging ratios in 63 patients who underwent imaging 0–3 hours after symptom onset were compared with those in 67 patients who underwent imaging more than 3 hours after onset by using the Student t test and receiver operating characteristic curves. The accuracy (sensitivity, specificity, and 95% confidence intervals [CIs]) of lesion visibility on FLAIR images in the prediction of a stroke onset time of less than 3 hours was assessed by two independent observers.
Results
Differences in imaging ratios between patients imaged 0–3 hours after symptom onset and those imaged more than 3 hours after onset were statistically significant (P < .001). The FLAIR ratio showed a positive correlation with the time from symptom onset (Pearson correlation coefficient, 0.63). Receiver operating characteristic curves indicated that the FLAIR ratio could reliably identify patients imaged 0–3 hours after symptom onset, reaching 90% sensitivity (95% CI: 83%, 98%) and 93% specificity (95% CI: 86%, 99%) when using a 7% cutoff. Stroke imaged within 3 hours could also be identified by means of visual inspection of FLAIR and DW MR images, with 94% sensitivity (95% CI: 88%, 100%) and 97% specificity (95% CI: 93%, 101%).
Conclusion
Signal intensity changes on 1.5-T FLAIR MR images can be used as a surrogate marker of stroke age, either qualitatively or quantitatively. This suggests that MR imaging might be used as a “clock” for determining stroke age in patients with an unknown onset time, potentially increasing the number of patients who are eligible for thrombolysis.
© RSNA, 2010
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Article History
Received March 5, 2010; revision requested May 10; revision received June 7; accepted June 16; final version accepted July 14.Published online: Dec 2010
Published in print: Dec 2010