Tareq Kasshout, MD

Emeriau S, Serre I, Toubas O, Pomboureq F, Oppenheim C, Pierot L. Can DWI-FLAIR Mismatch at 3 Tesla Identify Stroke Patients at < 4.5 hours? Stroke. 2013

Because there is some uncertainty about the value of the DWI/FLAIR mismatch on 3T MRI to discriminate patients imaged within the standard thrombolytic time window and those who had symptom onset beyond such time period, Emeriau and colleagues conducted a study to determine whether DWI-FLAIR mismatch at 3T may idiscriminate between both groups of patients.
In their retrospective study of 194 patients, delayed MRI acquisition was the only predictive factor of FLAIR visibility. This means that the 3T FLAIR sequence may provide information that can be use to estimate the age of stroke. But DWI/FLAIR mismatch in this study had moderate specificity and sensitivity and a low negative productive value to identify patients presenting <4.5 hours after symptom onset because 45% of patients imaged within that time frame already had FLAIR signal changes.

In short, the link between FLAIR signal intensity and time of symptom onset is not yet fully understood. This study, however, suggests that the cutoff delay between symptom onset and MRI that best predicts FLAIR positivity is 170 minutes, which is less than the thrombolysis delay.