FLAIR changes serve as clock for time since stroke onset
MedWire News: Signal intensity changes on fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) provide a sensitive indicator of time since stroke onset, report researchers.
The results may help clinicians determine whether patients with an unknown stroke onset time are within the 3-hour treatment window for thrombolysis, say Catherine Oppenheim (Centre Hospitalier Sainte-Anne, Paris, France) and colleagues.
"Providing stroke neurologists with a reliable marker of stroke age may help ensure that patients with an unknown stroke onset time are treated as urgently as those with a known onset time," they add.
As reported in the journal Radiology, the team compared MRI data from 63 patients who underwent imaging within 3 hours of symptom onset with that from 67 patients who underwent imaging between 3 and 12 hours after onset.
The ratio of the signal intensity between the affected and unaffected cerebral hemispheres correlated with time since stroke onset for FLAIR, diffusion-weighted imaging (DWI), and apparent diffusion coefficient (ADC) MRI sequences.
The FLAIR ratio, at a cutoff of 7%, identified patients within the 3-hour time window with 90% sensitivity and 92% specificity. It had positive and negative predictive values of 92% and 91%, respectively.
The diagnostic performances of the DWI ratio (cutoff 19%) and the ADC ratio (cutoff 14%) were considerably lower, with, for example, respective sensitivities of 65% and 56%.
Qualitative analysis by two observers also produced accurate classification of patients, with sensitivity of up to 95% and specificity of up to 97%.
The observers classed patients as hyperacute (ie, <3 hours from onset) if they had normal FLAIR images and acute if they had definite changes. Patients with subtle FLAIR changes were classified according to their DWI findings - patients with large DWI changes often have early FLAIR changes.
All but one of the patients with subtle FLAIR changes had a FLAIR ratio below 7%, leading Oppenheim et al to suggest that quantitative analysis can help to "counterbalance the subjectivity" of qualitative analysis.
They conclude: "In patients in whom the onset time is unknown or uncertain, MRI can help identify those who are highly likely to be within the 3-hour time window - namely, the time window for which intravenous thrombolysis has proved effective, is approved, and is recommended by international guidelines."
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By Eleanor McDermid