Multimodal CT that measures water uptake in stroke lesions can indicate the time of stroke onset, according to recent research. The approach could determine whether patients with unknown time of stroke onset are eligible to receive thrombolysis.

Credit: NPG

Use of intravenous thrombolysis is limited to a 4.5 h window after onset of ischaemic stroke. For up to one-quarter of patients, however, the time of onset is unknown because they awoke with symptoms or were unable to communicate.

In new work, André Kemmling and colleagues have developed a technique to predict whether patients with unknown time of onset are within the required 4.5 h window. They used two types of CT to measure water uptake in the infarct over time. “We combined the high sensitivity of perfusion CT to precisely target the core lesion, with the high specificity of density change in native CT to designate infarct-related water uptake,” explains Kemmling.

They derived the method with a cohort of 178 patients; 147 had undergone CT within 4.5 h of stroke onset, and 31 had undergone CT after 4.5 h. Density measurements of the core lesion relative to the same area on the contralateral side were used to calculate the extent of water uptake.

water uptake of < 9.6% indicates a 95% probability that stroke onset was within 4.5 h

These data were used to determine the extent of water uptake that indicates stroke onset within 4.5 h. An optimal cut-off of 11.5% was determined and validated in a cohort of 240 patients. In this cohort, the cut-off identified patients within 4.5 h of stroke onset with 100% specificity (95% CI 86.3–100.0) and 98.6% sensitivity (95% CI 94.7–99.8).

The researchers determined that water uptake of >14.4% indicated a 95% probability that stroke onset was >4.5 h ago, and water uptake of <9.6% indicated a 95% probability that stroke onset was within 4.5 h. “As water uptake within the early infarct increases beyond 10%, the probability of stroke onset being within 4.5 h drops sharply,” says Kemmling.

The authors conclude that their novel CT-based approach could be used to guide treatment decisions for patients who have an unkown time of onset of stroke.