Use of neuroimaging to guide the treatment of patients beyond the 8-hour time window.

Revascularization time windows for patients with acute ischemic stroke are generally restricted to 8 hours. Later treatment attempts require more accurate prediction of risk and benefit, as safety and efficacy at these time strata are less well demonstrated. Advanced imaging techniques identify irreversible infarction as well as tissue at risk. Diffusion-weighted MRI detects ischemia within minutes of onset, whereas perfusion-weighted MRI and CT perfusion studies disclose the ischemic penumbra. Combined, they provide information on mismatched tissue-potentially salvageable brain. In addition, noninvasive angiography is a useful adjunct to localize arterial occlusion.