Introduction

Diffusion and perfusion imaging are playing a greater role in the clinical setting of acute ischemic stroke. These newer imaging techniques are already utilized in stroke diagnosis, and in the future may be used for prognosis and treatment triage. Diffusion-weighted imaging (DWI) has already been proven to sensitively show tissue injured by ischemic stroke early in the postictal state. Lesion volumes have been observed with DWI to enlarge over time after an acute stroke. Baird et al., Barber et al. and van Everdingen et al. reported that 43%, 44% and 41% of their respective patients showed increases in lesion volume after the first imaging time point. Recently there has been an emphasis on the combined use of perfusion-weighted imaging (PWI) and DWI in the acute stroke setting in the hope that they will help to define tissue at risk for injury. Several studies have shown that the perfusion deficit (measured as a prolonged mean transit time or time-to-peak delay) is initially larger in this acute setting. It appears that, in 70% to 80% of patients imaged within the first 6 hours of stroke, measured PWI deficits are greater than DWI deficits. In addition, this pattern where PWI> DWI is larger on the initial image has been shown to predict DWI expansion into the surrounding lesion.