Combined diffusion-weighted and perfusion-weighted flow heterogeneity magnetic resonance imaging in acute stroke

Background and Purpose-The heterogeneity of microvascular flows is known to be an important determinant of the efficacy of oxygen delivery to tissue. Studies in animals have demonstrated decreased flow heterogeneity (FH) in s tates of decreased perfusion pressure. The purpose of the present study was to assess microvascular FH changes in acute stroke with use of a novel per fusion-weighted MRI technique and to evaluate the ability of combined diffu sion-weighted MRI and FH measurements to predict final infarct size. Methods-Cerebral blood flow, FH, and plasma mean transit time (MTT) were me asured in 11 patients who presented with acute (<12 hours after symptom ons et) stroke. Final infarct size was determined with follow-up MRI or CT scan ning. Results In normal brain tissue, the distribution of relative flows was mark edly skewed toward high capillary flow velocities. Within regions of decrea sed cerebral blood flow, plasma MTT was prolonged. Furthermore, subregions were identified with significant loss of the high-flow component of the flo w distribution, thereby causing increased homogeneity of flow velocities. I n parametric maps that quantify the acute deviation of FH from that of norm al tissue, areas of extreme homogenization of capillary flows predicted fin al infarct size on follow-up scans of 10 of 11 patients. Conclusions-Flow heterogeneity and MTT can be rapidly assessed as part of a routine clinical MR examination and may provide a tool for planning of ind ividual stroke treatment, as well as in targeting and evaluation of emergin g therapeutic strategies.