Early evolution of deficits in acute ischemic stroke: mean transit time, relative blood volume, and relative blood flow.

The objective of this prospective pilot study was to determine the evolution of imaging characteristics of perfusion-weighted imaging (PWI), including mean transit time (MTT), relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF), diffusion-weighted imaging (DWI), and magnetic resonance (MR) angiography in the first 48 hours after an acute cerebral infarction. In 5 patients with suspected middle cerebral artery (MCA) territory infarction, images were obtained on 4 occasions during the first 48 hours (6-10 hours, 15-18 hours, 22-24 hours, and 48 hours) by an imaging protocol that included echoplanar DWI, PWI, and MR angiography. No patients received thrombolytic or neuroprotective agents. Four of the 5 patients had MCA occlusions on the initial MR angiogram. Presumably, the MCA had recanalized in 1 patient before the first MR angiogram. Recanalization of the MCA was observed by the second scan in 1 patient and by the fourth scan in the remaining 3 patients. The mean MTT volume deficit was greater than the DWI volume (mismatch) until the final MR examination at 48 hours. The mean rCBV and rCBF volumes were larger than the DWI volume (mismatch) on the first MR examination but were smaller on the second and subsequent examinations. Decrease in the size of the MTT volume before recanalization of the MCA was most likely due to opening of collateral channels, but the greatest decrease in the size of the MTT volume occurred with recanalization of the MCA. All patients had progressive enlargement of the abnormal DWI volume. The MR changes following acute cerebral infarction are dynamic, with the volume of the diffusion abnormality nearly doubling between 6 to 10 hours and 48 hours. The volume of the acute MTT abnormality (6-10 hours) is approximately twice the size of the diffusion abnormality at 48 hours. The volume of the rCBV and rCBF between 6 and 10 hours after ictus is a good reflection of the diffusion abnormality at 48 hours.