MR Imaging in Acute Stroke: Diffusion-weighted and Perfusion Imaging Parameters for Predicting Infarct Size

Abstract

Diffusion-weighted imaging helped to predict the size of the lesion on T2-weighted images obtained after about 8 days in patients with a symptom onset of more than 4 hours (r = 0.96), while in patients with a symptom onset of less than 4 hours, perfusion imaging provided important additional information about brain tissue with impaired perfusion.

Significance of the perfusion‐diffusion mismatch in chronic cerebral ischemia

“…It included a T2W and DW sequence, an MRA investigation, and serial T2*-weighted (T2*W) measurements with 40 scans for measurement of tissue perfusion (7,21). The total scan time on the Siemens Magnetom Vision 1.5 T whole-body MR scanner (Siemens AG, Erlangen, Germany) was approximately 20 minutes.…”

“…At the time of the fourth scan, 15 mL of Gd-contrast agent (Magnevist ; Schering) were injected as a bolus at a rate of 5 mL/second, immediately followed by 15 mL of a 0.9% saline solution at the same rate. From the PWI data, TTP maps were calculated as detailed previously (7). Here the "TTP" refers to the time between the first scan and the time when the signal intensity reached its minimum produced by the bolus of contrast agent in the T2*W series of images ( Fig.…”

“…The mean voxel intensity as determined by manually drawn ROIs in the unaffected contralateral hemisphere at the level of the basal ganglia and in the dorsal part of the cerebral hemisphere, excluding artifacts and ventricles (30 -40 mL), served as reference (7). The method of referring to the contralateral tissue minimized the intersubject variation among the patients that resulted from differences in bolus delay due to individual cardiac output.…”

“…PWI and DWI allow actual ischemic lesions to be delineated with a relatively high sensitivity and specificity (1)(2)(3)(4)(5)(6)(7). In acute ischemic brain tissue DWI can detect decreased movement of water protons due to cytotoxic edema, which results in a decrease of the apparent diffusion coefficient (ADC) of water and an increase in the signal intensity.…”

“…Recent observations have shown that brain infarcts may become as large as predicted by the perfusion abnormalities in acute MR images (7,14), they may regress (15,16), or they may deteriorate despite arterial recanalization (17,18). Moreover, it is well established that chronic internal carotid artery (ICA) occlusion is accompanied by a prominent perfusion impairment in the downstream brain region (19).…”