CT Perfusion Imaging Improves Infarct Conspicuity in Hyperacute Stroke
Purpose: To compare infarct conspicuity and image quality of noncontrast CT (NCCT), CT perfusion (CTP), and CT subtraction cerebral blood volume (CT-CBV) images of patients with hyperacute stroke. Background: NCCT is typically the first imaging test obtained in the evaluation of acute stroke. Whole brain CTP imaging is performed, simultaneously with CT angiography, during the steady state administration of IV contrast. Subtraction of coregistered NCCT images from the CTP images yields maps of perfused blood volume (CT-CBV). Ischemic areas on each of the NCCT, CTP, and CT-CBV images appear as hypodense, low attenuation regions. Materials and Methods: We reviewed the images of 20 consecutive patients with MCA stem occlusion who underwent intra-arterial thrombolysis within 6 hours of stroke onset. All had NCCT and CT angiography with CTP imaging prior to thrombolysis. Subtraction CT-CBV maps were created and analyzed using proprietary software (IMIPS, Inc). For each of the NCCT, CTP, and CT-CBV images, infarct conspicuity was defined by dividing the mean attenuation difference between normal and maximally hypodense gray matter by the mean normal gray matter attenuation. Contrast-to-noise ratio (CNR) was defined by dividing the same numerator by the standard deviation of the normal gray matter attenuation values. Statistical analysis was by ANOVA and students t-test. Results: Overall infarct conspicuity was 0.11 for the NCCT, 0.22 for the CTP, and 0.98 for the CT-CBV images (p<0.003 for all maps). Mean CNR was 0.95 for the NCCT, 1.94 for the CTP, and 1.12 for the CT-CBV images (p<0.01, for the CTP maps only). Conclusions: CT perfusion and CT-CBV subtraction imaging improve infarct conspicuity over that of NCCT in patients with hyperacute stroke. True reduction in blood pool (as reflected by CT-CBV), rather than increase in tissue edema (as reflected by NCCT), may explain much of the improved infarct delineation in CTP imaging. Because CNR is greater for CTP than for subtraction images, concurrent review of NCCT, CTP, and CT-CBV images may be indicated for optimal CT assessment of hyperacute MCA stroke.