Low cerebral blood volume is predictive of diffusion restriction only in hyperacute stroke.

BACKGROUND AND PURPOSE Diffusion-weighted MRI (DWI) demonstrates ischemic tissue with high sensitivity. Although low cerebral blood volume (CBV) is also used as a marker for infarction, the quantitative relationship between diffusion abnormalities and CBV is unknown. We tested the hypothesis that CBV would decrease proportionally to the apparent diffusion coefficient in patients with acute stroke and thus could be used as a surrogate parameter for diffusion restriction. METHODS Perfusion-weighted imaging and DWI was performed in 54 patients within 28 hours of symptom onset. Mean apparent diffusion coefficient, cerebral blood flow, and CBV were measured within DWI lesions and contralateral regions. RESULTS Within DWI lesions, CBV (3.3 ± 1.9 mL/100 g) was significantly decreased relative to contralateral regions (4.1 ± 2.1 mL/100 g, P < 0.001). Relative CBV was not decreased in patients with evidence of early reperfusion (1.2 ± 0.5) or mild stroke (National Institutes of Health Stroke Scale < 4, 1.1 ± 0.6). Linear regression indicated that relative CBV was predictive of relative apparent diffusion coefficient only in patients imaged within 9 hours of symptom onset (R = 0.50, P = 0.02). Ischemic tissue volumes generated using a CBV threshold of the 50th percentile of normal tissue were correlated with DWI lesion volumes (R = 0.73, P < 0.001). The mean difference between the CBV threshold of the 50th percentile of normal tissue and DWI lesion volumes was 6.3 mL (95% limits of agreement, 0.1 to 12.6 mL). CONCLUSIONS Decreases in relative CBV are predictive of diffusion abnormalities in ischemic stroke. The pattern of CBV changes varies with clinical severity and symptom duration. Ischemic tissue volumes comparable to DWI lesions can be generated using CBV thresholds, but the use of this method is limited in patients with minor stroke.