CT Angiography Source Images Acquired with a Fast‐Acquisition Protocol Overestimate Infarct Core on Diffusion Weighted Images in Acute Ischemic Stroke

BACKGROUND AND PURPOSE: Studies have demonstrated that computed tomography (CT) angiography source images (CTA-SI) acquired under near-steady-state contrast concentration provide infarct core estimates equivalent to diffusion-weighted images (DWI). We sought to test this relationship using our current CTA protocol optimized for faster scan acquisition. METHODS: Forty-eight consecutive acute ischemic stroke patients met the following criteria: fast-acquisition CTA and magnetic resonance imaging (MRI) within 9 hours of symptom onset, CTA-to-MRI interval under 2 hours, and anterior circulation vessel occlusion. Collaterals were graded on CTA, and lesion volumes were calculated on CTA-SI, DWI, and MR mean transit time (MTT) maps. RESULTS: The mean CTA-to-MRI interval was 36 minutes (± 18 minutes). In paired analysis, lesion volumes on CTA-SI were significantly larger than on DWI (45.6 cm3 vs. 29.9 cm3; P < .0001). In 14 (29.2%) cases, there was major CTA-SI overestimation (>25 cm3 difference) of the DWI lesion. Lower collateral score (P = .001), higher National Institutes of Health stroke scale (NIHSS) score (P = .01), older age (P = .01), and proximal occlusion (P < .05) were univariate predictors of major overestimation, with collateral score being the only independent predictor. The interobserver agreement was worse for CTA-SI than for DWI (P < .001 for limits of agreement). CONCLUSIONS: CTA-SI performed using a fast-acquisition protocol overestimates the infarct core on DWI. Substantial differences are observed in over 25% of cases, and are associated with reduced collateralization.