Visual grading system for vasospasm based on perfusion CT imaging: Comparisons with conventional angiography and quantitative perfusion CT

Background: The purpose of this study was to compare simple visual grading of perfusion CT (PCT) maps to a more quantitative, threshold-based interpretation of PCT parameters in the characterization of presence and severity of vasospasm. Methods: Thirty-three patients with acute subarachnoid hemorrhage were enrolled in a prospective study and underwent a total of 40 paired PCT and digital subtraction angiography (DSA) examinations. A neuroradiologist and a neurologist reviewed the PCT mean transit time (MTT), cerebral blood flow (CBF), and cerebral blood volume maps independently; they evaluated five anatomical regions (frontal, temporal, parietal, occipital/thalami, and basal ganglia/insula) and graded them for abnormality (0 if normal, 1 if abnormal in <50% of the region, and 2 if abnormal in ≥50% of the region). A third neuroradiologist blinded to the PCT results reviewed the DSA examinations and assessed 19 segments for the presence or absence of vasospasm. Correlation between PCT and DSA scores was assessed, as well as the sensitivity and specificity of PCT compared to DSA used as a gold standard. Results: MTT (R² = 0.939) and CBF (R² = 0.907) scores correlated best with DSA scores (p < 0.001). MTT scoring had a sensitivity of 92% and a specificity of 86% compared to DSA; CBF scoring had a sensitivity of 75% and a specificity of 95%. The interobserver agreement between neuroradiologist and neurologist was found to have kappa = 0.789 for MTT and 0.658 for CBF. Conclusion: We propose a user-friendly visual grading system for PCT maps in patients with suspected vasospasm. This visual approach compares favorably to the results of DSA. Sensitive MTT maps should be used for screening, and specific CBF maps for confirmation of vasospasm.