Comparision of two different computed tomography post-processing methods in ischemic perfusion defects

Purpose We aim to search for visual and quantitative differences of two different CT perfusion (CTP) post processing metods and their variability according to critical stenosis in acute stroke patients. Material Method Fourty five of 47 patients with acute ischemic stroke were enrolled. Their CTP raw data were retrospectively processed with delay sensitive (SVD) and delay insensitive metod (SVD+). CBV, CBF and MTT maps were evaluated. Comparing with the contralateral normal hemisphere, relative and difference of metrics were calculated (rCBV, rCBF, rMTT and dMTT). Patients were categorized into 5 groups according to superiority in visual assessment of penumbra in post-processing metods. Locations of critical stenosis and their percentages in each group were identified and compared. Differences in perfusion values of penumbra obtained in both metods were analyzed with Wilcoxon Signed Ranks test. Inter-group and intragroup differences of measurements in both post-processing methods were analyzed with One Way ANOVA ve Post Hoc TUKEY tests. The statistical significance value was set at p ≤ 0,005. Results Penumbra threshold values were found as MTT > 145% and CBV > 1, 9 ml/ 100 gr. Compared to SVD+, 1.5 fold decrease in rCBF value and 1.3 fold increase in rMTT value was established in SVD metod. The most marked differences between two metods was noted in dMTT values. Values of dMTTs in SVD were 3 fold of those measured in SVD+. In group 1 (N:3), penumbra seen in SVD was noted as pseudohyperperfusion in SVD+. In group 2 (N:22) and 3 (N:9), penumbra was better distinguished in SVD than in SVD+ in decreasing easiness, respectively. In group 4 (N:9), penumbra assessment was similar in both methods. In group 5, penumbra was the better distinguished in SVD+ than in SVD. Group 1 and 5 were the groups in which the frequency of critical distal stenosis was % 100. Group 2, 3 and 4 were the groups having high rates of critical proximal stenosis in decreasing proportions, respectively (90%, 87%, 77%). There is no difference in rCBV values among metods. In inter-group assessment, both post-processing metods showed statistically significant rCBF, rMTT and dMTT differences. In 4 intra-group analysis, all groups had rMTT difference and all groups except group 5 had dMTT differences (p ≤0.005). Conclusion In both CTP post-processing methods, the most prominent difference was found in dMTT. Visually, penumbra is better distinguished in SVD in proximal critical stenosis whereas in SVD+ distal critical stenosis. In cases having both ipsilateral critical proximal and distal stenosis, penumbra in SVD was noted whereas pseudohyperperfusion in SVD+. Variability of CTP post-processing metods in penumbra evaluation according to locations of critical vessel stenosis were not investigated so far. This finding suggest that contrast delay substraction in SVD+ method may cause false results in cases of ipsilateral critical proximal and distal stenosis.