Purpose
To clarify whether CT-Perfusion (CTP) derived maps, namely regional cerebral blood flow (rCBF) map, regional cerebral blood volume (rCBV) map, and regional mean transit time (rMTT) map, provide feasible information to predict the fate of the ischemic tissue on acute stage of ischemia, and, if so, which is a best predictor among three.
Methods
13 patients with the obstruction of major artery were recruited. CTP was taken within six hours of onset in all cases. Seven regions of interest (ROI) were set on ischemic hemisphere at the level of basal ganglia. The value of rCBF, rCBV and rMTT in these ROI were calculated. Besides, ratio of these three parameters against the mirrored region on non-ischemic hemisphere, namely CBF ratio, CBV ratio and MTT ratio, were also calculated. Then discriminant analyses were performed to access whether threshold for the fate of ischemic tissue (infracted or salvaged) can be established on these six parameters. Then ROC analyses were taken to evaluate the sensitivity, specificity, and likelihood ratio on each parameter.
Results
Thresholds by discriminant analyses were 27.9 ml/100 g/min for rCBF, 0.63 for CBF ratio, 1.69 ml/100 g for rCBV, 0.85 for CBV ratio, 6.53 s for rMTT, and 2.2 for MTT ratio, respectively. Evaluated by sensitivity, the best predictor was 0.91 for each rCBF and CBF ratio; the other sensibilities were 0.84 for rCBV, 0.69 for CBV ratio, 0.86 for rMTT, and 0.88 for MTT ratio. Evaluated by specificity, the best predictor was 0.89 for MTT ratio; the other specificities were 0.75 for rCBF, 0.71 for CBF ratio, 0.59 for rCBV, 0.71 for CBV ratio, and 0.86 for rMTT. The highest likelihood ratio was 8.167 for MTT ratio; the other likelihood ratios were 3.625 for rCBF, 3.383 for CBF ratio, 2.054 for rCBV, 2.406 for CBV ratio, and 5.906 for rMTT. Areas under the ROC curve(mean±S.E) were almost equal for rCBF, CBF ratio, rMTT, and MTT ratio, these were 0.92 ± 0.03, 0.93 ± 0.03, 0.93 ± 0.03, and 0.91 ± 0.03, respectively, and larger than 0.77 ± 0.06 for rCBV, 0.80±0.06 for CBV ratio.
Discussion
These results suggest that parameters of CTP (namely rCBF, CBF ratio, rMTT, and MTT ratio) can predict the fate of cerebral ischaemia. There are some limitations that the range of slab is limited by width of detector, and because of using non-diffusible tracer, measured value is influenced by cardiac function and presence of vascular structure, but CTP enables the evaluation of cerebral circulation in a short time, and is feasible for therapeutic decision, particularly in determining the necessity of thrombolytic therapy for hyper acute cerebral ischemia.