Fig 4. ROC curve analysis for each CT perfusion parameter's ability to correctly identify the impaired cerebrovascular reserve. With optimal threshold value (–16%) of pcCBF, the sensitivity, specificity, PPV, and NPV for defining the impaired cerebrovascular reserve are 94.4%, 93.2%, 97.1%, and 87.2%, respectively (the area under the ROC curves = 0.98; A). For defining impaired CVR with pcMTT, statistical analysis gave a threshold value of 10%, with a sensitivity, specificity, PPV, and NPV of 85.2%, 65.9%, 86.0%, and 64.4%, respectively (the area under the ROC curves = 0.79; B).