A Relative Noncontrast CT Map to Detect Early Ischemic Changes in Acute Stroke

BACKGROUND AND PURPOSE Early ischemic changes on noncontrast computed tomography (NCCT) are often subtle. We developed a novel postprocessing technique that aids in detecting such changes. METHODS NCCT maps were generated that display the relative density difference between corresponding voxels in contralateral hemispheres (ratio maps of the NCCT [rNCCT]). Voxels with a relative density difference below .95 were designated as infarct. We pilot tested the rNCCT for infarct segmentation on 6 consecutive subjects enrolled in the CT Perfusion to predict Response in Ischemic Stroke Project (CRISP) study and applied the inclusion criteria of an adequate quality NCCT and successful endovascular reperfusion. rNCCT infarct segmentation was compared to baseline NCCT, baseline CTP, and day-5 follow-up fluid-attenuated inversion recovery (FLAIR). RESULTS Five of the six selected cases met the inclusion criteria. Their median time from symptom onset to CT was 4.95 hours (standard deviation [SD], ±3.5; range, 1.05-10.45), and median NIHSS was 13. Early ischemic changes were identified on the rNCCT in all five cases and on the standard NCCT in three of the five cases. Lesions outlined by the rNCCT maps trended toward a better estimation of the day-5 FLAIR volume (median difference = 6.2 mL) than the ischemic core volumes assessed on baseline CTP (median difference = 51.7 mL) in the four cases with a day-5 FLAIR (P = .1). CONCLUSION In this proof-of-concept study, the rNCCT appears promising for detecting and quantifying early ischemic changes. These findings should be confirmed in a larger cohort.