Spectral imaging and analysis of monophasic CT angiography to assess infarct core and penumbra in acute stroke.

Acute stroke imaging includes native CT, CT-angiography (CTA), and CT-perfusion (CTP). CTP assesses the irreversibly damaged infarct core (IC), and the potentially salvageable penumbra (PEN) and distinguishes these from areas of healthy parenchyma (HA). However, it requires additional contrast agent and radiation. Spectral-CT (SCT) enables spectral imaging like e.g., iodine-density imaging, and we evaluated its potential in estimating IC and PEN using monophasic CTA data only. We analysed 28 patients with mediainfarction. CTP-analysis derived areas of IC, PEN and HA on infarction side, as well as their healthy hemisphere's counterparts were transferred to CTA as Region of interest (ROI). Spectral measurements included Hounsfield-Units in monoenergetic maps (MonoE) at 40 keV, 70 keV, and 120 keV, plus iodine-density (ID) and electron-density (ED) values, totalling 2970 values. Unilateral absolute values and ratios to the healthy counterparts were evaluated. Visual infarct delineation on each map was also rated. In all spectral maps, the infarct areas could be distinguished from the healthy counterpart by absolute values (p < 0.05). IC, PEN and HA could be distinguished from each other by absolute values (p < 0.05) (except for ED), and by the ratio-value formed to the contralateral side (p < 0.05). Detection of IC and PEN were best possible in ID (IC (AUC = 0.9999, p < 0.0001); PEN (AUC = 0.9745, p < 0.0001)) and MonoE40 (IC (AUC = 0.9963, p < 0.0001); PEN (AUC = 0.9622, p < 0.0001)). Differentiation of IC and PEN was also best in ID (AUC = 0.93, p < 0.0001) and MonoE40 (AUC = 0.80, p < 0.0001). Similarly, visual delineation was best too in ID and MonoE40. Accordingly, IC and PEN can be detected and differentiated in monophasic CTA by using SCT-derived spectral maps like ID or MonoE40.