Abstract TP45: One Threshold Does not Fit All: Hounsfield Unit Thresholds to Segment Clot on NCCT are Patient Specific

Introduction: The hyperdense sign is a marker of thrombus on non-contrast computed tomography (NCCT). Currently, pre-specified Hounsfield unit (HU) threshold are used arbitrarily for clot segmentation. We aimed to test if HU thresholds best discriminating clot on thin slice NCCT are patient specific and dependent on factors such as age, hematocrit, and NCCT slice thickness. Methods: Data are from the ESCAPE randomized controlled trial. Only patients with thin slice baseline NCCT (<2.5mm) and M1-MCA occlusion on baseline CT-Angiography (CTA) were included. CTA was co-registered to NCCT using in-house software. Proximal and distal clot interface was identified on CTA and super-imposed onto the NCCT. Three Regions of Interest (ROIs) (36- 100 voxels) were placed on the NCCT in the 1) clot as defined on co-registered CTA, 2) contralateral brain tissue, and 3) contralateral patent M1 MCA artery. Optimal patient specific HU thresholds differentiating “clot” from “normal vessel” and “brain tissue” voxels were cal...