Abstract 54: Mapping of Cerebral Vascular Territories Using Whole Brain Perfusion CT Imaging: A New Method

Introduction: The nature and endurance of the collateral blood supply in acute stroke is speculated to play a key role in tissue survival, yet research in this area is limited by the lack of appropriate imaging modalities to characterize and quantify collateral flow. We present the first results of a novel post-processing technique that can label and quantify the extent of the major vascular territories, including the predominant source of collateral supply into the hypo-perfused regions, using a 320 slice whole brain perfusion CT acquisition. Hypothesis: We hypothesized that the perfusion territories determined by the algorithm would be anatomically consistent with what would be expected from the site of occlusion as determined on CTA. Methods: We retrospectively selected data from a cohort of 19 acute stroke patients imaged within 6 h of stroke onset on a Toshiba Aquilion One CT system. We applied an algorithm that uses subtle changes in bolus shape across voxels to infer the pathway of flow from the proximal vessels towards the periphery. Labels were assigned to each of the 6 feeding vessels and the vascular territory maps were generated. Each voxel is color coded by its dominant source of flow. Results: We were able to generate images in 15 of 19 cases [4 excluded due to head motion and poor signal enhancement during the bolus passage]. In general, the estimated distributions of vascular territories in the non affected hemisphere were in agreement with text book distribution patterns. In the affected hemisphere, the vascular territory of the occluded vessel was either diminished or absent and the tissue instead supplied by adjacent territories. In 2/15 cases the estimated collateral territory appeared questionable. The figure shows two typical cases: In patient 1 with a distal M1 occlusion, the MCA territory is partially taken over by the ACA and PCA territories. In patient 2, the PCA collateralisation recedes following partial reperfusion of the M2 branch occlusion. Conclusion: This perfusion CT post-processing technique opens a window to visualization and measurement of vascular supply territories using a routine perfusion CT scan, an application previously limited to arterial spin labelling MRI. This technique is complementary to standard perfusion maps, and we speculate that integration of collateral supply information may enhance the utility of perfusion imaging and ultimately lead to more accurate selection of treatment responders. This new post-processing method has the potential to characterise and quantify collateral circulation with no need for additional hardware or higher radiation doses.