Segmentation of blush size guides embolic endpoints in genicular artery embolization

OBJECTIVE: To identify a quantitative surrogate parameter for the embolic endpoint in genicular artery embolization (GAE). MATERIALS AND METHODS: Digital subtraction angiography (DSA) images were fused and converted into color maps. Using segmentation software, blush size was measured before and after embolization, and blush reduction ratio (BRR) was calculated. Osteoarthritis severity was graded on radiographs, and clinical outcome was evaluated using the Knee Injury and Osteoarthritis Outcome Score (KOOS) at 6 weeks, 3 months, and 6 months. Embolized vessels and embolic volume were recorded. Blush size and BRR were compared between osteoarthritis grades and across embolized vessels. RESULTS: GAE using 100-300 µm permanent microspheres was performed in 90 patients with mild to severe osteoarthritis and 23 patients with pain after total knee replacement (post-TKR) (404 vessels). The median number of vessels embolized per session was 4 (range: 1-6) with a median total embolic volume of 3.5 mL (1.1-8.0 mL). Pre-embolization blush size (+ 1116 mm²/osteoarthritis grade; p < 0.0001) and embolic volume (+ 1.1 mL/OA grade; p < 0.0001) increased with higher osteoarthritis grade and post-TKR. Blush size significantly decreased after embolization (p < 0.0001) with a median BRR of 0.81 (0.62-0.94). No significant differences in BRR were observed between osteoarthritis grades and different vessels. All KOOS subscales improved significantly at each follow-up (p < 0.0001). CONCLUSION: Segmentation of blush size enables quantitative assessment of embolic endpoints across all genicular arteries and osteoarthritis grades, including post-TKR cases. "Pruning" corresponds to a blush size reduction of 80%. Higher osteoarthritis grades are associated with larger blush areas, requiring higher embolic volumes to achieve comparable embolic endpoints. KEY POINTS: Question Standardized, quantitative assessment of embolic endpoints in GAE is lacking, as the angiographic endpoint "pruning" has so far been defined only subjectively. Findings Segmentation of angiographic blush using color-coded maps enables objective quantification of embolic endpoints. With increasing osteoarthritis grade, baseline blush size and embolic volume increase, while an 80% blush reduction defines the endpoint "pruning." Clinical relevance Objective blush quantification improves the reproducibility of embolic endpoint assessment in GAE and supports individualized embolization strategies across disease severity and vascular territories.