Vascular topological primitives resolve post-ischemic microvascular risk fields and enable early prediction in longitudinal OCTA.

Post-ischemic microvascular perfusion abnormalities appear in OCTA as regional hypoperfusion and heterogeneous attenuation within pre-existing vascular structures. However, most longitudinal OCTA analyses rely on image- or region-level readouts, making it difficult to assign local signal changes to the same baseline vascular elements or to interpret their spatial and topological context within the original vascular network. Here, we propose a baseline-referenced longitudinal OCTA framework in which vascular topological primitives (VTPs) serve as fixed structural coordinates for post-ischemic perfusion analysis. The pre-ischemic OCTA vascular network was decomposed into a baseline VTP template with explicit topological boundaries, fixed sampling domains, and graph connectivity, allowing follow-up signals to be read from the same vascular elements throughout the longitudinal sequence. In a photothrombotic mouse model of focal cerebral ischemia, this mapping generated VTP-level log-ratio attenuation trajectories and a continuous vascular risk field. VTP-level trajectories revealed heterogeneous attenuation magnitude and temporal evolution across baseline vascular structures. The resulting risk field delineated a core-centered spatial-topological organization, with core-proximal attenuation-risk VTPs located closer to OCTA-defined high-risk core VTPs than stable-background VTPs and risk scores decreasing outward along the baseline VTP graph. This spatial-topological organization was directionally consistent across six animals and was significant by one-sided exact sign test (