PROJECT SUMMARY/ABSTRACT The overall goal of this proposal is to determine the potentially pivotal and interactive roles of individual platelet expression of FcγRIIa [SA-1] and wall shear stress (WSS) calculated from patient-specific CT angiography (CTA) computational fluid dynamics (CFD) [SA-2] to explain recurrent ischemia after minor stroke or TIA due to ICAD. A precision model is developed [SA-3] to quantify risk of recurrent ischemic injury, accounting for FcγRIIa, WSS, anti-platelet therapies and platelet reactivity, across a diverse population of stroke and TIA patients with ICAD. Our central hypothesis is that high FcγRIIa plus high shear force pose individual and synergistic risk of stroke recurrence, providing a rational basis for the precision medicine of stroke prevention in ICAD. Our preliminary data reveal that greater platelet FcγRIIa expression identifies patients at greater risk of recurrent cardiovascular events including stroke and that high WSS on CTA CFD predicts recurrent stroke due to ICAD at 1 year. Our three independent specific aims leverage an established research infrastructure and ICAD network of 6 geographically distinct enrolling sites with race-ethnic diverse populations and a longstanding history of productive collaboration to recruit 250 participants with acute cerebral ischemia within 72 hours from symptom onset. The multicenter, observational study will enroll stroke or TIA patients due to 50-99% ICAD diagnosed on routinely acquired CTA and obtain brain MRI and blood sampling for FcγRIIa and platelet assays within 72 hours and again at 1 year after onset. Clinical outcomes will be ascertained at 90 days and at 1 year, with co-registration of serial MRI to quantify interval silent and symptomatic ischemic injury. The Platelet Biology Core at University of Vermont will quantify platelet FcγRIIa expression. The Neurovascular Imaging Research Core at UCLA will conduct central imaging analyses, including CTA CFD quantification of WSS, serial MRI co-registration and imaging adjudication of eligibility and interval endpoints. The Statistical Core will coordinate data management from 6 enrolling sites and the core facilities, conducting predictive statistics, stratification of key biological variables and novel application of clustering analytic strategies to maximally inform a precision model of ICAD stroke risk at 1 year. This timely culmination of synergistic work on shear stress-induced platelet activation in ICAD leverages our robust preliminary data on FcγRIIa, CTA CFD of WSS and precision medicine analytics in stroke, layered on a successful track record of multicenter, observational studies of the most common cause of recurrent stroke. Measurement of individual differences in FcγRIIa and shear stress induced by heterogenous arterial stenoses inform a logical precision medicine strategy to avert stroke. This novel strategy of using diagnostic data easily acquired shortly after stroke or TIA due to ICAD has clear...