SWI and T2*-GRE Microhemorrhage Counts in Anti-Amyloid Therapy Eligibility: A Real-World-Calibrated Simulation Study.

introductionAnti-amyloid therapy eligibility excludes patients with five or more cerebral microhemorrhages (CMHs), but current guidance allows either T2*-GRE or the more sensitive SWI. This may create sequence-dependent differences in eligibility classification.

methodsWe fitted a Bayesian right-censored zero-inflated Poisson model to single-center real-world SWI-based CMH counts from 130 memory clinic patients. We then simulated T2*-GRE counts under a directional binomial detection model across a range of relative detection probabilities and estimated two metrics:

resultsThe model estimated a zero-inflation probability of 0.57 and a Poisson mean of 2.29 in the susceptible subpopulation. In the illustrative 60% relative-detection scenario, the model estimated nearly 80% under-detection among SWI-ineligible patients, whereas approximately 5% of T2*-GRE-eligible patients would have been classified as ineligible by SWI. DISCUSSION: A uniform numeric CMH threshold may not be operationally equivalent across SWI and T2*-GRE. Standardized paired-sequence outcome studies are needed to determine whether SWI-defined and T2*-GRE-defined thresholds carry equivalent ARIA risk.