Leptomeningeal anastomoses (LMAs) play an essential role as collateral pathways that redistribute blood flow in the cerebral circulation. If LMAs do not function adequately, patients with severe stenosis or arterial occlusion may develop ischemic stroke. Therefore, LMAs have been regarded as promising therapeutic targets [1]. In addition, quantitative prediction of blood flow redistribution through LMAs can provide valuable information for intervention planning and prognosis assessment in various cerebrovascular diseases. However, LMAs are small vascular pathways with radii of less than 0.3 mm. Current medical imaging modalities cannot resolve LMA pathways or measure blood flow velocity within them. In this study, LMAs are mathematically modeled based on the anatomy of the cerebral circulation using a zero-dimensional (0D) model, which is then incorporated into the one- and zero-dimensional (1D–0D) simulation framework developed by the authors [2,3]. In the present 1D–0D model, blood flow in the Circle of Willis (CoW) is simulated using a 1D model, whereas blood flow in the peripheral regions, including LMAs, is simulated using a 0D model. The vascular geometry of the CoW is obtained from medical imaging data such as CT or MRA. The LMAs, represented as resistances, are calibrated to minimize discrepancies between 4D Flow MRI and SPECT measurements. The proposed 1D–0D model was applied to three patients, and the effects of LMAs on cerebral perfusion were investigated by comparing simulation results obtained with and without LMAs against the experimental data. REFERENCES [1] A. Shuaib, et al., The Lancet Neurology, Vol.10, pp.909–921,2011. [2] H. Zhang, et al., Annals of Biomedical, Vol.44, pp.2351–2363, 2016. [3] Yuhn, C., et al.,PLOS Computational Biology, Vol.18, e1009996, 2022.