IDH1 and glioblastoma: By leveraging the differences in water diffusivity properties in the peritumoral region of brain metastases and glioblastomas (Central Nervous System (CNS) World Health Organization (WHO) grade 4, Isocitrate-Dehydrogenase 1 (IDH1)-wildtype); consisting of purely vasogenic versus infiltrative edema respectively, we train a deep learning model to derive a novel voxel-wise peritumoral microenvironment index (PMI) without using any manual delineation of infiltrative regions.