I am trying to find the brain parenchymal fraction (BPF; defined as the ratio of brain parenchymal volume to the total volume within the brain surface contour) by using sienax (using only one time-point/scan). Given the normalized and unnormalized brain volume and the v-scaling factor gained by sienax, how would I calculate the BPF? My end goal is to gain some sort of atrophy percentage. Any help would be most appreciated. Thank you!