1. A system that measures perfusion through a volume of tissue, the system comprising: a non-transitory memory to store computer-executable instructions; and a processor that executes the computer-executable instructions to at least: receive an ultrasound signal response of a contrast agent within a volume of interest, wherein the ultrasound signal response comprises a time dimension and three position dimensions, and wherein the volume of interest comprises a tissue density and a geometry; and determine the perfusion through the volume of tissue based on a probabilistic constant related to the geometry, the tissue density, the ultrasound signal response, and a feature of the geometry.