1. A method of image processing to assess vascular function of a cardiac vasculature having at least one stenotic segment, the method comprising: receiving, by image processing circuitry, a first vascular model modeling the cardiac vasculature; determining at least one characteristic of flow through the stenotic segment in the first vascular model; modifying the first vascular model, to produce a difference in the characteristic of flow for the modified vascular model; determining the characteristic of flow for the modified vascular model corresponding to the characteristic of flow for the first vascular model; determining a flow index quantifying the vascular function of the cardiac vasculature modeled by the first vascular model, wherein the flow index is based on a ratio of the corresponding flow characteristics of the first and modified vascular models; and if the determined flow index is below a predetermined threshold, determining and outputting, to an electronic storage medium or display, indicia of one or more locations for interventional or surgical revascularization treatment options based on the determined flow index.