1. A vascular assessment apparatus comprising: a processor communicatively coupled to a medical imaging device; and a memory storing non-transitory computer-readable instructions, which when executed, cause the processor to: receive a set of medical images of a coronary vessel tree of a subject from the medical imaging device, wherein a first of the medical images of the set was acquired from a first viewing angle, and a second of the images of the set was acquired from a second viewing angle; perform image analysis to identify vascular features within and corresponding among the set of medical images; combine geometrical information for the corresponding vascular features to produce a stenotic model of the coronary vessel tree, the stenotic model having measurements of the coronary vessel tree at locations along vessels of the coronary vessel tree; determine a flow characteristic from the stenotic model; calculate a first index indicative of vascular function, based, at least in part, on the flow characteristic from the stenotic model; receive another medical image of the coronary vessel tree of the subject; analyze the other medical image to identify vascular features within the other medical image that correspond to vascular features that are represented in the stenotic model or provided in at least some of the medical images from the set; modify the geometrical information for the corresponding vascular features in the stenotic model to create an updated stenotic model from at least some of the identified vascular features within the other medical image; determine a modified flow characteristic from the updated stenotic model; and calculate a second index indicative of vascular function, based, at least in part, on the modified flow characteristic in the updated stenotic model.