1. A method for analysis of a vascular system comprising: accepting data characterizing a surface structure of a vascular system of a subject, the data identifying locations on the surface of vessels of the vascular system based on a segmented three-dimensional image of a portion of the subject's body including the vascular system; at each of the identified locations on the surface of the vessels, determining, using at least one processor, a local descriptor of vessel shape based on a computation of a Writhe Number that is based on a local neighborhood of the vessel surface corresponding to the identified location, based on quantitative relationships between each location of a plurality of locations in the local neighborhood and the identified location; and using the determined local descriptors of vessel shape relative to a threshold to determine diagnostic information for presentation.