1. A method of identifying a border on an image of a vascular object, comprising: acquiring RF data backscattered from vascular tissue; transforming said RF data into the frequency domain; identifying a plurality of parameters of said transformed RF data; using said plurality of parameters and previously stored data to identify at least a first and second portion of said transformed RF data that corresponds to a blood and non-blood portion of said vascular tissue, respectively; and determining said border on said image of said vascular object in accordance with said first and second portions of said transformed RF data.