1. A method for characterizing a blood vessel, having adventitia, media, and intima regions surrounding a lumen, by measuring the apparent intima-media thickness, the method comprising: providing an image of a blood vessel, the image having a longitudinal direction substantially corresponding to an axial direction of a blood vessel, a lateral direction substantially orthogonal thereto, and comprising pixels each having an intensity associated therewith; selecting a series of longitudinal positions and finding for each longitudinal position thereof the brightest pixel, having the greatest value of intensity with respect to other pixels positioned laterally therefrom; defining an adventitia datum by fitting a first curve to the lateral positions of the brightest pixels over a domain of the longitudinal positions; defining a lumen datum by fitting a second curve to lateral locations of the lumen substantially closest toward the adventitia and corresponding to the longitudinal positions; defining a media datum by fitting a third curve to pixels, a plurality of which correspond to the location of local minima distributed in a longitudinal direction and positioned between the lumen datum and the adventitia datum; locating the lumen-intima boundary, extending along the longitudinal direction, as the lateral location of local steepest ascent of intensity in a traverse from the lumen datum toward the media datum; locating the media-adventitia boundary, extending along the longitudinal direction, as the lateral location of local steepest ascent in intensity in a traverse from the media datum toward the adventitia datum; and calculating the intima-media thickness as the lateral distance between the lumen-intima boundary and the media-adventitia boundary.