example crosses whose branches encircle the stenosis zone or circles encircling these zones or rectangles whose major axis extends parallel to the central line of the vessel and which enclose these zones as shown in fig5 a the image of the region or vessel segment thus encircled or enclosed is referred to hereinafter as 34 icon 34 at this stage of the image processing method denoted as icon in fig2 therefore the number of points of the image to be examined has been substantially reduced actually if a full resolution image of 512 u00d7 512 pixels is examined initially all points are suspect so that there are approximately 260 000 suspect points at this stage of the invention where only remains the points localized in the icons fig5 a still need be examined the number of suspect points has been reduced to approximately from 200 to 1000 at this stage of the method therefore the vessels are individually examined in the 34 icons 34 each icon normally containing only a vessel segment via a segmentation operation the edges of this vessel are then detected in each 34 icon 34 the icon is first related to its own coordinate axes subsequently the edges of the vessel are determined for example by calculating the derivative of the intensity profile perpendicular to the axis of the central line of the vessel in the icon the edge point.