Apparatus and methods are described for receiving into at least one processor a set of images of blood vessels of a subject. A road map of the subject's blood vessels is generated, by automatically (a) deriving at least one image from the set of images of the blood vessels, based upon visibility of at least a portion of the blood vessels in the set of images, and (b) in the derived image, determining a location of edge lines of at least some of the portion of the blood vessels in the image. An output is generated by the processor, based on the road map. Other embodiments are also described.