1. A method for use with an endoluminal data-acquisition device configured to be moved through a lumen of a subject's body, the endoluminal data-acquisition device having a radiopaque marker coupled thereto, comprising: while the endoluminal data-acquisition device is being moved through the lumen: acquiring a plurality of endoluminal data points of the lumen using the endoluminal data-acquisition device; continuously injecting contrast agent into the lumen; and acquiring a plurality of angiographic images of the data-acquisition device; determining that endoluminal data points correspond to respective locations within the lumen, by determining locations of the radiopaque marker within the angiographic images of the lumen, by performing image processing on the angiographic images, the locations of the radiopaque marker within the angiographic images of the lumen corresponding to respective endoluminal data points; and generating an output in response thereto.