1. A method for co-registering vascular images with a 3D reconstruction of a vessel, comprising the steps of: triggering a first 2D external angiographic image in a first imaging plane; triggering a second 2D external angiographic image in a second imaging plane; reconstructing a 3D model image from the first 2D external angiographic image and the second 2D external angiographic image; inserting a catheter with an imaging device at its tip into the vessel to a starting point; triggering a first 2D external image that shows a tip location at the starting point in two dimensions in a first imaging plane without contrast agent injection; triggering a second 2D external image that shows the tip location at the starting point in two dimensions in a second imaging plane without contrast agent injection; reconstructing the starting point of the tip location in three dimensions from the first 2D external image and the second 2D external image and visualization in the previously obtained 3D model; starting a pull-back of the catheter and simultaneously acquiring vascular images until an endpoint of the pull-back is reached; defining a passed route of the catheter tip based on at least one of: a) a pullback speed and elapsed time; and b) an image rate and a sequential image number in the 3D model co-registering the vascular images with the route of the catheter tip in the 3D model; displaying the 3D model image on a display with a marker representing the position of the vascular image with respect to the position of the catheter tip along the route; displaying the vascular image co-registrated with the visualized marker.