1. A medical viewing system, the system comprising: at least one X-ray image acquisition device for acquiring a pre-interventional angiogram of vessels with injected contrast agent and for acquiring interventional live images thereof; at least one display unit; and a calculation unit connected to the at least one X-ray image acquisition device and the at least one display unit, wherein the calculation unit is configured for registration of vessel tree images extracted from the angiogram relative to the live images through object-based registration and for generating a region of interest border within which at least partial presence of a considered targeted object attains the potential to achieve an accurate registration; wherein the display unit is configured for overlaying the region of interest border onto the vessel tree images and the live images.