In part, the invention relates to processing, tracking and registering angiography images and elements in such images relative to images from an intravascular imaging modality such as, for example, optical coherence tomography (OCT). Registration between such imaging modalities is facilitated by tracking of a marker of the intravascular imaging probe performed on the angiography images obtained during a pullback. Further, detecting and tracking vessel centerlines is used to perform a continuous registration between OCT and angiography images in one embodiment.