A system comprises a catheter including a lens, for acquiring optical coherence tomography images within the vessel of interest as the catheter is being retracted from the vessel in the presence of contrast agent. An X-ray imaging system interface receives a first set of X-ray images of an anatomical region including the vessel of interest containing the catheter. The first set of X-ray images are acquired at points corresponding to the particular points within a heart cycle, while the catheter is stationary in the vessel, in response to a heart electrical activity representative signal and in the absence of contrast agent. An image data processor associates the received X-ray images and corresponding optical coherence tomography image data derived at corresponding time points within respective acquisition heart cycles.