In an image post-processing method and apparatus for 3D visualization of 2D/3D fused image data for use in catheter angiography in an endovascular interventional procedure, upon forward movement of a micro-catheter through blood vessel in the interventional procedure, x-ray images are acquired from different projection directions and are subjected to a pattern recognition algorithm for edge-based segmentation of the image regions filled by the micro-catheter, with all remaining image regions being masked out. The segmented projection exposures are prepared by a 3D reconstruction algorithm to obtain an image data set for (pseudo-) three-dimensional representation of the micro-catheter. This image data set are intraoperatively registered and fused with an image data set acquired from an angiographic pre-examination for three-dimensional visualization of the vessel topography. The reconstructed 3D representation of the catheter is mixed into the three-dimensionally prepared representation of endovascular blood vessel sections to be treated.