How images are obtained  
 

It is important to understand these concepts when looking at angiograms:

  1. It is the vessel lumen that is being opacified, the vessel wall is not seen.
  2. The images can be displayed with the opacified blood vessels appearing white or black.
  3. You must look at the entire sequence of films, not just one film, in order to interpret angiograms optimally.
  4. The degree of radioopacity produced by a contrast injection will depend on the relative proportions of blood and contrast. As more (unopacified) blood mixes in with the contrast bolus, the vessel lumen will become fainter.
  5. If the heart is not pumping forcefully, and/or if the flow of blood is slow through a region (e.g. the main artery supplying the region is obstructed), the bolus of contrast will move comparatively slowly through the arterial tree.