Catheter Angiography is an "invasive procedure", because it requires: 1) inserting a small plastic tube (catheter) into the patient; and, 1) the injection of radiopaque liquids that blocks X-Rays creating a shadow of the vessels. The radiopaque liquid substance is commonly called a "Contrast Agent" or "Dye".

Usually a very tiny tube, that has a special shape, is used to place the contrast into a particular artery or vein. While the artery or vein contains this radiopaque material, it will block the X-Rays, and will cast a shadow of the injected vessels onto the X-Ray film or fluoroscope. This image will reveal the shape of the artery, and can help to diagnose an obstruction, blockage, or narrowing ("stenosis").