Like an angiogram, a contrast dye has to be injected, in this case continuously, into the area to be studied. The dye is injected into a vein or into the bone marrow. The flow of dye has to be constant. In the vast majority of cases, this is accomplished by inserting a catheter into a vein in the groin and working it up to the area to be studied. As such, it is an invasive procedure.