As their name indicates, interventional radiologists intervene with the body more aggressively than by taking x-rays or injecting dyes.
Interventional radiologists function as radiologists diagnostically and as surgeons therapeutically.
It wasn't that long after x-rays were discovered that scientists began trying to do interventional procedures on themselves. Early in the last century, a dedicated scientist injected contrast into one of his own arteries, and the field of angiography was born. Within a few decades, radiologists were looking at the arteries that supply the legs, the aorta and its branches in the chest and abdomen, the arteries in the head and just about anywhere else in the body. The preferred means of access became the femoral artery in the groin which connects to just about every artery in the body. A particularly good curve, for example, was found for catheterizing the arteries that supply the brain.