This was an aortogram in a child with mild congenital aortic valvar stenosis.
The right coronary artery (arrow) takes a very high origin from the mid ascending aorta. It looks for all the world like a saphenous vein graft, which is of course not the case. It might be a little more confusing in an adult.
It is high enough that its origin might not be included in the scanned volume of a CT coronary angiogram. Keep an eye out for it.