You are absolutely correct that most patients have the option of having coronary angiography performed from either the femoral (
leg) or radial (arm) artery access sites.
For the femoral site, the catheter is introduced via a sheath in the femoral artery, and is advanced up the abdominal aorta, over the aortic arch, and dye is then injected into the coronary arteries. For the radial site, the right radial artery is most often used.