A cerebral angiogram represents the most comprehensive test to detect a brain aneurysm if the other two types of scans do not indicate where bleeding occurs, according to Mayo Clinic. Doctors insert a special catheter into veins in the leg, then thread the device up to the brain.
A device in the catheter takes x-ray images of the brain's blood vessels using contrast dyes to allow the radiation to detect any bleeding, notes Mayo Clinic. This procedure is also called a cerebral arteriogram. Doctors anesthetize the injection site, usually in the groin, before sliding the thin catheter through arteries up to the brain. Several x-ray images are taken at the site of the aneurysm.
An angiogram allows health care professionals to view the size, shape and location of an aneurysm, says the Brain Aneurysm Foundation. A magnetic resonance imaging scan helps doctors locate the bleeding. A computed tomography scan detects if there is any bleeding in the brain. A computed tomographic angiography combines a CT scan with x-ray dyes to show how blood flows into the brain's arteries. Magnetic resonance angiographies create better images than a normal MRI by using contrast dyes.
Angiograms carry risks of higher radiation exposure than other scans, and patients may have allergies to contrast dyes, according to Johns Hopkins Medicine. Because a cerebral angiogram is more invasive and goes all the way to the brain, patients may experience complications such as loss of consciousness, a transient ischemic attack, a blood clot, brain swelling or bleeding.