CT Angiogram of the Head

What it is

The brain is fed by a small set of arteries that loop and branch at the base of the skull. A head CT angiogram exists to show those vessels, not the brain. Contrast is injected and the scanner sweeps the head at the moment the dye is in the arteries, after which software strips away bone and leaves a three-dimensional model of the vessel tree that can be rotated and measured. Before this test existed, seeing those arteries meant threading a catheter from the groin up into the neck. Catheter angiography is still done when a vessel needs to be treated as well as seen, but the CT version answers the diagnostic question without entering an artery.

Why it is done

• To find an aneurysm — a weak bulge in an artery wall — after a sudden severe headache or a bleed, and to measure its size and position for planning treatment
• To locate the blocked vessel in someone having a stroke, which determines whether the clot can be removed mechanically
• To look for an arteriovenous malformation, a knot of abnormal connections between arteries and veins
• To follow an aneurysm or a treated vessel over time without repeating a catheter procedure

What to expect

An IV is placed in the arm and the dye is delivered by a power injector, so it arrives faster and feels more intense than a routine contrast scan — a strong warm rush and a metal taste that pass quickly. The head must stay completely still, because the reconstructions depend on the bone and the vessels lining up exactly between passes. The scanning takes seconds; most of the appointment is preparation. Kidney function and past contrast reactions are asked about before the injection.

Questions worth asking

• Was a CT angiogram of the neck arteries done at the same time? That is a separate code and a separate charge, even though it is one trip through the scanner.
• Three-dimensional reconstruction of the vessels is sometimes billed as its own line item. Is it included in the price I was quoted?
• If a plain head CT was done first and this followed, will I see two imaging charges for the same visit, and were both clinically needed?
• For surveillance of a known aneurysm, how does the cost of repeating this scan compare with an MR angiogram, which uses no x-rays?