Computerized tomographic angiography, also called CT angiography or CTA, is a test that combines the technology of a conventional CT scan with that of traditional angiography to create detailed images of the blood vessels in the body.
In a CT scan, x-rays and computers create images that show cross-sections, or slices, of your body. Angiography involves the injection of contrast dye into a large blood vessel, usually in your leg, to help visualize the blood vessels and the blood flow within them. When the contrast dye is used to visualize your veins, the study is called a venogram, and when it is used to visualize your arteries, it is known as an arteriogram. CT angiography is similar to a CT scan, but the contrast dye is injected into one of your veins shortly before the x-ray image is performed. Because the dye is injected into a vein rather than into an artery, as in traditional angiography, CT angiography could be considered less invasive.
During the study, you will lie down on a table, which passes through a donut-shaped device. Inside the device, a machine takes x-rays in arcs around the area of your body being examined. Tissues of varying densities absorb these x-rays in varying amounts. The computer assigns these densities different numerical values and then plots an image based on these values, in shades of gray. During the CT angiogram, a dose of contrast dye will be injected into one of your veins. As the dye flows through your circulatory system, it will highlight your blood vessels on the scan. A computer will produce 3-dimensional (3D) images of your blood vessels from the x-ray images.
Your physician will ask you to avoid foods and liquids for about 4 hours before the test. You will probably be allowed to continue taking any prescribed medications, but ask your physician before the exam to be sure.
Before the test is performed, you may be asked to change into a hospital gown and remove all jewelry and other metal objects, which can interfere with x rays.
Contrast material carries a slight risk of causing an allergic reaction. If you know that you are allergic to contrast material or dye, let your physician know before you receive the contrast material. In addition, allergies to iodine or shellfish may place you at increased risk for having an allergy to the contrast dye. If you are allergic to iodine or shellfish, alert your physician prior to the test. Medications can sometimes be given before the contrast material is administered to lessen the risk of allergic reactions in susceptible patients.
The contrast material is also eliminated by the kidneys and can damage kidney function, especially if you have kidney problems already. Let your doctor know if you have damaged kidney function. In this situation, medication and fluids, called hydration, can sometimes be given before the contrast material is administered to decrease the effects of the contrast dye on the kidneys. Blood tests may be done to evaluate your kidney function before the CT scan.
You may be unsuited for CT angiography if you:
- Have an allergy to contrast dye
- Have kidney problems
- Have severe diabetes
- Are pregnant, because radiation may harm the fetus
- Have unstable vital signs
- Weigh more than 350 pounds, because some x-ray tables cannot support the weight