CT (computed tomography) Angiography (CTA) is an examination that uses x-rays to visualize blood flow in arterial vessels throughout the body, from arteries serving the brain to those bringing blood to the lungs, kidneys, and the arms and legs. CT combines the use of x-rays with computerized analysis of the images. Beams of x-rays are passed from a rotating device through the area of interest in the patient's body from several different angles so as to create cross-sectional images, which then are assembled by computer into a three-dimensional picture of the area being studied. Compared to catheter angiography, which involves placement of a catheter and injecting contrast material into an artery, CTA is a much less invasive and a more patient-friendly procedure; contrast material is injected into a peripheral vein rather than an artery. This exam has been used to screen large numbers of individuals for arterial disease. Most patients have CT angiography without being admitted to a hospital.
Consume only clear liquids four hours prior to your study. You will be asked whether you have asthma or any allergies to foods or drugs, and what medications you are currently taking. If you are pregnant, you should inform the technologist before the procedure. You probably will not have to undress if you are having an exam of the head, neck, arms, or legs, but you will have to remove any jewelry, hair clips, dentures and the like that could show up on the x-rays and make them hard to interpret.
You should wear comfortable, loose-fitting clothing for your CT exam. Metal objects can affect the image, so avoid clothing with zippers and snaps. You may be asked to remove hairpins, jewelry, eyeglasses, hearing aids and any removable dental work that could obscure the images. Women should always inform their doctor or x-ray technologist if there is any possibility that they are pregnant.
Before the actual exam begins, you will have a dose of contrast material injected into a vein to make the blood vessels stand out. An automatic injector machine is used that controls the timing and rate of injection, which may continue during part of the time images are recorded. As the scan begins, you'll hear some humming, buzzing or clicking sounds and feel the table move. Do not be alarmed. The noise and table movement are a necessary and normal part of the exam. After the images are acquired, powerful computer programs process the images and make it possible to display them in different ways, for instance, in cross-sectional slices or as three-dimensional "casts" of the blood vessels.
CTA is commonly used to:
- Examine the pulmonary arteries in the lungs to rule out pulmonary embolism, a serious but treatable condition.
- Visualize blood flow in the renal arteries (those supplying the kidneys) in patients with high blood pressure and those suspected of having kidney disorders. Narrowing (stenosis) of a renal artery is a cause of high blood pressure (hypertension) in some patients, and can be corrected. A special computerized method of viewing the images makes CT renal angiography a very accurate examination. It is also done in prospective kidney donors.
- Identify aneurysms in the aorta or in other major blood vessels. Aneurysms are diseased areas of a weakened blood vessel wall that bulges out-like a bulge in a tire. Aneurysms are life-threatening because they can rupture.
- Identify dissection in the aorta or its major branches. Dissection means that the layers of the artery wall peel away from each other-like the layers of an onion. Dissection can cause pain and can be life-threatening.
- Identify a small aneurysm or arterio-venous malformation inside the brain which can be life-threatening.
- Detect atherosclerotic disease that has narrowed the arteries to the legs.
Typically the results of CTA are available within 24 hours, although in complicated cases special computer analysis may take somewhat longer. The radiologist will report the findings to your physician, who in turn will discuss them with you.