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 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 are then assembled by computer into a three-dimensional picture of the area being studied. Compared to catheter angiography, which involves placing a catheter and injecting contrast material into an artery, CTA is a much less invasive and more patient-friendly procedurecontrast 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
Uses of the Procedure
CTA is commonly used to:
CTA also is used to detect narrowing or obstruction of arteries in the pelvis and in the carotid arteries bringing blood from the heart to the brain. When a stent has been placed to restore blood flow in a diseased artery, CT angiography will show whether it is serving its purpose. Examining arteries in the brain may help reach a correct diagnosis in patients who complain of headaches, dizziness, ringing in the ears, or fainting. Injured patients may benefit from CTA if there is a possibility that one or more arteries have been damaged. In patients with a tumor, it may be helpful for the surgeon to know the details of arteries feeding the growth.
Diagnosis & Assessment
An interventional radiologist, a doctor specially trained in performing minimally invasive treatments using imaging for guidance, will use duplex ultrasound to assess the venous anatomy, vein valve function, and venous blood flow changes, which can assist in diagnosing venous insufficiency. The doctor will map the greater saphenous vein and examine the deep and superficial venous systems to determine whether the veins are open to pinpoint any reflux. This will help determine if the patient is a candidate for a minimally invasive treatment, known as vein ablation.
Preparation For The Procedure
Depending on the part of the body to be examined, you may be asked to take only clear liquids by mouth before CTA. 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.
A CT scanner is a specialized x-ray machine that looks like a large square doughnut. It has an opening measuring about two feet in diameter that surrounds a narrow table. Inside the frame of the scanner is a rotating device with an x-ray tube mounted on one side and a banana-shaped detector opposite it. Nearly all CTA studies use an advanced type of unit called a spiral CT machine that looks like any other type of CT unit, but is able to record a large number of pictures in a short time. This means that patients do not have to hold their breath for a prolonged period.
How The Procedure Works
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 which controls the timing and rate of injection is used, and may continue during part of the time images are recorded. During the examination, the rotating device spins around the patient, creating a fan-shaped beam of x-rays, and the detector takes snapshots of the beam after it passes through the patient. As many as one thousand of these pictures may be recorded in one turn of the detector. The real work of CTA comes after the images are acquired, when 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.
How the Procedure is Performed
Most of the time for a CTA examination is spent setting everything up. Actually recording the images takes only seconds. After changing into a hospital gown and having an IV set up, you will answer questions about things that might complicate the exam (such as allergies) and then will lie down on a narrow table. The part of your body to be examined will be placed inside the opening of the CT unit with the aid of crisscrossed positioning lights. A test image is taken to determine the best position, and a small dose of contrast material is given to see how long it takes to reach the area under study. Then the IV is hooked up to an automatic injector, the contrast material is injected, and the scan begins. Afterwards, the images will be reviewed and, if necessary, some will be repeated. No special measures are needed after the procedure.
What Will I Experience During The Procedure?
CTA takes about 10 to 25 minutes from the time the actual examination begins. Overall, you can expect to be in or near the examining room for 20 to 60 minutes. You may feel warm all over when contrast material is injected before the scan, but you should not feel pain at any time. Any CT study requires that you remain still during the exam. Pillows and foam pads may help make it more comfortable. At the same time, the nurse or technologist may use pads or Velcro straps to keep the area from moving. The examination table will move in and out of the scanner opening, but it is not enclosed and only a small part of your body will be inside at any one time. You may be asked to hold your breath for 10 to 25 seconds to be sure that the images will not be blurred. During the time that no actual imaging is taking place, you are free to ask questions or talk to the technologist, but friends or relatives will not be allowed in the examining room. Once the needed images have been recorded, you will be free to leave. You can eat immediately and it is a good idea to drink plenty of fluids in the hours after the exam to help flush contrast material out of the system.
Interpretation Of The Results
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.
Benefits vs. Risks