What is CT angiography?
CT angiography (CTA) is a safe outpatient procedure that uses specially designed X rays and intravenous contrast to see the detailed anatomy of the blood vessels throughout the body. It is most frequently used in the evaluation of arteries in the head, neck, chest, abdomen and legs.
Why is CT angiography an excellent alternative to catheter angiography?
While conventional catheter angiography is still considered the gold standard for diagnosing arterial disease, it does require an arterial puncture, typically in the groin. There is a small risk associated with the arterial puncture and with manipulating a catheter (a flexible tube) inside your arteries. In addition, there is a recovery time of up to six hours.
Compared to catheter angiography, CTA is a less invasive and more patient-friendly procedure. For CTA, contrast is injected into a vein, a technically less difficult procedure with a very low risk of complications. As a result, patients typically leave immediately following the procedure and can resume normal activities.
How is the procedure performed?
After we place an IV (typically in your arm), you will be placed on the CT scanning table and given intravenous contrast while the CT scanner acquires pictures of the area of interest. Most people experience a temporary warming sensation while the contrast goes in, which dissipates rapidly. The IV is removed and your scan is complete. The real work of CTA comes after the images are acquired, when our radiologists use sophisticated computer workstations, evaluate the source data, and create real anatomic displays of the vessels.
What is CT?
CT is computed tomography, a radiographic technique to visualize the internal organs. A traditional CT scan is an x-ray procedure that combines many x-ray images with the aid of a computer to generate cross-sectional views of the body. Cardiac CT uses advanced CT technology with intravenous (IV) contrast (dye) to visualize the anatomy of you heart, its internal blood vessels, as well as the major vessels arising from the heart.
How does CT machine work?
A CT scanner uses a precisely directed X ray beam that is focused on a specific part of the body. This beam passes through the body, and the pattern of shadows created by the body is recorded by a detector, which feeds the information it receives into a computer. The computer then analyzes the information on the basis of tissue density. Bone (being very dense) is depicted in white; air in black; and water and soft tissue in varying shades of gray depending on its density. The IV contrast makes the blood temporarily very dense, so blood vessels are depicted in light gray to white.
Why choose cardiac CT?
Cardiac CT can detect many conditions at an early stage, so treatment can be more effective. The excellent quality of CT images can also provide the best possible information if intervention is required, such as angioplasty, stent placement, or surgery. If an abnormality is present, CT can show its precise location, size, and extent. Your doctor uses the cardiac CT to evaluate:
- heart muscle and internal chambers
- coronary arteries
- pulmonary veins
- aorta (the major artery exiting from the heart)
- pericardium (sac around the heart)
- cardiac veins
How should I get ready for the exam?
- Do not eat any solid food for four hours prior to your scheduled appointment.
- Do not drink any beverage with caffeine for 12 hours prior to your scan.
- You may have clear liquids, such as water, Jell-O, black coffee, tea, broth, or apple juice up to one hour before the scan.
- You may take your medications as usual with sips of water.
- If you are diabetic, ask your physician how to adjust your medications the day of your test. If you think your blood sugar is low, tell the technologist immediately.
- If you are diabetic and are taking the medications containing metformin, you must be off this medication for 48 hours after undergoing the CT studies. Your kidney functions should be tested (by a blood test) before re-starting Metformin (Glucophage or Glucovance).
- Tell your technologist and your doctor if you are:
- Allergic to iodine or any medications
- Undergoing radiation therapy
- If you are over 60 years old, or have a history of kidney problems, you may be required to have a blood test to evaluate your kidney function prior to receiving any contrast.
What happens during my exam?
- You lie quietly on a table.
You will be asked to lie on a table that is connected to the CT scanner. Then the part of your body that is to be scanned will be positioned in the middle of a large, doughnut-shaped scanner ring. This ring holds the X ray tube and the electronic detectors that send information to the computer.
- The technologist may take preliminary scans.
If IV contrast is to be used during your exam, the technologist will probably take some preliminary scans before the radiologist injects the material.
- We may administer a contrast medium.
If a contrast medium is used, the technologist will inject it into a vein, probably in your arm. Some or all of the solution may be injected by a syringe or by an automatic injector. Alternatively, some or all of it may run slowly into your vein from an intravenous (IV) bottle that hangs in a pole next to the table.
- The scan will begin.
You will remain alone in the room after the procedure begins and the table may move a short distance every few seconds to position you for each new scan, or the table may move continuously very slowly. You will hear clicking or buzzing sounds as the mechanism in the scanner moves around your body. It is important that you lie very still during the procedure so that the scanner can get the best possible pictures.
Are there any risks with CTA?
In general, a CT scan is a low risk procedure. However, there are two important points you ought to know:
- Occasionally, patients experience an adverse reaction to the contrast agent. Some patients develop itching or a rash following the injection. These symptoms are usually self-limiting and resolve without further treatment. Antihistamines can be administered if needed for symptomatic relief. Rarely, a more serious allergic reaction, called an anaphylactic reaction, occurs that may result in breathing difficulty. This reaction is potentially life-threatening and may require medications and treatment to reverse the symptoms.
- CT scanners use X rays. For your safety, the amount of radiation exposure is kept to a minimum. Because X rays can harm a developing fetus, however, this procedure is not recommended if you are pregnant.