Computed tomography, commonly known as a CT scan, combines multiple X-ray images with the aid of a computer to produce cross-sectional views of the body. Cardiac CT is a heart-imaging test that uses CT technology with or without intravenous (IV) contrast (dye) to visualize the heart anatomy, coronary circulation, and great vessels (which includes the aorta, pulmonary veins, and arteries).
There are several types of CT scans used in the diagnosis of heart disease, including:
Calcium-Score Screening Heart Scan
The calcium-score screening heart scan is a test used to detect calcium deposits found in atherosclerotic plaque in the coronary arteries. State-of-the-art computerized tomography methods, such as this one, are the most effective way to detect early coronary calcification from atherosclerosis (hardening of the arteries), before symptoms develop. The amount of coronary calcium has been recognized as a powerful independent predictor of future heart problems and is useful in making lifestyle changes and guiding preventive care to reduce their risk.
Your doctor uses the calcium-score screening heart scan to evaluate risk for future coronary artery disease. If calcium is present, the computer will create a calcium "score" that estimates the extent of coronary artery disease based on the number and density of calcified coronary plaques in the coronary arteries.
Absence of calcium is considered a "negative" exam. However, since there are certain forms of coronary disease, such as "soft plaque" atherosclerosis, that escape detection during this CT scan, it is important to remember that a negative test indicates a low risk, but does not absolutely exclude the possibility of a future cardiac event, such as a heart attack.
The calcium-score screening heart scan takes only a few minutes to perform and does not require injection of intravenous iodine.
Coronary CT Angiography (CTA)
Coronary computed tomography angiography (CTA) is a noninvasive heart imaging test currently undergoing rapid development and advancement. High-resolution, 3-dimensional pictures of the moving heart and great vessels are produced during a coronary CTA to determine if either fatty or calcium deposits (plaques) have built up in the coronary arteries.
Before the test, an iodine-containing contrast dye is injected into an IV in the patient's arm to improve the quality of the images. A medication that slows or stabilizes the patient's heart rate may also be given through the IV to improve the imaging results.
During the test, which usually takes about 10 minutes, X-rays pass through the body and are picked up by special detectors in the scanner. The newer scanners produce clearer final images with less exposure to radiation than the older models. These new technologies are often referred to as "multidetector" or "multislice" CT scanning.
Another new technology, known as dual-source CT, uses two sources and two detectors at the same time. This technology provides full cardiac detail with about 50% less radiation exposure than traditional CT.
Since it's noninvasive, a coronary CTA can be performed much faster than a cardiac catheterization (also called a "cardiac cath" or coronary angiogram), with potentially less risk and discomfort to the patient, as well as less recovery time.
Although coronary CTA exams are growing in use, coronary angiograms remain the "gold standard" for detecting coronary artery stenosis, which is a significant narrowing of an artery that could require catheter-based intervention (such as stenting) or surgery (such as bypassing) to treat the narrowed area. However, coronary CTA has consistently shown the ability to rule out significant narrowing of the major coronary arteries. This new technology also can noninvasively detect "soft plaque," or fatty matter, in the coronary artery walls that has not yet hardened but that may lead to future problems without lifestyle changes or medical treatment.
Coronary CTA is most useful to determine whether symptoms of chest pain may be caused by a coronary blockage, particularly in individuals that may be at risk, such as those with a family history of cardiac events, diabetes, high blood pressure, smokers, and/or those with elevated cholesterol. However, there is still much controversy as to when a coronary CTA should be used.
Total Body CT Scan (TBCT)
The total body CT scan, or TBCT, is a diagnostic technique that uses computed tomography to help identify potential problems or diseases before symptoms even appear.
The scan can detect aortic aneurysms and calcium deposits within plaque in the coronary arteries. However, the presence of calcium deposits in the coronary arteries does not necessarily mean that an artery is dangerously narrowed by disease or that a severe health threat exists. For example, calcium deposits are often found in older people as a result of their age. In addition, the CT scan cannot give a precise location of the diseased portion of the artery.
For some high-risk individuals, the proposed benefit of having a TBCT scan lies in the potential of early detection and treatment. But overall, its use for early detection of heart disease is very controversial.
In the Pipeline: PET/CT Heart Scans
PET scans are a form of nuclear medicine -- "nuclear" being the small dose of radioactive material you are injected with before the test (the radiation exposure is similar to that of a standard X-ray). As with CTA, PET involves a doughnut-like scanning device that takes the images.
There is a debate among cardiologists over the appropriateness of PET/CTA for heart diagnosis; more research is needed.
Are These Tests Covered by Insurance?
In many cases, the calcium-score screening heart scan, coronary CTA, and total body CT scan are NOT covered by most insurance companies or Medicare. These tests are not typically covered because they are considered screening exams. Therefore, you will likely be responsible for paying for all costs associated with the exam and may be required to pay these fees at the time of the exam. Please check with your insurance provider to determine the services that are covered and ask your health care provider about the terms of payment.
How Should I Prepare for the CT Scan?
Please note it's important to inquire about the expertise and training of the doctors who will be performing and interpreting the results of these CT scans, as the number of adequately trained doctors is limited.
Your health care provider will provide specific instructions to prepare for the test. You may need to have an IV, blood work, or other lab tests before the CT scan, depending on the type of scan that is ordered.
Caffeine will interfere with the results of your test. Do not drink or eat caffeine products (soft drinks, energy drinks, chocolate products, coffee, or tea) for 24 hours before the test. Lastly, since many over-the-counter medications contain caffeine (such as diet pills, No Doz, Excedrin, and Anacin), do not take any over-the-counter medication that contains caffeine for 24 hours before the test. Ask your physician, pharmacist or nurse if you have questions about other medications that may contain caffeine.
You may be required to only drink clear liquids after midnight the night before the test. Clear liquids include clear broth, plain gelatin, and ginger ale.
CT scanners use X-rays. For your safety, the amount of radiation exposure is kept to a minimum. But, because X-rays can harm a developing fetus, this procedure is not recommended if you are pregnant. Tell your technologist and your doctor if you are:
- Undergoing radiation therapy
What Can I Expect During the CT Scan?
During the CT Scan:
- You will change into a hospital gown. The nurse may record your height, weight, and blood pressure.
- You will lie on a special scanning table.
- An IV may be inserted into a vein in your arm, depending on the type of test that is being performed.
- During the scan, you will feel the table move inside a doughnut-shaped scanner. The high-speed CT scan captures multiple images, synchronized with your heartbeat.
- A sophisticated computer program, guided by the cardiovascular radiologist, analyzes the images.
What Happens After the CT Scan?
You may continue all normal activities and eat as usual after a CT scan.
Your results will be examined and reviewed by a team of cardiovascular specialists, including a cardiovascular imaging specialist from radiology or cardiology. The team will evaluate the test results, along with other risk factor measurements (risk factor evaluation, blood pressure, lipid analysis), to determine your risk for future coronary artery disease and will make recommendations regarding your lifestyle, medications, or additional cardiac testing.
You and your primary care doctor will receive the full report outlining your risk assessment and follow-up recommendations. Ask your doctor if you have any questions about the CT test.