A CT scan (“cat scan”) is an x-ray technique that uses a computer to create cross-sectional (or slice-like) pictures of the heart.
How It Works
The CT scanner is a large x-ray machine that has a short, open-ended tube in the middle (like a very short tunnel). The patient lies on a scanning table, which slides through the middle of the CT scanner. The CT scanner takes many x-ray pictures of the heart, one thin slice at a time. A computer then puts the sliced images together to make a detailed picture. In some cases, contrast dye is injected into the bloodstream to help doctors get a clearer picture.
What To Expect
If a contrast dye is not going to be used during the CT scan, the patient should not eat for 2 hours before the test. If a contrast dye is going to be used, the patient should not eat for 4 hours before the test. The contrast dye causes a hot flushing feeling in some patients.
The patient is asked to wear a hospital gown. He or she will lie down on a table, which will be slowly moved through the hollow center of the CT scanner. The patient is then asked to lie still and hold his or her breath briefly as each picture is taken.
After the test, the patient may resume normal activities. An adverse reaction to the contrast dye is possible, but it is very rare. If this happens, the patient receives further treatment at the hospital. CT scanning is safe. Although radiation exposure is small, pregnant women should not have CT scans.
A CT scan does not get a moving picture of the heart. CT scans are used to see if part of the heart has calcified. This patient has had a heart attack that scarred the left ventricle. The red arrows point to the scarred part of the heart that has since formed a thick, calcified wall at the tip of the left ventricle.
A CT scan captures many images, which your doctor can look at one by one. New computer technology now lets technicians stack the images on top of each other to get a 3-D image that can be rotated and viewed from any angle. The red arrows in the images above show a large aneurysm on the abdominal aorta as seen from the front (left) and the side (right).
Coronary Calcium Detection Using CT Scan
CT can detect calcium buildup in the coronary arteries. The amount of calcium in the coronary arteries indicates the risk for coronary artery disease. CT provides a noninvasive way to detect blocked arteries. This method of detecting coronary artery disease (CAD) may help physicians and patients develop a prevention and/or treatment plan.
Who should get the procedure?
Coronary Calcium Detection CT Scan is indicated for men 40 to 65 years old and women 45 to 70 years old without symptoms of heart disease who have at least one of the traditional risk factors for coronary artery disease. Risk factors include family history of coronary artery disease, hypertension, smoking, borderline high cholesterol, and diabetes. After the scan is completed, it is evaluated by a cardiologist and a radiologist, who determine the Coronary Artery Calcium (CAC) score. A risk assessment report provides the patient with test scores, risk stratification tables, a summary of findings, and educational materials. The cardiologist then works with the patient to establish a plan to reduce the risk of CAD.
Does calcium in coronary arteries indicate CAD?
No. Calcium naturally occurs at higher levels in individuals as they age. Patients should consult their cardiologist to follow-up with testing (treadmill exercise, cardiac ultrasound, or heart catheterization) to determine whether or not coronary artery disease exists.
Is there anyone for whom this is not advised?
Patients who have already been diagnosed with coronary artery disease must be referred by a physician. Known cardiac disease includes previous myocardial infarction (MI), bypass surgery, or intervention (PTCA/Stent/Atherectomy).
Multi-Detector Computed Tomography (MDCT)
Ordinary CT scanning can take anywhere from 1 to 10 seconds per slice (or picture), but the faster MDCT scanners have many rows of detectors (up to 64!) that can take multiple x-rays of the heart at the same time. These scanners can also obtain pictures of the entire heart in about 1 ten-second breath hold.
The new MDCT scanners are used routinely to measure the amount of calcium in the coronary arteries—similar to EBCT—but are also now able to take images of the coronary arteries that are nearly comparable to those taken during a cardiac catheterization. For many patients, an MDCT scan of the heart is enough for doctors to determine whether coronary artery disease is present, and patients may not need cardiac catheterization.
The two MDCT views above show that the left coronary artery (red arrows) and its side branches are normal.
This 3D MDCT view is looking down on top of the left ventricle. It shows a normal coronary artery (black arrow) and side branches.
Texas Heart Institute www.texasheartinstitute.com/HIC/Topics/Diag/dicat.cfm