A cardiac computed tomography (CT) scan is a non-invasive medical imaging procedure that uses X-rays and computer processing to create detailed, cross-sectional pictures of the heart and its surrounding structures. This test is sometimes referred to as a “CAT scan” of the heart. Its purpose is to provide physicians with a clear, three-dimensional view of the heart without the need for surgery or traditional catheterization procedures.
How the Scan Creates Detailed Images
The CT machine is a large, ring-shaped device containing an X-ray tube that rotates rapidly around the patient while they lie on a moving table. As the tube spins, it captures thousands of X-ray projections from multiple angles. These images are fed into computers that reconstruct them into cross-sectional “slices” of the heart, a technique known as tomography.
This process allows for greater detail of soft tissues and blood vessels compared to a standard chest X-ray, which provides only a flat, two-dimensional image. Because the heart is constantly moving, image clarity is maintained through a technique called electrocardiogram (ECG) gating. ECG leads are placed on the patient’s chest to monitor the heart’s electrical activity.
The scanner synchronizes the X-ray exposure with the patient’s heart rhythm, often taking images during the brief period of least motion, typically the resting phase (diastole). This synchronization effectively freezes the heart’s movement, allowing the computer to stitch together high-resolution images of the coronary arteries. Modern multi-detector CT scanners can perform this rapid data acquisition, sometimes capturing the entire heart in under a second.
What the Scan Reveals About Your Heart
A cardiac CT scan provides specific information about the health and structure of the heart and its vessels, serving as a diagnostic tool for several conditions. The most common application is Coronary CT Angiography (CCTA), which requires an iodine-based contrast dye to visualize the coronary arteries. CCTA detects and quantifies fatty deposits, or plaque, within the artery walls, which can lead to narrowing and blockages.
Another use is a Coronary Artery Calcium (CAC) scoring scan, performed without contrast dye. This scan measures the amount of calcified plaque in the coronary arteries, providing a score that helps assess the future risk of a heart attack. A higher calcium score indicates a greater burden of atherosclerosis and increased risk.
Beyond the coronary arteries, the scan assesses the heart’s overall structure, including the heart muscle, valves, and great vessels like the aorta. It can detect structural abnormalities, evaluate bypass grafts, and provide precise measurements for planning complex procedures such as transcatheter valve replacement. This anatomical mapping assists physicians in understanding the extent of heart disease and planning treatment strategies.
Patient Experience During the CT
Preparing for a cardiac CT involves steps to ensure clear images. Patients are usually asked to fast for a few hours before the scan and may be advised to avoid caffeine, as these measures help keep the heart rate low and steady. Upon arrival, a technologist places ECG leads on the chest to monitor the heart rhythm, which is necessary for the gating process.
If CCTA is performed, an intravenous (IV) line is inserted, typically in the arm, for the injection of the iodine-based contrast dye. When administered, patients commonly experience a temporary warm or flushing sensation across the body, and sometimes a temporary metallic taste in the mouth. These sensations pass within moments and are considered normal.
The patient lies on a narrow table that slides into the center of the CT ring. The technologist communicates with the patient through an intercom system from an adjacent room. During the brief scanning period, the patient is asked to hold their breath for about 10 to 20 seconds to prevent motion from blurring the images. The entire process, from preparation to the end of the scan, typically takes less than 30 minutes.
Addressing Safety and Side Effects
The primary safety consideration is exposure to ionizing radiation, as the scan uses X-rays to create images. Modern CT scanners and sophisticated imaging protocols, such as prospective gating and dose modulation, significantly reduce the radiation dose. The physician weighs this minimal exposure against the benefit of obtaining diagnostic information.
For scans using contrast dye, such as CCTA, the main concern is the potential for an adverse reaction to the iodine-based agent. While rare, reactions can range from mild effects like hives or nausea to a more serious allergic response. Staff are trained to manage these events and will ask about previous allergies before the procedure.
The contrast dye is processed and eliminated by the kidneys, which introduces a risk of temporary kidney damage, particularly in patients with pre-existing kidney issues or diabetes. Blood work is performed before the test to assess kidney function, and precautions, such as increased hydration, are taken for patients at higher risk. The procedure is generally avoided during pregnancy due to the risk of radiation exposure to the fetus.