A computed tomography (CT) scan is a powerful, non-invasive imaging tool that provides a detailed view of the body’s internal structures. For individuals concerned about blocked or “clogged” arteries, a CT scan is a highly effective method for diagnosing atherosclerosis, the buildup of plaque within the artery walls. This technology allows physicians to visualize the coronary arteries, which supply blood to the heart muscle, and assess the extent of plaque accumulation. CT scans offer a clear picture of arterial health that helps guide medical decisions.
Specific CT Methods for Assessing Arteries
Physicians use two distinct cardiac CT methods to assess for clogged arteries and evaluate coronary artery disease.
Coronary Artery Calcium (CAC) Scoring
Coronary Artery Calcium (CAC) scoring is a quick scan that does not require contrast material. This method measures the quantity of hardened, calcified plaque present in the arteries, which indicates long-term plaque burden and future heart attack risk. CAC scoring is typically used as a screening tool for individuals who are not experiencing symptoms but have intermediate risk factors for heart disease.
Coronary CT Angiography (CTA)
Coronary CT Angiography (CTA) provides a detailed, three-dimensional view of the coronary artery lumen, the inner channel where blood flows. CTA uses an intravenous contrast dye to highlight the arteries and is the preferred test for patients experiencing symptoms like chest pain. CTA detects both calcified and non-calcified (“soft”) plaque, identifying the location and severity of any narrowing or blockage, known as stenosis. While CAC scoring predicts future risk, CTA is a diagnostic tool used to determine if current blockages are restricting blood flow.
The Visualization Process: Calcium Scoring and Contrast Dye
The two CT methods rely on different physical properties to visualize arterial plaque and narrowing.
Calcium Scoring Visualization
During a CAC scoring scan, the CT machine detects high-density material within the coronary arteries because calcium deposits absorb more X-ray radiation than surrounding soft tissue. The resulting images are processed to calculate an Agatston score, which quantifies the area and density of these calcium deposits. This score provides an objective measurement of the total calcified plaque burden.
Contrast Dye Visualization
Coronary CT Angiography requires an iodine-based contrast agent injected into a vein. This dye travels through the bloodstream, temporarily filling the coronary arteries and making them opaque to the X-ray beam. The contrast allows the CT scanner to produce high-resolution images that clearly outline the inner walls of the artery. Plaque, whether hardened or soft, appears as an indentation in the smooth column of contrast, allowing physicians to measure the degree of arterial narrowing.
What to Expect During the Procedure
Preparation for a cardiac CT scan involves specific steps to ensure the best image quality. Patients are advised to fast for about four hours before the test and avoid caffeine or energy drinks for at least 12 hours, as these can increase the heart rate. For CTA, a blood test is often required beforehand to check kidney function, since the kidneys process the contrast dye. If the patient’s heart rate is too fast, a beta-blocker may be administered to slow the heart and reduce motion blur in the images.
During the procedure, the patient lies on a narrow table that slides into the large, donut-shaped CT scanner. Small electrode patches are placed on the chest to monitor the heart’s rhythm, which is necessary to time the X-ray exposures precisely. For a CTA, an intravenous line is started for the injection of the contrast agent. The scan itself is quick, and the patient is often asked to hold their breath briefly to prevent movement that could distort the images.
The entire process, from preparation to completion, typically takes less than an hour, and patients can usually resume normal activities immediately afterward. While the procedure is generally painless, the contrast dye injection can cause a brief warm sensation or a temporary metallic taste in the mouth. Although CT scans involve a small amount of X-ray radiation, the diagnostic benefits for assessing cardiac risk generally outweigh the minimal exposure.
Interpreting the Results and Next Steps
The results of a Coronary Artery Calcium scan are reported as an Agatston score. A score of zero indicates no calcified plaque and the lowest risk of a heart event. Scores are categorized to estimate risk:
- A score between 1 and 99 suggests a small amount of plaque and mildly increased risk.
- A score of 100 to 300 indicates moderate plaque and a relatively high risk over the next three to five years.
- A score over 300 signifies extensive disease and a significantly higher likelihood of a heart attack.
For a Coronary CT Angiography, the images determine the degree of stenosis, which is the percentage of the artery narrowed by plaque. Findings are categorized as non-obstructive (less than 50% narrowing), moderate (50% to 69% narrowing), or severe (70% or greater narrowing). The presence of non-obstructive plaque identifies the patient as having coronary artery disease, prompting a discussion about preventative therapies.
The results provide the foundation for a patient’s subsequent medical plan. A low CAC score or a CTA showing no significant stenosis may allow a physician to de-escalate treatment or focus on lifestyle changes. Conversely, a high score or a finding of moderate to severe stenosis leads to more aggressive management. This may include starting cholesterol-lowering medication, such as statins, or a referral to a cardiologist for further testing, like an invasive catheter angiography.