A Computed Tomography (CT) scan uses X-rays taken from multiple angles to create cross-sectional images, or “slices,” of the body’s internal structures. These images provide detailed views of organs, soft tissues, and blood vessels. While a standard CT scan is not typically used to diagnose artery blockages, specialized CT procedures are specifically designed for this purpose. These advanced techniques can visualize the coronary arteries to detect plaque and measure the extent of any narrowings.
The Role of Standard CT vs. Specialized Imaging
A conventional CT scan, such as one performed for a lung issue or abdominal pain, provides only a basic view of large vessels. This scan is generally not sensitive enough to detect early-stage plaque buildup or soft, non-calcified blockages within the coronary arteries. Atherosclerosis, the disease process causing blocked arteries, often begins with soft plaque that does not show up clearly. Therefore, specialized cardiac imaging modalities are required for diagnostic detail.
One specialized, non-contrast method is the Coronary Artery Calcium Scoring (CACS) scan. This fast, low-radiation CT scan specifically measures the amount of calcium present in the walls of the coronary arteries. Calcium deposits mark long-term plaque accumulation, and the resulting score indicates an individual’s risk for future cardiac events.
A limitation of the CACS scan is that it only identifies calcified, or “hard,” plaque and cannot visualize the non-calcified, “soft” plaque that may be present. This soft plaque is often considered more vulnerable to rupture, which can lead to a heart attack. Consequently, a CACS result of zero, while indicating a low burden of calcified plaque, does not guarantee the complete absence of disease. A more comprehensive test is needed to visualize both types of plaque and determine the degree of blockage.
Coronary CT Angiography (CCTA): How it Works
The most effective CT-based tool for examining blocked arteries is the Coronary CT Angiography (CCTA). This non-invasive procedure combines advanced CT technology with an intravenous (IV) contrast agent to create high-resolution, three-dimensional images of the coronary arteries. Unlike a traditional angiogram, CCTA does not require a catheter to be threaded through the body’s vessels.
Before the scan, a healthcare professional inserts an IV line, usually in the arm, through which an iodine-based contrast dye is injected. This dye flows rapidly through the bloodstream, temporarily filling the coronary arteries and making them appear bright white on the X-ray images. The contrast allows the radiologist to visualize the inner channel, or lumen, of the artery and detect narrowing caused by plaque buildup.
Because the heart is constantly moving, the CCTA procedure requires specialized technology to capture sharp, clear images. Electrodes are placed on the patient’s chest to monitor heart rhythm using an electrocardiogram (ECG). This process, known as cardiac gating, synchronizes the CT scanner’s X-ray pulses with moments in the heart’s cycle when it is least in motion, typically during diastole.
To ensure image clarity and reduce motion blurring, patients are often given a beta-blocker medication before the scan to slow their heart rate, ideally below 60 beats per minute. Patients are also asked to hold their breath for 10 to 15 seconds while the rapid scan is performed. This careful coordination of contrast injection, heart rate control, and scan timing allows CCTA to produce detailed, diagnostic images of the coronary tree.
Analyzing the Severity of Blockages
Once CCTA images are acquired, a radiologist or cardiologist analyzes the data to assess the health of the coronary arteries. The primary measurement is the degree of stenosis, which quantifies how much the artery’s diameter has been narrowed by plaque. This measurement is expressed as a percentage, comparing the tightest point of the blockage to a healthy, adjacent segment of the artery.
The report includes a detailed characterization of the detected plaque. Plaque is categorized as calcified (hard), non-calcified (soft), or mixed, based on its density and appearance on the scan. Distinguishing between these types is important: soft plaque is often more prone to causing sudden events, while calcified plaque indicates a stable, long-term disease burden. The presence of low-attenuation plaque, a type of soft plaque, indicates a potentially vulnerable lesion.
Physicians use standardized reporting classifications, such as the Coronary Artery Disease Reporting and Data System (CAD-RADS), to communicate the severity of the disease. Findings are grouped into categories ranging from mild (typically less than 30% narrowing), to moderate (30% to 50%), and severe (defined as greater than 75% narrowing). These findings guide subsequent treatment decisions, determining whether a patient requires medical management and lifestyle changes or needs a more invasive procedure, such as stenting or bypass surgery.