Coronary CT calcium scan

Coronary CT Calcium Scan: An Insight into Heart Health

A coronary CT calcium scan is a specialized computed tomography (CT) imaging procedure primarily aimed at evaluating the extent of coronary artery disease. By specifically identifying calcium deposits within the coronary arteries, the scan aids in determining arterial blockages which can escalate the threat of a heart attack.

Coronary CT calcium scan showcasing calcium deposits in coronary arteries.

Principle and Indication

The central principle of the coronary CT calcium scan is to detect and quantify calcium deposits in the coronary arteries. The presence of these deposits can lead to arterial narrowing, thereby posing a potential risk for cardiac events.

Scoring and Its Significance

The outcome of the scan can be presented in terms of:

• Agatston Score
• Coronary Artery Calcium (CAC) Score

The CAC score, in particular, stands out as a crucial marker, serving multiple functions:

• Independent predictor of impending cardiac events
• Indicative of cardiac mortality risk
• Suggestive of all-cause mortality risk

In addition, the CAC score complements other cardiovascular risk markers, offering a more comprehensive prognostic picture.

Indications

The well-established indications for the use of the CAC score include stratification of global cardiovascular risk for asymptomatic patients: intermediate risk based on the Framingham risk score (class I); low risk based on a family history of early CAD (class IIa); and low-risk patients with diabetes (class IIa).

In symptomatic patients, the pre-test probability should always be given weight in the interpretation of the CAC score as a filter or tool to indicate the best method to facilitate the diagnosis. Therefore, the use of the CAC score alone is limited in symptomatic patients.

In patients with diabetes, the CAC score helps identify the individuals most at risk, who could benefit from screening for silent ischemia and from more aggressive clinical treatment.

However, coronary CT angiography (CTA) is superior to coronary CT calcium scanning in determining the risk of Major Adverse Cardiac Events (MACE).

There is potential to measure CAC on chest radiographs taken for other indications, possibly allowing some primary screening for coronary artery disease without adding to radiation exposure and with minimal marginal cost.

Agatston score

Lesion specific calcium score

The Agatston score, named after its developer Arthur Agatston, is a measure of calcium on a coronary CT calcium scan. The original work was based on electron beam computed tomography (also known as ultrafast CT or EBCT). The score is calculated using a weighted value assigned to the highest density of calcification in a given coronary artery. The density is measured in Hounsfield units, and score of 1 for 130–199 HU, 2 for 200–299 HU, 3 for 300–399 HU, and 4 for 400 HU and greater. This weighted score is then multiplied by the area (in square millimeters) of the coronary calcification. For example, a "speck" of coronary calcification in the left anterior descending artery measures 4 square millimeters and has a peak density of 270 HU. The score is therefore 8 (4 square millimeters × weighted score of 2). The tomographic slices of the heart are 3 millimeters thick and average about 50–60 slices from the coronary artery ostia to the inferior wall of the heart. The calcium score of every calcification in each coronary artery for all of the tomographic slices is then summed up to give the total coronary artery calcium score (CAC score).

Several variations of the Agatston score have been described, including mass-based calcium scoring, volume-based calcium scoring, or lesion-specific calcium-scoring have been developed.

Lesion-specific calcium score

A lesion-specific calcium score has been developed. Each individual calcified lesion is characterized and measured using parameters including the width, length, density, and distance from the entrance of the major coronary arteries. Research has shown that the lesion-specific calcium scoring method is superior to the traditional Agatston score for the prediction of significant blockages in the heart. A patent application protecting this method has been filed.

Radiation dosage

On average a single scan will expose a patient to about 2.3 millisieverts of radiation, equivalent to 23 chest x-rays (front and side views). That average covers a wide range of doses depending on equipment type and scanning protocol. Using modern equipment and protocols a 1 millisievert exposure is possible. Because the exact radiation exposure for a specific patient depends on the equipment type in use, the patients build and a variety of scanning options (such as retrospective vs prospective gating) it is difficult for a patient to know what their radiation exposure will be.

A 2009 study indicated that for every 100,000 people screened with CAC testing every 5 years between ages 45 to 75 years (men) or 55 to 75 years (women), there would be 42 (men) or 62 (women) additional radiation induced cancer cases.

Methodology

Typically, the coronary CT calcium scan is conducted without the use of radiocontrast. However, in some cases, it might be derived from contrast-enhanced images, as seen in coronary CT angiography.

Benefits of the Scan

• Early Detection: The scan can detect coronary artery disease even before symptoms start manifesting.
• Risk Assessment: It aids in gauging the risk level of severe cardiac events.
• Treatment Guidance: Depending on the severity, doctors can tailor interventions and treatment plans.

See Also

• Computed tomography (CT)
• Coronary arteries
• Cardiovascular diseases

External links

• Medline article on heart scans
• WebMD article on heart scans
• RadiologyInfo.org article on heart scans

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