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CT calcium scoring

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What is CT calcium scoring?

Computed tomography (CT) calcium scoring is a non-invasive method to detect the presence of calcium in the blood vessels that supply your heart (the coronary arteries). This is achieved through CT. Results are obtained rapidly – the CT scan takes about 20 seconds. However, extra time is needed to evaluate the results.


What does CT calcium scoring detect?

CT calcium scoring uses differences in densities to distinguish between calcium and other components of the heart/chest. Most CT scanners have software packages to facilitate automatic detection of calcium according to preset definitions. Figure 1 shows detected calcium in bone (pink) and in coronary arteries (red).

Figure 1Figure 1: Quantification of calcium score – calcium in bones is highlighted in pink, and calcium in coronary arteries in red.


Results of CT calcium scoring

The calcium score derived is a summation of all calcified lesions in the coronary arteries. The reported score is your individual patient score, with a reference range appropriate to your age and sex. This is because the population distribution of coronary calcium is not only age and sex dependent, but may also vary across ethnic groups. Table 1 shows the association between the CAC score and relative risk of cardiovascular events (e.g. heart attack).


Table 1:
Risk of cardiovascular event with increasing coronary artery calcification

ScoreDescriptionRelative risk of cardiovascular events
0No coronary calcification
1–99Mild coronary calcification1.9 (95% confidence interval 1.3–2.8)
100–399Moderate calcification4.3 (3.1–6.1)
400–999Severe calcification7.2 (5.2–9.9)
≥1000Extensive calcification10.8 (4.2–27.7)


Procedure

  • An ECG monitor may be used to monitor your heart’s electrical activity;
  • Once correctly positioned, the CT scan will be performed. This usually takes  about 20 seconds. During this time, x-rays are used to create an image of the heart, including the coronary arteries;
  • You may be asked to hold your breath for short periods while images are recorded;
  • Some machines require a lower heart rate to produce a better picture.  If this is the case and your heart rate is higher than desired, medication is available to slow your heart rate down.


Side effects

This procedure is usually not associated with any side effects. It is a painless procedure and there are not usually any complications. As the procedure uses x-rays, there is some exposure to radiation; however, this is minimal. In any case, pregnant females should notify their health professional before exposure. After the procedure is done, patients normally return home on the same day. You should be able to drive home safely if you are feeling well after the procedure.


Interpretation and clinical correlation of results

Scientific studies have shown that the presence of CAC increases the risk of a cardiovascular event (e.g. heart attack) by a factor of 4 over the next 3–5 years. Higher CAC scores are associated with higher rates of events.


Conditions associated with coronary artery calcification

There are several cardiovascular diseases associated with calcification of the coronary arteries, these include:


Clinical usefulness of CT calcium scoring

CAC scores are thought to be particularly useful in reclassifying patients previously classified as intermediate risk on conventional risk scores. The new classification would see these patients divided into intermediate-high risk and take medical therapy, or into lower risk groups in which behavioural management is appropriate. While this influences medical management, there are still several issues that need to be resolved. Currently, screening patients who do not have symptoms has not been justified.


Summary

Computed tomography (CT) calcium scoring is a safe, rapid and non-invasive method of detecting calcium in the coronary arteries. It is performed using a CT scanning machine.  Scanning time is often about 20 seconds, and radiation exposure is low. Clinically, CT scoring can be used as a predictor of future cardiovascular events. It can be used to reclassify patients previously assigned to intermediate risk by conventional risk scores to receive more appropriate management.


Article kindly written by:

Dr Clara K Chow MBBS, FRACP, PhD
Senior Research Fellow; Population Health Research Institute; Hamilton General Hospital, Canada
Editorial Advisory Board Member: Virtual Cardiac Centre.

References

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Dates

Posted On: 17 November, 2008
Modified On: 21 November, 2018

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