Cardiac CT

This is a procedure performed using a multi-slice CT. The current multi-slice CT that exquisitely produces coronary artery images, is a 64-slice CT scanner from Siemens.

This scanner has a special x-ray tube and rotation speed, capable of performing 3 rotations in a second. In each rotation, 64-slices are produced, giving us approximately 194 slices per second. This is the fastest scanner in the industry, currently.

Speed is extremely important in our ability to "freeze" the heart. Since the heart is a rapidly moving structure, the only way to image structures within it, is if we can scan as fast as the heart beats or close enough.

All scans are gated to the ECG trace. This allows us to position our data acquisition accurately in specific phases.

Using this modality we can perform the following procedures as part of a cardiac CT examination.

1.Calcium Scoring
2.Coronary artery imaging
3.Functional assessment

Calcium Scoring

Calcium scoring is a technique where the extent of calcification in the coronary arteries is measured and scored. It has been around for many years and was initially performed using EBCT (electron beam CT), but is now increasingly performed using multi-slice CT. As a rule, the faster the scanner, the more accurate is the calcium scoring.

There is a direct correlation between the extent of calcium in the coronary arteries and the risk of a future cardiac event. For example, a calcium score of more than 400 is considered severe and it would be necessary to take steps to prevent further advancement of atherosclerosis and plaque formation. The higher the calcium score, more likely is there a chance of severe stenosis as well.

A calcium score of 0 does not rule of soft plaques, but statistically rules out significant coronary artery disease. Though the calcium score does not show soft plaques (which however are best seen on a CT angiogram), the higher the calcium score, the more is it likely that there are soft plaques as well. Rupture of a soft plaque is the commonest cause of an acute coronary syndrome (i.e. a heart attack).

Calcium scoring is offered as a separate stand-alone test, but more and more, since we are reliably able to assess the coronary arteries themselves, it is being performed an an initial part of the entire cardiac CT examination.