Two types of CT heart scans are in general use, the older and simpler Coronary Artery Calcium Score and the newer CT Coronary Angiogram.
This type of CT scan is quicker and cheaper than its counterpart. There is less radiation exposure and no intravenous contrast dye is necessary.
This simplicity, however, results in less diagnostic information. Such a scan only detects calcification within the coronary arteries and quanitates the amount according to a standard algorithm, the Agatston score.
Atherosclerosis ("hardening of the arteries") in the body follows a typical process of lesion maturation with calcification as its final expression. It is this calcium in arterial lesions which the test detects and quantitates. All patients with calcium in their coronary arteries also have less mature or "soft" plaque which is not calcified and hence not detected with this more limited exam.
This newer type of CT heart scan, from the same patient imaged above, has been made possible by recent improvements in the temporal and spatial resolution of the latest generation of CT scanners. These scans actually image the coronary arteries and all types of plaque (soft, fibrotic, and calcific) that may be present.
Although narrowing or "stenosis" of the arteries can be identified and assessed quantitatively, this test is not yet equivalent to a cardiac catheterization and traditional angiogram which still offers higher spatial and temporal resolution. The CT angiogram, however, is superior to catheterization in its ability to demonstrate the full burden of atherosclerotic plaque in the arteries, including plaque which does not encroach upon the lumen of the vessel.
It is this ability of the CT Coronary Angiogram to detect atherosclerosis in its earliest stage--a soft plaque with minimal narrowing of the artery--that sets it apart from all other diagnostic tests, including traditional angiography. It does, however, require intravenous contrast dye and greater X-ray exposure than the simpler calcium score.