According to a Cleveland Clinic study published in JAMA:
"CT coronary angiography performed with 16-row scanners is limited by a high number of nonevaluable cases and a high false-positive rate. Thus, its routine implementation in clinical practice is not justified. "
Sensitivity for detecting more than 50% luminal stenoses was 89%; specificity, 65%; positive predictive value, 13%; and negative predictive value, 99%.
According to investigators:
"If you have a positive result on a cardiac CT, the diagnosis could be in doubt, but if the result is negative, you virtually exclude the possibility of having a blockage."
The study was done with the first generation of cardiac CT. Many centers now use more advanced scanners which have 64 detectors instead of just 16.
Accuracy of 16-Row Multidetector Computed Tomography for the Assessment of Coronary Artery Stenosis. JAMA. 2006;296:403-411.
Heart Scan Study. NBC4.TV.
Image sources: Wikipedia