What are the limitations of coronary CT angiography?

1. image quality is inversely correlated to heart rate, requiring premedication with beta-blockers which some patients will not tolerate.
2. arrhythmias, ectomy, or ECG artifacts will result in degradation of image quality
   
3. extensive coronary calcification (patients with high likelihood of significant coronary calcification ie elderly, preexisting CAD) obscures the coronary artery lumen and may substantially limit analysis
4. obesity increases radiation scatter
   
5. radiation exposure is significant, 12 mSv
6. delineates anatomy only and can therefore only infer the impact of any given luminal narrowing
   

Source

Chinnaiyan, K. et al. "Cardiac CT in the Emergency Department" Cardiol Clin. 2009.