Before interpreting the scan, assess the image quality. Walk through the 5 C’s:
Optimal timing is when contrast maximally opacifies the left ventricle and coronary arteries. If acquired too early, the right-sided chambers and superior vena cava will be brighter than the left.
The heart should sit in the middle of the image and fill most of the 512 × 512 display. Keep the FOV < 20 cm — anything bigger is too zoomed out to grade lesions.
Motion artifact appears when the heart rate is too elevated (ideal HR < 70 bpm). The RCA is the most susceptible because of its high intrinsic velocity — it loses its normal round shape and appears crescent-shaped. If the RCA is clean, the rest of the scan is almost certainly clean too.
The scan must reach above and below the coronaries. CT is acquired at end-inspiration (diaphragm and base of the heart pushed down), so coverage needs to capture the very bottom of the heart — but no further, to avoid unnecessary radiation.
Columnation artifact appears as misaligned bands. These can often be extinguished by adjusting the ECG gating to line the images up better — no rescan needed.