Imaging description

Coronary artery calcification is routinely encountered at coronary CT angiography. In some cases, large amounts of calcium may obscure the lumen of the vessel, limiting the accuracy of evaluation. The true severity of coronary artery stenosis in the presence of large plaques is frequently overestimated by CT secondary to blooming artifact and beam hardening, leading to false positive diagnoses. Use of a wide window and level at the workstation, sharp reconstruction kernels, and iterative reconstruction techniques are recommended to limit these artifacts as much as possible (Figures 29.1 and 29.2).

Importance

Heavy coronary calcification limits the accuracy of coronary CT, sometimes leading to overcalling of severity of disease. This may lead to unnecessary testing such as cardiac catheterization or stress testing, and the risks and expenses associated with those procedures.

Typical clinical scenario

Coronary artery calcification is very common, particularly in older patients with risk factors for coronary artery disease. Several studies have shown an increase in false positive coronary CT angiography (CCTA) results in the setting of extensive coronary calcium. In a meta-analysis of 19 published studies, specificity of coronary CT compared to the gold standard of catheter angiography was reduced to 42% in patients with calcium scores ≥ 400, as compared to 90% for patients with scores <10 and 88.5% for those with scores <100. In another study comparing calcified plaques evaluated by coronary CT and catheter angiography, concordance between the two modalities was reduced from 95% and 91% for small(occupying less than 50% of vessel diameter on CT) and moderate-(occupying 50–90% vessel diameter) sized plaques to 67% for large plaques (occupying more than 90% of vessel diameter). Despite the reduction in specificity, however, sensitivity of CCTA for detection of significant stenosis remains high (> 95%) in patients with extensive calcium.