Does a CT (Computed Tomography) coronary angiogram overestimate the degree of stenosis in the setting of extensive coronary artery calcification?

CT Coronary Angiography in Extensive Coronary Artery Calcification: Overestimation of Stenosis

Yes, CT coronary angiography (CCTA) does overestimate the degree of stenosis in the setting of extensive coronary artery calcification due to blooming artifacts that artificially enlarge calcified plaques. 1

Mechanism of Overestimation

The overestimation of coronary stenosis in heavily calcified vessels occurs primarily due to:

• Blooming artifacts: Calcium deposits appear artificially enlarged on CT images, making the vessel lumen appear narrower than it actually is 1
• Beam-hardening artifacts: X-ray beam attenuation by dense calcium affects image quality and measurement accuracy 2
• Limited spatial resolution: Even with modern CT technology, distinguishing between calcified plaque and contrast-enhanced lumen remains challenging in heavily calcified segments 1

Evidence of Overestimation

The European Society of Cardiology guidelines clearly state that "poor image quality, severe calcifications and non-expert interpretation may lead to overestimation of stenosis severity in coronary CTA" 1. This is supported by research evidence:

• In a study examining calcified coronary plaques, CCTA overestimated stenosis in:

  • 2 of 61 (3%) small calcified plaques
  • 2 of 22 (9%) moderate-sized calcified plaques
  • 14 of 43 (33%) large calcified plaques 2

• For large calcified plaques specifically, CCTA had:

  • 100% sensitivity (detects all true stenoses)
  • Only 44% specificity (many false positives)
  • 56% positive predictive value (overestimates stenosis severity)
  • 67% overall accuracy 2

• The ACR Appropriateness Criteria notes that CCTA has "relatively low specificity in high-risk patients due to impaired vessel visualization in the setting of heavy calcification" 1

Clinical Implications

This overestimation has important clinical consequences:

1. Increased false positives: Leading to unnecessary invasive coronary angiography procedures 1
2. Reduced diagnostic confidence: Radiologists report lower confidence when interpreting heavily calcified segments 3, 4
3. Impact on patient management: May lead to inappropriate revascularization decisions if relied upon without functional assessment 1

Solutions and Recommendations

When extensive coronary calcification is present:

1. Consider alternative or additional testing:

   • Functional testing (stress imaging) to assess hemodynamic significance 1
   • Fractional Flow Reserve (FFR) assessment for intermediate stenoses 5
   • Invasive coronary angiography as the gold standard for definitive assessment 1

2. Advanced CT techniques:

   • Subtraction CCTA can reduce false positives from 72% to 33% in well-aligned calcified segments, though misregistration artifacts remain common 4
   • Dual-energy or spectral CT may help distinguish between calcium and contrast material, though it may still overestimate high-grade stenosis 1

3. Interpretation considerations:

   • Recognize that stenoses estimated to be 50-90% by visual inspection on CCTA are not necessarily functionally significant 1
   • Consider CT-FFR for intermediate stenoses to determine hemodynamic significance 5

Conclusion

CCTA remains valuable for excluding coronary artery disease with high sensitivity, but in patients with extensive coronary calcification, stenosis severity is frequently overestimated. In these cases, additional functional assessment is necessary to determine the hemodynamic significance of stenoses before making revascularization decisions.