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Does slice thickness affect diagnostic performance of 64-slice CT coronary angiography in stable and unstable angina patients with a positive calcium score?

Background: Coronary calcification can lead to over-estimation of the degree of coronary stenosis. Purpose: To evaluate whether thinner reconstruction thickness improves the diagnostic performance of 64-slice CT coronary angiography (CTCA) in angina patients with a positive calcium score. Material and Methods: We selected 20 scans from a clinical study comparing CTCA to conventional coronary angiography (CCA) in stable and unstable angina patients based on a low number of motion artifacts and a positive calcium score. All images were acquired at 64×0.625 mm and each CTCA scan was reconstructed at slice thickness/increment 0.67 mm/0.33 mm, 0.9 mm/0.45 mm, and 1.4 mm/0.7 mm. Two reviewers blinded for CCA results independently evaluated the scans for the presence of significant coronary artery disease (CAD) in three randomly composed series, with ≥2 weeks in between series. The diagnostic performance of CTCA was compared for the different slice thicknesses using a pooled analysis of both reviewers. Significant CAD was defined as >50% diameter narrowing on quantitative CCA. Image noise (standard deviation of CT numbers) was measured in all scans. Inter-observer variability was assessed with kappa. Results: Significant CAD was present in 8% of 304 available segments. Median total Agatston calcium score was 181.8 (interquartile range 34.9–815.6). Sensitivity at 0.67 mm, 0.9 mm, and 1.4 mm slice thickness was 70% (95% confidence interval 57–83%), 74% (62–86%), and 70% (57–83%), respectively. Specificity was 85% (82–88%), 84% (81–87%), and 84% (81–87%), respectively. The positive predictive value was 30 (21–38%), 29 (21–37%), and 28 (20–36%), respectively. The negative predictive value was 97% (95–98%), 97% (96–99%), and 97% (96–99%), respectively. Kappa for inter-observer agreement was 0.56, 0.58, and 0.59. Noise decreased from 32.9 HU at 0.67 mm, to 23.2 HU at 1.4 mm (P<0.001). Conclusion: Diagnostic performance of CTCA in angina patients with a positive calcium score was not markedly affected by modest variations in reconstruction slice thickness.