Discrepancy of calcium detection between gray scale intravascular ultrasound and spectral analysis of radiofrequency data

BackgroundWe evaluated discrepancy of calcium detection between gray scale intravascular ultrasound (IVUS) and virtual histology (VH)-IVUS and the association between coronary calcium and plaque composition.MethodsStudy population consisted of 162 consecutive patients who underwent percutaneous coronary intervention with VH-IVUS study. Subjects were divided into 3 groups based on gray scale IVUS findings; No calcification group (n = 50), spotty group (n = 56) who had a lesion containing only small calcium deposits within an arc < 90° and diffuse group (n = 56) who had a diffuse calcified lesion with an arc ≥ 90° in ≥ 1 cross-sectional image of the lesion.ResultsNo calcification group was younger than spotty and diffuse groups (54.4 ± 13.0 years vs. 61.1 ± 10.7 years and 64.2 ± 9.9 years, p = 0.011 and p < 0.001, respectively). No calcification group had some degree of dense calcium (5. 7 ± 6.9 mm3) by VH-IVUS analysis. Furthermore, calcified volume by VH-IVUS in no calcification group was similar to those in spotty group (5.7 ± 6.9 mm3 vs. 5.4 ± 4.4 mm3). Dense calcium volume was correlated directly with plaque volume (r = 0.65, p < 0.001), fibrous volume (r = 0.54, p < 0.001), fibro-fatty volume (r = 0.29, p < 0.001) and lipid core volume (r = 0.77, p < 0.001). In multiple regression analysis, lipid core volume (β = 0.287, 95% confidence interval (CI) 0.187-0.388, p < 0.001) was an independent predictor of dense calcium volume.ConclusionsThis study showed that coronary calcium can be present even if invisible in gray scale IVUS and associated with lipid core volume, which is a characteristic of plaque vulnerability.