The estimation of coronary artery calcium thickness by computed tomography angiography based on optical coherence tomography measurements

Purpose Optical coherence tomography (OCT) is recommended to be the most appropriate modality in assessing calcium thickness, however, it has limitations associated with infrared attenuation. Although coronary computed tomography angiography (CCTA) detects calcification, it has low resolution and hence not recommended to measure the calcium size. The aim of this study was to devise a simple algorithm to estimate calcium thickness based on the CCTA image. Methods Consecutive patient who had CCTA for suspected coronary artery disease and subsequently went on to have OCT were included in the study. Calcium CT density was collected from CT profile curve. The method to estimate calcium thickness was devised from maximum CT density within the calcification and compared to the measured calcium thickness by OCT. The accuracy of this method was compared to full width at half maximum (FWHM) or inflection point (IP) method. Results A total of 68-patients (238-lesions) divided into derivation and validation dataset at 2:1 ratio (47 patients with 159 lesions and 21 with 79, respectively) were analyzed. Maximum Calcium density and measured calcium-border CT density had a good correlation with a linear equation of y = 0.58x + 201 (r = 0.892, 95% CI: 0.855–0.919, p < 0.001). The estimated calcium thickness derived from this equation showed strong agreement with measured calcium thickness in validation and derivation dataset (r2 = 0.481 and 0.527, 95% CI: 0.609–0.842 and 0.497–0.782, p < 0.001 in both, respectively), more accurate than the estimation by FWHM and IP method. Conclusion This novel method provided the estimation of calcium thickness more accurately than conventional methods.