Feasibility and Accuracy of Aortic Valve Calcium Quantification on Computed Tomographic Angiography in Aortic Stenosis.

Abstract

Traditionally, quantification of aortic valve calcium (AVC) has been performed with noncontrast computed tomography (NCCT) using the Agatston method. This study sought to derive and validate a systematic method enabling AVC quantification using computed tomographic angiography (CTA) in patients with aortic stenosis (AS). The study included 134 consecutive patients with AS who underwent both NCCT and CTA and were subdivided into derivation (n = 71) and validation cohorts (n = 63). AVC on NCCT (AVC_NCCT) was quantified using the Agatston method using the software developed for semiautomatic assessment of coronary calcium. On CTA, the mean contrast attenuation of the aorta in Hounsfield units (Aorta_HU) and SD was measured in the region of interest at the level of the sinotubular junction. Using an adjusted calcium detection threshold of Aorta_HU + 2 SD, we calculated AVC on CTA (AVC_CTA) using the same software without modifying other variables. Correlation between AVC_NCCT and AVC_CTA in the derivation cohort was excellent (r = 0.9679; P < .001). We used a linear regression model to derive a formula for predicting AVC_CTA that enabled conversion of AVC_CTA to AVC_Derived (AVC_Derived = 1.821 × AVC_CTA). Applying this formula in validation cohort, we calculated AVC_Derived, which showed excellent agreement with AVC_NCCT (intraclass correlation coefficient, 0.9648; 95% confidence interval, 0.9427-0.9782). Excellent correlation was also found between categorized AVC_NCCT and AVC_Derived scores (κ = 0.9044; 95% confidence interval, 0.7989-1.0000), with 95.24% (60 of 63) of scores falling within the same severity category. AVC quantification on CTA is feasible with high accuracy and reliability and shows excellent agreement with the standard AVC_NCCT score. With the systematic approach using "dynamic thresholds" being largely independent of the scan acquisition protocol, AVC_Derived can potentially replace AVC_NCCT, eliminating the need for separate NCCT acquisition solely for AVC quantification.