Vendor independent coronary calcium scoring improves individual risk assessment – the Multi-Ethnic Study of Atherosclerosis (MESA)
Authors: Dobrolinska M , Van Der Werf N R , Greuter M J W , Willemink M J , Fleischmann D , Bos D , Slart R H J A , Budoff M , Leiner T 
Published: October 2022

Abstract

Background
Coronary artery calcium (CAC) scoring improves event prediction of coronary heart disease (CHD) and can be used to guide initiation or deferral of statin therapy in asymptomatic individuals at low-to-intermediate risk. However, there is substantial variation of CAC scores acquired with different CT scanners. Therefore, CAC scoring discrepancies may lead to suboptimal patients' treatment and harmonization is needed.

Purpose
The aim of our study was twofold. Our first aim was to develop a calibration tool resulting in vendor neutral Agatston Score (vnAS). Second, we aimed to assess the effect of using this calibration tool in the existing Multi-Ethnic Study of Atherosclerosis (MESA) study cohort on both risk prediction of coronary heart disease (CHD), and initiation of statin therapy.

Methods
Two static anthropomorphic phantoms containing multiple CAC inserts were imaged on seven different CT systems and one EBT system. For each CT system, the vnAS calculator parameters were derived using regression analysis based on Agatston scores from EBT and CT. To validate our vnAS, we used CAC scoring information and clinical data of participants from MESA study. All included participants (Cohort I, n=3181) were assigned to one out of four calcium groups, which were defined as zero-calcium (AS and vnAS of 0), low-calcium (AS and vnAS of 1–99) high-calcium (AS and vnAS ≥100), and reclassified individuals (AS &lt;100 and vnAS ≥100). The occurrence of CHD events in each group was assessed and multivariable Cox regression models were used to assess the added value of the vnAS in the prediction of CHD events
For a sub-cohort of 890 participants at intermediate cardiovascular risk, the potential benefit from statin therapy was estimated based on the number needed to treat (NNT). NNT were determined for patients with vnAS ≥100 and vnAS ≥300 with original AS below 100 (group I) or 300 (group II), respectively.

Results
For all CT systems, a high degree of correlation with EBT Agatston scores was shown (R2 &gt;0.932). Using the vnAS, 85 individuals (2.7%) were reclassified from a lower to a higher risk category. For the reclassified participants, CHD event rates increased significantly from 7% to 15% (p=0.008) with a CHD hazard ratio of 3.39 (95% CI 1.82–6.35, p=0.001) (Figure 1). In intermediate risk cohort, the NNT was smaller for reclassified individuals as compared to their original (low) calcium group, at 7 vs 12 for group I and 2 vs 15 for group II, respectively. The summary of vnAS applicability is depicted in Figure 2.

Conclusions
We developed a calibration tool, which enables to calculate vendor neutral AS (vnAS). Based on vnAS, 85 individuals from MESA study, who were reclassified from a lower to a higher calcium category, did indeed have a higher CHD event rate. Consequently, the potential benefit from statin therapy, based on vnAS, was also increased for reclassified participants at intermediate cardiovascular risk.

Funding Acknowledgement
Type of funding sources: None.