Coronary calcium test phantom containing true CaHA microspheres for evaluation of advanced CT calcium scoring methods

Background

Test phantoms with simulated micro-calcifications of true calcium hydroxyapatite (CaHA) density were not available to validate advanced calcium scoring methods or plaque density measurements.

Objectives

We evaluated a coronary calcium scoring (CCS) test phantom containing very small CaHA microspheres and validated a new scoring method for measurements of plaque densities.

Methods

The semianthropomorphic CCS phantom was constructed with CaHA microspheres (volumes, 0.05–3.1 mm³) with the approximate density of biologic calcifications. QRM and CCS phantoms were scored with a new calibrated and automated calcium scoring method (N-vivo; Image Analysis). The densities of the microspheres and 609 individual patient plaques were measured.

Results

The range of measured densities of the CaHA microspheres was approximately equivalent to that measured in the patient coronary calcifications. The smallest microspheres scored with the calibrated/automated and the Agatston methods had volumes of 0.075 mm³ and 0.27 mm³, respectively. The standard deviations of the mass scores of the microspheres ranged from 0.02 to 0.17 mg with regression slope of 0.962 and R² = 0.997. The relationship of measured density to measured mass of the patient plaques was similar to that of the microspheres, suggesting that vascular calcifications are CaHA density.

Conclusions

The CaHA microspheres of the CCS test phantom were found to be representative in density and size of coronary calcifications. The measurements show that CT calcium scoring underestimates plaque density and greatly overestimates volume. The heterogeneity of calcium concentration densities measured in the patient plaques was due largely to CT scanner measurement errors.

Keywords: Atherosclerotic plaque characterization, Calcium scoring phantom, Cardiac multidetector CT (MDCT), Coronary calcium scoring, Coronary plaque, Plaque density, Small vascular plaque