In vitro evaluation of a new iterative reconstruction algorithm for dose reduction in coronary artery calcium scoring

Abstract

Background: Coronary artery calcium (CAC) scoring is a widespread tool for cardiac risk assessment in asymptomatic patients and accompanying possible adverse effects, i.e. radiation exposure, should be as low as reasonably achievable. Purpose: To evaluate a new iterative reconstruction (IR) algorithm for dose reduction of in vitro coronary artery calcium scoring at different tube currents. Material and Methods: An anthropomorphic calcium scoring phantom was scanned in different configurations simulating slim, average-sized, and large patients. A standard calcium scoring protocol was performed on a third-generation dual-source CT at 120 kVp tube voltage. Reference tube current was 80 mAs as standard and stepwise reduced to 60, 40, 20, and 10 mAs. Images were reconstructed with weighted filtered back projection (wFBP) and a new version of an established IR kernel at different strength levels. Calcifications were quantified calculating Agatston and volume scores. Subjective image quality was visualized with scans of an ex vivo human heart. Results: In general, Agatston and volume scores remained relatively stable between 80 and 40 mAs and increased at lower tube currents, particularly in the medium and large phantom. IR reduced this effect, as both Agatston and volume scores decreased with increasing levels of IR compared to wFBP (P < 0.001). Depending on selected parameters, radiation dose could be lowered by up to 86% in the large size phantom when selecting a reference tube current of 10 mAs with resulting Agatston levels close to the reference settings. Conclusion: New iterative reconstruction kernels may allow for reduction in tube current for established Agatston scoring protocols and consequently for substantial reduction in radiation exposure.

Reproducibility of calcium scoring of the coronary arteries: comparison between different vendors and iterative reconstructions

“…For a method to be credible, it is crucial that the variability in measurement is as low as possible. There are several studies assessing the variability in CCS using identical machines, interscan variability, and ways to reduce this variability (7,8). McCollough et al.…”

“…There are several studies assessing the variability in CCS using identical machines, interscan variability, and ways to reduce this variability (7,8). McCollough et al (9) reported the standardized quantification of coronary artery calcium results from equivalent calcium scores, acquired using different computed tomography (CT) systems.…”

The Influence of Iterative Reconstruction Technique on the Diagnosis of Coronary Artery Calcification

“…In 49% of coronary arteries, there was reduction in total Agatston scores with higher strength levels of IR. This phenomenon was reported in many studies [3,17,21,24]; and most likely caused as reported by Gassenmaier, et al and AlShammakhi & Sun [21,29] as a result of sharpening the calcifications and thus reducing the number of pixels with densities over the scoring threshold and thus suppressing the blooming artifacts and improve estimation of the true degree of luminal narrowing.…”

“…The Agatston score has been defined by Agatston and Janowitz and dates back into the 1980s [20]. This score still represents the most common established method for CCS quantification [21][22][23].…”

“…In comparison with standard filtered back projection (FBP), iterative reconstruction (IR) techniques result in substantial image noise reduction, and thus improve diagnostic image quality [25,26]. However; the current literature has contradictory on the effect of IR on the quantification of coronary calcification [3,17,21,24,25,27,28]. Therefore, this study aimed to define the threshold for the size and density in detection of CAC.…”