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Purpose: Computed tomography (CT) might be a good diagnostic test to accurately quantify calcium in vascular beds but there are multiple factors influencing the quantification. The aim of this study was to investigate the influence of different computed tomography protocol settings in the quantification of calcium in the lower extremities using modified Agatston and volume scores., Methods: Fresh-frozen human legs were scanned at different tube current protocols and reconstructed at different slice thickness. Two different iterative reconstruction protocols for conventional CT images were compared. Calcium was manually scored using modified Agatston and volume scores. Outcomes were statistically analyzed using Wilcoxon signed-rank tests and mean absolute and relative differences were plotted in Bland-Altman plots., Results: Of the 20 legs, 16 had CT detectable calcifications. Differences between thick and thin slice reconstruction protocols were 129 Agatston units and 125% for Agatston and 78.4 mm 3 and 57.8% for volume (all p ≤ 0.001). No significant differences were found between low and high tube current protocols. Differences between iDose 4 and IMR reconstruction protocols for modified Agatston were 34.2 Agatston units and 17.7% and the volume score 33.5 mm 3 and 21.2% (all p ≤ 0.001)., Conclusions: Slice thickness reconstruction and reconstruction method protocols influenced the modified Agatston and volume scores in leg arteries, but tube current and different observers did not have an effect. This data emphasizes the need for standardized quantification of leg artery calcifications. Possible implications are in the development of a more universal quantification method, independent of the type of scan and vasculature., (Copyright © 2021 The Author(s). Published by Elsevier B.V. All rights reserved.)

Purpose: To determine the effect of model-based iterative reconstruction (IR) on coronary calcium quantification using different submillisievert CT acquisition protocols., Methods: Twenty-eight patients received a clinically indicated non contrast-enhanced cardiac CT. After the routine dose acquisition, low-dose acquisitions were performed with 60%, 40% and 20% of the routine dose mAs. Images were reconstructed with filtered back projection (FBP), hybrid IR (HIR) and model-based IR (MIR) and Agatston scores, calcium volumes and calcium mass scores were determined., Results: Effective dose was 0.9, 0.5, 0.4 and 0.2mSv, respectively. At 0.5 and 0.4mSv, differences in Agatston scores with both HIR and MIR compared to FBP at routine dose were small (-0.1 to -2.9%), while at 0.2mSv, differences in Agatston scores of -12.6 to -14.6% occurred. Reclassification of risk category at reduced dose levels was more frequent with MIR (21-25%) than with HIR (18%)., Conclusions: Radiation dose for coronary calcium scoring can be safely reduced to 0.4mSv using both HIR and MIR, while FBP is not feasible at these dose levels due to excessive noise. Further dose reduction can lead to an underestimation in Agatston score and subsequent reclassification to lower risk categories. Mass scores were unaffected by dose reductions., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

Objective: To assess the maximally achievable computed tomography (CT) dose reduction for coronary artery calcium (CAC) scoring with iterative reconstruction (IR) by using phantom-experiments and a systematical within-patient study., Methods: Our local institutional review-board approved this study and informed consent was obtained from all participants. A phantom and patient study were conducted with 30 patients (23 men, median age 55.0 (52.0-56.0) years) who underwent 256-slice electrocardiogram-triggered CAC-scoring at four dose levels (routine, 60%, 40%, and 20%-dose) in a single session. Tube-voltage was 120 kVp, tube-current was lowered to achieve stated dose levels. Data were reconstructed with filtered back-projection (FBP) and three IR levels. Agatston, volume and mass scores were determined with validated software and compared using Wilcoxon signed ranks-tests. Subsequently, patient reclassification was analyzed., Results: The phantom study showed that Agatston scores remained nearly stable with FBP between routine-dose and 40%-dose and increased substantially at lower dose. Twenty-three patients (77%) had coronary calcifications. For Agatston scoring, one 40%-dose and six 20%-dose FBP reconstructions were not interpretable due to noise. In contrast, with IR all reconstructions were interpretable. Median Agatston scores increased with FBP from 26.1 (5.2-192.2) at routine-dose to 60.5 (11.6-251.7) at 20% dose. However, IR lowered Agatston scores to 22.9 (5.9-195.5) at 20%-dose and strong IR (level 7) with Agatston reclassifications in 15%., Conclusion: IR allows for CAC-scoring radiation dose reductions of up to 80% resulting in effective doses between 0.15 and 0.18 mSv. At these dose-levels, reclassification-rates remain within 15% if the highest IR-level is applied., (Copyright © 2016 Society of Cardiovascular Computed Tomography. Published by Elsevier Inc. All rights reserved.)

Objectives: To analyse the effects of radiation dose reduction and iterative reconstruction (IR) algorithms on coronary calcium scoring (CCS)., Methods: Fifteen ex vivo human hearts were examined in an anthropomorphic chest phantom using computed tomography (CT) systems from four vendors and examined at four dose levels using unenhanced prospectively ECG-triggered protocols. Tube voltage was 120 kV and tube current differed between protocols. CT data were reconstructed with filtered back projection (FBP) and reduced dose CT data with IR. CCS was quantified with Agatston scores, calcification mass and calcification volume. Differences were analysed with the Friedman test., Results: Fourteen hearts showed coronary calcifications. Dose reduction with FBP did not significantly change Agatston scores, calcification volumes and calcification masses (P > 0.05). Maximum differences in Agatston scores were 76, 26, 51 and 161 units, in calcification volume 97, 27, 42 and 162 mm(3), and in calcification mass 23, 23, 20 and 48 mg, respectively. IR resulted in a trend towards lower Agatston scores and calcification volumes with significant differences for one vendor (P < 0.05). Median relative differences between reference FBP and reduced dose IR for Agatston scores remained within 2.0-4.6%, 1.0-5.3%, 1.2-7.7% and 2.6-4.5%, for calcification volumes within 2.4-3.9%, 1.0-5.6%, 1.1-6.4% and 3.7-4.7%, for calcification masses within 1.9-4.1%, 0.9-7.8%, 2.9-4.7% and 2.5-3.9%, respectively. IR resulted in increased, decreased or similar calcification masses., Conclusions: CCS derived from standard FBP acquisitions was not affected by radiation dose reductions up to 80%. IR resulted in a trend towards lower Agatston scores and calcification volumes., Key Points: In this ex vivo study, radiation dose could be reduced by 80% for coronary calcium scoring. Iterative reconstruction resulted in a trend towards lower Agatston scores and calcification volumes. Caution should be taken for coronary calcium scoring with iterative reconstruction.

Purpose: To determine the influence of dose reduction on coronary calcium scoring using hybrid and model-based iterative reconstruction (IR) techniques., Methods: Fifteen ex vivo hearts were scanned in a phantom representing an average adult person at routine dose and three levels of dose reduction; 27, 55 and 82% reduced-dose, respectively. All images were reconstructed using filtered back-projection (FBP), hybrid IR (iDose4, levels 1, 4 and 7) as well as model-based IR iterative model reconstruction (IMR, levels 1, 2 and 3). Agatston, mass and volume scores found with iDose4 and IMR were compared to FBP reconstruction (routine dose) as well as objective image quality., Results: With FBP calcium scores remained unchanged at 82% reduced dose. With IR Agatston scores differed significantly at routine dose, using IMR level 3 and iDose4 level 7, and at 82% reduced dose, using IMR levels 1-3 and iDose4 level 7. The maximum median difference was 5.3%. Mass remained unchanged at reduced dose levels while volume was significantly lower at 82% reduced dose with IMR (maximum median difference 5.0%). Objective image quality improved with IR, at 82% reduced dose the CNR of iDose4 level 7 was similar to the reference dose CNR, and IMR levels 1-3 resulted in an even higher CNR., Conclusion: Calcium scores were not affected by radiation-dose reduction with FBP and low levels of hybrid IR. Objective image quality increased significantly using hybrid and model-based IR. Therefore low level hybrid IR has the potential to reduce radiation-dose of coronary calcium scoring with up to 82%.

To compare coronary plaque size and composition as well as degree of coronary artery stenosis on coronary Computed Tomography angiography (CCTA) using three levels of iterative reconstruction (IR) with standard filtered back projection (FBP). In 63 consecutive patients with a clinical indication for CCTA 55 coronary plaques were analysed. Raw data were reconstructed using standard FBP and levels 2, 4 and 6 of a commercially available IR algorithm (iDose(4)). CT attenuation and noise were measured in the aorta and two coronary arteries. Both signal-to-noise-ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. The amount of lipid, fibrous and calcified plaque components and mean cross-sectional luminal area were analysed using dedicated software. Image noise was reduced by 41.6% (p < 0.0001) and SNR and CNR in the aorta were improved by 73.4% (p < 0.0001) and 72.9% (p < 0.0001) at IR level 6, respectively. IR improved objective image quality measures more in the aorta than in the coronary arteries. Furthermore, IR had no significant effect on measurements of plaque volume and cross-sectional luminal area. The application of IR significantly improves objective image quality, and does not alter quantitative analysis of coronary plaque volume, composition and luminal area.