Abstract
We aimed to determine the proper modified thresholds for detecting and weighting CAC scores at 100 kV through histogram matching in comparison with 120 kV as a standard reference. From the training set (680 participants), modified thresholds at 100 kV were obtained through histogram matching of calcium pixels to 120 kV. From the validation set (213 participants), a standard CAC score at 120 kV, and modified CAC score at 100 kV using modified thresholds were compare through the paired t test and the Bland–Altman plot. Agreement for risk categories (no, minimal, mild, moderate, and severe) was evaluated using kappa statistics. Radiation doses were also compared. For the validation set, there was no significant difference between standard (median, 18.7; IQR, 0.0–207.0) and modified (median, 17.3; IQR, 0.0–220.9) CAC scores (P = 0.689). A small bias was achieved (0.74) with 95% limits of agreement from − 52.35 to 53.83. Agreements for risk categories were excellent (κ = 0.994). The mean dose-length-product of 100-kV scanning (30.1 ± 0.8 mGy * cm) was significantly decreased compared to 120-kV scanning (42.9 ± 0.6 mGy * cm) (P < 0.001). Histogram-derived modified thresholds at 100 kV can enable accurate CAC scoring while reducing radiation exposure.
Highlights
We aimed to determine the proper modified thresholds for detecting and weighting CAC scores at 100 kV through histogram matching in comparison with 120 kV as a standard reference
Lowering tube voltage remains a challenge for CAC scoring because the computed tomography (CT) attenuation of calcium is closely related to photon energy; the thresholds established by Agatston are not applicable to other tube v oltages[7]
We were able to attain modified thresholds for CAC scoring with 100 kV from histograms using the cumulative distribution function, and CAC scoring was accurate with good agreement of a small bias and acceptable 95% limits of agreement compared to standard CAC scoring with 120 kV
Summary
We aimed to determine the proper modified thresholds for detecting and weighting CAC scores at 100 kV through histogram matching in comparison with 120 kV as a standard reference. The Agatston score is easy to obtain with acceptable inter-scan and inter-observer reproducibility, cumulative clinical evidence supports its use for risk stratification in primary prevention settings[2] It remains the gold standard and the most commonly used CAC score in clinical practice even though the Agatston scores tend to show a large degree of a rbitrariness[5]. In contrast to coronary CT angiography which incorporates advanced imaging acquisition and reconstruction techniques to reduce radiation exposure, the CAC scanning protocol remains largely unchanged from the initial technique proposed in 1990, especially for tube voltage settings. We aimed to determine modified thresholds appropriate for detecting and weighting CAC scores at 100 kV through an intuitive and eidetic method using histograms with a large-scale population and temporal independent validation
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