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. 2023 Jun 1;13(11):1934.
doi: 10.3390/diagnostics13111934.

Validation of a Length-Adjusted Abdominal Arterial Calcium Score Method for Contrast-Enhanced CT Scans

Raul Devia-Rodriguez  1 , Maikel Derksen  1 , Kristian de Groot  1 , Issi R Vedder  2 , Clark J Zeebregts  1 , Reinoud P H Bokkers  2 , Robert A Pol  1 , Jean-Paul P M de Vries  1 , Richte C L Schuurmann  1
Affiliations

Validation of a Length-Adjusted Abdominal Arterial Calcium Score Method for Contrast-Enhanced CT Scans

Raul Devia-Rodriguez et al. Diagnostics (Basel). .

Abstract

Background: The Agatston score on noncontrast computed tomography (CT) scans is the gold standard for calcium load determination. However, contrast-enhanced CT is commonly used for patients with atherosclerotic cardiovascular diseases (ASCVDs), such as peripheral arterial occlusive disease (PAOD) and abdominal aortic aneurysm (AAA). Currently, there is no validated method to determine calcium load in the aorta and peripheral arteries with a contrast-enhanced CT. This study validated a length-adjusted calcium score (LACS) method for contrast-enhanced CT scans.

Method: The LACS (calcium volume in mm3/arterial length in cm) in the abdominal aorta was calculated using four-phase liver CT scans of 30 patients treated between 2017 and 2021 at the University Medical Center Groningen (UMCG) with no aortic disease. Noncontrast CT scans were segmented with a 130 Hounsfield units (HU) threshold, and a patient-specific threshold was used for contrast-enhanced CTs. The LACS was calculated and compared from both segmentations. Secondly, the interobserver variability and the influence of slice thickness (0.75 mm vs. 2.0 mm) was determined.

Results: There was a high correlation between the LACS from contrast-enhanced CT scans and the LACS of noncontrast CTs (R2 = 0.98). A correction factor of 1.9 was established to convert the LACS derived from contrast-enhanced CT to noncontrast CT scans. LACS interobserver agreement on contrast-enhanced CT was excellent (1.0, 95% confidence interval = 1.0-1.0). The 0.75 mm CT threshold was 541 (459-625) HU compared with 500 (419-568) HU on 2 mm CTs (p = 0.15). LACS calculated with both thresholds was not significantly different (p = 0.63).

Conclusion: The LACS seems to be a robust method for scoring calcium load on contrast-enhanced CT scans in arterial segments with various lengths.

Keywords: atherosclerosis; calcified plaques; calcium score; four-dimensional computed tomography; vascular diseases.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Steps for the determination of the length-adjusted arterial calcium score using abdominal aorta images from 4-phased liver contrast-enhanced CT scans. (A) Measurement of the contrast Hounsfield units (HU) in the upper region of interest, used for the determination of the patient-specific HU threshold. (B) Manual selection of the arterial calcified regions (colored in red) using the overlay. (C) Classification of calcified areas (colored in blue) by the preset HU threshold. (D) Measurement of the region of interest’s length using the center lumen line. SD: standard deviation.
Figure 2
Figure 2
Length-adjusted arterial calcium score (LACS) determined in contrast-enhanced and noncontrast computed tomography (CT) scans. (A) Correction factor to convert from the LACS on contrast-enhanced to noncontrast CT of 1.9 was determined with linear regression. All data points are plotted as grey circles. (B) Comparison of the corrected LACS from contrast-enhanced scans (using the correction factor of 1.9) to LACS from noncontrast CT. CI: confidence interval. All data points are plotted as grey circles. (C) The LACS was determined in contrast-enhanced and noncontrast CT scans. Outlier data points are plotted as white circles. (D) Number of segmented calcium lesions in contrast-enhanced and noncontrast CT scans. * indicates p < 0.05.
Figure 3
Figure 3
Analysis of the impact of interobserver variability in the length-adjusted arterial calcium score (LACS) outcomes determined in contrast-enhanced computed tomography (CT) scans. (A) Box plot comparing patient-specific thresholds calculated by two observers in contrast-enhanced CT scans. Outlier data points are plotted as white circles. (B) Box plot comparing the LACSs determined by two observers in contrast-enhanced CT scans. Outlier data points are plotted as white circles. (C) Bland–Altman plot comparing the LACSs determined in contrast-enhanced CT scans by two observers. CI: confidence interval. All data points are plotted as grey circles. (D) Box plot comparing the number of calcium lesions calculated by two observers in contrast-enhanced CT scans.
Figure 4
Figure 4
Analysis of the impact of slice thickness in length-adjusted arterial calcium score (LACS) outcomes. (A) Box plot comparing patient-specific thresholds calculated in 2.0 mm and 0.75 mm slice thickness contrast scans. Outlier data points are plotted as white circles. (B) Box plot comparing the LACS determined in 2.0 mm and 0.75 mm slice thickness contrast scans. (C) Bland–Altman plot comparing the LACS determined in contrast-enhanced computed tomography (CT) scans of two different thicknesses (2.0 mm vs. 0.75 mm). CI: confidence interval. All data points are plotted as grey circles. (D) Box plot comparing the number of calcium lesions calculated in 2.0 mm and 0.75 mm slice thickness contrast-enhanced CT scans. * indicates p < 0.05.
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