Rationale and Objectives
Cardiac computed tomography (CT) has been used extensively to measure coronary artery calcification. However, extracoronary calcifications, such as aortic valve calcification (AVC), may have independent clinical significance as well. The ability to track calcification is dependent on the reproducibility of the original measurement, and the variability of extracoronary calcification measurements still is unknown. Accurate quantification of calcification of the aortic valve, mitral annulus (MAC), and thoracic aortic (TAC) may be possible by using cardiac CT.
Methods
A total of 1,729 randomly chosen participants (ages 45–84, 53% female, 28% African-American, 36% Caucasian, 11% Chinese, 25% Hispanic) of the Multi-Ethnic Study of Atherosclerosis underwent dual scanning by electron beam CT (EBT) or multidetector CT (MDCT) to assess coronary and extra-coronary calcifications. Two calcium measurement methods—Agatston score (AS) and volume score (VS)—were measured for each scan. Concordance for calcium positivity was assessed among all scans. Mean absolute and relative differences between calcium measures on scans 1 and 2, excluding cases for which both scans had a measure of zero, was modeled by using linear regression to compare variability between scanner types. A repeated measures analysis of variance test was used to compare variability across calcium measures, with mean percentage absolute difference as the outcome measure.
Results
Concordances for the presence of calcium between duplicate scans were high and similar for both EBT and MDCT. Concordance was high for all three extracoronary measures, with a kappa statistic of κ = 0.94–0.96. For all three extracoronary sites, Bland-Altman plots demonstrated excellent agreement, with almost all measures falling within the boundaries of the 95% confidence limits of reproducibility. AVC interscan variability was approximately 8% for both AS and VS, with improved variability for EBT as compared with MDCT. Mitral annular calcification demonstrated slightly lower variability than AVC for both scanner types (approximately 6%), with no significant differences between MDCT and EBT. Of the three extracoronary sites, TAC had the highest variability (10%), with MDCT variability slightly lower than EBT variability (9.3 vs. 10.2%, respectively, P = NS). Agatson and volume scores for each of the three extracoronary sites were similar.
Conclusions
Overall rescan measurement variabilities for extracoronary calcification are low and should not be an impediment to the use of this test for studying progression of extracoronary calcification over time.
Atherosclerosis is a systemic process with a predilection for certain anatomic locations. Emerging evidence indicates that calcifications in valvular and thoracic aorta are manifestations of generalized atherosclerosis ( ). Population-based studies have shown that aortic sclerosis and atherosclerosis share similar risk factors ( ).
Large studies have demonstrated computed tomography (CT) scanning to be a highly reproducible method for quantifying coronary artery calcification ( ), whereas smaller studies also have demonstrated excellent reproducibility of this technique for quantifying aortic valve calcification (AVC) ( ). However, no large studies have characterized the reproducibility of CT scanning for quantifying calcification of the thoracic aorta (TAC) or the mitral annulus (MAC). Also, no previous studies have compared the reproducibilities of two CT technologies, electron beam computed tomography (EBT), and multidetector computed tomography (MDCT) for quantifying AVC, TAC, and MAC. Because establishing measurement reproducibility is a necessary condition for following progression of calcification over time, demonstration of measurement reproducibility is an important step toward the eventual use of CT scanning for monitoring progression.
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Methods
Study Population
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CT Techniques
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Data Analysis
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Results
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Table 1
Agreement of Extracoronary Measures for Presence of Calcium Between Scans 1 and 2 by Scanner Type
EBT ( n = 972) MDCT ( n = 757) Scan 1 Calcium = 0 Scan 1 Calcium >0 κ (95% CI) Scan 1 Calcium = 0 Scan 1 Calcium >0 κ (95% CI) AVC Scan 2 Calcium = 0 821 (85%) 3 (0.3%) κ = 0.97 (0.95–0.99) 633 (84%) 8 (1%) κ =0.91 (0.87–0.95) Scan 2 Calcium >0 5 (0.5%) 143 (15%) 10 (1%) 106 (14%) MAC Scan 2 Calcium = 0 849 (87%) 3 (0.3%) κ = 0.96 (0.93–0.98) 650 (86%) 2 (0.3%) κ = 0.95 (0.92–0.98) Scan 2 Calcium >0 5 (0.5%) 114 (12%) 7 (0.9%) 97 (13%) TAC Scan 2 Calcium = 0 636 (65%) 13 (1%) κ = 0.94 (0.91–0.96) 470 (62%) 6 (1%) κ = 0.97 (0.95–0.99) Scan 2 Calcium >0 14 (1%) 309 (32%) 5 (1%) 276 (37%)
κ: kappa statistic; CI: confidence interval; EBT: electron beam computed tomography; MDCT: multidetector computed tomography; AVC: aortic valve calcification; MAC: mitral annulus calcification; TAC: thoracic aorta calcification.
Table 2
Mean Absolute Rescan Difference for Extracoronary Calcium Measures by Scanner Type
Calcium Measure Mean Absolute Rescan Difference ⁎ Among Those With Both Scans >0 EBT MDCT_P_ Value AVC_n_ 151 124 Agatston score (95% CI) 11.08 (9.34–13.14) 11.68 (9.67–14.11) .685 Volume score (95% CI) 9.98 (8.46–11.79) 11.02 (9.18–13.25) .433 MAC_n_ 122 106 Agatston score (95% CI) 14.95 (12.10–18.47) 17.32 (13.80–21.73) .352 Volume score (95% CI) 12.01 (9.74–14.81) 17.87 (14.27–22.35) .012 TAC_n_ 336 287 Agatston score (95% CI) 20.68 (18.27–23.41) 16.58 (14.48–18.97) .019 Volume score (95% CI) 16.68 (14.69–18.93) 13.08 (11.39–15.01) .011
CI: confidence interval; EBT: electron beam computed tomography; MDCT: multidetector computed tomography; AVC: aortic valve calcification; MAC: mitral annulus calcification; TAC: thoracic aorta calcification.
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Table 3
Mean Relative Rescan Differences and Coefficients of Reproducibility for Each Scanner Type
Agatston Score (%) Volume Score (%)P Value (Agatston vs Volume Score) AVC EBT 6.8 6.1 .572 MDCT 9.9 9.7 .886 Both 8.1 7.7 .644 Reproducibility coefficient 0.295 0.298 NA MAC EBT 5.4 4.9 .624 MDCT 6.3 6.8 .697 Both 5.8 5.7 .949 Reproducibility coefficient 0.354 0.271 NA TAC EBT 11.3 10.3 .565 MDCT 8.9 8.0 .562 Both 10.2 9.3 .422 Reproducibility coefficient 0.140 0.135 NA
AVC: aortic valve calcification; EBT: electron beam computed tomography; MDCT: multidetector computed tomography; MAC: mitral annulus calcification; TAC: thoracic aorta calcification.
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Table 4
Agreement of Extracoronary Measures for Presence of Calcium Between Scans 1 and 2 ( n = 1729)
Scan 1 Calcium = 0 Scan 1 Calcium >0 κ\* (95% CI) AVC Scan 2 calcium = 0 1454 (84.1%) 11 (0.6%) κ = 0.94 (0.92–0.96) Scan 2 calcium >0 15 (0.9%) 249 (14.4%) MAC Scan 2 calcium = 0 1499 (86.8%) 5 (0.3%) κ = 0.96 (0.93–0.98) Scan 2 calcium >0 12 (0.7%) 211 (12.2%) TAC Scan 2 calcium = 0 1106 (64.0%) 19 (1.1%) κ = 0.95 (0.94–0.97) Scan 2 calcium >0 19 (1.1%) 585 (33.8%)
κ: kappa statistic; CI: confidence interval; AVC: aortic valve calcification; MAC: mitral annulus calcification; TAC: thoracic aorta calcification.
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Discussion
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