Reproducibility of three different scoring systems for measurement of coronary calcium

Artificial intelligence using a deep learning versus expert computed tomography human reading in calcium score and coronary artery calcium data and reporting system classification

BACKGROUND

Artificial intelligence (AI) applied to cardiac imaging may provide improved processing, reading precision and advantages of automation. Coronary artery calcium (CAC) score testing is a standard stratification tool that is rapid and highly reproducible. We analyzed CAC results of 100 studies in order to determine the accuracy and correlation between the AI software (Coreline AVIEW, Seoul, South Korea) and expert level-3 computed tomography (CT) human CAC interpretation and its performance when coronary artery disease data and reporting system (coronary artery calcium data and reporting system) classification is applied.

METHODS

A total of 100 non-contrast calcium score images were selected by blinded randomization and processed with the AI software versus human level-3 CT reading. The results were compared and the Pearson correlation index was calculated. The CAC-DRS classification system was applied, and the cause of category reclassification was determined using an anatomical qualitative description by the readers.

RESULTS

The mean age was age 64.5 years, with 48% female. The absolute CAC scores between AI versus human reading demonstrated a highly significant correlation (Pearson coefficient R  = 0.996); however, despite these minimal CAC score differences, 14% of the patients had their CAC-DRS category reclassified. The main source of reclassification was observed in CAC-DRS 0-1, where 13 were recategorized, particularly between studies having a CAC Agatston score of 0 versus 1. Qualitative description of the errors showed that the main cause of misclassification was AI underestimation of right coronary calcium, AI overestimation of right ventricle densities and human underestimation of right coronary artery calcium.

CONCLUSION

Correlation between AI and human values is excellent with absolute numbers. When the CAC-DRS classification system was adopted, there was a strong correlation in the respective categories. Misclassified were predominantly in the category of CAC = 0, most often with minimal values of calcium volume. Additional algorithm optimization with enhanced sensitivity and specificity for low values of calcium volume will be required to enhance AI CAC score utilization for minimal disease. Over a broad range of calcium scores, AI software for calcium scoring had an excellent correlation compared to human expert reading and in rare cases determined calcium missed by human interpretation.

Magnetic Resonance Imaging and Computed Tomography for the Noninvasive Assessment of Arterial Aging: A Review by the VascAgeNet COST Action

Magnetic resonance imaging and computed tomography allow the characterization of arterial state and function with high confidence and thus play a key role in the understanding of arterial aging and its translation into the clinic. Decades of research into the development of innovative imaging sequences and image analysis techniques have led to the identification of a large number of potential biomarkers, some bringing improvement in basic science, others in clinical practice. Nonetheless, the complexity of some of these biomarkers and the image analysis techniques required for their computation hamper their widespread use. In this narrative review, current biomarkers related to aging of the aorta, their founding principles, the sequence, and postprocessing required, and their predictive values for cardiovascular events are summarized. For each biomarker a summary of reference values and reproducibility studies and limitations is provided. The present review, developed in the COST Action VascAgeNet, aims to guide clinicians and technical researchers in the critical understanding of the possibilities offered by these advanced imaging modalities for studying the state and function of the aorta, and their possible clinically relevant relationships with aging.

Assessing Agreement When Agreement Is Hard to Assess-The Agatston Score for Coronary Calcification

Method comparison studies comprised simple scatterplots of paired measurements, a 45-degree line as benchmark, and correlation coefficients up to the advent of Bland-Altman analysis in the 1980s. The Agatston score for coronary calcification is based on computed tomography of the heart, and it originated in 1990. A peculiarity of the Agatston score is the often-observed skewed distribution in screening populations. As the Agatston score has manifested itself in preventive cardiology, it is of interest to investigate how reproducibility of the Agatston score has been established. This review is based on literature findings indexed in MEDLINE/PubMed before 20 November 2021. Out of 503 identified articles, 49 papers were included in this review. Sample sizes were highly variable (10-9761), the main focus comprised intra- and interrater as well as intra- and interscanner variability assessments. Simple analysis tools such as scatterplots and correlation coefficients were successively supplemented by first difference, later Bland-Altman plots; however, only very few publications were capable of deriving Limits of Agreement that fit the observed data visually in a convincing way. Moreover, several attempts have been made in the recent past to improve the analysis and reporting of method comparison studies. These warrant increased attention in the future.

Quantification of Calcium in Peripheral Arteries of the Lower Extremities: Comparison of Different CT Scanners and Scoring Platforms

OBJECTIVES

The aim of this study was to investigate the interscanner and interscoring platform variability of calcium quantification in peripheral arteries of the lower extremities.

MATERIALS AND METHODS

Twenty human fresh-frozen legs were scanned using 3 different computed tomography (CT) scanners. The radiation dose (CTDIvol) was kept similar for all scanners. The calcium scores (Agatston and volume scores) were quantified using 4 semiautomatic scoring platforms. Comparative analysis of the calcium scores between scanners and scoring platforms was performed by using the Friedman test; post hoc analysis was performed by using the Wilcoxon signed rank test with Bonferroni correction.

RESULTS

Sixteen legs had calcifications and were used for data analysis. Agatston and volume scores ranged from 12.1 to 6580 Agatston units and 18.2 to 5579 mm3. Calcium scores differed significantly between Philips IQon and Philips Brilliance 64 (Agatston: 19.5% [P = 0.001]; volume: 14.5% [P = 0.001]) and Siemens Somatom Force (Agatston: 18.1% [P = 0.001]; volume: 17.5% [P = 0.001]). The difference between Brilliance 64 and Somatom Force was smaller (Agatston: 5.6% [P = 0.778]; volume: 7.7% [P = 0.003]). With respect to the interscoring platform variability, OsiriX produced significantly different Agatston scores compared with the other 3 scoring platforms (OsiriX vs IntelliSpace: 14.8% [P = 0.001] vs Syngo CaScore: 13.9% [P = 0.001] vs iX viewer: 13.2% [P < 0.001]). For the volume score, the differences between all scoring platforms were small ranging from 2.9% to 4.0%. Post hoc analysis showed a significant difference between OsiriX and IntelliSpace (3.8% [P = 0.001]).

CONCLUSIONS

The use of different CT scanners resulted in notably different Agatston and volume scores, whereas the use of different scoring platforms resulted in limited variability especially for the volume score. In conclusion, the variability in calcium quantification was most evident between different CT scanners and for the Agatston score.

Fully automated quantification method (FQM) of coronary calcium in an anthropomorphic phantom

Objective

Coronary artery calcium (CAC) score is a strong predictor for future adverse cardiovascular events. Anthropomorphic phantoms are often used for CAC studies on computed tomography (CT) to allow for evaluation or variation of scanning or reconstruction parameters within or across scanners against a reference standard. This often results in large number of datasets. Manual assessment of these large datasets is time consuming and cumbersome. Therefore, this study aimed to develop and validate a fully automated, open‐source quantification method (FQM) for coronary calcium in a standardized phantom.

Materials and Methods

A standard, commercially available anthropomorphic thorax phantom was used with an insert containing nine calcifications with different sizes and densities. To simulate two different patient sizes, an extension ring was used. Image data were acquired with four state‐of‐the‐art CT systems using routine CAC scoring acquisition protocols. For interscan variability, each acquisition was repeated five times with small translations and/or rotations. Vendor‐specific CAC scores (Agatston, volume, and mass) were calculated as reference scores using vendor‐specific software. Both the international standard CAC quantification methods as well as vendor‐specific adjustments were implemented in FQM. Reference and FQM scores were compared using Bland‐Altman analysis, intraclass correlation coefficients, risk reclassifications, and Cohen’s kappa. Also, robustness of FQM was assessed using varied acquisitions and reconstruction settings and validation on a dynamic phantom. Further, image quality metrics were implemented: noise power spectrum, task transfer function, and contrast‐ and signal‐to‐noise ratio among others. Results were validated using imQuest software.

Results

Three parameters in CAC scoring methods varied among the different vendor‐specific software packages: the Hounsfield unit (HU) threshold, the minimum area used to designate a group of voxels as calcium, and the usage of isotropic voxels for the volume score. The FQM was in high agreement with vendor‐specific scores and ICC’s (median [95% CI]) were excellent (1.000 [0.999‐1.000] to 1.000 [1.000‐1.000]). An excellent interplatform reliability of κ = 0.969 and κ = 0.973 was found. TTF results gave a maximum deviation of 3.8% and NPS results were comparable to imQuest.

Conclusions

We developed a fully automated, open‐source, robust method to quantify CAC on CT scans in a commercially available phantom. Also, the automated algorithm contains image quality assessment for fast comparison of differences in acquisition and reconstruction parameters.

Coronary artery calcification in lung cancer screening

Lung cancer screening has been shown in the National Lung Screening Trial (NLST) to result in a statistically significant decrease in lung cancer specific mortality. Also within that trial there was shown to be a 7% decrease in all-cause mortality. While the reasons for this benefit are not entirely clear, it may relate to the detection and treatment of other important findings. Smokers not only have a higher risk of lung cancer, but also increased risk of atherosclerosis. The latter can be detected by the discovery of aortic and/or coronary artery calcium on unenhanced CT. As coronary artery calcium scoring can be used as a screening tool to detect asymptomatic coronary artery atherosclerosis, its detection on lung cancer screening exams has the potential to provide both a teachable moment and treatment aimed at the reduction of major coronary artery events and mortality. In this review we will discuss the use of coronary artery calcium scoring for the detection of atherosclerotic disease and its potential application to lung cancer screening populations.

Current and future applications of CT coronary calcium assessment

INTRODUCTION

Computed tomographic (CT) coronary artery calcium scoring (CAC) has been validated as a well-established screening method for cardiovascular risk stratification and treatment management that is used in addition to traditional risk factors. The purpose of this review is to present an update on current and future applications of CAC. Areas covered: The topic of CAC is summarized from its introduction to current application with focus on the validation and clinical integration including cardiovascular risk prediction and outcome, cost-effectiveness, impact on downstream medical testing, and the technical advances in scanner and software technology that are shaping the future of CAC. Furthermore, this review aims to provide guidance for the appropriate clinical use of CAC. Expert commentary: CAC is a well-established screening test in preventive care that is underused in daily clinical practice. The widespread clinical implementation of CAC will be decided by future technical advances in CT image acquisition, cost-effectiveness, and reimbursement status.

The Influence of Iterative Reconstruction on Coronary Artery Calcium Scoring-Phantom and Clinical Studies

RATIONALE AND OBJECTIVES

We compared the effect of iterative model reconstruction (IMR), filtered back projection (FBP), and hybrid iterative reconstruction (HIR) on coronary artery calcium (CAC) scoring.

MATERIALS AND METHODS

CAC scans of 30 consecutive patients (18 men and 12 women, age 70.1 ± 12.2 years) were reconstructed with FBP, HIR, and IMR, and the image noise was measured on all images. Two radiologists independently measured the CAC scores using semiautomated software, and interobserver agreement was evaluated. Statistical analysis included the Spearman correlation coefficient and Bland-Altman analysis.

RESULTS

The mean image noise on FBP, HIR, and IMR images was 48.0 ± 7.9, 29.6 ± 4.8, and 9.3 ± 1.3 Hounsfield units, respectively. The difference among all reconstruction combinations was significant (P < .01). The CAC score on HIR and IMR scans was 4.2% and 8.9% lower, respectively, than the CAC score on FBP images. There was no significant difference in the mean CAC score among the three reconstructions. The interobserver correlation was excellent for all three reconstructions (r² = 0.96 FBP, 0.99 HIR, 0.99 IMR); the best Bland-Altman measure of agreement was with IMR, followed by HIR and FBP.

CONCLUSION

For CAC scoring, IMR can reduce the image noise and blooming artifacts, and consequently lowers the measured CAC score. IMR can lessen measurement variability and yield stable, reproducible measurements.

Arterial haemodynamics and coronary artery calcification in adult patients with juvenile idiopathic arthritis

OBJECTIVE

To compare arterial haemodynamics in adults with long-term juvenile idiopathic arthritis (JIA) to that of healthy controls, and explore the influence of traditional cardiovascular risk factors and disease characteristics on arterial haemodynamics plus coronary artery calcification.

METHODS

87 JIA patients (median age 38.4 years) with persistently active disease at least 15 years after disease onset (registered by longitudinal follow-up), were re-examined after median 29 years and compared with 87 matched controls. Arterial haemodynamics were characterised by arterial stiffness and blood pressure. Sphygmocor was used to measure the arterial stiffness markers pulse wave velocity (PWV) and augmentation index (AIx). Coronary calcification was assessed by CT.

RESULTS

Compared to controls, patients had significantly higher PWV (7.2 vs 6.9 m/s, p=0.035), and systolic and diastolic blood pressure (SBP, p=0.050 and DBP, p=0.029). AIx was numerically higher in the patients compared to the controls, but no statistically significant difference was found. Coronary calcification was present in 22 (26%) of the patients. Daily smoking was more frequent (p=0.043), and insulin resistance was higher (p=0.034) in patients than controls.In patients, DBP, but no disease variables were determinants of PWV. Disease variables as well as traditional cardiovascular risk factors were associated with higher AIx, DBP and the presence of coronary calcification.

CONCLUSIONS

JIA patients with long-term active disease had altered arterial haemodynamics compared with controls in our study. PWV was mainly determined by increased DBP, a parameter that again was associated with JIA disease and treatment variables.

Atherosclerotic lesions in lymphoma survivors treated with radiotherapy

BACKGROUND AND PURPOSE

Radiotherapy causes premature atherosclerosis in Hodgkin's lymphoma survivors (HLSs). We determined whether atherosclerosis within the radiation field was predicted by traditional risk factors independent of radiation and compared the extent of atherosclerosis in HLSs treated with mantle field radiotherapy with non-irradiated patients.

MATERIAL AND METHODS

Forty-three HLSs (median age 50 years, range 38-63) treated with mantle field radiotherapy were included. Cardiovascular risk factors were registered at first follow-up (FU-1) 5-13 years after treatment. A second follow-up (FU-2) occurred 18-27 years after treatment. At FU-2, in-field atherosclerosis was assessed by computed tomography with calculation of coronary artery calcium volume score (CACS) and pre-cranial artery atherosclerosis score (PAS). Peripheral endothelial dysfunction was assessed by ante-brachial strain-gauge plethysmography. CT angiography of pre-cranial vessels was also performed in 43 non-irradiated patients.

RESULTS

Multiple linear regression analyses showed that cholesterol at FU-1 was a predictor of CACS (β 308 (95% CI 213-403), p < 0.001), PAS (β 3.67 (95% CI 2.29-5.04), p < 0.001) and peripheral endothelial dysfunction (β 2.74 (95% CI 0.47-5.01), p = 0.02). There were more atherosclerotic lesions in HLSs (n = 141) than in non-irradiated patients (n = 73, p = 0.001).

CONCLUSION

Irradiated arteries are characterized by widespread atherosclerotic lesions aggravated by elevated levels of cholesterol.

Screening for Ischemic Heart Disease with Cardiac CT: Current Recommendations

Cardiovascular disease remains the leading cause of mortality in the US and worldwide, and no widespread screening for this number one killer has been implemented. Traditional risk factor assessment does not fully account for the coronary risk and underestimates the prediction of risk even in patients with established risk factors for atherosclerosis. Coronary artery calcium (CAC) represents calcified atherosclerosis in the coronary arteries. It has been shown to be the strongest predictor of adverse future cardiovascular events and provides incremental information to the traditional risk factors. CAC consistently outperforms traditional risk factors, including models such as Framingham risk to predict future CV events. It has been incorporated into both the European and American guidelines for risk assessment. CAC is the most robust test today to reclassify individuals based on traditional risk factor assessment and provides the opportunity to better strategize the treatments for these subjects (converting patients from intermediate to high or low risk). CAC progression has also been identified as a risk for future cardiovascular events, with markedly increased events occurring in those patients exhibiting increases in calcifications over time. The exact intervals for rescanning is still being evaluated.

Prevalence and risk factors for coronary artery calcification following kidney transplantation for systemic lupus erythematosus

OBJECTIVES

Patients with SLE who undergo kidney transplantation are at increased risk of premature cardiovascular disease. The current study aimed to investigate the prevalence of coronary artery calcification in transplanted SLE patients without coronary symptoms and to explore risk factors associated with coronary atherosclerosis.

METHODS

This was a cross-sectional study in transplanted SLE patients with a functioning graft. Evaluation included laboratory tests, SLE disease activity indices, multi-slice CT for quantification of coronary calcification (Agatston score >400 = high calcification, <400 = mild to moderate calcification). Arterial and aortic stiffness was assessed by carotid-femoral pulse wave velocity (PWV).

RESULTS

Thirty-nine patients were analysed, three of whom had a prior history of coronary events. Coronary artery calcification was present in 82% of patients (n = 32), with 36% (n = 14) with a high level of arterial calcification. Multivariate regression analysis showed the following factors to be independently associated with high coronary calcification: PWV (0.41, 95% CI 0.17, 0.66, P = 0.001), time since diagnosis of LN (0.66, 95% CI 0.43, 0.71, P < 0.001) and BMI (0.39, 95% CI 0.15, 0.63, P = 0.002). Immunosuppression regimen was not significantly different between groups.

CONCLUSIONS

Coronary artery calcification is widespread in transplanted SLE patients despite a normal profile of conventional cardiovascular risk factors. The risk of calcification increases with disease duration, BMI and PWV in this population.

Relation of coronary artery calcium score to premature coronary artery disease in survivors >15 years of Hodgkin's lymphoma

Long-term survival in Hodgkin lymphoma (HL) survivors is complicated by an increased risk for coronary artery disease (CAD) due to radiation-induced endothelial damage. Our objective was to quantify total coronary artery calcium (CAC) in long-term HL survivors who had survived >or=15 years after treatment and relate it to the presence of verified CAD. Forty-seven HL survivors 50 +/- 7 years of age who had survived 22 +/- 3 years after mediastinal radiotherapy underwent CAC scoring (Agatston and volume scores) in a multidetector computed tomographic scanner. Total volume score was higher in 7 patients (15%) with verified CAD (median 439, range 8 to 2,057) compared to those without (median 68, 0 to 767, p = 0.022). Ten patients had CAC scores >200. Of these 10, 5 had undergone revascularization of coronary arteries. None of the 8 patients with a CAC score 0 had symptomatic CAD. In conclusion, postirradiation CAC can be quantified by CAC score and this may be a simple and suitable method to screen for CAD in long-term HL survivors. Patients with a CAC score >200 often have clinically significant CAD, and further investigation including angiography may be justified. Lower CAC scores, however, do not exclude CAD and further studies should be undertaken to define the best algorithm for follow-up of this patient group.

The association of coronary artery calcification and carotid artery intima-media thickness with distinct, traditional coronary artery disease risk factors in asymptomatic adults

Coronary artery calcification (CAC) and common carotid artery intima-media thickness (CIMT) are measures of subclinical vascular disease. This 2000-2006 study aimed to characterize the associations among coronary artery disease risk factors, CAC quantity, and CIMT and to estimate shared genetic and environmental contributions to both CAC and CIMT among 478 asymptomatic Amish adults in Lancaster County, Pennsylvania. Heritability for CAC quantity and CIMT, adjusted for age and sex, was 0.42 (P = 0.0001) and 0.29 (P = 0.003), respectively. CAC quantity and CIMT were modestly correlated (adjusted r = 0.14, P = 0.003) but showed little evidence of shared genetic or environmental factors. However, significant genetic correlations were found for CAC quantity and total cholesterol (0.44 (standard error, 0.19); P = 0.03), for CAC quantity and low density lipoprotein cholesterol (0.55 (standard error, 0.17); P = 0.005), and for CIMT and waist circumference (0.58 (standard error, 0.25); P = 0.046), suggesting shared genes for these risk factors and measures of subclinical disease. Results suggest that some of the same genes influence variation in CAC and low density lipoprotein cholesterol, whereas a different set of genes influences variation in CIMT and waist circumference.

Coronary artery calcification scores in patients with chronic kidney disease prior to dialysis: reliability as a trial outcome measure

BACKGROUND

Coronary artery calcification (CAC) is prevalent in patients with chronic kidney disease (CKD). Data on the reliability and validity of high-resolution computerized tomography (HRCT) in patients with CKD is lacking. The purpose of this study was to evaluate the inter- and intra-reviewer agreement and inter-scan reproducibility of CACS measurement with HRCT in a cohort of patients with CKD prior to dialysis, and to compare the change in CACS at 30 minutes to the change in CACS over 1 year.

METHODS

Thirty-three patients with CKD not yet on dialysis underwent an HRCT scan at baseline and 1 year to assess for CAC and CAC progression. Two radiologists independently reviewed films and each radiologist re-reviewed a randomly selected subset of films they had previously viewed, to assess for inter-reviewer and intra-reviewer reliability, respectively. Patients underwent a repeat scan within 30 min of the first baseline scan to assess for inter-scan reproducibility.

RESULTS

At baseline, eight patients (24%) had no CAC. Of the 25 patients (76%) with CAC, 10 (40%) had severe calcification. Intra-reviewer agreement was 83%. Inter-reviewer agreement ranged between 77 and 94%. Six (27%) of the patients with >30 baseline CACS had >15% change in CACS following repositioning. Four of these patients had an increase in CACS with position change [18% (95% CI: 5-40%)]. Of the 21 patients who underwent a follow-up scan at 1 year, 7 (33%) demonstrated CACS progression.

CONCLUSIONS

There is significant imprecision in HRCT-derived CACS in CKD patients. This suggests a need for standardization of methods of CACS measurement with HRCT.

The interscan variation of CT coronary artery calcification score: analysis of the Calcium Acetate Renagel Comparison (CARE)-2 study

RATIONALE AND OBJECTIVES

In the Calcium Acetate Renagel Evaluation (CARE)-2 study, the effects of calcium acetate plus atorvastatin (Lipitor) on the progression of coronary artery calcifications (CACs) are evaluated versus those of Renagel, monitored using dual electron beam tomography (EBT) scans (two scans at study initiation and two at follow up). The aim of this study is to estimate the interscan variation for the Agatston score and for the volume score determined in patients with end-stage renal disease (ESRD) in the CARE-2 study.

MATERIALS AND METHODS

CAC score and volume were measured at study initiation in 463 ESRD subjects (mean age: 59.4 +/- 12.5 years, 48.3% female). All patients underwent dual scanning using an EBT, as first scan of two needed to measure the progression of CAC when treated with sevelamer (Renagel) compared with calcium acetate with or without atorvastatin. All scans in all participants were completed by using an EBT system (GE Imatron, South San Francisco, CA). Interscan variability was defined by the following formula: abs (scan A - scan B) / (0.5 x scan A + 0.5 x scan B) x 100%, where A and B denote the first and second scan, respectively, of the dual scan procedure performed before treatment. We evaluated the reproducibility of the cutpoints commonly used for calcium scores clinically, namely 1-30, 31-100, 101-400, and >400.

RESULTS

The CAC interscan variability was 11.8% using the Agatston score and 10.3% using the volume score. The reproducibility was then assessed using cutpoints 1-30, 31-100, 101-400, and >400. Agatston score variability for the four subgroups was 61.3%, 23%, 16.1%, and 8.2%, respectively (mean variability, 11.8%). Volume score variability was 60.0%, 14.4%, 14.6%, and 7.7%, respectively (mean variability, 10.3%). The correlation coefficient for scan A to scan B goes up significantly with increasing calcium scores and reaches 0.99 for scores greater than 400 (P < .0001).

CONCLUSION

Interscan variability was sufficiently small for patients with calcium scores greater than 30. Our study thus demonstrates a sufficient reproducibility of the calcium score using EBT. This score allows for accurate serial assessment of these patients and for comparing different therapies.

Role of cardiac computed tomography and magnetic resonance imaging in the evaluation of acute chest pain in the emergency department

Evaluation of patients presenting with chest pain to the emergency department remains a challenging task because of a variety of etiologies that range from benign to potentially fatal. Although majority of patients do not have myocardial ischemia as the cause of their presentation, the clinical work up can be time consuming, costly and inconclusive. Recent technical advances in cardiac computed tomography and magnetic resonance imaging have led to better diagnostic accuracy in evaluating patients with chest pain. In this paper, we review the role of cardiac computed tomography and magnetic resonance imaging in evaluating patients with chest pain in the emergency department.

Determinants of coronary artery and aortic calcification in the Old Order Amish

BACKGROUND

Coronary artery calcification (CAC) is associated with an increased risk of cardiovascular disease; little is known, however, about thoracic aortic calcification (AC). Our goal was to characterize risk factors for CAC and AC and to estimate the genetic contribution to their variation.

METHODS AND RESULTS

The presence and quantity of CAC and AC were measured with electron beam computed tomography and fasting blood tests and cardiovascular risk factors were obtained in 614 asymptomatic Amish subjects. CAC prevalence was higher in men than women (55% versus 41%; P<0.0001), although there was no sex difference in AC prevalence (51% and 56% in men and women, respectively; P=0.95). Age was more strongly associated with AC presence (odds ratio [OR], 2.7 for 5 years) than CAC presence (OR, 1.9 for 5 years) (homogeneity P=0.001). Subjects with AC had a 3.3-fold higher odds of having CAC. Heritabilities of CAC and AC presence were 0.27+/-0.17 (P=0.04) and 0.55+/-0.18 (P=0.0008), respectively, whereas the heritabilities of quantity of CAC and AC were 0.30+/-0.10 (P=0.001) and 0.40+/-0.10 (P<0.0001), respectively. The genetic correlation between CAC and AC quantity was 0.34+/-0.19, whereas the environmental correlation between these 2 traits was 0.38+/-0.09.

CONCLUSIONS

CAC and AC have similar risk factors, except male gender is associated only with CAC and age is more strongly associated with AC. The patterns of correlations suggest that CAC and AC share some common sets of genes and environmental factors, although it is likely that separate genes and environmental factors also influence calcification at each site.

Vessel wall calcifications at multi-detector row CT angiography in patients with peripheral arterial disease: effect on clinical utility and clinical predictors

PURPOSE

To evaluate retrospectively the effect of vessel wall calcifications on the clinical utility of multi-detector row computed tomographic (CT) angiography performed in patients with peripheral arterial disease and to identify clinical predictors for the presence of vessel wall calcifications.

MATERIALS AND METHODS

The study was approved by the hospital institutional review board, and informed consent was obtained from all patients. For this study the authors included patients from two randomized controlled trials that measured the costs and effects of diagnostic imaging in patients with peripheral arterial disease. All patients underwent CT angiography and were followed up for 6 months. Clinical utility was measured on the basis of therapeutic confidence (rated on a 10-point scale) in the results of initial CT angiography and the need for additional vascular imaging. Univariable and multivariable logistic and linear regression analysis and the area under the receiver operating characteristic curve were used to evaluate the effect of vessel wall calcifications on the clinical utility of CT angiography and the use of patient characteristics to predict the number of calcified segments at CT angiography.

RESULTS

A total of 145 patients were included (mean age, 64 years; 70% men). The authors found that the number of calcified segments was a significant predictor of the need for additional imaging (P = .001) and of the confidence scores (P < .001). The number of calcified segments discriminated between patients who required additional imaging after CT angiography and those who did not (area under the receiver operating characteristic curve, 0.66; 95% confidence interval: 0.54, 0.77). Age, diabetes mellitus, and cardiac disease were significant predictors of the number of calcified segments in both the univariable and multivariable analyses (P < .05).

CONCLUSION

Vessel wall calcifications decrease the clinical utility of CT angiography in patients with peripheral arterial disease. Diabetes mellitus, cardiac disease, and elderly age (older than 84 years) are independently predictive for the presence of vessel wall calcifications.

Influence of scoring parameter settings on Agatston and volume scores for coronary calcification

Current multi-detector CT and electron beam tomography (EBT) technology enables the evaluation of coronary calcification. Multiple software packages are available to quantify calcification using several scoring algorithms implementing user-definable scoring parameters. We investigated the effect of scoring parameters on the calcium score outcome. Three parameters (four-connected or eight-connected, lesion size threshold and interpolation) are evaluated. Their theoretical influence on the scoring outcome is shown using simplified examples. To evaluate the effect in real data, we performed calcium scoring on randomly chosen EBT scans from 50 participants in an epidemiological study. Both the Agatston and volume scores were calculated. Changing from eight-connected to four-connected connectivity decreased both Agatston and volume scores (mean variability Agatston 3.15% and volume score -3.52%). Decreasing the threshold from 4 to 2 pixels increased the calcium scores because smaller lesions were also selected as calcified plaques (mean variability Agatston 16.23% and volume score 18.66%). Finally, the use of interpolation had a large negative effect on the volume score (mean variability -29.67%) and almost no effect on the Agatston score. Parameter settings in software for quantification for coronary calcification affect the calcium score outcome. Therefore, parameter settings for calcium scoring should be standardized.

Evaluating Changes in Coronary Artery Calcium: An Analytic Method That Accounts for Interscan Variability

OBJECTIVE

Coronary calcium measured by electron beam CT is associated with coronary disease and can be used to predict coronary disease events. Studies investigating changes in coronary calcium need to address interscan variability as it relates to the overall coronary calcium score in defining progression or regression of coronary calcium over time. SUBJECTS AND METHODS. Electron beam CT was performed on 1,074 participants. Coronary calcium volume scores were repeated 5 min apart. Interscan variability was examined using Bland-Altman plots and homogeneity tests. Transformations of the Box-Cox family (including power, roots, and logarithm) were applied to calcium volume scores. The transformation that stabilized the variation in calcium volume scores was applied to progression of calcium volume scores in 109 subjects with diabetes.

RESULTS

The variability in calcium volume score increased as the level of coronary calcium increased (rho = 0.67, p < 0.001 for the relation between the absolute difference and the mean value of calcium volume scores). This heterogeneity was removed using the square root transformation of the calcium volume score (rho = 0.09, p < 0.15 for the relation between the absolute difference in the square root of the calcium volume score and the mean square root of the calcium volume score). This transformation was applied to calcium volume scores taken a mean of 2.7 years apart in 109 subjects with diabetes. A significant change in calcium volume score was defined as a difference between the square root-transformed to calcium volume scores greater than or equal to 2.5 mm(3) (> 99th percentile of interscan variability). Significant progression was observed in 10% of the subjects. The square root of the calcium volume score corrected for the bias in progression of calcium volume because of the level of coronary calcium.

CONCLUSION

Using the square root of the calcium volume score stabilized interscan variability across the range of coronary calcium. Defining change in coronary calcium as greater than or equal to 2.5 mm(3) of the difference in the square root-transformed calcium volume scores provided an estimate that was unbiased with respect to baseline coronary calcium. This analytic technique may facilitate investigations of the relevance of changes in coronary calcium to clinical outcomes and the use of changes in coronary calcium as a measure of the therapeutic impact on subclinical disease in clinical trials.