Measuring coronary calcium on CT images adjusted for attenuation differences
ABSTRACT To quantify scanner and participant variability in attenuation values for computed tomographic (CT) images assessed for coronary calcium and define a method for standardizing attenuation values and calibrating calcium measurements.
Institutional review board approval and participant informed consent were obtained at all study sites. An image attenuation adjustment method involving the use of available calibration phantom data to define standard attenuation values was developed. The method was applied to images from two population-based multicenter studies: the Coronary Artery Risk Development in Young Adults study (3041 participants) and the Multi-Ethnic Study of Atherosclerosis (6814 participants). To quantify the variability in attenuation, analysis of variance techniques were used to compare the CT numbers of standardized torso phantom regions across study sites, and multivariate linear regression models of participant-specific calibration phantom attenuation values that included participant age, race, sex, body mass index (BMI), smoking status, and site as covariates were developed. To assess the effect of the calibration method on calcium measurements, Pearson correlation coefficients between unadjusted and attenuation-adjusted calcium measurements were computed. Multivariate models were used to examine the effect of sex, race, BMI, smoking status, unadjusted score, and site on Agatston score adjustments.
Mean attenuation values (CT numbers) of a standard calibration phantom scanned beneath participants varied significantly according to scanner and participant BMI (P < .001 for both). Values were lowest for Siemens multi-detector row CT scanners (110.0 HU), followed by GE-Imatron electron-beam (116.0 HU) and GE LightSpeed multi-detector row scanners (121.5 HU). Values were also lower for morbidly obese (BMI, > or =40.0 kg/m(2)) participants (108.9 HU), followed by obese (BMI, 30.0-39.9 kg/m(2)) (114.8 HU), overweight (BMI, 25.0-29.9 kg/m(2)) (118.5 HU), and normal-weight or underweight (BMI, <25.0 kg/m(2)) (120.1 HU) participants. Agatston score calibration adjustments ranged from -650 to 1071 (mean, -8 +/- 50 [standard deviation]) and increased with Agatston score (P < .001). The direction and magnitude of adjustment varied significantly according to scanner and BMI (P < .001 for both) and were consistent with phantom attenuation results in that calibration resulted in score decreases for images with higher phantom attenuation values.
Image attenuation values vary by scanner and participant body size, producing calcium score differences that are not due to true calcium burden disparities. Use of calibration phantoms to adjust attenuation values and calibrate calcium measurements in research studies and clinical practice may improve the comparability of such measurements between persons scanned with different scanners and within persons over time.
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ABSTRACT: Obstructive sleep apnea (OSA) is a common condition associated with cardiovascular disease. Its potential effect on progression of subclinical atherosclerosis is not well understood. We tested the hypothesis that self-reported OSA is associated with progression of coronary artery calcium (CAC). We also evaluated whether traditional cardiovascular risk factors accounted for the association.Journal of the American Heart Association 09/2014; 3(5). DOI:10.1161/JAHA.114.001241 · 2.88 Impact Factor
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ABSTRACT: The absence of coronary artery calcium (CAC) in middle age is associated with very low short-term risk for coronary events. However, the long-term implications of a CAC score of 0 are uncertain, particularly among individuals with high cardiovascular lifetime risk. We sought to characterize the association between predicted lifetime risk and incident CAC among individuals with low short-term risk. We included 754 Dallas Heart Study participants with serial CAC scans (6.9 years apart) and both low short-term risk and baseline CAC=0. Lifetime risk for cardiovascular disease was estimated according to risk factor burden. Among this group, 365 individuals (48.4%) were at low lifetime risk and 389 (51.6%) at high lifetime risk. High lifetime risk was associated with higher annualized CAC incidence (4.2% versus 2.7%; P < 0.001). Similarly, mean follow-up CAC scores were higher among participants with high lifetime risk (7.8 versus 2.4 Agatston units). After adjustment for age, sex, and race, high lifetime risk remained independently associated with incident CAC (OR 1.60; 95% CI 1.12 to 2.27; P=0.01). When assessing risk factor burden at the follow-up visit, 66.7% of CAC incidence observed in the low lifetime risk group occurred among individuals reclassified to a higher short- or long-term risk category. Among individuals with low short-term risk and CAC scores of 0, high lifetime risk is associated with a higher incidence of CAC. These findings highlight the importance of lifetime risk even among individuals with very low short-term risk. © 2014 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.Journal of the American Heart Association 10/2014; 3(6). DOI:10.1161/JAHA.114.001280 · 2.88 Impact Factor
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ABSTRACT: Objectives Retired National Football League (NFL) players were reported to have high prevalence of cardiovascular risk factors. Lipoprotein Associated Phospholipase A2 (LpPLA2) has shown to be associated with cardiovascular disease in the general population, but it is unknown whether such an association exists in retired NFL players. Our objective was to assess whether LpPLA2 mass was associated with coronary artery calcium (CAC) and carotid artery plaque (CAP) in retired NFL players. Methods LpPLA2 mass was assessed using a dual monoclonal antibody immunoassay. CAC presence was defined as CAC score>0. CAP was defined as focal thickening ≥50% than that of the surrounding vessel wall with a minimal thickness of 1.2 mm on carotid ultrasound. Results In 832 NFL players, the median (IQR) age and LpPLA2 levels were 54 (45–63) years and 142 (109–181) ng/mL respectively. LpPLA2 mass was positively correlated with low-density lipoprotein (LDL) cholesterol and high-density lipoprotein cholesterol; negatively correlated with LDL particle concentration and body mass index; and not correlated with high-sensitivity C-reactive protein. CAC was present in 659 (79%) and CAP in 544 (65%) players. In a fully adjusted model, LpPLA2 was not associated with CAC (OR per 1-SD increase, 0.85; 95% CI 0.71–1.02) or CAP (0.90, 0.75–1.08). LpPLA2 was also not associated with CAC burden in those with CAC>0. Results were similar when highest and lowest LpPLA2 tertiles were compared, and also in various subgroups. Conclusion LpPLA2 mass was not associated with coronary or carotid subclinical atherosclerosis in retired NFL players.Atherosclerosis 10/2014; 236(2):251–256. DOI:10.1016/j.atherosclerosis.2014.07.011 · 3.97 Impact Factor