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Measuring coronary calcium on CT images adjusted for attenuation differences.
Jennifer Clark Nelson1, Richard A Kronmal, J Jeffrey Carr
1Center for Health Studies, Group Health Cooperative, Metropolitan Park East, Suite 1600, 1730 Minor Ave, Seattle, WA 98101, USA. nelson.jl@ghc.org
Radiology
|April 29, 2005
Summary
Image attenuation values in computed tomographic (CT) scans vary by scanner and body size, impacting coronary calcium measurements. Standardizing attenuation values using calibration phantoms can improve the comparability of calcium scores across different scanners and over time.
Area of Science:
- Radiology
- Medical Imaging
- Cardiovascular Imaging
Background:
- Coronary calcium scoring using computed tomographic (CT) imaging is crucial for cardiovascular risk assessment.
- Variability in CT scanner technology and patient body mass index (BMI) can influence image attenuation values.
- Inconsistent attenuation values may lead to inaccurate coronary calcium measurements and affect clinical decision-making.
Purpose of the Study:
- To quantify variability in CT image attenuation values related to scanners and participants.
- To develop a method for standardizing attenuation values and calibrating coronary calcium measurements.
- To assess the impact of this calibration method on Agatston score accuracy.
Main Methods:
- Applied an image attenuation adjustment method using calibration phantom data to standardize attenuation values.
- Utilized data from two large, population-based, multicenter studies (Coronary Artery Risk Development in Young Adults and Multi-Ethnic Study of Atherosclerosis).
- Employed analysis of variance and multivariate linear regression to analyze variability and the effect of covariates (scanner, BMI, age, race, sex, smoking status).
Main Results:
- Mean attenuation values varied significantly by CT scanner type and participant BMI (P < .001).
- Lower attenuation values were observed with Siemens scanners and in participants with higher BMI (morbidly obese).
- Calibration adjustments to Agatston scores ranged widely and varied significantly by scanner and BMI, indicating substantial impact on measurements.
Conclusions:
- CT image attenuation is significantly influenced by scanner type and patient body size, not solely by true calcium burden.
- A calibration method using phantoms can standardize attenuation values and improve the comparability of coronary calcium measurements.
- This standardization is essential for accurate research and clinical practice, especially when comparing results across different scanners or over time.