Should adults with type 2 diabetes be screened for atherosclerotic cardiovascular disease?

Detection and quantification of coronary calcium from dual energy chest x-rays: Phantom feasibility study

PURPOSE

We have demonstrated the ability to identify coronary calcium, a reliable biomarker of coronary artery disease, using nongated, 2-shot, dual energy (DE) chest x-ray imaging. Here we will use digital simulations, backed up by measurements, to characterize DE calcium signals and the role of potential confounds such as beam hardening, x-ray scatter, cardiac motion, and pulmonary artery pulsation. For the DE calcium signal, we will consider quantification, as compared to CT calcium score, and visualization.

METHODS

We created stylized and anatomical digital 3D phantoms including heart, lung, coronary calcium, spine, ribs, pulmonary artery, and adipose. We simulated high and low kVp x-ray acquisitions with x-ray spectra, energy dependent attenuation, scatter, ideal detector, and automatic exposure control (AEC). Phantoms allowed us to vary adipose thickness, cardiac motion, etc. We used specialized dual energy coronary calcium (DECC) processing that includes corrections for scatter and beam hardening.

RESULTS

Beam hardening over a wide range of adipose thickness (0-30 cm) reduced the change in intensity of a coronary artery calcification (ΔI_CAC ) by < 3% in DECC images. Scatter correction errors of ±50% affected the calcium signal (ΔI_CAC ) in DECC images ±9%. If a simulated pulmonary artery fills with blood between exposures, it can give rise to a residual signal in DECC images, explaining pulmonary artery visibility in some clinical images. Residual misregistration can be mostly compensated by integrating signals in an enlarged region encompassing registration artifacts. DECC calcium score compared favorably to CT mass and volume scores over a number of phantom perturbations.

CONCLUSION

Simulations indicate that proper DECC processing can faithfully recover coronary calcium signals. Beam hardening, errors in scatter estimation, cardiac motion, calcium residual misregistration etc., are all manageable. Simulations are valuable as we continue to optimize DE coronary calcium image processing and quantitative analysis.

Cardiovascular risk assessment and screening in diabetes

Diabetes used to be considered as a coronary heart disease equivalence and universally classified high cardiovascular risk population. However increasing epidemiological evidence now indicates the heterogeneity of risk among the diabetic patients and imposes animportance of stratifying those with relative low-risk from high-risk ones. Despite the existing risk assessment tools, current cardivoascualr disease prevention guidelines fail to provide more detailed stratification strategies for patient with diabetes and expose them to either overtreatment or undertreatment. On the other hand, various screening modality, including novel biomarkers and subclinical asthrosclerosis scanning, including coronary calcium scanning, carotid intima-media thickness, myocardial perfusion imaging and coronary computed tomography angiography, have provided very promising usage is risk stratification. With better developed test techniques and more extensive evidence, these modalities may serve in standardized screening algorithm to improve the cardiovascular risk assessment of patients with diabetes and better instruct their individualized preventive therapy.