Coronary CT angiography study rules out coronary artery disease in a 58-year-old asymptomatic man. Image source: U. Joseph Schoepf, MD, Medical University of South Carolina, Charleston

Researchers were able to dramatically lower the radiation dose of CT angiography (CTA) in an overweight and obese sample while preserving diagnostic accuracy, according to a study published Oct. 15 in the American Journal of Cardiology.

The researchers sought to assess whether reducing CCTA voltage from 120 kV to 100 kV and the resulting radiation exposure to patients could still yield diagnostically adequate images in a patient with high body mass index (BMI). “Lowering the voltage to 100 kV increases the image noise and could ultimately result in unacceptable image degradation,” wrote John S. Ho, MD, and co-authors from the Cooper Clinic in Dallas. "It is unknown whether one could use a 100 kV CCTA protocol with overweight or obese patients.”

Two physicians read 914 coronary CCTA images, including 302 retrospective 120 kV images, 220 retrospective 100 kV images and 359 prospective 100 kV images. Patients referred from the CCTA readings for invasive angiography intervention were followed in order to determine each imaging grate’s positive predictive value (PPV).

Radiation doses were reduced from 18.0 mSv (standard deviation, SD, 5.9) to 5.0 mSv (SD, 1) from the 120 kV to 100 kV retrospective studies, and finally down to 1.8 mSv (SD, .2) in the prospective 100 kV group, the authors estimated. The reduced tube voltage was associated with increased image noise and decreasing signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR). Despite the worsened image quality, the researchers found that PPVs remained at adequate levels, from 84 percent with 120 kV to 90 percent at 100 kV. In patients with BMIs above 30 kg/m², the PPV fell to 82 percent.

The authors concluded that despite the reductions in image quality associated with lower voltage/radiation doses and overweight patients, the safer dose still produced images that were adequate for diagnosis in overweight and obese patients with BMIs below 35 kg/m². The authors also noted that image quality worsened as BMI increased in all groups, regardless of the CCTA voltage.

The article noted that the study design did not allow for the measurement of the negative predictive value of the reduced voltage/radiation, though the authors said that previous studies had reported high negative predictive values. The authors also noted that the radiation doses were estimations, not measurements.

Even so, the authors concluded that the 100 kV dose was dramatically lower and that the safer “100 kV coronary CCTA is feasible in overweight and many obese subjects.”