Radiation dose can be greatly reduced during a coronary CT angiography (CTA) while also maintaining image quality by reducing tube voltage to 80-kVp in exams of patients with normal body mass index (BMI), according to a study published in the November issue of the American Journal of Roentgenology .
Troy M. LaBounty, MD, of the department of imaging at Cedars-Sinai Medical Center in Los Angeles, and colleagues noted that previous studies have shown a reduced tube voltage of 100-kVp lowered dose in CTA exams of nonobese patients, and the researchers wanted to determine if the voltage could be further reduced without compromising image quality.
“Coronary CTA using an even lower tube voltage, 80-kVp, is often performed for pediatric examinations and has been reported to be feasible and result in high image quality in slender adult patients,” wrote the authors.
LaBounty et al performed a prospective, multicenter, multivendor trial that randomized 208 consecutive patients with a normal BMI ( <25 kg/m 2) to receive either 80-kVp imaging or 100-kVp imaging. Blinded readers then rated interpretability, image quality, study signal, noise and contrast.
Results showed imaging with 80-kVp was associated with a 47 percent lower median radiation dose when compared with 100-kVp imaging. The studies obtained with 80-kVp had a 27 percent increase in signal, 25 percent higher contrast and 50 percent greater noise, which resulted in a 15 percent decrease in signal-to-noise ratio and a 16 percent decrease in contrast-to-noise ratio.
However, there was no significant difference in interpretability or image quality as the resulting images from both groups had the same median scores from the readers.
“Coronary CTA using 80-kVp instead of 100-kVp was associated with a nearly 50 percent reduction in radiation dose with no significant difference in interpretability and noninferior image quality despite lower signal-to-noise and contrast-to-noise ratios,” wrote the authors. “The use of 80-kVp tube voltage should be considered in dose-reduction strategies for coronary CTA of individuals with a normal BMI.”
The researchers noted that the doses calculated for their study were lower than those calculated for previous studies involving the lowering of tube voltages, and attributed the differences to the use of prospective ECG triggering. Prospective ECG triggering has been estimated to reduce dose by 78 percent compared with retrospective ECG gating, and prospective ECG triggering was used in 93 percent of patients in the current study.
Differences in chest size between men and women had little effect on image quality, according to the authors, allowing for 80-kVp tube voltage to be used as a dose reduction strategy in patients of normal BMI regardless of sex.