Increased dose of IV contrast can compensate for reduced radiation dose, and vice versa, while maintaining signal-to-noise and contrast-to-noise ratios, offering protocol adjustments that can reduce age-specific risk, according to a study published in the February issue of the American Journal of Roentgenology.

The study was designed to evaluate whether an abdominal CT protocol could maintain image quality while reducing the lifetime risk of cancer in younger patients while reducing the risk of contrast induced nephropathy (CIN) in older patients. Lifetime risk of cancer is greater in younger patients and older patients and those with reduced renal function are at a higher risk for CIN, explained authors Tobias Fält, MD, and colleagues from Skåne University Hospital, Lund University, Malmö, Sweden.

Study participants were divided into four age groups of 25 patients each: group 1, 16-25 years; group 2, 26-50 years; group 3, 51-75 years; and group 4, older than 75 years. Tube load ranged from 100 to 300 mAs and IV contrast dose ranged from 600 to 350 mg I/kg. Group 3 served as the reference group.

The protocol was able to reduce the effective radiation dose in the youngest group by 57 percent, while reducing the IV contrast dose administered to elderly patients by 18 percent, reported the authors.

Results showed no statistically significant differences between groups for signal-to-noise and contrast-to-noise ratios.

Despite the only modest differences in objective measurements of image quality, visual analysis conducted by four readers was altered in certain groups. “Subjective image quality was affected by increased noise level on the images but was judged acceptable in all groups except the one with the lowest radiation dose,” wrote Fält and colleagues.

The authors suggested the subjective judgment that group 1 images were not acceptable could be due to high noise levels affecting image quality, but also speculated that the readers were not accustomed to reading high-noise-level images in their daily practice.

As for increasing radiation dose and reducing IV contrast in older patients, the authors wrote that their results “support this concept, and this may be an important finding for reducing the risk of CIN in examinations of older patients with reduced renal function.”