Effect of body size on dose reduction with longitudinal tube current modulation in pediatric patients

The purpose of the study was to evaluate whether dose reduction by tube current modulation in pediatric abdominal CT depends on patient body size.

A 12-month (February 2012 through January 2013) retrospective evaluation of consecutive abdominal 128-MDCT examinations was performed. All studies were performed with longitudinal (z-axis) tube current modulation. Dose reduction from tube current modulation in every CT acquisition was recorded and compared with body weight. In addition, 100 randomized CT abdominal scans were evaluated for average and SD of the water-equivalent diameter along the z-axis.

The results include 466 abdominal CT scans of 369 children (172 girls, 197 boys; age range, 3 weeks-18 years; average, 9.2 years; body weight range, 3.5-130 kg; average, 31 kg). The average tube current-time reduction was 19%. Dose reduction was least effective (p<0.05; average, 11%) for body weight less than 20 kg. The least variability (SD/average) of water-equivalent diameter along the z-axis was found for body weights greater than 20 kg (5.0%) and 20-40 kg (5.9%) (p<0.05). Dose reduction was most effective (p<0.05; average, 30%) at the body weight range of 60-100 kg.

Dose reduction with automated tube modulation depends on body weight and is less effective in children with a small body size. One of the reasons for this phenomenon could be a closer to uniform water-equivalent diameter along the z-axis in children with a small body size.