Comparison of gonadal radiation doses from CT enterography and small-bowel follow-through in pediatric patients.

OBJECTIVE. CT enterography is superior to small-bowel follow-through (SBFT) for diagnosis of inflammatory bowel disease (IBD). It is widely assumed that the radiation dose from CT enterography is greater than that from SBFT in the pediatric patient. This study was designed to compare gonadal doses from CT enterography and SBFT to verify the best imaging choice for IBD evaluation in children. This study also challenges the assumption that CT enterography imparts a higher radiation dose through comparison of calculated radiation doses from CT enterography and SBFT. MATERIALS AND METHODS. Patients 0-18 years old who underwent either CT enterography or SBFT over a 2-year period were included. The CT enterography group consisted of 39 boys and 51 girls, whereas the SBFT group consisted of 89 boys and 113 girls. CT enterography was performed at 120 kVp and approximately 132 mAs (range, 54-330 mAs) using weight-based protocols. SBFT used automated control of kilovoltage and tube current-exposure time product. Patient demographics and technical parameters were collected for CT enterography and SBFT, data were cross-paired between CT enterography and SBFT, and gonadal dose was calculated. RESULTS. Mean (± SD) CT enterography testis and ovarian doses were 0.93 ± 0.3 cGy (n = 39) and 0.64 ± 0.2 cGy (n = 51), respectively. Mean SBFT testis and ovarian doses were 2.3 ± 1.6 cGy (n = 89) and 1.49 ± 0.3 cGy (n = 113), respectively. Mean fluoroscopy time for SBFT was 2.6 ± 2 minutes. Gonadal dose for CT enterography was significantly lower than that for SBFT in boys and girls (p < 0.001). SBFT dose was lower in girls than boys (p < 0.001), whereas CT enterography dose was higher in boys than girls (p < 0.001). CONCLUSION. Gonadal dose for CT enterography was lower than that for SBFT for boys and girls of all sizes and age. Controlled exposure time made CT enterography dose more consistent, whereas the range of dose for SBFT was highly operator dependent and related to extent of disease. Thus, for IBD, CT enterography is preferred over SBFT for all children.

Optimization of kilovoltage and tube current-exposure time product based on abdominal circumference: an oval phantom study for pediatric abdominal CT.

OBJECTIVE: This CT study evaluates image noise and radiation dose using a modified CT dose index phantom to approximate pediatric abdominal shape. Contrast-to-noise ratio (CNR) and radiation dose were measured. MATERIALS AND METHODS: The oval shape was simulated by fixing 1000-mL saline bags aside cylindric phantoms with variable circumferences. The doses at the center and peripheral holes in the phantom were recorded. Measurements were obtained at 50-400 mAs and 80-140 kVp. Diluted iodine contrast agent filled the center hole, and distilled water filled the peripheral holes. CNR was defined as the difference in CT number between diluted iodine and water divided by the standard deviation (SD) of CT number of water. RESULTS: Dose increased linearly with increases in tube current-exposure time product and by a power function (proportional to kVp(n), where n = 2.64-3.09) for increases in kilovoltage. A range of scanning parameters was established for each circumference from which technique optimization curves were created to determine the best tube current-time product and kilovoltage pairs when noise was less than 20 HU and dose was less than 2.5 cGy. CNR increased by 40% as kilovoltage was reduced from 140 to 80 kVp. A dose reduction of 70% was observed for 140 versus 80 kVp for the same CNR. CONCLUSION: Because pediatric patients of the same age and weight come in all shapes and sizes, abdominal circumference is a useful clinical parameter on which to base CT scan techniques controlling radiation output--namely kilovoltage and tube current-time product. Low-kilovoltage techniques for patients with small circumference show better iodine CNR.