Optimization of kVp and mAs for pediatric low-dose simulated abdominal CT: is it best to base parameter selection on object circumference?

Objective: The objective of our study was to determine the effect of mAs and kVp reduction on pediatric phantoms based on patient circumference to optimize dose reduction and maintain image quality for abdominal CT.

Subjects And Methods: Three polymethylmethacrylate right cylindric CT dose index (CTDI) phantoms with diameters of 10, 16, and 32 cm simulated the abdomen of an infant, child, and adolescent, respectively. Using a National Institute of Standards & Technology ion chamber and Victoreen 660 electrometer, doses at centerline were recorded on a 16-MDCT scanner. Measurements were obtained in incremental steps from 50 to 400 mAs and from 80 to 140 kVp. Noise was calibrated to clinical images through a calibration factor.

Results: For phantoms of all circumferences, doses increased linearly with an increase in mAs and by the power function of kVp(n) for increases in kVp. There was an associated decrease in noise for all circumferences and a sharp decrease at lower doses with a plateau at higher doses. Using a noise threshold of 20 HU and a dose threshold of 2.5 cGy, a range of imaging parameters was established for each circumference from which technique optimization curves were created to determine optimal mAs and kVp pairs. The mean measured dose was 2.435 ± 0.019 cGy. The mean measured noise was 29.35 ± 1.45 HU.

Conclusion: For pediatric CT, the most accurate way to strike the balance between image quality and radiation dose is to adjust dose to abdominal circumference, not body weight or age. Our data support the use of technique optimization curves to optimize kVp and mAs.