Dose reduction in pediatric CT: a rational approach

To determine size-dependent technique factors for pediatric computed tomography (CT) by using physically measured objective data.

Six phantom cylinders (10-32 cm in diameter) were scanned with a clinical multi-detector row CT scanner. CT noise was statistically characterized for CT technique factors from 80 to 140 kVp and from 10 to 300 mAs. Dose measurements were performed with each phantom. Dilute iodine and tissue contrast were determined with computer calculations validated with measured data. The dose, noise, and contrast data were computer fit, and pediatric CT technique factors (milliampere seconds) necessary to maintain the contrast-to-noise ratio (CNR) were computed.

As compared with that in a reference cylindric adult abdomen of 28 cm in diameter, CNR was maintained at a constant level in pediatric patients of 25, 20, and 15 cm in diameter, respectively, when milliampere second values of 0.557, 0.196, and 0.054 of the adult milliampere second values were used. The corresponding doses were reduced to 0.642, 0.287, and 0.090 of the 28-cm-diameter adult dose, respectively. CT techniques for examination of pediatric heads measuring 15 and 13 cm, respectively, can involve the use of milliampere second values of 0.572 and 0.366 of those used for examination of a standard 17-cm-diameter adult head.

CT technique charts for pediatric abdominal and head examinations were produced on the basis of physically measured data; use of these tables will enable pediatric radiation dose to be reduced while CNR is preserved.