Marilyn Joy Siegel MD, Presenter: Nothing to Disclose

David Bradley, Abstract Co-Author: Nothing to Disclose

Bernhard Schmidt PhD, Abstract Co-Author: Nothing to Disclose

Christoph Suess PhD, Abstract Co-Author: Nothing to Disclose

To evaluate the effect on radiation dose and image quality in 16-slice computed tomography by varying kilovoltage peak (kVp) and milliampere second (mAs) for different object sizes simulating pediatric patients.

Four new tissue-equivalent oval-shaped phantoms ranging in size from neonate to 5-year-old, 12-year-old and adult patients (12 x 8, 21 x 14, 27 x 18, 33 x 22 cm^2) were scanned with a 16-slice scanner CT (Sensation16, Siemens Medical Solutions, Germany). The phantoms also had holes in the center and the periphery to allow dose measurements (CTDIw). CT scans were obtained with X-ray potentials ranging from 80 to 140 kVp. Radiation dose, image noise, and iodine contrast were measured at constant mAs and variable mAs appropriate for age at each tube voltage. For example at 120 kV we used 20, 35, 85 and 165 mAs to adapt the tube current to the increasing sizes. Image contrast and noise were evaluated by sampling iodine-filled cylinders.

Radiation doses were reduced by decreasing kVp. For example, at 80 kVp average doses for a circular phantom simulating a neonate, 5-year old, 12year-old and adult were 4.6, 3.7, 2.9, and 2.5 mGy/100 mAs, respectively. At 120 kVp, doses were 14.3, 11.6, 9.6, and 7.8 mGy/100 mAs, respectively. Noise increased for larger cross-section, but was very minimal for the small phantoms. The adaptation of tube current to object size reduced the dose and the noise. Iodine contrast increased for lower tube voltages. For example, for the 5-year old phantom, contrast increased from 172 HU at 120 kVp to 324 HU at 80 kVp. Signal to noise ratio (SNR) normalized to the same dose showed an improvement of SNR for lower tube voltages and smaller phantom cross-sections.

Our phantoms study on oval-shaped phantoms suggests that reducing the tube voltage to 80 kVp is justified for performing contrast-enhanced CT examinations in smaller patients. Lowering the tube voltage and tube current reduces patient dose, while maintaining image quality.

B.S.,C.S.,D.B.: works for Siemens Medical Solutions

Siegel, M, Bradley, D, Schmidt, B, Suess, C, Radiation Dose and Image Quality in Pediatric Contrast-enhanced 16-Slice CT.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4414849.html