ABSTRACT
BACKGROUND: The Norwegian Radiation Protection Authority recommends bismuth to protect radiosensitive surface organs during CT imaging. A study based on the use of phantoms was therefore initiated to investigate the usefulness of this protection on the breasts of young girls undergoing high-resolution computed tomography (HRCT) of the chest. MATERIAL AND METHODS: Shields covered with one, two or three layers of bismuth were placed on a homogenous phantom. CT numbers (pixel values in the images which describe the density of the tissue imaged), noise and artifacts were evaluated from the images of the phantom. Dosimeters were used for dose measurements in an anthropomorphic phantom of a child. RESULTS: Areas close to the shield in the images of the phantom had CT numbers up to 33 % higher with two and three layers of bismuth than in the images without shielding. With one layer the CT numbers were up to 8 % higher. Noise in the same area was up to 56 % higher with two and three layers of bismuth than without, and up to 14 % higher with one layer. The surface dose in the breast region was reduced with 30 % with one layer of bismuth, 45 % with two and 75 % with three layers of bismuth. INTERPRETATION: Shielding with one layer of bismuth seems to have little effect on the CT images. The Department of pediatric radiology at Ullevaal University Hospital now uses bismuth protection with one layer as a routine during HRCT of girls up to 16 years of age.
