Evaluation of the efficacy of a bismuth shield during CT examinations

The purpose of the study was to evaluate the efficacy of a bismuth shield (Attenurad F&L Medical Products, Vandergrift, PA) in reducing the dose to surface organs during Computed Tomography (CT) examinations. The shield was evaluated for reduction of the dose to breast during chest examinations and reduction of the dose to the lens of the eye during brain examinations.

The dose was measured on patients (10 for the eye and 30 for the breast), and on an anthropomorphic phantom (Alderson Rando). The reduction of image quality was evaluated both qualitatively by an expert radiologist, and in terms of increased noise on the phantom images (Rando).

The use of the protective device reduced the dose by 34% to the breast and 50% to the lens. These figures are confirmed by the measurements taken both on patients and on the anthropomorphic phantom. The protective device reduced image quality in the regions immediately beneath it, but in the cases considered, those regions were of no diagnostic interest, while in the brain and lung regions, the quality is only slightly reduced, always allowing a correct diagnostic evaluation. Numerical analysis also led to the conclusion that a modest increase in noise is only statistically significant for the anterior portions of the lung. When present, the artifacts appeared outside the field of clinical interest. That is mainly due to the use of a foam pad (0.7 - 1 cm thick) to protect the breast.

The protection proved effective both in the case of breast and of lens, leading to a significant reduction in dose, without excessively affecting image quality. The shield proved easy to use, and did not increase the examination time.