Quantitative assessment of selective in-plane shielding of tissues in computed tomography through evaluation of absorbed dose and image quality.

This study aimed at assessment of efficacy of selective in-plane shielding in adults by quantitative evaluation of the achieved dose reduction and image quality. Commercially available accessories for in-plane shielding of the eye lens, thyroid and breast, and an anthropomorphic phantom were used for the evaluation of absorbed dose and image quality. Organ dose and total energy imparted were assessed by means of a Monte Carlo technique taking into account tube voltage, tube current, and scanner type. Image quality was quantified as noise in soft tissue. Application of the lens shield reduced dose to the lens by 27% and to the brain by 1%. The thyroid shield reduced thyroid dose by 26%; the breast shield reduced dose to the breasts by 30% and to the lungs by 15%. Total energy imparted (unshielded/shielded) was 88/86 mJ for computed tomography (CT) brain, 64/60 mJ for CT cervical spine, and 289/260 mJ for CT chest scanning. An increase in image noise could be observed in the ranges were bismuth shielding was applied. The observed reduction of organ dose and total energy imparted could be achieved more efficiently by a reduction of tube current. The application of in-plane selective shielding is therefore discouraged.