Organ-based tube current modulation and bismuth eye shielding in pediatric head computed tomography

Exposure of the eye lens to ionizing radiation results in cataract. Several dose optimization techniques to protect the lens are available for computed tomography (CT). The radiation dose to the eye lens, volume CT dose index (CTDI${}_{vol}$) and image quality of various methods of dose optimization were evaluated for pediatric head CT: automated tube current modulation (ATCM), automated tube voltage selection (ATVS), organ-based tube current modulation (OBTCM) and bismuth shielding. An anthropomorphic phantom of a 5-year-old child was scanned with nine protocols: no dose optimization technique and then adding different dose optimization techniques alone and in combination. Dose to the eye, thyroid and breast were estimated using metal oxide semiconductor field effect transistor (MOSFET) dosimetry. CTDI${}_{vol}$, influence of timing of shield placement, image noise and attenuation values in 13 regions of interest of the head and subjective image quality were compared. The eye shield significantly reduced the eye lens dose when used alone, to a similar degree as when using all software-based techniques together. When used in combination with software-based techniques, the shield reduced the eye lens dose by up to 45% compared to the no dose optimization technique. Noise was significantly increased by the shield, most pronounced in the anterior portion of the eye. The combination of ATCM, ATVS, OBTCM and a bismuth shield, with the shield placed after acquiring the localizer image, should be considered to reduce the radiation dose to the eye lens in pediatric head CT.