Topogram-based tube current modulation of head computed tomography for optimizing image quality while protecting the eye lens with shielding.

Abstract

Multiple rounds of head computed tomography (CT) scans increase the risk of radiation-induced lens opacification. To investigate the effects of CT eye shielding and topogram-based tube current modulation (TCM) on the radiation dose received by the lens and the image quality of nasal and periorbital imaging. An anthropomorphic phantom was CT-scanned using either automatic tube current modulation or a fixed tube current. The lens radiation dose was estimated using cropped Gafchromic films irradiated with or without a shield over the orbit. Image quality, assessed using regions of interest drawn on the bilateral extraorbital areas and the nasal bone with a water-based marker, was evaluated using both a signal-to-noise ratio (SNR) and contrast-noise ratio (CNR). Two CT specialists independently assessed image artifacts using a three-point Likert scale. The estimated radiation dose received by the lens was significantly lower when barium sulfate or bismuth-antimony shields were used in conjunction with a fixed tube current (22.0% and 35.6% reduction, respectively). Topogram-based TCM mitigated the beam hardening-associated artifacts of bismuth-antimony and barium sulfate shields. This increased the SNR by 21.6% in the extraorbital region and the CNR by 7.2% between the nasal bones and extraorbital regions. The combination of topogram-based TCM and barium sulfate or bismuth-antimony shields reduced lens doses by 12.2% and 27.2%, respectively. Image artifacts induced by the bismuth-antimony shield at a fixed tube current for lenticular radioprotection were significantly reduced by topogram-based TCM, which increased the SNR of the anthropomorphic nasal bones and periorbital tissues.