Trade-off between breast dose and image quality using composite bismuth shields in computed tomography: A phantom study

Introduction: Many researchers have suggested that bismuth com-posite shields (BCS) reduce breast dose remarkably; however, the level of this reduction and its impact on image quality has not been assessed. This study aimed to evaluate the efficiency of nano-and micro-BCS in reducing the dose and image quality during chest computed tomog-raphy (CT) scans.Materials and methods: Bismuth shields composed of 15 weight-ing percentage (wt%) and 20 wt% bismuth oxide (Bi2O3) nano -and micro-particles mixed in silicon rubber polymer were constructed in 1 and 1.5 mm thicknesses. The physical properties of nanoparti-cles were assessed using a scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX). Breast ra-diation doses were measured experimentally during chest CT using PMMA standard dosimetry phantom (body phantom, 76-419-4150, Fluke Biomedical) in the presence of the shields. The image quality was assessed by calculating signal and noise values in different regions.Results: The SEM images showed that the average size of Bi2O3 nano -and micro-particles was about 70 nm and 150 mu m, respectively. The breast doses were reduced by increasing the shield thickness/bismuth weight percentage. The maximum dose reduction was related to the20% weight of Bi2O3 nano-particles and a thickness of 1.5 mm. The minimum dose reduction was related to the 15% weight of Bi2O3 micro-particles with a thickness of 1 mm. The mean noise was higher in nano-particle bismuth shields than in micro-particles.Conclusion: Composite shields containing bismuth nano-and micro-particles can reduce the breast dose during chest CT exami-nations while negatively impacting diagnostic image quality. Several critical factors, such as bismuth concentration, particle size, and shield thickness, directly affect the efficiency.