Materials and Methods: Three groups were included in this experimental research in which phantom was scanned without using nano bismuth shield (group 1), using 0.5 mm nano bismuth shield (group 2), and employing nano bismuth shield with 1 mm thickness (group 3). The polymethyl methacrylate phantom was applied to present the main organ of the chest including the breast and lung. Multi-detector 6-slice CT scan system was utilized for the tests. In addition, the breast radiation dose was measured by ion-chamber which was placed at 12 o"clock position in the phantom according to dosimetry protocol. Further, chest CT image processing was performed once without shield and once in the presence of 10% nano bismuth shield with different thicknesses. Finally, image quality was compared by adding the shield for correct diagnosis. Tests were repeated three time and data were analyzed by ANOVA.

Results: Based on the results, using nano bismuth shields, breast dose reduced by 7.2% and 13.8% for 0.5 and 1 mm thickness of the shield, respectively. Furthermore, the CT number and noise increased from 121.3 to 126.36 HU and from 24.53 to 28.1 HU, respectively. Finally, the dose reduction ratio approximately doubled by increasing the thickness from 0.5 to 1 mm.

Conclusions: Generally, nano bismuth shields have a noticeable potential for reducing the breast dose with the smallest change in the noise.