2020 Volume 47 Issue 4 Pages 167-174
Purpose Bismuth-impregnated latex shields are known to effectively reduce the radiation dose on the lens when performing head computed tomography (CT) scanning. The degree of shielding effect differs depending on how the shield is used. Following a phantom study performed in our institution, the present study prospectively examined the degree of deterioration of image quality in clinical images to determine whether bismuth shielding negatively affects the imaging diagnosis.
Material and Method We included a total of 50 patients who underwent head CT scanning with bismuth shielding in our institution and had also undergone previous head CT scanning with the same scan setting. In the patients with shields and without shields, we measured CT values and noise at 22 individual points, and then two radiologists evaluated visual quality. A paired two-sample t-test was used to evaluate significant differences between these two groups.
Result We excluded 13 of the 50 patients, because of severe degradation of image quality. CT value in the non-shielded patients were significantly different from those the shielded patients, except at three points; however, the difference was <2 HU except for the eyeballs. Image noise was also significantly different at five points, but the difference was <1 HU. Visual evaluation found a significant decrease in the image quality of the eyeball in the shielded patients, but no other effects were observed.
Discussion and conclusion This study showed no significant decrease in the image quality of the head CT, except for the eyeballs. The results indicated that bismuth shielding can be considered an effective technique for reducing lens exposure. With the advancement in the new CT equipment in recent years, dose reduction is being without using shields. If this equipment becomes widespread, bismuth shielding would become unnecessary. However, as this will definitely take some time,, Bismuth shielding remains in significant use.