Application of Bismuth Shielding and Organ Dose Modulation Techniques in Brain CT Scanning with Different Scanning Baselines

Objective: To investigate the effects of bismuth shielding and organ dose modulation (ODM) on image quality and lens radiation dose in brain computed tomography (CT) with different scanning baselines. Methods: GE (General Electric Company) Revolution CT was used to scan isolated skull specimens, with the glabellomeatal and orbitomeatal lines established as the scanning baselines. The volume CT dose index (CTDIvol) remained constant. Four scanning methods were adopted as follows: fixed mA, fixed mA combined with bismuth shielding, ODM, and ODM combined with bismuth shielding. The lens radiation dose for each scan was measured using a dosimeter. CT values and image noise levels were measured in the left cerebellum, temporal lobe of the brain, and left adipose body of the orbit. Results:The lens dose was highest when the baseline was the orbitomeatal line with a fixed mA (43.49 mGy), while the dose was lowest when the baseline was the glabellomeatal line with ODM combined with bismuth shielding (14.81 mGy). The CT values and image noise levels in the adipose body of the orbit increased when bismuth shielding and ODM combined with bismuth shielding were used. No significant difference was observed in image quality among the other groups. Conclusion: The organ dose of the eye lens could be reduced using the glabellomeatal line, and bismuth shielding combined with ODM were used for brain CT. However, the image quality of the intraorbital soft tissue might be decreased. In clinical practice, appropriate scanning methods can be used according to different patient conditions and diagnostic requirements.