Computer tomography of human brain, from base of the skull to top. Taken with intravenous contrast medium.
The debate over the use of bismuth shields during CT procedures continues. In May of this year, the Radiological Society of North America (RSNA) published an article prefacing the American Association of Physicists in Medicine (AAPM) position statement on this issue. The RSNA article outlines the benefits and possible shortcomings of using bismuth shields to reduce dose to the patient in CT.
Many facilities do not have standardized procedures for use of bismuth shields. At the University of California at San Francisco Hospital for example, their policy only states that, “Bismuth or lead shields are applied to breasts, thyroid, gonads, and eyes whenever possible, especially in pediatric patients, to minimize their exposure to radiation.”
In the 2008 edition of the book, MDCT: From Protocols to Practice by M.K. Kalra et al., the authors write,
“Recently, thinly layered bismuth-impregnated radioprotective latex shields have been used to reduce the surface dose to the breast, thyroid, and lens when these structures lie in the area of interest. However, the use of gonadal shielding during CT examinations is controversial. A testis capsule (shield) can reduce the absorbed dose to the testes in abdominal CT, whereas a lead apron is not appropriate for dose reduction to the ovaries (due to their frequently irregular position).”
The authors go on to say,
“Recent studies suggested that although the use of in-plane bismuth shields can reduce exposure to important parts of the body, such as thyroid, breasts, and lens, they also lead to changes in the image noise and CT attenuation values or Hounsfield units . Geleijns et al. therefore recommended that the use of these shields should be avoided by achieving dose reduction with tube-current reduction .”
We are not aware of any hospitals that have a written policy on the use of bismuth shields, and it may be prudent to wait to develop one until the AAPM releases their position statement on the use of bismuth shields in CT. A recent presentation by Dr. McCollough, Director of the CT Clinical Innovation Center at the Mayo Clinic, adds more data to the growing body of research.
IEMA regulations do not comment on the use of bismuth shields, but only on the use of lead shields, as in 32 Ill. Adm. Code 360.40 m) “Gonadal Shielding. Except for cases in which it would interfere with the diagnostic procedure, gonadal shielding of not less than 0.5 millimeter of lead equivalent shall be used for patients (who have not passed the reproductive age) during those radiographic procedures in which the gonads are in the useful beam.”
 Geleijns J, Salvado Artells M, Veldkamp WJ et al (2006) Quantitative assessment of selective in-plane shielding tissues in computed tomography through evaluation of absorbed dose and image quality. Eur Radio 16:2334-40 52.