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AAPM recommends bismuth shield alternatives

by Brendon Nafziger, DOTmed News Associate Editor | March 23, 2012
The American Association of Physicists in Medicine advises providers to look for alternatives to bismuth shields to protect patients from radiation during CT scans.

In a position statement released Wednesday, the group said while effective at limiting the anterior organ dose, the shields can result in image artifacts and often are pointless when using CT scanners with automated image capture systems, which will simply compensate for the shield by delivering a higher dose.

"Other techniques exist that can provide the same level of anterior dose reduction at equivalent or superior image quality that do not have these disadvantages," the AAPM said in the statement. "The AAPM recommends that these alternatives to bismuth shielding be carefully considered, and implemented when possible."

The bismuth-impregnated latex shields are often placed across, say, women's breasts during CT scans to absorb some of the X-rays. But the group said they have a few problems. For one, they can lead to imaging artifacts. Another is what happens when used with automated exposure control (AEC) and tube current modulation systems. For the automated system, providers take a CT radiograph for patient attenuation correction before the actual scan. However, if the shield is put on before the CT radiograph, it means the CT scanner will compensate by using too much power. If it's put on after, the CT scanner is calibrated for a weaker attenuation so will be underpowered.

Instead of the shields, the group recommends simply lowering X-ray tube current by the same percentage as achieved by shielding to get images at the same noise level but without the artifacts and while also reducing dose to lateral and posterior surfaces.

The group said the statement was approved by the board of directors on Feb. 7.

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