Orlando Augusto Micheli MD, Presenter: Nothing to Disclose

Andrew R. Cunningham, Abstract Co-Author: Nothing to Disclose

Kai H. Lee PhD, Abstract Co-Author: Nothing to Disclose

Patrick M. Colletti MD, Abstract Co-Author: Nothing to Disclose

The female breast is the most radiosensitive tissue exposed during chest CT. Bismuth breast shields have been used to reduce breast exposure during the AP portions of chest CT acquisitions. It may be argued that this passive technique results in the inefficient use of radiation, with proportional noise increase. We tested the radiation and S/N effects of breast shielding with an anthropomorphic phantom and pin diode radiation detectors in a MDCT system.  

An anthropomorphic whole body phantom was scanned with standard chest MDCT-16 with and without a bismuth breast shield. Anterior, lateral, and posterior exposure was measured with a pin diode radiation system. Images were observed for artifacts. Measurements of attenuation numbers and noise were compared with and without the shield.

As expected, the shield caused tangential beam hardening artifacts presenting as streaks anterior and tangential to the shield. With the shield in place during the scout image, the detected increased attenuation resulted in a 31% drop in anterior exposure, but with14% lateral and 12% posterior increases. With the shield applied after the scout acquisition, there was a 40% reduction in anterior exposure, an 8% decrease laterally, and a 4% increase posteriorly. CT numbers increased anteriorly outside (+37HU), anteriorly within (+10HU), and  posteriorly within (+98HU). Noise increased anteriorly outside (+41%), anteriorly within (+34%) and decreased posteriorly within (-10%).

1. Breast shields cause beam hardening artifact that is generally tangential to the image. 2. Breast shields should be applied after the scout image is acquired. 3. Breast shields can reduce anterior exposure by 40%. 4. Breast shields may increase measured attenuation values. 5. Breast shields are associated with increased noise.

The reduction in anterior chest CT exposure associated with bismuth breast shields is offset by proportional increased image noise. Simple exposure reduction may achieve similar results.

Micheli, O, Cunningham, A, Lee, K, Colletti, P, Are Bismuth Breast Shields Effective to Reduce Exposure during Chest CT?.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12031630.html