Xiaowei Zhu, Presenter: Nothing to Disclose

Sabah Servaes MD, Abstract Co-Author: Nothing to Disclose

Previous studies have reported effects on radiation dose with Breast Shield using pre-scan tube modulations. The purpose of this study was to assess the effect of bismuth breast shield on radiation dose during pediatric chest imaging using axial and angular (Real Time) tube current modulation.

CT scans were performed on a 5-y old specially designed anthropomorphic phantom using 64-slice MDCT. The phantom has 5 pencil ionization chamber slots allowing measurements similar to that of standard CT Dose Index (CTDI) phantom. During the topographic scan, no breast shield was placed on the phantom. After topographic scan, the chest CT scans were performed with the bismuth breast shield(s) using both axial and angular dose modulations. The axial tube current was modulated during AP topographic scan. The angular tube current modulation was performed real time during CT scan. Radiation doses were measured with pencil-ionization chamber during CT scans at 5 locations: at center, at 1cm from the edge of 12, 3, 6, and 9 o'clock locations.

At 120 kVp, 0.03 mm-Pb equivalent breast shield reduced dose to the breast by 20%, and overall CTDI (therefore effective dose) by 12%; At 100 kVp, the reductions were 17% and 7%, respectively. At 120 kVp, 0.06 mm-Pb equivalent breast shield reduced dose to breast by 28%, and overall CTDI by 17%; At 100 kVp, the reductions were 28% and 16%, respectively. Changes in Hounsfield Unit (HU) of the scanned regions and standard deviation of HU were observed. However, due to real time current modulation, signal to noise levels were maintained. With 0.06 mm-Pb shield, striking artifacts observed were deemed clinically unacceptable.

Without significantly losing image quality, dose reduction to both breast and overall effective dose can be achieved with 0.03 mm-Pb equivalent breast shield using real time tube modulation of the CT scanner tested. Due to the changes in HU, breast shield should not be used for diagnosis when quantitative analysis of HU is required.

Using of 0.03 mm-Pb breast shield can be considered for non-quantitative studies with the understanding of effectiveness of real-time tube current modulation of a specific CT scanner.

Zhu, X, Servaes, S, Multiple Detector CT (MDCT) Chest Image Using Axial and Angular (Real Time) Tube Current Modulation with Breast Shielding: A Phantom Study.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6017356.html