Ferdinand Lueck DIPLPHYS, Presenter: Employee, Artemis Imaging GmbH

Michaela Weigel Dipl Phys, Abstract Co-Author: Nothing to Disclose

Daniel Kolditz, Abstract Co-Author: Employee, Artemis Imaging GmbH

Sabrina Viviane Vollmar, Abstract Co-Author: Nothing to Disclose

Martin Hupfer DIPLPHYS, Abstract Co-Author: Employee, Artemis Imaging GmbH

Willi A. Kalender PhD, Abstract Co-Author: Consultant, Siemens AG Consultant, Bayer AG Founder, CT Imaging GmbH Scientific Advisor, CT Imaging GmbH Shareholder, CT Imaging GmbH Founder, Artemis Imaging GmbH CEO, Artemis Imaging GmbH Shareholder, Artemis Imaging GmbH

The purpose of this study was to investigate the effect of shaped filters specifically designed for a dedicated breast CT scanner on dose and image quality.

Optimization of filter shape and thickness was performed with the goal to yield homogeneous distributions of dose and CT values in the breast. Different filter materials (aluminum, copper, carbon, polytetrafluorethylen) and breast diameters (8-18 cm) were considered. The filter thickness as a function of fan angle was determined iteratively and taken into account in calculations of the 3D dose distributions with a Monte Carlo tool (ImpactMC, CT Imaging, Erlangen, Germany) and in the simulation of 3D CT images based on ray-tracing methods. In addition, the distribution and intensity of noise and scattered radiation was evaluated. Both the overall dose reduction and the decrease of noise and scatter were determined. For validation purposes, measurements were conducted in an experimental breast CT scanner with a shaped filter of aluminum. The resulting CT value and dose distributions were determined in a homogeneous breast “CTDI” phantom. Dose was assessed in the center and periphery using an ionization chamber calibrated for low kV values and thermoluminescence dosimeters.  

The results for a standard breast (cylinder of 14 cm in diameter and 10 cm height) scanned with an average glandular dose (AGD) of 6 mGy were as follows: The dose in the periphery was up to 45 % higher than in the center of the breast. With the shaped filter a homogeneous dose distribution was achieved and the AGD was reduced by about 40 % to a value of 3.6 mGy. Since the filter is considered in the analytical precorrection during the reconstruction, CT value homogeneity was achieved with an accuracy of +/- 4 HU. The use of the shaped filter at a constant dose of 6 mGy decreased scatter and noise by 30 to 40 % in the center and 10 to 15 % in the periphery.

By means of shaped filters designed for breast CT, significant dose reduction can be achieved with unimpaired image quality or a decrease of noise and scatter with a constant dose can be realized.

Shaped filters have to be considered for breast CT scanners just as for clinical CT.

Lueck, F, Weigel, M, Kolditz, D, Vollmar, S, Hupfer, M, Kalender, W, Effect of Shaped Filters Designed for Breast CT on Dose and Image Quality.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11010918.html