Michaela Weigel Dipl Phys, Presenter: Nothing to Disclose

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

Robert Brauweiler, Abstract Co-Author: Nothing to Disclose

Martin Hupfer, Abstract Co-Author: Nothing to Disclose

Tristan Nowak, Abstract Co-Author: Nothing to Disclose

Willi A. Kalender PhD, Abstract Co-Author: Consultant, Siemens AG Founder, VAMP GmbH Scientific Advisor, VAMP GmbH Shareholder, VAMP GmbH

The purpose of this study was to determine the optimal photon energy and tube voltage for dedicated breast CT by optimizing the dose-weighted signal-to-noise ratio. Minimal dose for a desired level of image quality as a function of breast diameter and lesion type was the goal.

Simulations of dose and image quality were performed for a dedicated high-resolution breast CT scanner with spatial resolution of about 100 µm. Simulations were conducted for x-ray energies between 20 and 100 keV and tube voltages between 25 and 120 kV. We used water cylinders with 6 to 18 cm in diameter and 10 cm in length to mimic the female breast. Inserts were placed centrally to mimic typical breast lesions: water with a density difference of 10 % to approximate a soft tissue lesion, water mixed with 100 mg/cm3 calcium hydroxyapatite (CaHA) to mimic the contrast of micro-calcifications and water with 20 mg/ml iodine to simulate iodine as a contrast agent. Dose was assessed by Monte Carlo simulations using CTDI values with the software tool ImpactMC (Vamp GmbH, Erlangen, Germany). To verify dose and image quality assessment, measurements were performed with the 10 cm phantom using an experimental micro-CT scanner.

Optimal x-ray energies and voltages strongly depended on breast diameter and the type of the lesion. For iodine, the optimal photon energy was slightly above the K-edge (at 33.2 keV) for all breast sizes. The optimal energy for CaHA rose with increasing phantom diameter, from 23 keV to 32 keV for the 6 cm and 18 cm phantoms. Higher optimal energies were obtained for the density difference, between 52 and 72 keV for the smallest and the largest phantom respectively. Polychromatic simulations yielded results in analogy to the monochromatic ones. Measurement verifications were in good agreement with the simulations. Dose could be reduced by changing the energy to the optimal one while retaining the image quality.

Choosing optimal voltages as a function of breast diameter reduces dose to acceptable levels without a decrease in image quality.

Dedicated breast CT potentially offers better sensitivity and specificity for breast cancer detection and diagnosis at acceptable dose values.

Weigel, M, Vollmar, S, Brauweiler, R, Hupfer, M, Nowak, T, Kalender, W, Optimization of Spectra for Dedicated Breast CT with Respect to Image Quality and Dose.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8002365.html