Michaela Weigel Dipl Phys, Presenter: Nothing to Disclose

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

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 average dose absorbed in the breast at optimal conditions in dedicated breast CT (BCT) for a sufficient visibility of different types of lesions and to evaluate the potential dose reduction.

Simulations of dose and image quality were performed for a high-resolution BCT scanner to investigate the optimal tube voltages by optimizing the dose-weighted contrast-to-noise ratio and the dose necessary to achieve a contrast-to-noise ratio of 5. Simulations were conducted for tube voltages between 30 and 140 kV with 0.3 mm Cu filter, a focal spot size of 300 µm and 1000 projections. For breasts 6 to 18 cm in diameter and consisting of 50% adipose and 50% glandular tissue simulations of image noise and dose were conducted. The contrasts of adipose tissue, calcium hydroxyapatite and iodine contrast agent relative to glandular tissue mimicking typical breast lesions were investigated. The potential dose reduction was calculated when changing from 80 kV to the respective optimal tube voltage. In the next step, the dose necessary to achieve a contrast-to-noise ratio of 5 was calculated as a function of pixel size (100-500 µm), lesion type and lesion size (100-5000 µm) at the optimal tube voltages.

The optimal tube voltage for imaging iodine enhanced lesions was around 48 kV independent of the breast diameter. Optimal tube voltages for calcification and mass detection increased from 30 to 34 and 46 kV, respectively, with breast diameters from 6 to 18 cm. Potential dose reduction relative to 80 kV was between 19 and 88% retaining the image quality. At the optimal tube voltage, a 1 mm mass in a 14 cm breast is expected to be detectable assuming 0.5 mm effective pixel size and an average glandular dose of 3 mGy. Microcalcifications turned out to be visible at larger pixel sizes, too, at lower CT numbers due to partial volume effects.

Changing to lower tube voltages in BCT is meaningful as all contrasts were optimally visible in the range of 30-50 kV. At these voltages, BCT is expected to provide sufficient detectability of lesions at the same dose as in mammography.

Dedicated breast CT restricted to the same dose as in mammography may improve breast cancer detection.

Weigel, M, Vollmar, S, Kalender, W, Estimations of Dose for Dedicated Breast CT at Optimized Settings with Respect to Lesion Type and Size.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9002796.html