Sabrina Viviane Vollmar, Presenter: Nothing to Disclose

Michaela Weigel Dipl Phys, 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

To evaluate the influence of the angular scan range on image quality and dose distribution in pendant-geometry cone-beam breast CT.

Simulations of dose and image quality were performed for dedicated breast CT for a scan range of 180° plus fan angle α and of 360°. We used cylindrical phantoms with 8 to 18 cm diameter with soft-tissue tumour-equivalent inserts and micro-calcification clusters. Simulations were made for monochromatic rays at optimized energy for the respective diameter and for polychromatic x-ray spectra at optimized tube voltage. Dose assessment was achieved by Monte Carlo calculations with a MC software tool (ImpactMC, VAMP GmbH, Erlangen, Germany). For image reconstruction a Feldkamp algorithm was used with Parker weighting in the case of partial scans. We analyzed image noise, spatial resolution and dose distribution homogeneity to assess the performance. To verify dose and image quality assessment, measurements were performed for partial and for full scans with 10 and 20 cm diameter cylinders at 70 kV.

Results of measurements and simulations were in good agreement. At the same exposure level the noise level was the same in 180° +α and 360° scanning with a slightly higher and projection angle dependent variation of about ±10% in 180°+α scanning. Spatial resolution was not affected by the partial scan. Dose distribution is less homogeneous in 180° +α scanning; dose in the directly exposed half was about 20% to 40% higher than the average dose in 360° scanning whereas dose in the other half of the breast was typically 20% to 40% lower. The peak value of dose can be up to 40% higher in 180° +α than in 360° scanning.

180° +α scanning may be an alternative in dedicated breast CT as it does not impair image quality at a given average glandular dose. This finding may allow for more flexibility in mechanical design and applications.

Dedicated breast CT potentially offers better sensitivity and specificity for breast cancer detection and diagnosis.

Vollmar, S, Weigel, M, Kalender, W, Dose Distributions and Image Quality in CT of the Breast as a Function of Projection Angle Range.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6007041.html