Estimation of scattered radiation in digital breast

13 Digital breast tomosynthesis (DBT) is a promising technique to overcome the tissue 14 superposition limitations found in planar 2D X-ray mammography. However, as most 15 DBT systems do not employ an anti-scatter grid, the levels of scattered radiation 16 recorded within the image receptor are significantly higher than that observed in planar 17 2D X-ray mammography. Knowledge of this field is necessary as part of any correction 18 scheme and for computer modelling and optimisation of this examination. Monte Carlo 19 (MC) simulations are often used for this purpose, however they are computationally 20 expensive and a more rapid method of calculation is desirable. This issue is addressed 21 in this work by the development of a fast kernel-based methodology for scatter field 22 estimation using a detailed realistic DBT geometry. Thickness-dependent scatter 23 kernels, which were validated against the literature with a maximum discrepancy of 4% 24 for an idealised geometry, have been calculated and a new physical parameter (air gap 25 distance) was used to estimate more accurately the distribution of scattered radiation 26 for a series of anthropomorphic breast phantom models. The proposed methodology 27 considers, for the first time, the effects of scattered radiation from the compression 28 paddle and breast support plate, which can represent more than 30% of the total 29 scattered radiation recorded within the image receptor. The results show that the 30 scatter field estimator can calculate scattered radiation images in an average of 80 31 minutes for projection angles up to 25 with equal to or less than a 10% error across 32 most of the breast area when compared with direct MC simulations. 33 PACS numbers: 87.10.Rt(MC simulations), 87.57.rh (Mammography), 87.59.ej(Digital 34 mammography) 35 Submitted to: Phys. Med. Biol. 36 Estimation of scattered radiation in digital breast tomosynthesis 2