A Model of Scattered Radiation
Scatter is a major degrading factor in the appearance of mammographic images therefore removal of its effects improves perceived image quality. Scattered radiation degrades mammographic images by imparting a smoothly varying energy component to the intensifying screen. This component carries no information about the breast tissue on the specific x-ray path from x-ray source to pixel, although, as we show, scatter does contain information about the breast tissue in the immediately surrounding area. This chapter develops a method to model and remove scattered radiation. The model is based on the conjecture that the amount of scattered radiation reaching a given pixel is related to the energies imparted in a neighbourhood surrounding the pixel. Of course, the exact relationship is highly complex, and we introduce a number of approximations. Still the proof of the pudding is in the eating, and the range of results we show later in the monograph demonstrates that the approximations are reasonable in practice. In essence, the energies imparted in a neighbourhood are used to estimate the composition of the local tissue and from this composition the scatter component is estimated from published data. However, tissues nearer to the central pixel affect the scatter component more than those tissues further away, and so the energy values need to be weighted to reflect this. Estimation of scatter plays a crucial role in allowing quantitative measures of the breast tissue to be found.
KeywordsScattered Radiation Central Pixel Scattered Photon Mammographic Image Total Scatter
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