INCORPORATION OF SCATTERED RADIATION INTO DUAL-ENERGY RADIOLOGIC THEORY AND APPLICATION TO MAMMOGRAPHY

A previous analysis of dual-energy imaging is extended to incorporate scattered radiation. The analysis is general and can include polyenerg etic beams and nonideal detectors. In the dual-material basis plane, s catter generates a displacement of the vectors representing the imaged materials. This changes the target versus background signal differenc e and the projection angle for cancellation of background contrast due to varying amounts of two materials. Complete cancellation is not pos sible, because vectors representing various mixtures of the two backgr ound constituents are displaced differently and thus no longer lie on a straight line in the dual-material plane. The effect can be minimize d by allowing a typical amount of scatter to reach the image receptor when determining the parameters of the transformation from log attenua tion to equivalent materials thicknesses. The analysis has been applie d to dual-energy mammography. The presence of scatter has minimal effe ct on the optimum beam energies with an ideal detector, which are abou t 20 and 70 keV.