A QUASIMONOCHROMATIC X-RAY SOURCE FOR MAMMOGRAPHY

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The objective of the proposed program is to investigate the use of parametric x-ray radiation (PXR) as a tunable, quasimonochromatic x-ray source for mammography. PXR is generated by placing natural or synthetic crystals, or multilayer structures into the path of a relativistic electron beam. The virtual photons associated with the fields of the electrons are Bragg reflected by the periodic crystal lattice and real x-rays appear at the Bragg angle. The production process is thus analogous to x-ray diffraction by crystals, except that the x-ray beam incident at the Bragg angle is replaced by a relativistic electron beam. This laser-like source is quasi-monochromatic, directional, easily tunable, and polarizable. Such a source would permit the determination of the optimum photon energy which minimizes dosage and maximizes contrast between tumors and normal breast tissue. We propose to develop a Monte Carlo simulation of mammography, which will calculate image quality and dosage as a function of the photon energy and bandwidth of our PXR source. We will determine the needed photon flux for mammography that can be obtained from a PXR source. To make the source more practical, we will investigate methods for reducing the needed electron beam energy to below 20 MeV. Experimental confirmation of PXR generation at low to moderate electron beam energies will be attempted using an existing experimental setup.