Measurements of an optimized beam for x-ray computed mammotomography
Simulation results from previous studies indicate that a quasi-monochromatic x-ray beam can be produced using a newly developed beam filtration technique. This technique utilizes heavy filtration with novel high Z filter materials having k-edges just above those of CsI, producing a near monochromatic beam with mean energy optimized for detection. The value of a near monochromatic x-ray source for a fully 3D tomography application is the expected improved ability to separate tissues with very small differences in attenuation coefficients for a range of uncompressed breast sizes while maintaining dose levels at or below existing dual view mammography. In this study, we experimentally investigate a set of filter materials (Al, Cu, Ag, Ce, W, and Pb), filter thicknesses (10 th, 100 th, and 200 th VL), and tube potentials (40-80 kVp) using a newly constructed test apparatus. Initial experimental results corroborate simulations and indicate that this approach can improve image quality (SNR) at constant dose. Al, Cu, W, and Pb provide optimal exposure efficiency results at 60 kVp and above. Decreasing relative improvements are observed above 100 th VL filter thickness at 78 cm SID. Results are obtained without significant tube heating (except at 40 kVp). In addition, simulations indicate significant reductions in beam hardening. This optimized beam will be incorporated into a novel cone-beam x-ray computed mammotomography sub-system together with an emission tomograph in a dual modality CT/SPECT application specific emission and transmission tomography system for fully 3D uncompressed breast imaging.
McKinley, RL; Samei, E; Brzymialkiewicz, CN; Tornai, MP; Floyd, CE
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