A study of characteristics of transmitted Bremsstrahlung spectra through various filter materials and thickness for optimal radiographic images at different energy levels.

摘要

The characteristics of the transmitted Bremsstrahlung spectrum of 50, 75, and 100 keV endpoint energies are evaluated using the recently reported photon attenuation coefficients. The peak energy and full width at half maximum of the beam, which is considered a measure of the monochromatization of the poly-energetic beam, are evaluated. In these evaluations, the characteristic X-rays of the anode are not considered. In general, it is noticed that the peak energy of the bremsstrahlung spectrum increases and the full width at half maximum decreases. The effect of K edge is seen clearly on the transmitted spectra for Cu to Pb filters. Filters of Al, Cu, Ag, and Au are evaluated by passing different energies from a diagnostic x-ray unit through different thicknesses of these filters. Evaluation is based on two separate criteria. The amount of energy, which passes through the filter, measured by an ion chamber, and the enhanced contrast differences, measured by film densities. Both of these measurements were taken through low, medium, and high atomic number materials and the data is compared. The filter material and thicknesses have the expected effect on the energy of the beam. Higher atomic number filters and greater filter thicknesses both reduce the overall transmitted energy. The film contrast data shows the different effect beam filter materials can have on film contrast differences within a specific object (e.g. lung) and film contrast differences between different objects (e.g. lung and bone). Different filter types and thicknesses may be used to achieve better film contrast depending on the type of object (i.e. density, atomic number) and the thickness of the object being imaged. The present analysis suggests that, for diagnostic radiology, depending on the endpoint energy of the spectrum, better monochomatization (narrower width) of the bremsstrahlung beam and smaller surface dose can be achieved by carefully choosing proper metallic filters other than Al.