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20 April 2005 Advantages of monochromatic x-rays for imaging
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Abstract
The contrast of X-ray imaging depends on the radiation energy and acquires its maximum value at a certain optimum energy typical for the object under investigation. Usually, higher energies result in reduced contrast, lower energies are absorbed in the object thus having a smaller probability of reaching the detector. Therefore, broad X-ray spectra contain non-optimal quanta to a large extent and deliver images with deteriorated contrast. Since investigations with monochromatic X-rays using synchrotrons are too complex and expensive for routine diagnostic imaging procedures, we propose a simpler approach. A conventional mammography system (Siemens Mammomat 300) with an X-ray tube with a molybdenum anode was supplemented with an X-ray HOPG monochromator (HOPG = Highly Oriented Pyrolytic Graphite) and an exit slit selecting those rays fulfilling Bragg’s condition. The detector is a CCD (Thales TH9570), 4092 x 200 pixels, 54 μm in size. At this slot-scan setup1, measurements have been carried out at 17.5 keV as well as with a polychromatic spectrum with 35 kV tube voltage. The modulation transfer function (MTF) and the detective quantum efficiency (DQE) have been determined from images of a lead bar pattern and flat-field images. Both MTF and DQE depend on orientation (scan or detector direction) for the 17.5 keV monochromatic case. Above 3 mm-1 the DQE values are smaller than those for polychromatic radiation. The contrast yielded by foils of different materials (Al, Cu, Y, Ag) has been studied. In all cases the monochromatic X-rays give rise to about twice the contrast of a polychromatic spectrum.
© (2005) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
M. Hoheisel, R. Lawaczeck, H. Pietsch, and V. Arkadiev "Advantages of monochromatic x-rays for imaging", Proc. SPIE 5745, Medical Imaging 2005: Physics of Medical Imaging, (20 April 2005); https://doi.org/10.1117/12.593398
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