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Proceedings Paper

Advantages of monochromatic x-rays for imaging
Author(s): M. Hoheisel; R. Lawaczeck; H. Pietsch; V. Arkadiev
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Paper 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.

Paper Details

Date Published: 20 April 2005
PDF: 9 pages
Proc. SPIE 5745, Medical Imaging 2005: Physics of Medical Imaging, (20 April 2005); doi: 10.1117/12.593398
Show Author Affiliations
M. Hoheisel, Siemens AG Medical Solutions (Germany)
R. Lawaczeck, Schering AG Diagnostics and Radiopharmaceuticals Research (Germany)
H. Pietsch, Schering AG Diagnostics and Radiopharmaceuticals Research (Germany)
V. Arkadiev, Institut fur Angewandte Photonik e.V. (Germany)
Institute for Scientific Instruments GmbH (Germany)

Published in SPIE Proceedings Vol. 5745:
Medical Imaging 2005: Physics of Medical Imaging
Michael J. Flynn, Editor(s)

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