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Proceedings Paper

New K-edge-balanced contrast phantom for image quality assurance in projection radiography
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Paper Abstract

X-ray-absorber step-wedge phantoms serve in projection radiography to assess a detection system's overall exposure-related signal-to-noise ratio performance and contrast response. Data derived from a phantom image, created by exposing a step-wedge onto the image receptor, are compared with predefined acceptance criteria during periodic image quality assurance (QA). For contrast-related measurements, in particular, the x-ray tube potential requires accurate setting and low ripple, since small deviations from the specified kVp, causing energy spectrum changes, lead to significant image signal variation at high contrast ratios. A K-edge-balanced, rare-earth-metal contrast phantom can generate signals that are significantly more robust to the spectral variability and instability of exposure equipment in the field. The image signals from a hafnium wedge, for example, are up to eight times less sensitive to spectral fluctuations than those of today’s copper phantoms for a 200:1 signal ratio. At 120 kVp (RQA 9), the hafnium phantom still preserves 70% of the subject contrast present at 75 kVp (RQA 5). A copper wedge preserves only 7% of its contrast over the same spectral range. Spectral simulations and measurements on prototype systems, as well as potential uses of this new class of phantoms (e.g., QA, single-shot exposure response characterization) are described.

Paper Details

Date Published: 5 June 2003
PDF: 12 pages
Proc. SPIE 5030, Medical Imaging 2003: Physics of Medical Imaging, (5 June 2003); doi: 10.1117/12.479942
Show Author Affiliations
Marc Cresens, Agfa-Gevaert NV (Belgium)
Ralph Schaetzing, Agfa-Gevaert AG (Germany)

Published in SPIE Proceedings Vol. 5030:
Medical Imaging 2003: Physics of Medical Imaging
Martin J. Yaffe; Larry E. Antonuk, Editor(s)

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