Contrast effects of a gadolinium filter

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Abstract
The use of heavy metal filters with K edges in the diagnostic energy range to reduce the width of the X-ray spectrum and hence reduce patient radiation exposure is considered. This spectral narrowing also increases subject contrast and permits an increase in tube potential. Results of contrast measurements are presented for a 250 .mu. Gd filter. It was found that Al-filter contrast could be matched by using 8-10 kilovolt peak (kVp) higher potential with the Gd filter. Similar results were found for Calcium tungstate and rare-earth screens. Measurements were also done to determine skin exposure and milliampere-second ratios for both constant contrast and constant kVp technique conversion methods. A simple theory with 1 adjustable parameter gives a reasonable fit to the experimental results.