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There many instances where the use of a quasi-monochromatic x ray source (QMS) would be an advantage in radiology. One instance is dual-energy imaging, where two images may be processed in order to enhance visualization of a particular element, typically iodine, but also possibly gadolinium. Another instance is fluoroscopy, where the radiation and/or contrast doses may be minimized by using a radiation source with an energy peak that lies just above the contrast K edge. The most straightforward method of implementing a QMS is to incorporate appropriate heavy elements into an x ray tube anode and then to filter the resulting spectrum appropriately. Science Research Laboratory, Inc. has embarked on a program to develop anode materials that can withstand the power loadings encountered in a useful tube. Thus far, we have developed and tested one relevant anode material (erbia) and demonstrated that it could withstand a power of 0.25 MW/cm2 at a tip speed of 3300cm/sec without harm. The destructive limit was determined to be at least a factor of two higher due to overwriting of the electron beam in certain regions. Under the condition of no overwriting, coating survivability should scale directly with tip speed. For futures studies we have designed an apparatus that increases the tip speed by a factor of 4.8. In the longer term, the tip speed could be increased by as much as a factor of 20.
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