Application of spectrometry to high voltage measurement follows from the fact that the energy of the high-frequency limit of the continuous x-ray spectrum is numerically equal to the applied high voltage. The current device uses a curved crystal in transmission to disperse the spectrum on an imaging detector. Spectra appear as mirror images where distance between corresponding features is approximately linear in wavelength. A significantly overdetermined calibration is obtained using the well known location of K-edges in elements from Mo through Sn. Data fitted to the formal dispersion function give residues below 0.1 kV, i.e., well below currently understood clinical significance.

This year, the sensitivity and ease of use of the curved-crystal spectrometer has been increased. A pinhole camera was introduced along the centerline of the instrument. This assists transverse alignment while the size of the image of the focal spot monitors source degradation due to aging of the anode. The spectral image is registered with a large format dental CCD whose sensitivity was increased by a factor of three by retrofitting it with a thicker scintillation screen. The largest gain in system sensitivity was realized by use of a quartz crystal (the 10-1-1 reflection) which gave an eightfold improvement arising from the Sumbaev effect, a quasimosaic phenomenon (due to structural and elastic anisotropy) leading to parabolic bowing of the reflecting planes as the crystal is bent cylindrically.

In the framework of the supporting grant from the Army's Breast Cancer Research Program, cooperative studies have been undertaken at the Center for Devices and Radiological Health (a component of the Food and Drug Administration), Georgetown University Medical Center, the University of Alabama Department of Radiology, the University of California-Davis Medical Center, and Radcal Corporation, the commercial licensee. Through Radcal's efforts, the first commercial model (aimed at the research market) is to be available by the second quarter of 1996. (Hudson, Henins, Deslattes)