SU‐FF‐I‐83: Derivation of Diagnostic X‐Ray Spectra Using An Interpolation Program with Calculated and Measured Input Parameters

Abstract

Purpose: To determine diagnostic x‐ray photon spectra using simple transmission measurements. Method and Materials: A database of measured and calculated x‐ray photon spectra values from the Catalogue of Spectral Data for Diagnostic X‐rays, R. Birch, M. Marshall and G.M. Ardran, Diagnostic Topic Group of the Hospital Physicists' Association, England, 1979 was collected and used to form a multidimensional interpolation matrix. These researchers measured x‐ray spectra using a Ge(Li) detector for various x‐ray systems in the diagnostic energy range and derived a calculation method to calculate x‐ray spectra which agreed closely with measured spectra for different conditions. X‐ray spectra for tungsten targets and different inherent filtration in Al and Cu were coded in relative number of photons per mm2 per keV for kVps ranging from 30 to 140 kVp at 10 kVp intervals. Other parameters were given such as mean photon energy in keV, photon flux at 0.75 m in photons‐mA−1‐s−1‐mm−2, output in micro Gy‐mA−1‐s−1 and exposure in mR‐mA−1‐s−1 and 1st, 2nd, and 3rd half‐value layer (HVL) in mm Al. Most spectra were derived for constant potential units but some with ripple were also derived. Target angles included 10, 17, 20 and 22 degrees. Results: From this input, interpolation curves were derived which enables one to interpolate between the 10 kVp intervals and to derive the inherent filtration for a particular unit in Al equivalent from simple transmission measurements in Al and mR/mAs at a particular distance. The kVp of the unit was also derived from the transmission measurements by comparison with the calculated curves. Conclusion: With some additional data, this method could be used to derive the x‐ray spectra for any unit in this energy range, 30 to 140 kVp for different parameters.