Measured primary and transit fluoroscopic X-ray spectra

Abstract

A NaI(Tl) spectrometer system was used to measure primary X-ray spectra and transit X-ray spectra, following passage through an Alderson phantom, for a typical fluoroscopic X-ray unit. A digital computer was used to correct the observed spectrum for distortions introduced by the spectrometer system. Scattered X-ray spectra, originating in small areas adjacent to the primary beam and incident upon the detector element corresponding to the primary beam, were also measured. The corrected spectra are normalized to an exposure of 1 R and the output is given as photons per keV interval. X-ray spectra for the primary, transit and scattered spectra were measured from 65 to 130 kVp. HVL, equivalent photon energy, Ee, as derived from the HVL measurement, and mean photon energy, E, as derived from the spectrum measurement, were obtained for both the primary and transit spectra from 65 to 130 kVp. The output intensity, as measured in mR per mA s, was measured for both the primary and transit spectra. The effective attenuation in the phantom of the primary beam was derived as a function of photon energy. The relative intensity of the primary and scattered X-ray spectra, incident upon the detector element was measured at different field sizes from 65 to 130 kVp.