Parameterization of X-ray spectra appropriate for microCT scanners

Non-filtered X-ray spectra from three tubes (Oxford Instruments Ultrabright microfocus W anode, Apogee Series 5000 with W and Mo anodes) appropriate for microCT scanners have been measured using a CdTe solid-state detector. The normalized and efficiency-corrected spectra have been parameterized using Boone et al. third-order polynomial expression, obtaining good agreement with the data (typical mean ratio between parameterization and measurement equals 1.02, with standard deviation 0.10). Attenuation of the computed spectra by external filters was analytically simulated, obtaining results that agree well with direct measurements. The air kerma angular distribution of the X-ray beams was measured and the magnitude of the heel effect was evaluated. Tungsten collimators provided by the detector manufacturer had to be used to reduce dead time and it was found that their apertures do not necessarily agree with the nominal values.