To simulate the effect of the condition of the anode surface on x-ray output the surface roughness of anode fragments of replaced clinical x-ray tubes was determined. A mean roughness of 1.32-5.22 microm giving effective tungsten absorption layers of up to 18 microm thickness in the direction of the x-ray beam was determined. X-ray spectra were then simulated using the measured surface profiles. The most prominent effect was the reduction of the kerma output of the tube with increasing roughness (-33% at 50 kV tube voltage and 5 microm roughness). The effects of beam hardening are less pronounced. The corresponding changes in the spectral parameters are generally small but largest for tube voltages up to 70 kV. For higher voltages the increased photon attenuation above the K-edge of tungsten reduces the effects of roughness on spectral parameters. The maximum shifts in mean photon energy of about 1 keV and in HVL of about 0.2 mm Al were obtained for an anode roughness of 5 microm.

A method for the determination of total inherent filtration for clinical x-ray units using attenuation curves was devised. A model for the calculation of x-ray spectra is used to calculate kerma values which are then adjusted to the experimental data in minimizing the sum of the squared relative differences in kerma using a modified simplex fit process. The model considers tube voltage, voltage ripple, anode angle and additional filters. Fit parameters are the thickness of an additional inherent Al filter and a general normalization factor. Nineteen sets of measurements including attenuation data for three tube voltages and five Al-filter settings each were obtained. Relative differences of experimental and calculated kerma using the data for the additional filter thickness are within a range of -7.6% to 6.4%. Quality curves, i.e. the relationship of additional filtration to HVL, are often used to determine filtration but the results show that standard quality curves do not reflect the variety of conditions encountered in practice. To relate the thickness of the additional filter to the condition of the anode surface, the data fits were also made using tungsten as the filter material. These fits gave an identical fit quality compared to aluminium with a tungsten filter thickness of 2.12-8.21 microm which is within the range of the additional absorbing layers determined for rough anodes.