Monte Carlo simulation of the effects of anode surface roughness on x‐ray spectra

Abstract

The effects of anode surface roughness on x-ray spectra were successfully simulated by a Monte Carlo method. It was proved that the effect of the anode surface roughness could not be modeled by simple filters made from the anode material. The surface roughness (Ra) was found to be an inadequate quantity to describe the effect of anode surface roughness on x-ray spectra.

Geometrical model for calculating the effect of surface morphology on total x‐ray output of medical x‐ray tubes

“…Other authors found comparable results in the sense that increased tube aging rather manifests in decreasing x-ray output when investigating low α take off and high U tube than in changed HVL. 1,2,11 The roughness, that is, R a , might be a value that is easier and faster to obtain than a fully three-dimensional dataset of the surface. Figure 10 shows R measured plotted against the measured R a values.…”

“…The surface roughness of recovered rotating anodes after failure rarely exceeds R a /S a = 10 µm or R z = 45 µm. 1,3,7,26 For example, the surfaces shown in Figs. 1(a) and 1(b) calculate to R a = 1.8 µm, R z = 15 µm and R a = 4.5 µm, R z = 32 µm.…”

“…This process is called tube aging and is mainly caused by the degradation of the anode surface. [1][2][3][4] Especially in computed tomography (CT), tube aging can lead to photon starvation during image acquisition and reduces the diagnostic value of the acquired data. Inside an x-ray tube, electrons which are originating from the cathode, are accelerated toward the anode surface to generate x rays on the impact.…”

“…10 The decrease in output is caused by locally increased absorption due to the modification of the surface, which creates an increase in internal path length for photons. [1][2][3][4][5]7,11 When accelerated electrons hit the surface of the W anode, only a small portion of the incoming electrical power, at normal conditions around 1%, will generate x rays. Literature values for the average penetration depth of electrons, d e -, in W at an acceleration voltage of 100 keV range from 1 µm to 1.6 µm 4,12 .…”

“…[13][14][15][16][17][18][19][20][21] In contrast to earlier publications, in which the surface roughening was also successfully linked with measurements or simulations, this work uses high-resolution surface data that accurately depicts the surface morphology of modern high-performance x-ray anodes. 1,3,5,7 In addition to the changes in the internal filtration due to surface roughening investigated in the past, the extensive shading effects of large surface features can be made visible. The latter turned out to be decisive for the calculation of the x-ray output, which showed a good agreement with the air kerma data of the stationary anode test system.…”