Advanced correction algorithms for ultrafast X-ray computed tomography

Ultrafast electron beam X-ray computed tomography is a unique imaging technique for the investigation of multiphase flows. It provides high-resolution cross-sectional images at rates of up to 4,000 fps from two tomography planes, which also allows axial velocities to be determined. As is typical for such complex measurement systems, there are several physical effects leading to deviations from the ideal imaging system. On the one hand, these are deviations associated to X-ray computed tomography (CT) in general, such as photon scattering and beam hardening. On the other hand, there are several effects originating from the electron beam deflection, which are in particular related to electron beam X-ray CT. For example, some uncertainties about the final size and position of the X-ray focal spot path on the target are remaining. This paper addresses effects and corresponding practical correction algorithms for both categories. Scattering and beam hardening as interlinked phenomena are treated by correction based on fast ray-tracing in-plane simulations. The topic of focal spot path uncertainties has been analysed in detail with respect to different parameters. The problem is tackled with two approaches. The first approach searches the correct angular positions of the X-ray focal spot on the target by maximizing the grey value variance in the resulting reconstructed images. The second approach evaluates the resulting distance map between the two imaging planes by combining simulated distributions with measured values.