Image reconstruction for fast X-ray computed tomography of multiphase flows

Electron beam X-ray computed tomography is a measurement method, which allows imaging of cross sectional density distributions of an object of interest with a frame rate of more than 1000 images per second. This is very attractive for multiphase flow measurements because flow velocities of 1 m/s and more can be resolved without influencing the flow.
Contrary to conventional tomography, electron beam X-ray CT comprises no mechanical rotated components but a fast moving X-ray source generated by a deflected electron beam. Unfortunately, the static arrangement of the system impedes the acquisition of a complete tomography data set of one imaging plane. Either, there is an offset between source and detector plane or the data acquisition is limited to an angular range smaller than 180°. In the first case, the image resolution in flow direction is reduced depending on the offset, whereas the image reconstruction of the second case tends to limited-angle artifacts in form of skewed object structures.
To minimize the artifacts in image reconstruction the algorithms were adapted to this special limited-angle case. They are mostly based on the iterative reconstruction algorithms ART and MART (additive and multiplicative algebraic reconstruction technique), because they are more flexible and modifiable than common filtered backprojection methods. Especially the reconstruction of two-phase flows permits the incorporation of a priori knowledge into the reconstruction process because only the phase distribution of one known attenuation coefficient has to be recovered.
We will explain the measurement setup and our reconstruction methods in detail. Furthermore, we will present the results of the reconstruction of simulated 2D and 3D two-phase flow data as well as measured data from static and dynamic phantoms imitating real flow scenarios.