Ground-truth verification of dynamic x-ray micro-tomography images of fluid displacement

X-ray micro computed tomography (jtCT) is a method of choice for the non-destructive imaging of static 3d samples. A fundamental constraint of conventional X-ray jtCT is that the sample must remain static during data acquisition. It therefore can not be directly applied to the study of dynamic (i.e. 4D) processes such as pore-scale fluid displacements in porous materials. The process must be halted whilst data acquisition occurs devaluing the experiment (e.g. the fluid displacement rate can no longer be studied with any confidence). Recent "proof-of-concept" studies have shown that "dynamic tomography" reconstruction algorithms incorporating a priori knowledge of the underlying physics of the process, may be capable of true high-resolution, time-resolved 4D imaging of continuous, complex processes at existing X-ray jtCT facilities. In this paper, we seek to establish: (i) that the a priori information used in dynamic tomography is appropriate, i.e. does not bias the algorithm towards incorrect results; and (ii) that the results of the dynamic tomography algorithm agree with those produced by conventional techniques in the limiting case of a slowly changing sample. This investigation is performed using experimental data collected at the ANU jtCT facility