Gas-particle flow in fluidized beds is generally complex and difficult to observe. But exact information on voidage distribution and solid transport is urgently needed for assessment, monitoring, modelling, and optimization of fluidized bed operation. So far, there was a lack of suitable measurement and imaging techniques to disclose the complex flow structures in fluidized beds with high spatial and temporal resolution. The ultrafast X-ray computed tomography technique, which has been developed in recent years, is superior for such types of multiphase flows and its performance for the analysis of fluidized beds has been demonstrated in this study. Spatial resolution of two millimetres and temporal resolution of several thousand cross-sectional images per second allow at the same time imaging and analysis of voidage structures as well as single particle movement. In this study, the capability of imaging fluidized bed behaviour at different column diameters and gas flow rates has been analysed. (C) 2012 Elsevier B.V. All rights reserved.