Multiphase flows are omnipresent in the chemical industry. The flow phenomena in multiphase reactors strongly affect the processes performance. Nonetheless, even basic information on flow patterns, flow regimes and effects of internals etc. is often not available, which is a strong obstacle for a reliable design and scale-up. Non-invasive tomographic techniques are promising measurement tools to visualize opaque multiphase flows. The contribution provides a short survey about today's tomographic imaging techniques and introduces the principles of radiation-based tomography. In particular, two gamma-ray computed tomography designs and their application for sparger performance study in large bubble columns and for flow regime determination in inclined rotating fixed-bed reactors are presented.