This brief review focuses on the work performed at the Chemical Reaction Engineering Laboratory (CREL) at Washington University, St. Louis, in using Computer Aided Radioactive Particle Tracking (CARPT) and Gamma Ray Computed Tomography (CT), in generating velocity and phase holdup profiles in different multiphase reactors. This data is used for validation of the Euler-Euler interpenetrating fluid model executed in the framework of FLUENT and CFDLIB. Data for holdup and velocity profiles, as well as for mixing parameters, obtained in liquid-solid and gas-solid risers, slurry bubble columns, and stirred tanks, are discussed. It is shown that Euler-Euler simulations are capable of predicting such data well for the cases studied. Extension of CARPT-CT to industrial systems is briefly discussed.