The effect of internals on the fluidization dynamics in three-dimensional (3D) cylindrical fluidized beds was studied using real-time magnetic resonance imaging. Instantaneous snapshots of particle velocity and particle position were acquired for gas velocities U below and above the minimum fluidization velocity U-mf. Below U-mf, we found local fluidization and gas bubbling in areas adjacent to an inserted horizontal tube, likely caused by the gas locally exceeding U-mf as it flows around the insert. Above U-mf, the presence of the insert in the bed affected the fluidization dynamics. The wake region above the insert exhibited a lower average particle velocity and reduced velocity fluctuations as well as a substantially reduced number and size of gas bubbles as compared to a reference bed without internals. The extent of this wake region was found to be approximately as wide as the insert, and it extended from the top of the insert to the free surface of the bed. Moreover, the presence of internals also affected the regions below the insert by showing an increased rate of bubble formation directly below the inserted tube. The present work can provide relevant information on the design of fluidized beds with internals. Moreover, the data gathered in this work can be used to validate the accuracy of 3D numerical models of gas-solid systems. (C) 2019 Elsevier Ltd. All rights reserved.