A liquid-solid circulating fluidized bed is a potential reactor of interest in a variety of industrial processes, such as petroleum refining, and in the synthesis of fine chemicals, petrochemicals, and foodstuffs, Rapid deactivation of the solid catalyst in these processes necessitates regeneration and recirculation of the solids into the riser section in which the principal reaction is accomplished In this study we show that computer-automated radioactive particle tracking (CARPT) can be used to obtain solids velocity patterns in the riser and that backflow of solids exists set the tested liquid velocities. gamma-ray computed tomography (CT) reveals slightly higher solids concentrations in the center of the column. This is in contrast to gas-solid riser reactors in which the concentration of solids is higher at the walls.