The potential of the radioisotope tracer technique of positron emission tomography (PET) and the related techniques of positron emission projection imaging (PEPI) and positron emission particle tracking (PEPT) is illustrated with reference to laboratory scale studies of particulate motion in rotating drums, operating either in batch or continuous flow modes. Sand grains, glass beads and TiO2 granules down to 0.5mm diameter were labelled. Using PEPT the transition between rolling and slumping modes has been identified and the velocity profile within the active layer has been determined for a range of drum diameters. PEPI has been used to measure and explain residence time distributions, while all three techniques have been used to study segregation based on particle size, both radially and axially within the drum. Data on particle motion within a novel baffled drum is also presented.