An investigation of motion tracking for freely moving animals in PET

Stereo optical motion tracking has been shown to b e a feasible and accurate way of measuring head pose in positron emission tomography (PET) studies of minimally restrained awake animals. The aim of this work was to determine the number and arrangement of binocular trackers to optimize continuity of head tracking for a freely moving animal. We established a performance criterion for continuous tracking of a freely moving subject based on head motion measurements obtained from tube-bound rats. By measuring the angular detection capability of a single tracker we were able to simulate the tracking performance of a variety of multi-tracker configurations. Based on these simulations, tracking can be maintained 96% of the time using four elevated and symmetrically positioned trackers compared with 70% of the time using two elevated trackers on opposite sides of the gantry. A pilot experiment tracking a freely moving rat using the latter configuration resulted in successful head tracking 85% of the time. We conclude that an ensemble of commercial trackers may provide sufficient tracking performance for the freely moving animal, avoiding the need to develop a customized system. This work is an important step towards implementing motion tracking for freely moving animals in PET.