A Motion Adaptive Animal Chamber for PET Imaging of Freely Moving Animals

Small animal positron emission tomography (PET) is a powerful method for studying the molecular origins of debilitating brain disorders such as dementia, depression and schizophrenia. However, its full potential in such investigations has not yet been realized due to the use of anesthesia to avoid motion artifacts. In spite of preventing motion, anesthestics have the propensity to alter brain function compared to the unanesthetized state. Use of anesthesia also precludes studying an animal´s behavior concurrently with imaging. Methods enabling PET imaging without the need for anesthesia would, therefore, serve to improve the quality of, and increase the scope of, PET investigations. Previously, we have reported a motion correction approach for PET imaging of unanesthetized animals confined to a tube. We are currently developing an extension of this technique that allows PET imaging of freely moving rats. Here we report a robot-controlled motion adaptive animal chamber to maintain the head of a freely moving rat within the PET field of view (FOV) during imaging. The chamber is adjusted in the horizontal plane in response to changes in head position reported by a motion tracking system. In live animal experiments within a simulated microPET environment, the motion adaptive chamber led to an increase in the time the head was inside the FOV for all rat behavior types studied. The best improvement (resulting in almost 100% confinement to the FOV) was seen for low activity behaviors. Higher activity behaviors were harder to compensate for completely due to the faster head motion. Overall, for the individual studied the robotic compensation increased the time spent in the FOV from 10% to 88% during approximately 5 hours of trials. We conclude that a robot-controlled motion adaptive chamber is a feasible approach for keeping the animal inside the FOV and an important step towards imaging the brain function of freely moving animals with PET.