Markerless Motion Tracking of Awake Animals in Positron Emission Tomography
Noninvasive functional imaging of awake, unrestrained small animals using motion-compensation
removes the need for anesthetics and enables an animal's behavioral response to stimuli or
administered drugs to be studied concurrently with imaging. While the feasibility of
motion-compensated radiotracer imaging of awake rodents using marker-based optical motion
tracking has been shown, markerless motion tracking would avoid the risk of marker detachment,
streamline the experimental workflow, and potentially provide more accurate pose estimates
over a greater range of motion. We have developed a stereoscopic tracking system which relies
on native features on the head to estimate motion. Features are detected and matched across
multiple camera views to accumulate a database of head landmarks and pose is estimated based
on 3D-2D registration of the landmarks to features in each image. Pose estimates of a
taxidermal rat head phantom undergoing realistic rat head motion via robot control had a
root mean square error of 0.15 and 1.8 mm using markerless and marker-based motion tracking,
respectively. Markerless motion tracking also led to an appreciable reduction in motion
artifacts in motion-compensated positron emission tomography imaging of a live, unanesthetized
rat. The results suggest that further improvements in live subjects are likely if nonrigid
features are discriminated robustly and excluded from the pose estimation process.