Refraction-compensated motion tracking of unrestrained small animals in positron emission tomography

Motion-compensated radiotracer imaging of fully conscious rodents represents an important paradigm shift for preclinical investigations. In such studies, if motion tracking is performed through a transparent enclosure containing the awake animal, light refraction at the interface will introduce errors in stereo pose estimation. We have performed a thorough investigation of how this impacts the accuracy of pose estimates and the resulting motion correction, and developed an efficient method to predict and correct for refraction-based error. The refraction model underlying this study was validated using a state-of-the-art motion tracking system. Refraction-based error was shown to be dependent on tracking marker size, working distance, and interface thickness and tilt. Correcting for refraction error improved the spatial resolution and quantitative accuracy of motion-corrected positron emission tomography images. Since the methods are general, they may also be useful in other contexts where data are corrupted by refraction effects.

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► We model refraction-induced position and pose error in stereo motion tracking.
► We examine the dependencies of this error and describe a method to correct for it.
► The correction improves image-based quantification in motion-compensated PET.
► The methods are applicable to commercial and custom-designed stereo tracking systems.