Investigation of Subject Motion Encountered During a Typical Positron Emission Tomography Scan

Subject motion has a known detrimental effect on brain Positron Emission Tomography image resolution. Numerous motion compensation techniques exist to address this issue, however prior to their application every effort should be made to limit subject motion. Using a Polaris motion tracking system subject motion was observed under typical scanning conditions for both healthy and Parkinson's disease (PD) volunteers. Motions in the range of 0 to 5 mm were observed for healthy subjects, and 0 to 20 mm for PD subjects. The most common source of motion was due to interaction between the subject and the attending nurse/scanning staff, especially during examination of the subject's symptoms (motions up to 8 mm). Less common activities resulting in significant motions were the use of a bedpan (20 mm), the removal of a cushion from under the subject's legs (5 mm) and leg readjustments (3 mm). Awareness of the effect each of these activities had on head motion can be used to motivate further limitations on these motions. Measured motions were also extrapolated to various regions in the brain, specifically the cerebellum, occipital cortex, and striatum. Subject head rotation about the vertical and horizontal axes resulted in the greatest displacement of regions in the cerebellum, while rotations about the subject's long axis primarily impacted the displacement of the occipital cortex region. This measurement provides motion related information about the expected accuracy of time activity curves for different brain regions.