Motion capture of chest and abdominal markers using a flexible multi-camera motion-tracking system for correcting motion-induced artifacts in cardiac SPECT

Patient motion is inevitable in SPECT and PET due to the lengthy period of time patients are imaged. Motion of only 2 pixels (~13 mm) is enough to create minor to moderate defects in SPECT studies. The use of external tracking devices provides additional information independent of SPECT data that should result in a more robust correction. We have been investigating the use of stereo-imaging of retro-reflective markers on stretchy bands wrapped about the chest and abdomen of patients to provide 6-DOF tracking of the patient during cardiac SPECT. Herein we summarize the performance of a motion-capture system (Vicon MX) which utilizes 5 near-infrared (NIR) cameras to track markers via stereo-imaging. Tracking with the 5 cameras is integrated such that only 2 of the 5 camera views are required, at any instant, to track a given marker in 3D. The ability of the Vicon system to track 6 DOF motion with sub- millimeter and sub-degree accuracy was established with a Tc^99m labeled 7-sphere phantom. We also established temporal synchronization between motion-tracking data and list-mode SPECT acquisitions. In addition, we were able to track 3 retro-reflective markers on an anthropomorphic phantom with a precision that allowed us to correct motion such that no loss in visual quality was noted in motion-corrected images relative to motion-free images. Finally with months of clinical usage of the system tracking chest and abdomen markers, we have looked at various combinations of cameras to determine optimal placement and number required for robust tracking in our clinic.