A flexible multicamera visual‐tracking system for detecting and correcting motion‐induced artifacts in cardiac SPECT slices

Abstract

Patient motion is inevitable in SPECT and PET due to the lengthy period of time patients are imaged. The authors hypothesized that the use of external-tracking devices which provide additional information on patient motion independent of SPECT data could be employed to provide a more robust correction than obtainable from data-driven methods. Therefore, the authors investigated the Vicon MX visual-tracking system ͑VTS͒ which utilizes near-infrared ͑NIR͒ cameras to stereo-image small retroreflective markers on stretchy bands wrapped about the chest and abdomen of patients during cardiac SPECT. The chest markers are used to provide an estimate of the rigid-body ͑RB͒ motion of the heart. The abdomen markers are used to provide a signal used to bin list-mode acquisitions as part of correction of respiratory motion of the heart. The system is flexible in that the layout of the cameras can be designed to facilitate marker viewing. The system also automatically adapts marker tracking to employ all of the cameras visualizing a marker at any instant, with visualization by any two being sufficient for stereo-tracking. Herein the ability of this VTS to track motion with submillimeter and subdegree accuracy is established through studies comparing the motion of Tc-99m containing markers as assessed via stereo-tracking and from SPECT reconstructions. The temporal synchronization between motion-tracking data and timing marks embedded in list-mode SPECT acquisitions is shown to agree within 100 ms. In addition, motion artifacts were considerably reduced in reconstructed SPECT slices of an anthropomorphic phantom by employing within iterative reconstruction the motion-tracking information from markers attached to the phantom. The authors assessed the number and placement of NIR cameras required for robust motion tracking of markers during clinical imaging in 77 SPECT patients. They determined that they were able to track without loss during the entire period of SPECT and transmission imaging at least three of the four markers on the chest and one on the abdomen bands 94% and 92% of the time, respectively. The ability of the VTS to correct motion clinically is illustrated for ten patients who volunteered to undergo repeat-rest imaging with the original-rest SPECT study serving as the standard against which to compare the success of correction. Comparison of short-axis slices shows that VTS-based motion correction provides better agreement with the original-rest-imaging slices than either no correction or the vendor-supplied software for motion correction on our SPECT system. Comparison of polar maps shows that VTS-based motioncorrection results in less numerical difference on average in the segments of the polar maps between the original-rest study and the second-rest study than the other two strategies. The difference was statistically significant for the comparison between VTS-based and clinical vendor-supplied software correction. Taken together, these findings suggest that VTS-based motion correction is superior to either no...

Quantitative study of rigid-body and respiratory motion of patients undergoing stress and rest cardiac SPECT imaging

“…This may occur due to the obstruction of the line of sight of the Vicon cameras either by the camera-heads of the SPECT system itself, or by the patient's arms, other parts of the body, or clothing. In a separate study [11] reporting motiontracking in 77 patients undergoing cardiac-SPECT imaging, we determined that at least three of the four markers on the chest and one on the abdomen bands could be tracked without loss in 94% and 92% of the studies, respectively, during the entire period of SPECT and transmission imaging. The accuracy of VTS for motion tracking was also established to be submillimeter and subdegree through studies comparing the motion of Tc-99m containing markers as determined from stereotracking and SPECT reconstructions.…”

Motion Detection Methods in SPECT – A Review

“…A flexible multicamera visual-tracking system was used for detecting motion in cardiac SPECT slices by Joseph E. McNamara et al (1). The authors investigated the Vicon MX visual-tracking system (VTS), which utilizes near-infrared (NIR) cameras to stereo-image small retroreflective markers on stretchy bands wrapped about the chest and abdomen of patients during cardiac SPECT.…”

Real-Time Range Imaging in Health Care: A Survey

“…In addition, RI-based body surface tracking is of particular interest for motion compensation in nuclear medical imaging such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) [32]. Based on previous concepts for motion compensation in PET/SPECT using marker-based tracking [33,34,35], dense and real-time RI has been attracting interest in this field lately [36,37] Open issues in this context such as the calibration and synchronization to the scanner are discussed in Sect. 6.…”