Stereo-infrared tracking to monitor and characterize rigid-body motion and respiration during cardiac SPECT imaging: progress towards robust clinical utilization

Patient motion during cardiac SPECT imaging can cause diagnostic imaging artifacts. Our approach is to monitor patient motion during cardiac SPECT imaging using the Polaris stereo-IR real-time motion-tracking system. In our earlier work we obtained excellent correlation of axial and vertical motion as measured by our SPECT system with the Polaris. We also showed a good correlation for Polaris tracking of respiration for volunteers with data from a pneumatic bellows. Herein, we show the successful monitoring of patients during cardiac SPECT perfusion imaging. We wrapped elastic belts with four IR reflecting spheres on each about the chest and abdomen of the patients. The Polaris system reported the 3D location of these spheres in a random order intermixed with the location of "phantom" spheres. We developed routines to automatically recognize and discard the phantom spheres, consistently order the true spheres, and covert Polaris coordinates to SPECT coordinates given a calibration. For our 12 analyzed clinical patients the data shows that both males and females at rest were primarily abdomen breathers with the male peak to peak average vertical respiration amplitude larger at 9.2 mm than that for the females at 5.6 mm. The male chest average vertical amplitude was also a bit larger at 1.6 mm vs. 1.4 mm for females. During the 16 minute SPECT acquisition the average vertical axis difference between end-expiration levels for the abdomen for combined males and females was -4.2 mm, with males slightly larger at -4.72 mm vs. females at -3.81 mm. The largest vertical end expiration change was -9.0 mm, and was observed in the male with the highest body mass index (BMI) of 44.2.