Abstract
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Objectives This study evaluates different cardiac and respiratory gating methods for PET, one based on ECG signals for cardiac gating and video signals for respiratory gating as a gold standard, two others based on measured inherent list mode events.
Methods 29 patients underwent an ECG-gated list mode FDG scan of the heart. 17 were monitored by a video camera registering a marker on the patient's abdomen, capturing the respiratory motion (VID method). Additionally, respiratory and cardiac gating information was deduced by dividing the list mode stream in 50 ms frames, determining the number of coincidences (SENS method) and computing the axial center of mass and standard deviation of the measured count rates (COM/STD method). The gated data were reconstructed without attenuation correction. Measured wall thicknesses, maximum displacements of the left ventricular (LV) wall, and LV ejection fraction (EF) served as a relative measure for the success of gating.
Results All methods successfully captured respiratory motion, significantly decreasing motion-induced blurring. COM resulted in larger LV wall displacements than SENS (p<0.02), other differences were non-significant. List mode-based cardiac gating worked well for patients with high FDG uptake using COM/STD (EF correlation coefficient compared to ECG-based gating: r=0.95). SENS did not always result in valid cardiac gating information, even in patients with high FDG uptake.
Conclusions Valid gating signals during PET scans can not only be obtained by tracking ther external motion or applying an ECG, but also by simply analyzing the PET list mode stream on a frame-by-frame basis.
- © 2009 by Society of Nuclear Medicine