Analyzing a cardiac PET list-mode stream on a frame-by-frame basis obtains valid gating signals just as well as by tracking external motion or applying electrocardiography (ECG), according to a study in the June issue of the Journal of Nuclear Medicine.
Florian Büther, MD, and colleagues from the University of Münster in Münster, Germany, evaluated two different cardiac and respiratory gating methods:
- ECG signals for cardiac gating and video signals for respiratory gating;and
- measured inherent list-mode events.
The researchers said that 29 patients with coronary artery disease underwent a 20-minute ECG-gated, single-bed, list-mode PET scan of the heart. Of these, 17 were monitored by a video camera registering a marker on the patient's abdomen, thus capturing the respiratory motion for PET gating (video method). Additionally, respiratory and cardiac gating information was deduced without auxiliary measurements by dividing the list mode stream in 50-ms frames and then either determining the number of coincidences (sensitivity method) or computing the axial center of mass and SD of the measured counting rates in the same frames (center-of-mass method).
The investigators found that all methods successfully captured respiratory motion and significantly decreased motion-induced blurring in the gated images. The center-of-mass method resulted in significantly larger left ventricular wall displacements than did the sensitivity method; other differences were nonsignificant.
List mode-based cardiac gating was found to work well for patients with high 18F-FDG uptake when the center-of-mass method was used, leading to an ejection fraction correlation coefficient of r = 0.95 as compared with ECG-based gating, according to the authors. However, they noted that the sensitivity method did not always result in valid cardiac gating information, even in patients with high 18F-FDG uptake.
Büther and colleagues concluded that emission event-driven methods for respiratory gating were successfully used in a list mode-based cardiac PET/CT feasibility study, and their "performance was comparable to that of conventional video-based tracking of respiratory motion."
Cardiac gating information can be obtained in scans with high tracer uptake, and the event-driven center-of-mass-based method resulted in the best performance for respiratory and cardiac gating, the authors wrote. They also noted that list mode-based gating methods do not require additional hardware and can easily be applied in cardiac PET/CT.