Randoms and TOF gain revisited.

Time-of-flight (TOF) positron emission tomography (PET) typically reduces the variance in the images by a factor that is proportional to the size of the object to be scanned, and inversely proportional to the time resolution of the PET scanner. Attempts to better characterize this relationship and understand its limits have been published, showing that such gain also increases with random fraction. In this paper, new experimental and simulated data are analyzed and old results are incorporated in the study. The proportionality of TOF gain with time resolution is confirmed, the proportionality constant is measured, the effect of the randoms is validated, and the limit of the model for small objects is investigated.