Comparison of TOF and non-TOF iterative reconstruction at low statistics

In this paper, Monte Carlo generated data are used to simulated a time-of-flight (TOF) positron emission tomography (PET) scanner with improving time resolution, down to 200-ps time resolution. TOF and non-TOF ordered subsets expectation maximization (OSEM) reconstructions were compared in terms of contrast recovery and signal-to-noise ratio, with the purpose of characterizing the differences of TOF and non-TOF at very low counts. This study shows that there is a lower limit to the number of counts in a PET scan, in order to obtain a "reliable" PET image. Below such limit, the reliability of the measurement is very poor. The use of TOF information has the beneficial effect of lowering this statistical limit, allowing for shorter reliable PET scans. Another interesting finding derives from the comparison with TOF filtered back projection (FBP) images: if time resolution can be improved, TOF FBP images become very competitive with TOF MLEM and OSEM algorithms, not only in terms of contrast recovery but also in terms of reduced noise level.