Improvement in signal-to-noise ratio at variable random fraction in TOF PET

Time of Flight (TOF) Positron Emission Tomography (PET) produces an improvement in signal-to-noise ratio (SNR) over conventional non-TOF reconstruction. This improvement increases with the size of the patient and with better coincidence time resolution of the system. As a first approximation in TOF PET reconstruction, this gain in SNR is independent of the scatter and random components of the total signal. On the other hand, recently a model has been proposed in which the SNR gain of TOF PET vs. conventional PET is a growing function of the random events fraction. This would provide an additional advantage of TOF PET reconstruction over conventional PET, particularly in the presence of a large random fraction. In this work we show measurements on a NEMA image quality phantom on a Siemens Biograph mCT TOF PET/CT scanner, which confirms the prediction of the model for filtered back projection reconstruction algorithms, in the case of a non uniform source distribution. The implication is that not only is TOF reconstruction more advantageous for large patients, but also the improvement is higher for PET scans performed at higher count rates, compared to a conventional non-TOF reconstruction.