Sensitivity Improvement of TOFPET by the Utilization of the Inter-Slice Coincidences

Conventional multi-slice positron tomographs have suffered from an inefficient use of the inter-slice coincidence information due to a lack of an appropriate reconstruction algorithm. In order to overcome this deficiency, most multi-slice tomographs use the nearest neighbor coincidence lines and approximate the position of the slice by summing the two sets of lines. This still leaves a fair number of coincidence lines which are discarded. TOFPET, with its ability to localize the positions of the annihilation, overcomes this limitation with a new technique of utilizing all the inter-slice coincidence lines. Each coincidence event is localized in three dimensions and then placed in one of the imaae slices for tomographic reconstruction. With a proper design of the positron camera, this can result in a sensitivity increase of 60% over cameras of similar design but utilizing only the nearest neighbor inter-slice coincidences. We show how this new technique is implemented in the TOFPET camera being constructed at our institution.