Sensitivity improvement of tofpet by the utilization of the inter-slice coincidences

Conventional multislice 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 multislice 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 image 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 i.s implemented in the TOFPET camera being constructed at our institution.