Performance results of a prototype depth-encoding PET detector

The results of a feasibility study for a high-resolution PET detector system are presented. The detector is based on (he use of etched LSO scintillation crystals viewed from just one end. We have demonstrated that this configuration yields Depth-of-lnteraction (DOI) information whilst also preserving good energy and coincidence-time resolution. A prototype detector was built using a 4×4 crystal array coupled to 61pixel hybrid photodiodes. The measurements demonstrate a DOI resolution of 5∼7mm FWHM in a 30mm deep detector. The signal level was measured to be in the range 250 to 600 photoelectrons depending on the location of the 511 keV energy deposit in the crystal. A resolving-time of less than 5ns FWHM was estimated based on indirect measurements. The technique depends on the assumption that all of the events detected above a selected threshold value are, in fact, fullenergy deposits. The validity of this assumption and the impact of the photons scattered in the object have been studied using a Monte Carlo simulation of the proposed small animal PET imager.