Basic study on pulse height distribution of DOI detectors constructed of stacked crystal elements

As part of the next generation PET development project, performances of one-dimensional GSO crystal arrays were measured and analyzed for the development of the depth-of-interaction (DOI) detector constructed of three-dimensional GSO crystal arrays. We considered two structures of one-dimensional crystal arrays, one is a "straight line type" which has the crystals of the array stacked in series, and the other is a "U shaped type" which is a crystal block of stacked crystals bent at the center. By scanning collimated gamma rays along the crystals, we measured the pulse height distributions from one end or both ends of the crystal array for different conditions of the surface of each crystal (rough or chemical etching) and arrangement of the reflector. The analysis of these data showed how these conditions affected the performances of the DOI detector. We also measured two-dimensional pulse height distributions for the "U shaped type". The analysis of the data on the combination of crystal surface treatment and reflector arrangement provided a method to optimize performances of the DOI detector.