Isotropic resolution PET detector Xtal cube using a monolithic scintillator segmented by laser processing

We are developing a DOI-PET detector Xtal cube which detects scintillation photons from six sides of the crystal block. The Xtal cube is aimed at obtaining isotropic resolution by effective readout of scintillation photons. The Xtal cube is composed of 3D segmented cubic crystals and arrays of multi pixel photon counters (MPPCs). To fabricate the 3D scintillator array easily, we expect a sub-surface laser engraving (SSLE) technique instead of making a conventional segmented scintillation array. For this paper, we developed the Xtal cube using the SSLE technique and evaluated resolution performance of the Xtal cube to show a proof-of-concept of isotropic resolution. The 3D grids of 2 mm pitch were fabricated into an 18 x 18 x 18 mm3 monolithic LYSO crystal by the SSLE technique. 4 x 4 MPPCs were optically coupled to each surface of the 3D segmented LYSO. Each crystal was identified on the 3D position histogram by Anger-type calculation from 96 channel MPPC signals. The Xtal cube was uniformly irradiated by 511-keV gamma rays and the 729 crystals on the 3D position histogram could be separated clearly. In particular, the Xtal cube made by the SSLE technique provided higher crystal identification capability than the block array of segmented crystals. Response functions of the Xtal cube were measured by scanning a 22Na point source. The gamma ray beam was scanned in 0.25 mm steps by positioning the Xtal cube in vertical and 45-degree directions. The average FWHM resolutions in both directions were 2.3 mm. For our next step, we are developing a one-pair prototype system to show resolution performance of reconstructed images.The 2011 IEEE Nuclear Science Symposium and Medical Imaging Conferenc