Sub-millimeter resolution PET detector module using Multi-Pixel Photon Counter array

The aim of this study is to design a novel PET detector module using an array of sub-millimeter LSO crystal read out by an array of surface-mount type of Multi-Pixel Photon Counter (MPPC). The volume of one MPPC sensor is 2.4 × 1.9 × 0.8 mm
³
and the sensitive area is 1 × 1 mm
²
. The 9 MPPCs were arranged into a 3 by 3 array held by a Teflon base with 9 pockets. This provides an 8.6 × 8.6 mm
²
sensing area to decode a 10 by 10 array with 0.8 × 0.8 × 3 mm
³
LSO crystals of 0.86 mm pitch. After all the components were assembled, the base was mounted to a readout board that consists of quenching resistors, coupling capacitors, resistive charge divider, and current feedback pre-amplifiers. A light guide was fabricated to control the distribution of scintillation lights generated from the LSO array on the MPPC sensitive area so as to get a better localization of each gamma-ray event. A Monte Carlo simulation program was utilized to assist the light guide design. For the flood image measurement, a Na-22 point source was used. The energy resolution was measured with a Ge-68 source for each LSO crystal by a Gaussian fit to the photopeak in its energy spectrum. Timing resolution was measured against a plastic scintillator coupled to a Hamamatsu H5783 PMT using a standard time-to-amplitude converter. Linearity test was performed with gamma-ray sources of various energies. The 10 by 10 array of 0.8 mm LSO crystals can be clearly resolved in the flood image. Timing resolution of the single channel MPPC was estimated to be 620 picoseconds FWHM. Mean energy resolution and standard deviation value were 18.8% FWHM and ± 2.7% at 511 keV. The nonlinearity is observed at the single MPPC and the corner crystals in the MPPC array, but less significant for central crystal. These results demonstrate that the proposed PET detector module can be used for high resolution PET insert applications. It can potentially be used for MR compatible PET applications.