Verification of concepts for DOI determination in a three-layer small animal PET

Abstract

Improved spatial resolution without sacrificing sensitivity is one of the most challenging development goals for small animal PET scanners. The 3-layer configuration that we proposed utilizes relative offsets of half a crystal pitch in x-and y-directions, and pulse shape discrimination to obtain depth of interaction (DOI). Three layers of crystals with a dimension 1.5 1.5 7.0 mm 3 were composed of a L 0.2 GSO (Lu 0.4 Gd 1.6 SiO 4 : Ce) crystal layer and a L 0.9 GSO (Lu 1.6 Gd 0.4 SiO 4 ) crystal layer aligned with each other, and a L 0.9 GSO crystal layer offset of at half a crystal pitch in x-and y-directions. The L 0.2 GSO crystal layer was attached to a Hamamatsu H9500 flat-panel PMT. The devised small animal PET scanner has a diameter of 84 mm with one detector ring, and can be upgraded to two detector rings. GEANT4 Monte-Carlo simulation was used to estimate sensitivities of ~12 % and ~20%, respectively, at the center of one and two PMT ring system. We present flood images with peak-to-valley ratios of about 5~6 obtained using 22 Na and layer identification capability of ~95% with pulse shape analysis using a 100 mega-sample per second (MSPS) Analog-to-Digital Converter (ADC), and verified the basic concepts of the multi-layer small animal PET. Index Terms-Depth of Interaction (DOI), Cerium Doped lutetium Gadolinium Oxyorthosilicate (LGSO), Three-layer Crystal, Animal PET