A dual layer GSO PET system for small animal: K-PET II

Using two types of GSO of different Ce concentration, we are now developing a dual layer PET system for small animal, named K-PET II (Kobe-PET II). For the detector, GSO of 1.5 mol% (decay time: 35ns) and that of 0.5 mol% (decay time: 60ns) was used. These two types GSOs were optically coupled in DOI direction and combined to form a block of which GSO cells were arranged into 11 x 37 matrixes. The size of a single GSO cell were 1.9mm x 1.9mm x 6mm (for front layer) and 1.9mm x 1.9mm x 9mm (for back layer) for GSO of 1.5 mol% and 0.5 mol% Ce, respectively. The GSO block was optically coupled to three position sensitive photomultiplier tubes (PSPMTs) to from a block detector. For the PSPMTs, one inch square cross wire anodes type was used. Sixteen block detectors were arranged on the 112mm diameter ring. The axial field-of-view was 74mm. Analog signals from the GSO block were weighted summed and were fed to analog-to-digital (A-D) converters which continuously digitize the signals in 100MHz. Digitized signals were digitally integrated, position calculated, pulse shape analyzed, time stamped, and checked the coincidence by a digital board in the data acquisition system. Coincidence data were stored in list node. With this configuration, we could obtained reasonable position response and pulse shape discrimination. Timing resolution was around 5ns FWHM. Three dimensional (3D) list mode algorism is schedule to be used for reconstruction. The K-PET II will be useful for molecular imaging using small animals where the high sensitivity as well as high resolution is required.