Development of a Small Animal PET Scanner Using DOI Detectors

A small animal PET scanner using 256-channel PS-PMTs has been designed, constructed, and evaluated. The scanner has twelve detector modules, each of which consists of a double-layer array of LYSO crystals and three PS-PMTs (Hama- matsu R8400-00-M256). In the LYSO crystal block, 32 times 53 crystal elements are optically coupled to 32 times 54 crystal elements with a shift of half the element pitch in the axial direction. The dimension of each crystal element is 1.275 times 2.675 mm² in cross section and 7 mm in depth. The twelve detector modules are positioned on a 182 mm diameter ring to form 107 detector rings with 1.4 mm pitch. The transaxial FOV is 100 mm in diameter and the axial FOV is 151 mm, which is sufficient to cover the whole body of a mouse. In order to compensate for non-uniform outputs from the multi-anodes of the PS-PMTs, ASICs having 64-channel variable gain amplifiers and summing amplifiers are used in the front-end circuits. The preliminary experimental results are the transaxial resolution of 2.0 mm FWHM in the CFOV, and the axial resolution of 2.8 mm FWHM on the axis of the ring. The absolute coincidence sensitivity is 8.1% for a point source at the CFOV with setting an energy window of 350-750 keV and a timing window of 10 ns. The applicable imaging capability of the scanner was demonstrated by animal studies with a rat.