MicroPET II: An ultra-high resolution small animal PET system

MicroPET II is a second-generation microPET scanner dedicated to high resolution PET imaging of small animals. The system consists of 90 scintillation detector modules arranged in a 3-ring configuration with a radius of 16.0 cm, and an axial extent of 4.9 cm. Each detector module consists of a 14x14 array of lutetium oxyorthosilicate crystals coupled to a multi-channel photomultiplier tube (Hamamatsu H7546) through a coherent optical fiber bundle. Printed circuit boards with a charge-division readout scheme were used to decode the 196 crystals in each array from 64 anode signals. Electronics from Concorde Microsystems, Inc. was used for signal amplification, digitization, and coincidence processing. Preliminary data showed a system with peak sensitivity of 2.26%. Energy resolution ranges from 28% to 75% with a mean of 42%. Image resolution ranges from 1.07 mm FWHM at the center of field of view (CFOV) to 1.40 mm FWHM in the radial direction and 1.14 mm FWHM in the tangential direction at 1 cm offset from CFOV. Further improvements in image and energy resolution are expected when the system geometry is fully modeled and the crystal lookup tables are improved.