A next generation preclinical PET/EPRI: performance evaluation of the complete PET subsystem

We report on a PET system that has been recently completed after the last several years of development work. The PET system is a sub-component of PET/EPR hybrid imaging system for investigating tumor hypoxia in small animal, and will be deployed to replace the current PET subsystem of the PET/EPR imager. The new PET system possesses several superior features over the existing system for small animal imaging: the axial field-of-view is increased 4 times from $\sim 25$ mm to $\sim 106 \mathrm{~mm}$, and constituent scintillator pixel size is reduced from 3.0 mm to 1.0 mm to achieve sub-millimeter image resolution. The PET system is modularized and built by using 14 detector modules (DM). Each DM consists of 8 detector units (DU) in a row, and each DU in turn is a 12 x 12 array of $1 \mathrm{x} 1 \mathrm{x} 10 \mathrm{~mm}^{3}$ LYSO crystals coupled to a Hamamastu 14161-3050HS-04 MPPC array. The PET system employs a new signal readout method to efficiently handle a greatly increased number of detector outputs by combining a conventional resistive network (RN) and a strip-line (SL) method. Due to the highly multiplexing feature of the readout, each DM generates the total of 6 outputs only (2 SLs and 4 RNs) for digitization. After the evaluation test, BASP-10011 readout board (Brightonix Imaging, Korea) was adopted for high throughput and performance data acquisition needed for routine animal imaging studies, and was incorporated into the PET system. Following successful development and integration of all components, we started to conduct phantom imaging for performance evaluation of the PET system before installing it inside the EPR magnets. $\mathrm{A}^{22} \mathrm{Na}$ point source image shows 0.8 mm FWHM resolution in both transverse and axial direction. Image of a NEMA image quality phantom was acquired to assess the imaging performance of the PET system. We present the completed PET system and initial results on phantom imaging. More thorough performance results from on-going systematic evaluation will be reported at the conference.