First measurements of a 512 PSAPD prototype of a sub-mm resolution clinical PET camera

We present measurements from a first prototype of a 1 mm<;sup>3<;/sup> resolution clinical PET camera dedicated to breast imaging. This first prototype consists of two cartridges of 8 detector layers. Each detector layer comprises 16 dual LYSO-PSAPD modules arranged side by side. The LYSO scintillator is an 8×8 array of 0.9×0.9×1 mm<;sup>3<;/sup> crystal pixels. Each array is coupled to a PSAPD. The modules are oriented edge-on with respect to the incoming 511 keV photons. The two cartridges thus contain 256 PSAPDs and 16,284 crystals each. The entire camera will have 2 imaging heads of 9 cartridges each. Charge created by the PSAPDs was routed towards a signal conditioning board that was connected to another circuit board that houses the RENA-3 ASIC. The RENA3 chip contains 36 channels each with preamplifier, leading edge discriminator and sample and hold circuitry. The RENA3-boards were connected to a DAQ board that linked to a host PC using 8 USB2 connections. We measured an energy resolution of 10.62 + 0.04% FWHM at 511 keV, together with a coincidence time resolution of 15.7 + 0.2 ns FWHM. We determined a crystal misidentification probability of <; 0.5% on average. In order to determine the intrinsic spatial resolution we measured an average point-spread-function of 0.84 + 0.02 mm, not corrected for finite source width ( 0.25 mm diameter ) , positron range (²²Na), or photon acolinearity. We also present a reconstructed Derenzo phantom, obtained with 34 μCi/ml FDG. Although we only used a small subset of the final system and thus had a relatively low count rate, the 1.6 mm cylinders are distinctly visible. Randoms rate was estimated to be 20 %.