We investigate an economic readout for depth-of-interaction (DOI) and time-of-flight capable PET detector that consists of an N×N array of crystals whose light outputs at the front- and back-end surfaces are detected by using silicon photomultipliers (SiPM). The N×N SiPMs at the front-end (back-end) of the detector are read by a stripline configured to support discrimination of the row (column) position of the signal-producing crystal, producing only four outputs for the detector. To evaluate this design, we built 4×4 and 8×8 detector modules (DM) by using 3.0×3.0×20 mm3 lutetium-yttrium oxyorthosilicates. The outputs were sampled at 2 GHz and processed offline. For both DMs, crystal discrimination was successful. For the 4×4 (8×8) DM, we obtained a crystal-level energy resolution ranging from 11.3% to 19.3% with an average of 14.1% (9.5% to 21.6% with an average of 13.9%), an average DOI resolution of 2.5 mm (3.1 mm), and a best coincidence resolving time (CRT), measured in coincidence with a single-pixel reference detector with a 302 ps CRT, of 391 ps (603 ps). The CRT deteriorated with the (8×8) DM possibly due to intercrystal scattering.

We report a PET detector module (DM) designed for developing a preclinical positron emission tomography (PET)-electron paramagnetic resonance imaging (EPRI) hybrid system. The DM consists of a linear array of eight detector units, each of which is a 12×12 array of lutetium–yttrium oxyorthosilicate (LYSO) crystals read by a 4×4 silicon photomultiplier (SiPM) array. The crystal size is approximately 1.0×1.0×10 mm3. All surfaces of the crystal are polished; except for that coupled to SiPMs they are also covered with BaSO4 to reduce light loss. The pitches of the LYSO and SiPM arrays are about 1.05 mm and 3.2 mm, respectively. The front face of the resulting DM is about 1.28×10.24 cm2 in extext and its thickness is approximately 1.8 cm. A highly multiplexing readout is devised to produce only six outputs for a DM, including two outputs that are derived from the SiPM cathode signals for determining the event time and the active DU, and four outputs that are derived from the SiPM anode signals for determining the event energy and the active crystal within the active DU. At present, these outputs are acquired by waveform sampling and analyzed offline. We have successfully developed two DMs, both showing well discriminated DUs and crystals, and an average energy resolution of about 15%. Even though time-of-flight (ToF) is not needed for the proposed system, our data shows that the DM can potentially achieve a 300-400 ps ToF resolution.