SiPM-based dual-ended-readout DOI-TOF PET module based on mean-time method

Positron emission tomography (PET) with high resolution and high sensitivity is desirable for detecting cancers and neurological diseases. In this work, a depth-of-interaction (DOI)-time-of-flight (TOF) PET has been attempted to achieve both high spatial and high timing resolution. Dual-ended readout is a simple technique that can provide excellent timing and DOI resolutions and consistent signal arrival times, regardless of the DOI position along the scintillation crystal, as a mean-time method is used. A dual-ended readout DOI-TOF PET module consisting of a 6 x 6 array of 2 x 2 x 20 mm(3) saw-cut cerium-doped lutetium-yttrium oxyorthosilicate (LYSO) crystals is constructed. Both ends of the LYSO crystal array are optically coupled to a multi-pixel photon counter (MPPC) with 4 x 4 channels. The sixteen MPPC outputs are reduced to four position signals using a charge division circuit (CDC) board, and the timing signal is extracted from the common cathode of the MPPC. The four position signals from the MPPC are digitized by a DRS4-based high-speed waveform digitizer with a sampling rate of 5 GSa/s. A Na-22 source is placed in front of a reference detector and at the side of the dual-ended readout DOI-TOF PET module in five steps of 2 mm, 6 mm, 10 mm, 14 mm, and 18 mm to measure the DOI, coincidence timing resolutions (CTRs), and mean-times. The full-width-half-maximums (FWHMs) of DOI resolutions and CTRs varied from 3.0 mm to 3.8 mm, with an average of 3.5 mm, and from 333 ps to 367 ps, with an average of 349 ps, respectively. The average of the slopes of the mean-time versus DOI position, for the 36 crystals, was -0.60 +/- 1.68 ps/nm, which was consistent with the null value. The dual-ended readout DOI-TOF PET module based on the mean-time method produced both good DOI and CTRs, and consistent signal arrival times. The found solution would be the most advantageous in the small aperture PET systems, such as those for brain and breast imaging.