A time-based single transmission-line readout with position multiplexing

We developed a time-based single-transmission-line readout method for time-of-flight positron emission tomography (PET) detectors. The 2D position of a silicon photomultiplier (SiPM) array was encoded in the upper and lower widths of a specially prepared L-shaped tag pulse followed by the original scintillation signal. A PET detector setup was configured using a 4 × 4 array of LSO crystals optically coupled one-to-one to a 4 × 4 SiPM array. Two pulse width modulator circuits were employed per SiPM anode signal channel and a total of 32 width-modulated digital pulses were summed and merged with a delayed common-cathode signal. The final output was analyzed using timestamps crossing two-level threshold voltages. All 16 crystals were clearly separated on a positioning map. The average energy and coincidence time resolutions were 15.0 ± 1.1% and 288.7 ± 29.3 ps after proper correction process, respectively. A 3D position decoding capability was also shown by the remarkable discrimination performance in a phoswich PET detector setup (LSO and LGSO), resulting from well-preserved scintillation signals. The proposed method enables a time-based single-channel readout with 3D gamma ray interaction position decoding capability without compromising on detector performance. This method provides gamma ray energy and arrival time information as well as 2D and depthwise interaction positions of the phoswich detectors through one channel readout. Thus, channels can be reduced by at least 4-5 times compared to typically employed charge-sharing-based position multiplexing method; this significantly reduces the burden of data acquisition on the PET system.