Front-End Electronics for a 100 ps Coincidence Time Resolution TOF-PET Detector With 24-Fold LVDS Timing Channel Multiplexing

We have refined analog-to-digital signal processing electronic techniques to develop a highly compact design for time-of-flight positron emission tomography (TOF-PET) detector modules employing side readout of scintillation crystal elements to achieve 100 ps coincidence time resolution (CTR) and 3-D positioning of 511-keV interactions. Detector modules comprise 64 “layer” units, each containing a
$2\times 4$
array of
$3\times 3\times 10$
mm3 LGSO (Lu
$_{{2}{x}}$
Gd
$_{{2 - 2}{x}}$
SiO5:Ce) elements side-coupled to a
$6\times 4$
array of
$3\times 3$
mm2 silicon photomultipliers (SiPMs). To achieve high packing fraction, the electronic readout is implemented with a four-layer rigid FR4 PCB that is only 0.4 mm thick and has a width matching the
$6\times 4$
SiPM array (13.3 mm). Among several novel features, the circuit multiplexes 24 SiPM timing channels into 1 to reduce the readout complexity. In the configuration reported here, all external connectors have been removed and replaced with 0.4 mm pitch fine connectors for scalable signal routing at the detector module level. The timing performance of this 24:1 multiplexed readout of the 24 SiPM detector array units measured in coincidence with a reference detector resulted in an average of
$107~\pm ~1.3$
ps full-width at half-maximum (FWHM) CTR, not significantly different than the single crystal element CTR results of
$106~\pm ~2.3$
ps. The proposed side readout of scintillation crystal elements and readout electronics configured in a layer topology achieves CTR performance that is scalable to large area, high packing fraction detector module building blocks for a ~100 ps CTR TOF-PET system.