Preliminary results of a low-cost 4-channel time-correlated single photon counting system for time-domain diffuse optical tomography

Time-domain diffuse optical tomography (TD-DOT) provides information-rich data that have not yet been fully exploited for image reconstruction, notably to increase imaging spatial resolution. Current TD-DOT scanners suffer from a very low sensitivity owing to their small number of detection channels. This leads to excessively long acquisition times for in vivo imaging. To obtain a higher number of detection channels, thus increasing detection density, a low-cost time-correlated single photon counting (TCSPC) system dedicated to TD-DOT imaging was designed and developed, resorting solely to off-the-shelf electronic components to reduce costs, in distinction to custom application-specific integrated circuit (ASIC) solutions. It features 4 input channels with a 13.02 ps bin width and a 18.1 ps FWHM accuracy throughout a measurement dynamic range of 12.5 ns. Each channel includes a leading-edge discriminator, with a programmable threshold, for direct interfacing with off-the-shelf photodetector modules. A software-programmable delay line was added to the channel signal path to compensate for undesired propagation delays. The system also supports a virtually unlimited number of TCSPC channels using a daisy-chain configuration through an onboard Ethernet switch.