Towards spatially dense time-domain multi-view detection in diffuse optical tomography with single-photon avalanche diodes and integrated TCSPC electronics

The advent of high timing resolution (<50ps) single photon avalanche diodes (SPADs) and progresses in time-correlated single photon counting (TCSPC) integrated electronics opens the way to multi-view higher spatial detection density time-domain (TD) diffuse optical tomography (DOT) scanners with unprecedented temporal resolution down to possibly below 30ps. The alternative to achieve high spatial density TD optical detection is to resort to time-gated cameras. However, such cameras have timing resolutions of ~300ps, and the time gate over which photons are acquired needs to be scanned resulting in a waste of useful photons and increased acquisition times compared to what could possibly be achieved. In recent years my group has been developing a TD DOT scanner for small animal imaging using discrete detectors and high performance TCSPC electronics. A first generation scanner using photomultiplier tubes (PMTs) has been realized, achieving a temporal resolution of ~200 ps. This scanner comprises 7 dual-wavelength channels for detecting excitation and fluorescence light. Its performances in terms of number of channels, acquisition time, and temporal resolution are, however, limited by the use of PMTs, expensive TCSPC cards and routers. Recently, work has been initiated on the development of a second generation scanner using SPADs and fully parallel TCSPC electronics (one TCSPC channel per detector). The development of the first generation scanner and a first prototype of the second generation scanner will be presented, along with results obtained therewith. Future work and promising applications of such technology, notably in in vivo FLIM-FRET imaging will also be described.