Applications of CMOS SPAD arrays in clinical imaging and spectroscopy: (Invited)

Single photon detection offers enhanced measurement through observation of timing dynamics on the picosecond to nanosecond scale. This has been widely exploited across many fields, including biological or medical technology. However practical application to clinic is often limited due to acquisition limitations of single point detectors combined with practical and cost limitations to employing larger numbers of detectors in combination. However, recent advancements in CMOS single photon avalanche diodes (SPADs) enable massively multiplexed time correlated single photon counting (TCSPC) in a compact format suitable for practical application. This work describes our efforts to employ this technology to enhance a range of technologies, including fibre optic spectroscopy, endoscopic imaging, and widefield clinical imaging. We have demonstrated multiple applications to improve signal to noise in fibre optic probes with this technology. This includes: improved Raman spectroscopy with single fibre optic probes through time resolved separation of unwanted background; better disambiguation of fluorescently labelled bacteria through fluorescent lifetime measurements in both spectroscopic and endoscopic imaging modalities; and fibre optic fluorescence spectroscopy of tissue autofluorescence indicating disease state. Further we detail a time resolved widefield imaging system applied to the observation of diffuse photons transmitted from fibre optic light sources placed deep within tissue (porcine and human cadavers), where transiting photons are observed from outside the body. This technology is now being translated to initial clinical investigation for locating inserted medical devices.