Fluorescence lifetime imaging (FLIM) is a valuable technique which can be used to provide label free contrast between different tissue types and provide information about their molecular makeup and local environment. FLIM systems based on single photon avalanche diode (SPAD) arrays are increasingly being used in applications such as medical imaging due to their high sensitivity and excellent temporal resolution [1]. Additionally, SPAD arrays are also commonly employed for time of flight (ToF) imaging techniques such as light detection and ranging (LiDAR) [2]. Here we demonstrate a system which employs both of these modalities into a single instrument, allowing us to acquire both depth and widefield FLIM images simultaneously using a single 32 x 32 pixel SPAD array operating in time correlated single-photon counting (TCSPC) mode with 50 ps temporal resolution. Initial results show that we can correctly measure depths and distances of sample objects with < 1 cm resolution while maintaining excellent and consistent fluorescence contrast. Lifetime is consistent over a distance of 10 cm with a standard deviation of < 0.5 ns, showing that it is possible to decouple depth and lifetime data. We believe this work is the first demonstration of a widefield FLIM system capable of 3D imaging. The next step will be the addition of a miniaturized system [1] and future applications for this technology include fields such as surgical guidance, endoscopy and diagnostic imaging.

We propose a handheld single photon avalanche diode (SPAD) micro-camera probe for wide-field in-vivo fluorescence lifetime imaging (FLIm) applications. The presented probe includes a novel 3D stacked 1.4 mm × 1.4 mm SPAD array, an integrated excitation light source, and imaging optics. The spatial and temporal performance of the integrated system was characterised using a USAF test target and range of fluorescence lifetime beads.