Novel sequential RGB+NIR fluorescence lifetime imaging with a single nanosecond time-gated CAPS camera

Fluorescence imaging has long been used in a variety of applications, especially in fluorescence-guided surgery. There is rising interest in using fluorescence lifetime by employing different fluorescence dyes to get deeper insights into a tissue’s features.

Current imaging systems used in fluorescence-guided surgery are primarily designed to provide surgeons with a combined view of natural color (RGB) images and fluorescence overlays. However, these systems rely on separate cameras, which can cause problems with aligning the images and create a bulky setup.
Our novel approach is sequentially illuminating the scene with red, green, and blue pulses along with Near Infrared (NIR) pulses, captured selectively with a single fast time-gated camera. The camera is synchronized to the pulsed illumination and positions its time-gates to capture only one of the illumination pulses; afterwards overlaying the NIR fluorescence lifetime image (FLI) on the natural color image. The camera was developed by the VUB-ETRO team based on Current-Assisted Photonic Sampler (CAPS) image sensor technology which intends to offer real-time FLI, particularly in the NIR (700-900nm) area.
This work focuses on utilizing RGB LEDs in an annular configuration arranged around the camera lens pulsing in the order of milliseconds period. An additional time-gate is added for the picosecond NIR fluorescence pulsed laser which is synchronized with the gate window. The experiments are performed on various fluorescence phantoms overlaying the FLI on natural color images.
The capabilities of the system are demonstrated in an experimental setup, where the sample is sequentially illuminated with RGB pulses, along with a NIR pulse for FLI. Due to its fast time-gating mechanism, our CAPS sensor can distinguish and image these colors separately, while the human eye merely sees white illumination.