Multimodality optical imaging combining Optical Coherence Tomography (OCT) and Fluorescence Lifetime Imaging (FLIM) for morphological and biochemical tissue characterization

Here we report on our current efforts to simultaneously quantify both morphological and biochemical tissue information by combining optical coherence tomography (OCT) and fluorescence lifetime imaging (FLIM). The Fourier domain OCT module is built around a custom designed high-speed spectrometer (bandwidth of 102 nm, 3 dB rolloff of 1.2 mm, lines rates of up to 59 kHz). A 40 nm bandwidth SLED centered at 830 nm provided an axial resolution of 7.6 mm for OCT. The objective lens provided 10 um lateral resolution for OCT and 100 um for FLIM. Lateral OCT and FLIM beam scanning was accomplished using a set of galvo mirrors. The FLIM module excites and collects the fluorescence decay signal pixel by pixel coincident with OCT A-line collection. Each 2-D FLIM image has a corresponding coregistered OCT volume. Fluorescence excitation for FLIM was provided by a solid-state pulse laser (355 nm, 1 ns FWHM, 50 kHz rep rate). The fluorescence signal was detected with a MCP-PMT coupled to a 1.5 GHz digitizer (250 ps temporal resolutions). In addition, simultaneous multispectral time-resolved fluorescence detection was achieved by separating the fluorescence emission in three bands using a series of dichroic mirrors and bandpass filters, and launching each band into three fibers of different lengths (providing a time delay of 50 ns among bands) focused onto the MCP-PMT. The resulting OCT/FLIM system is capable of a maximum A-line rate of 59 kHz for OCT and a maximum pixel rate of at least 30 kHz for FLIM. The multimodality OCT/FLIM imaging system was validated on biological tissue. Future efforts include evaluating its potential for oral cancer diagnosis and intravascular imaging.