A compact handheld system for simultaneous multispectral frequency-domain (FD) FLIM imaging is presented. The handheld endoscope consists of a handheld enclosure (10 X 5 X 3 cm3 in volume) with a rigid probe (0.8 cm diameter, 12 cm length). The customized enclosure holds the MEMS scanner and a dichroic mirror whose tip and tilt angle can be adjusted. The rigid probe includes four achromatic lenses (f = 30mm). Two of the four lenses form a relay system to extend the length of the probe. The most distal lens works as an objective to focus the light onto the sample. An additional lens is placed in the intermediate image plane of the relay system to increases the imaging FOV from ~3.6 mm to ~5 mm. The excitation for the handheld FD FLIM system is a 375nm CW diode laser modulated at 1.25MHz and 20MHz. The fluorescence emission is spectrally divided in three emission bands (405/40nm, 440/40nm, and 525/50nm) and detected by three independent APDs. The multispectral signals are further digitized and processed by a FPGA. Phase shift and decreased magnitude are computed at 1.25MHz, 20MHz and its harmonic frequencies (40MHz, 60MHz, 80MHz and 100MHz) via Discrete Fourier Transform (DFT) for lifetime estimation. The current pixel rate is 12.5 KHz which is limited by the SNR. The system is validated by imaging standard fluorescent dyes and human healthy oral mucosa in vivo. This handheld FLIM system offers a cost reduction of at least 50% compared to previous time-domain implementations.
Shuna Cheng, Michael Serafino, Rodrigo Cuenca, Beena Ahmed, Brian Applegate, and Javier Jo, "Compact and cost-effective handheld multispectral fluorescence lifetime imaging (FLIM) system for oral mucosa in vivo imaging based on a frequency-domain implementation (Conference Presentation)," Proc. SPIE 10469, Optical Imaging, Therapeutics, and Advanced Technology in Head and Neck Surgery and Otolaryngology 2018, 104690O (Presented at SPIE BiOS: January 28, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2287855.5751467575001.
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