Ultraminiature optical design for multispectral fluorescence imaging endoscopes

A miniature wide-field multispectral endoscopic imaging system was developed enabling reflectance and fluorescence imaging over a broad wavelength range. At 0.8-mm diameter, the endoscope can be utilized for natural orifice imaging in small lumens such as the fallopian tubes. Five lasers from 250 to 642 nm are coupled into a 125-μm diameter multimode fiber and transmitted to the endoscope distal tip for illumination. Ultraviolet and blue wavelengths excite endogenous fluorophores, which can provide differential fluorescence emission images for health and disease. Visible wavelengths provide reflectance images that can be combined for pseudo-white-light imaging and navigation. Imaging is performed by a 300-μm diameter three-element lens system connected to a 3000-element fiber. The lens system was designed for a 70-deg full field of view, working distance from 3 mm to infinity, and 40% contrast at the Nyquist cutoff of the fiber bundle. Measured performance characteristics are near design goals. The endoscope was utilized to obtain example monochromatic, pseudo-white-light, and composite fluorescence images of phantoms and porcine reproductive tract. This work shows the feasibility of packaging a highly capable multispectral fluorescence imaging system into a miniature endoscopic system that may have applications in early detection of cancer.