Rapid multiexcitation spectrofluorimeter for in-vivo tissue diagnosis

Abstract

We have designed, fabricated and tested a compact excitation-emission spectrofluorimeter with optical fiber light delivery and collection for use in rapid analysis of tissues in a clinical setting. This system provides ten different excitation wavelengths, permitting collection of all ten emission spectra from biological tissues in approximately 500 ms. It uses a nitrogen laser which pumps a sequence of dyes placed in cuvettes on a rotating wheel. All dye cuvettes utilize a common optical resonant cavity, which simplifies the coupling of the different excitation wavelengths into the delivery fiber of an optical fiber probe. A filter wheel containing one long-pass filter for each excitation wavelength is synchronized with the dye wheel for compactness and ease of control. A white light excitation source permits acquisition of the tissue diffuse reflectance spectrum on each cycle. The fiber optic probe is composed of seven optical fibers arranged at the distal tip in the form of a central delivery fiber surrounded by six collection fibers, with an optical shield. Return fluorescence and reflected light are dispersed by a small spectrograph and detected by a photodiode array detector. The system can collect a single shot spectrum from biological tissue with a signal-to-noise ratio in excess of 50:1. This unique design for providing rapidly variable excitation wavelengths facilitates the collection of multi- excitation fluorescence spectra for the diagnosis of diseases in vivo.