Polymer-capped fiber-optic Raman probe for in-vivo non-invasive Raman tomography and spectroscopy

摘要

As advances in fiber optic probe design move Raman spectroscopy into the clinic, there remain important practical problems. Most in-vivo non-invasive applications employ specialized fiber optic probes. Much effort has been devoted to minimizing Raman and fluorescence background from fiber. Less attention has been paid to the need to generate reference Raman signals proportional to delivered laser power without direct measurement of tissue albedo. Knowledge of laser power is needed for quantification of changes in tissue composition. The need is especially acute in diffuse Raman tomography, where accurate modeling of light transport through the tissue is required for accurate reconstruction of subsurface features.We describe a fiber optic probe that incorporates a transparent polymer cap at the end of each excitation fiber. As laser light propagates through the cap it generates Raman bands whose intensity can directly measure power delivered to the tissue of interest. Our first implementation uses a fluorinated ethylene-propylene copolymer (FEP) cap that is attached to the ferrule at the distal (delivery) end of each excitation fiber. FEP is transparent and functions as a waveguide with only a small insertion loss, about 5%. Importantly, there are few overlaps between the Raman bands of FEP and the bands of tissue constituents. The cap increases the diameter of the structure in contact with the specimen, but with extensive photon diffusion this makes little difference in performance. We present here latest non-invasive bone spectroscopy results with the calibrator, hi addition, extensive enhancement of the calibration signal using a fluorocarbon optical fiber is discussed.