Medical Raman spectroscopy: In vivo and ex vivo tissue analysis for cancer diagnosis

Raman spectroscopy provides detailed information about the molecular composition and structure of tissue. In the literature, it has been used to study healthy and diseased artery, brain, breast, skin and gastrointestinal tissues. The majority of this work was performed on excised tissues which were freeze stored or formalin-fixed. A study is presented, where spectral artefacts are identified which are due to tissue storage and/or sample preparation. The most significant of these was dehydration which caused significant disruption of protein and lipid peaks.; To fulfill the diagnostic potential of Raman spectroscopy, it must be performed in vivo with fiber optic probes. An in vivo Raman spectroscopy system (IVRS) and specialized fiber optic probes have been designed to obtain spectra from tissue. These probes are filtered to reduce the background signal from the fiber optics and the collection fibers utilize beam steering to optimize the collection efficiency. The spatial point response functions of these probes demonstrated that the beam steering effectively changed the sample volume, and hence, the collection efficiency. Relative to unfiltered probes, the in vivo probes collected spectra from various tissues with reduced fiber optic background signal and significantly higher signal-to-noise ratios.; The first spectra collected in vivo from human gastrointestinal tissues are presented. These were obtained during endoscopy with 100 mW of 785 nm excitation light and a collection time of 5 s. Spectra of esophagus and colon had a signal-to-noise ratio of 3--8. Variation of probe-tissue pressure and angle did not significantly affect the spectra. However, some variation in spectral baseline was observed with probe bending. The performance of the IVRS in a clinical setting is described and suggestions are made for improvements. Future work includes the development of diagnostic algorithms to grade tissue pathology (especially low- versus high-grade dysplasia) based on in vivo spectra.