Near-IR Laser and Raman Spectroscopy of Colon Mucosal Tissues: A Comparative Study on Metabolite Characterisations for Early Diagnosis of Inflammation and Ulceration

Mucosal tissues exhibit extended near-IR transparency in the 900 – 1300 nm window, which overlaps nicely with the technologies developed for optical communication systems operating in the 800 – 1700 nm range. In this work, we have demonstrated a laser, based on an ytterbium-ion (Yb ³⁺ )-doped tellurium oxide glass gain medium, emitting in a narrow window of 1050 – 1055 nm, for use in the first instance as a histopathological microscopic application for bowel tissue examination. The light scattering properties of tumorous and healthy human bowel tissues were characterised using this laser. It was found that both types of tissue were highly transparent at this wavelength and that the laser scattering was significantly lower in the tumorous than that in the healthy tissue.Raman spectra were obtained for inflamed (ulcerative colitis) and healthy bowel tissues. A clear difference was identified in the concentrations of carotenoids, which were twice as strong in the inflamed, and in the phospholipids, which were lower in the inflamed. Myoglobin was another metabolite which was also identified. Using multivariate statistical analysis, we show that the intensities of five peaks (three carotenoid peaks at Raman shifts of 1003, 1155 and 1518 cm ⁻¹ and two phospholipid peaks at 1440 and 2762 cm ⁻¹ ) are significantly different between healthy and inflamed tissues. Both the near-IR scattering and Raman data allow differentiation between the healthy and inflamed or tumorous tissues and show a potential methodology for early diagnosis tools for ascertaining the presence of inflammation.