RAPID FIBER-OPTIC RAMAN SPECTROSCOPY, OPTICAL COHERENCE TOMOGRAPHY AND MUELLER MATRIX SPECTROSCOPIC IMAGING FOR OPTICAL DIAGNOSIS OF HUMAN TISSUE IN VIVO

Abstract

Raman spectroscopy (RS) is a label-free optical vibrational technique capable of probing biochemical and biomolecular structures and conformations associated with disease transformation. In vivo RS clinical applications, however, have been hindered not only by the difficulty in capturing inherently very weak tissue Raman signals, but also by the slow speed of Raman spectral measurements (>5s). Further, currently reported biomedical RS systems are focused on either the fingerprint (FP) (800-1800 cm-1) or high-wavenumber (HW) (2800-3600 cm-1) regime, and are mostly coupled with volume-type Raman probes lacking of ability for selectively probing superficial tissue Raman signals but having a relatively deep tissue Raman interrogation. Besides, RS technique only provides a point-wise biochemical information (i.e., proteins, lipids, deoxyribonucleic acid and tissue water) without tissue morphology. To tackle the challenges and enhance the endoscopic applications of RS, in this thesis work, we have developed a novel beveled fiber-optic Raman probe together with a simultaneous FP and HW RS technique for enhancing in vivo diagnosis and characterization of cancer and precancer in gastrointestinal (GI) tracts at endoscopy. We have also developed an integrated Mueller-Matrix (MM) near-infrared (NIR) imaging and MM point-wise diffuse reflectance (DR) spectroscopy technique to investigate the polarization properties (i. e., depolarization, diattentuation and retardance) of GI tissue (e. g., colon) and assess their potential for enhancing GI tissue diagnosis. We have also developed a hybrid Raman spectroscopy (RS)-optical coherence tomography (OCT) technique to simultaneously uncover both the morphological and biochemical information about the tissue in vivo, facilitating real-time, in vivo tissue diagnosis and characterization. Specifically, the beveled fiber-optic Raman probe developed provides a 19-fold higher epithelium to stromal Raman photon ratio than that using a volume-type Raman probe, demonstrating its great potential for enhancing the epithelial tissue Raman measurements as evidenced by a significantly improved diagnostic accuracy of 93.0% for identifying gastric dysplasia from normal gastric tissue compared with that (88.4%) using a volume-type Raman probe. The complementary biochemical/biomolecular tissue information arising from the superficial epithelial layer harvested by the integrated FP/HW fiber-optic Raman spectroscopy offers an enhanced diagnosis of cancer and precancer not only in the upper gastrointestinal (GI) tract, but also in the lower GI tract. The esophagus squamous cell carcinoma, gastric dysplasia, and colorectal polyps are diagnosed with diagnostic accuracies of 97.3%, 95.8% and 81.8%, respectively using the simultaneous FP/HW RS technique developed, superior to using either the FP or HW RS technique alone. Further, the hybrid RS-OCT technique developed provides both micron-scale tissue morphology and biochemical/biomolecular information about tissue, facilitating real-time, in vivo tissue diagnostics. The integrated MM NIR imaging and MM point-wise DR spectroscopy technique enables point-wise MM DR spectra acquired from suspicious tissue areas indicated by MM imaging, revealing decreased tissue depolarization and retardance while significantly increased tissue diattentuation in the colon associated with colonic cancer. Therefore, the novel technical development and first clinical implementation of the rapid fiber-optic Raman spectroscopy, Mueller-Matrix near-infrared spectroscopic imaging and hybrid Raman spectroscopy-optical coherence tomography in the thesis work has laid a foundation for enhancing optical detection and diagnosis of early cancer and precancer in humans in vivo.