Fiberoptic Confocal Raman Spectroscopy for Real-Time In Vivo Diagnosis of Dysplasia in Barrett's Esophagus

Abstract

Barrett’s esophagus (BE) is a metaplastic precursor of esophageal adenocarcinoma (EAC). Since the late 1970s, despite extensive efforts for prevention (eg, periodic surveillance of high-risk BE patients), EAC still has had a substantial rise in incidence rates (>350%), and is growing more rapidly than other cancers in the developed countries. Given the poor therapeutic response of symptomatic EAC, early identification of high-risk lesions (ie, dysplasia) together with therapeutic interventions is the most critical measures to improving survival rates of BE patients. However, dysplastic lesions or grossly inconspicuous cancers are endoscopically indistinguishable from the surrounding benign tissue. This is because conventional endoscopy heavily relies on visual assessment of structural and morphologic changes of the tissue surface, resulting in poor diagnostic accuracy. Existing diagnostic guidelines recommend extensive biopsy samplings (typically 4-quadrant samplings) at every 1to 2-cm interval along suspicious Barrett’s segments during endoscopic inspections of BE patients. This approach produces a vast number of negative biopsies and is clinically labor intensive and a burden to the patients. Because only a minute amount of the mucosa is sampled (as little as 5%), tissue biopsies may not accurately characterize BE segments. Foci of dysplasia in a background of intestinal metaplasia are frequently overlooked, even when the biopsies are diligently performed by the experienced endoscopists using extensive 4-quadrant biopsy protocols. Taken into account the enormous rise in incidence rates of EAC and the existing clinical challenges, the need for new advanced endoscopic modalities has never been greater. The objective targeting of high-risk tissue areas (eg, high-grade dysplasia [HGD]) with a noninvasive or minimally invasive technique could greatly reduce random biopsy sampling errors as well as health care expenses on the patients. Recent attention has thus been directed toward molecular diagnosis using optical spectroscopy and imaging. Raman spectroscopy represents a unique optical vibrational technique based on the fundamental premise of inelastic light scattering for tissue diagnosis and characterization. When an incident laser light induces a polarization change of molecules, a small proportion of incident light photons (w1 in 10) is inelastically scattered with the frequency shifts corresponding to the specific Raman active vibrational modes of the molecules in the sample. Taking advantage of the Raman spectroscopic ability of harvesting a wealth of fingerprint information from interand/or intracellular components (eg, proteins, lipids, and DNA) in cells and tissue, Raman technique has shown great promise for histopathologic assessments (ie, optical biopsy) at the biomolecular level. In the last 2 decades, there has been accumulating evidence on the accurate diagnostic capability of Raman spectroscopy through comprehensive in vitro studies. In vivo Raman endoscopic applications, however, have been limited not only by the difficulty in capturing inherently very weak tissue Raman signals, but also by the slow speed of spectral measurements (>5 s). The miniaturization of flexible fiberoptic Raman probes with depth-resolving capability that can pass down the instrument channel of medical endoscopes for effective tissue Raman light collections presents another technical challenge in endoscopic applications of Raman spectroscopy. To tackle these challenges, we have developed a novel beveled fiberoptic confocal Raman probe coupled with a ball lens capable of enhancing in vivo epithelial tissue Raman measurements at endoscopy. We present this work on in vivo clinical applications of the fiberoptic confocal Raman spectroscopy for real-time objective diagnosis of dysplasia in BE at endoscopy. The direct assessment of the biomolecular contents of epithelial cells and tissue in vivo enables the gastroenterologists to perform noninvasive or minimally invasive optical biopsies in real-time during clinical endoscopy.