Advances in Endoscopic Imaging of Barrett’s Esophagus

Abstract

o B b t a l a t w F r c i l r creening and surveillance of Barrett’s esophagus may prevent esophageal adenocarcinoma by detecting precursor esions. In most cases, however, dysplasia is invisible to the eye f the endoscopist. Therefore, surveillance requires extensive andom biopsies and histologic examination of the excised issue for dysplasia. This biopsy strategy has several limitations, ncluding sampling errors, increased time and cost of endosopy, and limited reliability of histologic interpretation of dyslasia. Over the past 10, years there have been major advances n optical methods for detection of dysplasia and early carcioma. These methods include imaging methods focused on oth anatomic and functional changes of dysplasia, as well as ther non–image-based optical methods such as spectroscopy. lthough many of the imaging methods remain experimental, 005 and 2006 saw the introduction of advanced imaging ethods into mainstream endoscopic systems such as narrow and imaging (Olympus Corp, Melville, NY), intelligent chrooendoscopy (Fujinon, Wayne, NJ), and integrated optical coerence tomography systems (Pentax, Golden, CO). The value f these systems has not yet been established; however, they are eing rapidly adopted into practice. In this review, I discuss the echnological basis of these systems and speculate on their pplications. The currently available advanced endoscopic imaging sysems all rely on anatomic imaging, seeing the actual tissue or ven cells, but using methods to increase magnification and ontrast, and focus on regions relevant to distinguishing nonysplastic from dysplastic Barrett’s epithelium. At a fundamenal level, dysplasia is classified based on both cytologic (inreased nuclear size, density, irregularity) and histologic distortion of the single-layer epithelium and uniform crypt attern). In addition, there are vascular changes that mirror hese, such as increased vascularity and increasing irregularity f capillary arcades. Each imaging method aims at identifying ne or more of these pathologic changes. Imaging of cytologic changes is largely restricted to optical oherence tomography and confocal endomicroscopy and is the ubject of previous reviews.1 Macroscopic anatomic imaging nd functional imaging are now the most common methods of etection of dysplastic changes in Barrett’s esophagus. The two urrently available methods—narrow band imaging and intellient chromoendoscopy— both rely on similar methods. Narrow and imaging uses 2 characteristics of light to enhance surface ontracts and highly vascular changes. The first of these is the se of short wavelength light in the visible spectrum (blue light) o illuminate the tissue. Because light of shorter wavelength is ighly scattered by dense cell nuclei and collagen, only light rom the most superficial layers of the mucosal and submucosa re visualized. Although not often recognized, standard white ight endoscopy visualizes a thick slab of tissue at least 5–10 m thick as evidenced by the routine appearance of deep ubmucosal vessels on routine endoscopy. The surface characeristics of the mucosa are often lost because of the diffusion of he light from multiple layers at the same time. Using narrow ands of blue light overcomes this problem by allowing more solated imaging of the thin slab of tissue at the mucosal urface (Figure 1). The second method is aimed at increasing the visualization f small blood vessels by increasing the contrast and resolution. lood typically appears red owing the absorption of blue light y hemoglobin. When tissue is illuminated with the full specrum of visible light, the blue light is absorbed and the red light, mong other colors is reflected. Connective tissues and epitheial cells typically reflect the full spectrum of light and thus ppear white. The contrast between vasculature and connective issue/epithelium can be increase by selectively illuminating ith blue light so that the vessels appear black and the sur-