Although the basic platform of flexible endoscopes is similar to that devised 50 years ago, numerous recent technological advances are becoming available to the endoscopist. Novel self-propelled endoscopes and shape-conforming overtubes may permit simpler colonoscopic exams. An abundance of new imaging modalities may facilitate early detection of dysplasia and other pathologic entities. Many of these techniques remain investigational and are currently in clinical trials to determine patient benefit. Thus, as endoscopic technology and its indications progress in tandem, the endoscopist’s armamentarium continues to expand.
One of the challenges in modern endoscopy, especially colonoscopy, is the formation of undesired loops in the shaft of a flexible scope. Loop formation impedes expeditious and safe passage to the cecum by transmitting the force of insertion to the colon wall or mesentery rather than to forward progression. Two technical advances aim to prevent loop formation: variable stiffness endoscopes and shape-locking overtubes.
Variable Stiffness Endoscopes
Conventional colonoscopes have a static level of column strength throughout the length of the insertion tube. The column strength determines the amount of buckling of the instrument that occurs during insertion and the level of elasticity that remains during reduction of loops. Variable stiffness endoscopes permit alteration of the column strength through an adjustable tensioning coil. The data from studies comparing variable stiffness colonoscopes to conventional scopes are inconclusive. Some studies reports faster cecal intubation using variable stiffness endoscopes with less need for adjunct maneuvers, while other similar studies report no significant differences.
Shape Locking Device
The ShapeLock Endoscopic Guide (ShapeLock, USGI Medical, San Clemente, CA) consists of a reusable skeleton of multiple titanium links, a disposable inner plastic lining, an atraumatic foam tip, and a disposable smooth external skin. A squeeze handle at the base of the device converts it from a flexible mode to a rigid mode. The shape locking device is made in 40 cm and 60 cm lengths with an inner diameter of 20 mm. A small clinical study has been reported using the shape locking device. No devicerelated complications were noted, but the optimal strategy for employing the device was uncertain. Additionally, a separate report extolled the ability to rapidly redeploy the colonoscope when using the shape locking device should specimen retrieval and reinvestigation of the colon be necessary.
New Scope Technology
While the construction of standard endoscopes has remained largely unchanged over many decades, novel scope designs are being developed to either simplify colonoscopic examinations or enhance mucosal visualization. Other than double balloon enteroscopy, these technologies are chiefly limited to small clinical trials, but their application could gain momentum in the coming years.
In an effort to simplify the process of colonoscopic screening, self-propelled endoscopes are in development. The Aer-O-Scope (GI View, Ltd, Ramat Gan, Israel) is a user-independent, self-propelled, self-navigating colonoscope. The device consists of a disposable rectal introducer, supply cable, and a scope embedded within a scanning balloon. A small pilot study examined the proof of concept of the Aer-O-Scope. In a cohort of young volunteers (ages 18-43 years), the device successfully reached the cecum in 83% of cases. There were no device-related complications. The device contains no working channel for therapeutic interventions, therefore it is intended for screening purposes only. Another self-propelled colonoscope, the ColonoSight (Stryker Corp, Kalamazoo, MI) employs airassisted propulsion in a disposable system. A pneumatic mechanism generates the pressure to create the forward force while an operator directs the scope using handles. The system uses light emitting diode optics, rather than video or fiber optics, and has disposable working channels. A pilot study for ColonoSight reported intubation of the cecum in 88% of cases at a mean time of 12 minutes without any device-related complications.
Computer-controlled partially-automated colonoscope
The Neo-Guide Endoscopy System (Neo-Guide Systems, Los Gatos, CA) is designed to avoid loop formation by adjusting an endoscope’s insertion tube to match the configuration of the colon. The distal tip is guided similarly to conventional colonoscopy, and the insertion tube is comprised of multiple steerable segments connected to an actuation control unit. Using a sophisticated computer program, data from physician-determined tip orientation and insertion depth is used to create a 3-dimensional map of the colon.
Miniature Auxiliary Imaging Device
To detect mucosal lesions situated behind haustral folds, an auxiliary imaging device has been developed. The Third-Eye Retroscope (Avantis Medical Systems, Sunnydale, CA) is passed through the working channel of a standard colonoscope. The 3.4 mm device then provides a retroflexed image of haustral folds, a perspective that might be absent when using a forward-viewing colonoscope. In an in vitro study, the auxiliary imaging device was shown to enhance the detection of polyps located on the proximal aspect of haustral folds.
The double balloon system consists of a dedicated 200 cm endoscope with a balloon mounted distally and a 145 cm overtube with a balloon. The purpose of the overtube is to prevent stretching of the small bowel though which the enteroscope has already traversed. The balloons, whose pressure measures 45 mm Hg when inflated, serve to maintain the position of the scope and overtube. Clinical studies have documented 88% success of complete examination of the small bowel in total enteroscopy (upper and lower) cases.
There have been many recent advances in endoscopic imaging techniques. The purpose of most of these techniques is early detection of dysplasia, which might elude standard endoscopic visualization. Clinical use of new imaging is limited principally to specialized centers, but future widespread application of an imaging method for early dysplasia detection is a certainty.
The aim of chromoendoscopy is to detect subtle mucosal abnormalities. Commonly used agents include Lugol’s solution, methylene blue, indigo carmine, and Congo red. A 2%-3% solution of potassium iodide (Lugol’s solution) reacts with glycogen in keratinized squamous epithelium. Normal squamous epithelium stains a deep brown, but inflammation, dysplasia, and carcinoma do not stain because of a lack of glycogen. Lugol’s solution has been shown to be effective in detecting Barrett’s esophagus as well as screening for squamous cell carcinoma of the esophagus.
In magnification endoscopy, a cap with a magnifying lens is fitted to the tip of an endoscope. The mucosa in contact with the lens is magnified without impairing the maneuverability of the scope. Degrees of magnification range from 1.5x to 115x and can be changed on the scope by turning a dial at the hand controls. The technique of magnification endoscopy is frequently used in conjunction with chromoendoscopy. Chromoendoscopy is used for broad surveillance of the mucosa followed by focused examination of suspicious lesions in magnification mode. This combined examination has been reported in case series to enhance detection of Barrett’s esophagus, chronic gastritis, Helicobacter pylori infection, gastric dysplasia, and early gastric cancer.
Confocal Fluorescence Microendoscopy
Standard endoscopy uses white light to visualize a large surface area with relatively low resolution. In contrast, confocal endoscopy aims to visualize the mucosa and submucosa with subcellular resolution, a technique deemed optical biopsy. The process of confocal magnification reduces out-of-focus light from above and below the focal plane at a magnification of 1000x. The system is designed to measure tissue fluorescence, therefore an exogenous fluorophore (a molecule which causes another molecule to be fluorescent) is usually administered. Varying depths of tissue are examined by altering the focal plane, and images from different depths are stacked together to create an optical slice of tissue, thus the term optical biopsy.
Narrow Band Imaging
In narrow band endoscopy filtered light is used to preferentially enhance the mucosal surface, especially the network of superficial capillaries. Narrow band imaging is often combined with magnification endoscopy. Both adenomas and carcinomas have a rich network of underlying capillaries and enhance on narrow band imaging, thereby appearing dark brown against a blue green mucosal background.
Autofluorescence endoscopy relies on several principles: tissue architecture changes such as mucosal thickening dampen submucosal autofluorescence; neovascularization alters the light emitting and scattering properties of surrounding tissue; the biochemical microenvironment, such as high oxidationreduction activity, alters autofluorescence; and different tissue types have unique distribution of fluorophores. Autoflurescence endoscopy has been shown in pilot studies to improve the detection of dysplasia in Barrett’s esophagus and chronic ulcerative colitis.
Optical coherence tomography
Endoscopic optical coherence tomography is an emerging technology analogous to endoscopic ultrasound. The technique uses reflection of near-infrared light to produce real-time two-dimensional cross sectional images of the gastrointestinal tract. These true anatomic images correspond to the histologic layers (mucosa, submucosa, muscularis propria). The images obtained have a resolution 10- fold greater than endoscopic ultrasound. Endoscopic optical coherence tomography is not yet in widespread use.
Light Scattering Spectroscopy
Light scattering spectroscopy mathematically analyzes the intensity and wavelength of reflected light to estimate the size and degree of crowding of surface epithelial nuclei. The technique relies on absorption and scattering of white light. Small clinical trials using light scattering spectroscopy have shown efficacy in detecting Barrett’s esophagus and early colonic dysplasia. The technique relies on graphing mathematical computations rather than an optical biopsy in other emerging imaging techniques. Light scattering spectroscopy might be used in combination with optical biopsy for detection of early dysplasia.
In the near future there will likely be a multifunctional endoscope with a combination of imaging technologies available. Standard white light will be used for screening and surveillance, and then the scope might be switched to autofluorescence mode for guidance to a neoplastic lesion. With the same scope, confocal microscopy might then be used to perform an optical biopsy, and optical coherence could be used to grade the depth of the lesion. If necessary, the same scope might have several working channels for interventions.
New endoscopic technology conjures the imagination as the application of endoscopes expands from intralumenal to translumenal therapy. Shape locking devices or guided endoscopes could be used for stabilization of the translumenal operative field. High resolution and magnifying scopes could enhance the optics of an operative field, and other advanced imaging technology could be applied to solid organs for detecting neoplastic lesions. Scopes specifically designed for translumenal endoscopic surgery are likely to be developed. Thus, as the technology expands, so too will the applications of advanced endoscopic therapy.
Isenberg G, Sivak MV Jr, Chak A, Wong RC, Willis JE, Wolf B, Rowland DY, Das A, Rollins A. Accuracy of endoscopic optical coherence tomography in the detection of dysplasia in Barrett’s esophagus: a prospective, double-blinded study. Gastrointest Endosc. 2005 Dec;62(6):825-31.
Chiu HM, Chang CY, Chen CC, Lee YC, Wu MS, Lin JT, Shun CT, Wang HP. A prospective comparative study of narrow-band imaging, chromoendoscopy, and conventional colonoscopy in the diagnosis of colorectal neoplasia. Gut. 2006
Monkemuller K, Weigt J, Treiber G, Kolfenbach S, Kahl S, Rocken C, Ebert M, Fry LC, Malfertheiner P. Diagnostic and therapeutic impact of double-balloon enteroscopy. Endoscopy. 2006 Jan;38(1):67-72