18 Advanced Imaging Methods
Ralf Kiesslich and Arthur Hoffman
Advanced imaging methods in gastrointestinal endoscopy are additional technological tools or endoscopic techniques, which should help refining in vivo diagnosis during ongoing endoscopy.
The aim of advanced imaging is to improve single or all parts of the diagnostic workflow of endoscopic procedures. Three steps are important: recognition, characterization, and confirmation. Recognition involves identification of all relevant lesions or changes of the inspected mucosa. Characterization is defined as differentiation of neoplastic from nonneoplastic changes and to decide whether an endoscopic treatment is possible or not (prediction of submucosal involvement in neoplastic changes). Confirmation is characterized by establishment of a definite diagnosis, which is mainly based on histologic evaluation of removed specimens. However, advanced imaging methods can correlate closely with final histology or display in vivo histology and can be used as reliable techniques for in vivo diagnosis (▶Fig. 18.1).
18.2 High-Definition Endoscopes
The development of advanced imaging technologies occurred in parallel with innovations of information technologies. Most important is the development of high-definition (HD) endoscopes (with and without optical zoom function) that has enabled to clearer identify vessel and mucosal surface architecture.
The chips used in current HD endoscopes produce signal images with resolutions that range from 850,000 pixels to more than 1 million pixels. HD video imaging can be displayed in a 16:9 aspect ratio. However, the 16:9 aspect ratio is not useful for display of images originating from round endoscopic lenses. Thus, HD endoscopic video chips display images in either 4:3 or 5:4 aspect ratios. 1
18.3 Virtual Chromoendoscopy
Virtual or electronic chromoendoscopy can be switched on and switched off during endoscopy by pushing a button at the hand piece of the endoscope. The emitted light to the mucosa or the reflecting light from the mucosa is altered using narrow band or postprocessing filters (▶Fig. 18.2). Virtual chromoendoscopy technologies include narrow-band imaging (NBI) (Olympus Medical Systems Tokyo, Japan), flexible spectral imaging color enhancement (FICE) (Fujinon, Fujifilm Medical Co, Saitama, Japan), and i-Scan (Pentax Endoscopy, Tokyo, Japan). 2
The goal of virtual chromoendoscopy is to highlight vessel structures or surface architecture.
18.4 Narrow-Band Imaging
NBI is an endoscopic optical image enhancement technology, proprietary of Olympus Medical Systems. NBI is based on the penetration properties of light, which is directly proportional to wavelength. Short wavelengths penetrate only superficially into the mucosa, whereas longer wavelengths are capable of penetrating more deeply into tissue. Two narrow bands of light are emitted and centered at the specific wavelengths of 415 and 540 nm. The specific wavelengths correspond to light absorption peaks of hemoglobin. Because most of the NBI light is absorbed by the blood vessels in the mucosa, the resulting images emphasize the blood vessels in sharp contrast with the nonvascular structures in the mucosa. 2
18.5 Flexible Spectral Imaging Color Enhancement
FICE is a proprietary digital imaging postprocessing system of Fujinon. FICE takes white-light endoscopic images from the video processor and mathematically processes the image by emphasizing certain ranges of wavelengths. Three single-wavelength images can be selected and assigned to the red, green, and blue monitor inputs, respectively, to display a composite color-enhanced image in real time. 2
Fujifilm has recently developed a new technique of virtual chromoendoscopy. The so-called Lasero system uses laser for its illumination. The laser is used as a function for narrow-band light that utilizes the characteristics of laser light as standard. Lasero has four observational modes and employs three kinds of illumination with different spectral distributions. 3
18.6 i-Scan and Optical Enhancement
i-SCAN is a software-based digital, postprocessing image enhancement technology from Pentax Endoscopy that provides digital contrast to endoscopic images. Similar to FICE, i-Scan provides enhanced images of the mucosal surface and the blood vessels through postimage processing. There are three i-Scan modes: i-Scan 1, i-Scan 2, and i-Scan 3. Touching a button on the endoscope can access these modes. The switch from WLE to i-Scan occurs almost instantaneously.
i-Scan 1 is a surface-enhancement (SE) and contrast-enhancement (CE) mode that enhances contrast and thereby mucosal surface detail including enhanced mucosal surface texture and sharpened views of surface vessels. The image remains as bright as conventional WLE. i-Scan 2 increases the contrast between the mucosa and blood vessels, thereby improving the visibility of blood vessels and tissue architecture. i-Scan 3 differs from i-Scan 2 primarily in its ability to illuminate more distant regions better 2 (▶Fig. 18.3).
Most recently Pentax has introduced optical enhancement (OE) filtering, which uses similar technology as NBI. OE was developed to further highlight superficial vessel architecture in conjunction with bright illumination. 4
Flat lesion (Paris classification type IIa) is visible within the colonic mucosa. i-Scan imaging is displayed on the right simultaneously (twin-mode). The lesion is highlighted and the border can be clearly delineated.
18.7 Clinical Application of Virtual Chromoendoscopy
Virtual chromoendoscopy can be used in upper and lower endoscopy. Areas of interest are gastroesophageal reflux disease with special focus on Barrett’s esophagus, squamous cell cancer, gastric cancer colonic polyps, and inflammatory bowel diseases.
In Barrett’s esophagus, virtual chromoendoscopy is able to achieve the so-called PIVI guidelines. The goals for Barrett’s esophagus were to develop an imaging technology with targeted biopsies that should have a per-patient sensitivity of greater than or equal to 90% and a negative predictive value (NPV) of greater than or equal to 98% for detecting high-grade dysplasia or early cancer, compared with the current standard protocol, and the imaging technology should have a specificity that is sufficiently high (80%) to allow a reduction in the number of biopsies (compared with random biopsies). A recent meta-analysis concluded that the pooled sensitivity, NPV, and specificity for electronic chromoendoscopy by using NBI for detecting Barrett’s associated dysplasia were 94.2% (95% confidence interval [CI], 82.6–98.2), 97.5% (95% CI, 95.1–98.7), and 94.4% (95% CI, 80.5–98.6), respectively. 5
Virtual chromoendoscopy was also shown to be effective in characterizing small polyps in the colon and the so-called NICE classification was established using NBI technology. Virtual chromoendoscopy in expert hands can be used to guide the decision to leave suspected rectosigmoid hyperplastic polyps 5 mm or smaller in place (without resection), virtual chromoendoscopy provides a 90% or greater NPV (when used with high confidence) for adenomatous histology. 6
Virtual chromoendoscopy seems not to be effective enough identifying colitis-associated dysplasia. Here, standard chromoendoscopy using intravital dyes remains standard of care for surveillance in ulcerative colitis. 2 , 7