Advanced imaging

Published on 21/04/2015 by admin

Filed under Gastroenterology and Hepatology

Last modified 22/04/2025

Print this page

rate 1 star rate 2 star rate 3 star rate 4 star rate 5 star
Your rating: none, Average: 0 (0 votes)

This article have been viewed 2594 times

CHAPTER 6 Advanced imaging

6.1 Confocal endomicroscopy

Kerry B. Dunbar

Summary

Introduction 140
1. Indications 140
2. Equipment 140
3. Contrast agents 142
4. Technique 142
5. Complications 142
6. Special considerations 142

Key Points

• Confocal laser endomicroscopy has been used to image many disorders of the gastrointestinal tract.
• Intravenous fluorescein sodium is the most commonly used contrast agent when performing endomicroscopy.
• Obtaining a stable position is key when using either the confocal endoscope or confocal probes to obtain clear microscopic images.
• When learning endomicroscopy, it is helpful to work with someone already trained in endomicroscopy and to study image atlases.
• When learning endomicroscopy, confirmation of the microscopic imaging findings with a mucosal biopsy is essential, until competence is achieved.

Introduction

Confocal laser endomicroscopy (CLE) is one of the newer advanced imaging methods for the gastrointestinal tract. Microscopic images of the gastrointestinal mucosa are obtained by illuminating the mucosa with blue laser light (488 nm), which causes fluorescence. The light reflected is collected through a pinhole-sized aperture and processed, creating a microscopic image. The laser light and collected light are ‘confocal’, meaning they are in the same focal plane. The images produced allow visualization of small structures, such as capillaries and colonic crypts and gastric pits (Figs 1–4), as well as individual cells, such as epithelial cells and red blood cells.

image

Figure 1 Endomicroscopy of the colonic mucosa. The colonic crypts (solid arrow) and goblet cells (dashed arrow) can be seen.

image

Figure 2 Normal gastric mucosa seen by endomicroscopy.

image

Figure 3 Mucosa of the squamous esophagus. Intrapapillary capillary loops are visible.

image

Figure 4 Normal duodenal mucosa. Small goblet cells (dark) are visible.

1 Indications

Endomicroscopy has been used to study many gastrointestinal disorders. Several of the earliest studies looked at patients undergoing colorectal cancer screening and examined polyps with endoscope-based endomicroscopy (eCLE). Other colonic disorders studied include patients with inflammatory bowel disease undergoing surveillance for dysplasia, collagenous colitis, and pouchitis. Small bowel disorders investigated with endomicroscopy include celiac disease and graft-versus-host disease. Gastric cancer and Helicobacter pylori gastritis have been imaged with CLE. In the esophagus, Barrett’s esophagus and squamous cell esophageal cancer have been studied. Endomicroscopy has been used to help target biopsies in all these disorders as well, and may also reduce the number of biopsies needed to achieve a diagnosis. Examination of biliary strictures at ERCP to differentiate cholangiocarcinomas from benign strictures has recently been reported.

2 Equipment

There are currently two endomicroscopy systems available (Table 1). One is an endoscope-based endomicroscopy (eCLE) system, the EC-3870CIFK colonoscope, and EG-3870CIK upper endoscope (Pentax, Tokyo, Japan). A probe-based endomicroscopy (pCLE) system, the Cellvizio (Mauna Kea Technologies, Paris, France) is also available. Both systems allow standard endoscopic imaging while providing the ability to obtain microscopic views of the mucosa, but there are several differences between the two systems. Each system has an endomicroscopic image processor and separate screen for viewing endomicroscopic images. The confocal endoscope comes in lengths appropriate for colonoscopy and one for upper endoscopy, although the colonoscope-length endoscope can also be used for investigation of the upper GI tract. The confocal endoscope has the standard wheels, air, water, suction and photo buttons, and a standard-size biopsy channel. The miniprobes for pCLE can be used with a standard endoscope that has a 2.8 mm channel and the probes are attached to a special processor. They come in lengths appropriate for upper endoscopy, colonoscopy, and cholangioscopy. Both systems require a contrast agent to be used to collect images. The confocal endoscope can image sequentially from the surface, down to a depth of 250 µm, while the confocal probes have set ranges of imaging depth, ranging from 55–65 µm from the surface for the Gastroflex UHD probe to 70–130 µm for the Gastroflex probe. The resolution of the images is higher with the confocal endoscope than the probes, with a lateral resolution of 0.7 µm compared with 1–3.5 µm. The imaging rate for the confocal probe is higher than the confocal endoscope, with an imaging rate of 12 images per second compared with 0.8–1.6 images per second. The pCLE system also creates a ‘mosaic’ of images collected together to show a larger portion of the mucosa. Both systems allow image capture and export.

Table 1 Endomicroscopy systems

image

3 Contrast agents

Several contrast agents can be used for imaging with the confocal endoscope and the confocal probe systems. Fluorescein sodium is the most commonly used contrast agent and is used in ophthalmology for retinal vascular imaging. The standard dosing with the confocal endoscope is 5 mL of 10% fluorescein sodium, given intravenously. In studies using the confocal probe, 2.5–10 mL of 10% fluorescein sodium is used. Fluorescein highlights the vessels and intracellular spaces, and lamina propria of tissues, but does not stain nuclei. Goblet cells in the colon, small bowel, and in Barrett’s esophagus appear dark when fluorescein is used for contrast. Capillaries appear bright, with individual red blood cells visible. All patients who receive fluorescein sodium intravenously will have yellowing of the skin, eyes, and urine that lasts several hours. Rare allergic reactions have been reported with fluorescein sodium and some patients may have nausea. Topical acriflavine 0.05% has also been used as a contrast agent during endomicroscopy and stains the nuclei of cells. However, acriflavine is used less frequently, as it binds nuclei and there is concern for potential mutagenicity. Topical cresyl violet 0.25–1% has been used in a few studies and is also helpful as it functions as a surface chromoendoscopy agent. Cresyl violet highlights the cytoplasm, thus some nuclei can be seen and appear dark.

4 Technique

When performing either eCLE or pCLE, complete the white light portion of the endoscopic exam before proceeding with endomicroscopy. This will allow you to select areas to image and will ensure that your contrast agent is still present when you are ready to begin imaging. If you are using topical contrast, clearing the mucosa with water may help you get more even staining of the mucosa. In the colon, a poor bowel preparation will significantly limit the use of topical contrast agents as they will not reach the mucosa and will also limit imaging with intravenous contrast, due to the presence of stool on the imaging window.

When ready to obtain eCLE images, place the tip of the confocal endoscope directly on the mucosa. The imaging window is located on the lower left portion of the tip and can be seen on the edge of the endoscopic image (Fig. 5). Applying suction using the endoscope can help stabilize your position. Once a stable position is obtained, press the home button (button 3), which will return the imaging to the surface (Fig. 6). Press button 4 to begin sectioning down through the mucosa. Depressing the button moves the imaging plane 4 µm deeper. The direction of imaging can be reversed towards the surface by quickly depressing button 4 twice. Microscopic images can be captured using the foot pedal, the mouse, or the touch screen.

image

Figure 5 The tip of the confocal endoscope has the normal light channel, and air and water channel, but also has the confocal microscope built into the tip (arrow).

image

Figure 6 The handle of the confocal endomicroscope. Button 3 (solid arrow) and button 4 (dashed arrow) are used to return the imaging plane to the surface and to section down and up through the mucosa.

To use the pCLE system, the probes are attached to the processor and passed through the instrument channel of a standard endoscope. The tip of the probe is placed directly on the surface of the mucosa and images are acquired. To obtain a stable image with the confocal probe system, a plastic cap on the end of the endoscope can be helpful, such as the plastic caps that come with the endoscopic mucosal resection (EMR) kits. Images can be obtained and saved, as can mosaic video sequences.

5 Complications

Complications during endomicroscopy are rare. The standard risks of endoscopy are present and the additional risk is related to the contrast agent used. All patients who receive fluorescein should be alerted that they will have yellow skin, eyes, and urine for several hours after the procedure.

In one review of 2272 eCLE and pCLE endomicroscopy cases performed at 16 academic medical centers, no serious adverse events were reported. The most common mild adverse reactions reported (1.4% of patients) were nausea and vomiting, transient hypotension, rash, injection site erythema, and epigastric discomfort. However, the package insert for fluorescein sodium and ophthalmologic reviews list several other reported complications, such as seizures, hypotension, syncope, wheezing, thrombophlebitis, and anaphylaxis.

6 Special considerations

6.1 Learning

There are two components needed to acquire competence in endomicroscopy: the technical ability to acquire good quality images and the cognitive ability to interpret the images properly. To learn endomicroscopy, it is ideal to perform cases supervised by an endoscopist already trained in endomicroscopy. This can be very helpful when learning to use the imaging systems and acquire stable images. When beginning your endomicroscopy career, start by collecting images in the colon and stomach, as these organs are the easiest to obtain stable images. The esophagus is most challenging, due to the movement of the heart, lungs, and esophageal peristalsis, which can make obtaining a stable image difficult. To track your own learning, record your interpretation for each imaging site and then obtain a mucosal biopsy so you can determine if your endomicroscopic interpretation is correct. Studying endomicroscopic images to become familiar with normal and abnormal microscopic images is also helpful and some resources are listed below.

6.2 Research and informed consent issues

Both the confocal endoscope and confocal probes are commercially available in the USA and Europe. Depending on the planned use at your institution, whether clinical or research or both, you will need to obtain consent from patients for endomicroscopy. The consent forms should include language discussing the risks of the contrast agent used, which typically is fluorescein sodium.

6.3 Further research

Studying endomicroscopic images and learning the tissue patterns is important. Review articles summarizing the latest endomicroscopic research are readily available. The references below have multiple images for review.

• Atlas of Endomicroscopy. Kiesslich R, Galle PR, Neurath MF, editors (Springer Medezin Verlag, 2008, Heidelberg). The first book of endomicroscopy, which contains numerous endomicroscopic images, with corresponding pathology and endoscopic images. Discusses endomicroscopic technique in detail, and has sections on normal and abnormal conditions of the GI tract.
• www.endomicroscopy.org A website which includes more information about technique, and case studies that include eCLE images with corresponding histopathology and endoscopic photos.
• www.maunakeatech.com/atlas/atlasmedgi A website which includes an image library of pCLE cases.
• http://daveproject.org Search ‘endomicroscopy’ and several videos of endomicroscopy are available.

Further Reading

Bojarski C, Gunther U, Rieger K, et al. In vivo diagnosis of acute intestinal graft-versus-host disease by confocal endomicroscopy. Endoscopy. 2009;41:433-438.

Dunbar KB, Okolo P3rd, Montgomery E, et al. Confocal laser endomicroscopy in Barrett’s esophagus and endoscopically inapparent Barrett’s neoplasia: a prospective, randomized, double-blind, controlled, crossover trial. Gastrointest Endosc. 2009;70:645-654.

Kiesslich R, Burg J, Vieth M, et al. Confocal laser endoscopy for diagnosing intraepithelial neoplasias and colorectal cancer in vivo. Gastroenterology. 2004;127:706-713.

Kiesslich R, Goetz M, Burg J, et al. Diagnosing Helicobacter pylori in vivo by confocal laser endoscopy. Gastroenterology. 2005;128:2119-2123.

Kiesslich R, Goetz M, Lammersdorf K, et al. Chromoscopy-guided endomicroscopy increases the diagnostic yield of intraepithelial neoplasia in ulcerative colitis. Gastroenterology. 2007;132:874-882.

Kiesslich R, Hoffman A, Goetz M, et al. In vivo diagnosis of collagenous colitis by confocal endomicroscopy. Gut. 2006;55:591-592.

Kitabatake S, Niwa Y, Miyahara R, et al. Confocal endomicroscopy for the diagnosis of gastric cancer in vivo. Endoscopy. 2006;38:1110-1114.

Leong RW, Nguyen NQ, Meredith CG, et al. In vivo confocal endomicroscopy in the diagnosis and evaluation of celiac disease. Gastroenterology. 2008;135:1870-1876.

Lipson BK, Yannuzzi LA. Complications of intravenous fluorescein injections. Int Ophthalmol Clin. 1989;29:200-205.

Pech O, Rabenstein T, Manner H, et al. Confocal laser endomicroscopy for in vivo diagnosis of early squamous cell carcinoma in the esophagus. Clin Gastroenterol Hepatol. 2008;6:89-94.

Trovato C, Sonzogni A, Fiori G, et al. Confocal laser endomicroscopy for the detection of mucosal changes in ileal pouch after restorative proctocolectomy. Dig Liver Dis. 2009;41:578-585.

Wallace MB, Meining A, Canto MI, et al. The safety of intravenous fluorescein for confocal laser endomicroscopy in the gastrointestinal tract. Aliment Pharmacol Ther. 2010;31:548-552.

6.2 New endoscopic imaging modalities

Ian Penman, Denis Heresbach

Summary

Introduction 144
1. Technical principles 144
2. Clinical applications of new imaging techniques 149
Conclusion 153

Key Points

• Many novel imaging modalities have been developed in recent years to improve detection and characterization of early neoplasia in the upper and lower GI tract.
• Although several such systems are now commercially available, definite evidence of their superiority over high-resolution white light endoscopy is lacking for most indications.
• Narrow band imaging (NBI) endoscopy, combined with magnification and targeted biopsies, may be superior to systematic or random biopsy protocols for detection of dysplasia in Barrett’s esophagus or ulcerative colitis.
• Autofluorescence systems are not yet adequate for detection of early neoplasia and suffer from high false-positive rates but are likely to improve in the near future.
• Other modalities such as optical coherence tomography and spectroscopic methods remain investigational at present.

Introduction

The prognosis of gastrointestinal cancers depends upon their stage at presentation and most recent improvements in diagnostic endoscopy have therefore focused on earlier diagnosis. The introduction of videoendoscopy over 20 years ago was considered a major advance but merely hinted at the technological improvements that were possible in endoscopy. Progress since then has focused on improving image resolution, particularly by using optical or electronic magnification and by increasing the number of pixels and photodiodes per pixel. Monochromatic light or light containing only certain wavelengths or narrow spectral bands and use of wavelengths outside the visible light spectrum (ultraviolet or near infrared) have all recently been developed for endoscopy, as alternatives to standard white light of the visible spectrum. Combined with improvements in image definition and magnification, these novel imaging modalities offer enormous possibilities for diagnosis of early neoplasia. Multiple systems exist either commercially or as prototypes: narrow band imaging (NBI) endoscopy; confocal laser endomicroscopy (CLE); autofluorescence (AFI); optical coherence tomography (OCT); endocytoscopy; spectral fluorescence, and Raman effect or light-scattering spectroscopy. Two strategies are evolving beyond the impressive technological progress in miniaturizing the charge coupled devices (CCDs) at the tip of a flexible videoendoscope:

• Improving visualization of small lesions, which may not be detectable by white light videoendoscopy
• Determining the architecture and, if possible, the dysplastic nature of a lesion previously detected by videoendoscopy.

To achieve the first of these objectives, NBI and AFI techniques are undergoing clinical validation, while for the second, methods involving CLE, endocytoscopy, OCT or elastic or non-elastic light-scattering spectroscopy (LSS) are being developed. NBI, AFI and CLE methods are currently available commercially, while OCT and other methods are only at the prototype stage of development. The use of these technologies is set to expand, but there are currently few controlled, randomized comparative studies to determine precisely the utility of these new tools in endoscopy. The range of potential applications is wide, but for the moment the main focus is on areas as outlined in Box 1.

Box 1 Established and investigational uses of advanced endoscopic imaging modalities

• Detection of intestinal metaplasia, dysplasia or early cancer in Barrett’s esophagus.
• Detection of early squamous esophageal neoplasia in high-risk groups.
• Detecting dysplasia during surveillance of chronic ulcerative colitis.
• Detection of flat colonic polyps – reducing miss-rates at colonoscopy.
• Characterization of colonic polyps as hyperplastic or adenomatous.

1 Technical principles

White light of the visible light spectrum is characterized by a wavelength of 400–700 nm. This light beam is partly absorbed in its tissue target depending on the wavelength but also on the composition of naturally occurring tissue fluorophores and chromophores, and on their vascularity.

1.1 Principle of narrow band imaging (FICE or NBI system)

The penetration of the mucosa and submucosa by light depends on its wavelength and increases as the wavelength approaches infrared. Target tissues can be illuminated by specific wavelengths or a spectral band corresponding to the absorption spectrum of specific structures in the illuminated tissue. Preference may be given to wavelengths with known absorption by certain tissue components. NBI endoscopy conventionally uses three wavelengths at around 430, 460, and 575 nm; the shorter (blue) wavelengths provide better visualization of vascular structures, particularly in the mucosa and, to a lesser degree, the submucosa (Fig. 1). There are several ways of preferentially using these wavelengths and their narrow spectral band (usually 30 or 50 nm), which can be limited to three bands or, by contrast, a range of 9–12 narrow spectral bands can be offered; a combination of these predetermined (by the manufacturer) or chosen (by the gastroenterologist) provides a wider palette of virtual color and enhancement of the vascular structures and mucosal crypt orifices. Of the methods currently available, the one developed by Fujinon offers a choice of nine narrow bands (FICE system); the method developed by Olympus uses three fixed narrow bands (NBI system); and the iSCAN system from Pentax similarly has nine ‘tone enhancement’ modes. These are obtained using a mechanical light filter (NBI) or an electronic selection technique based on spectral analysis of the pixels forming the image in each spectral band, which are then reallocated (selected or deleted) to reconstitute an image corresponding to the narrow band selected (FICE). These selections are made for each of the narrow bands and are then fused to produce a single image. One of the current advantages of FICE technology is that it can be used with a standard endoscope or a high resolution videoendoscope with zoom (>400 000 or up to 800 000–1 million pixels), whereas the advantage of the NBI system is that the narrow band imaging endoscopy can be connected to high definition television (HDTV), which doubles the number of horizontal lines of pixels, producing better horizontal resolution. The drawback of the FICE technique is that it needs a light source and a 4400 series processor, whereas the drawback of the NBI system is that it uses the Exera II system, i.e. a dedicated light source, processor, and specific videoendoscopes. Magnifying videoendoscopes are required in both cases, since fine structures can be enhanced for analysis of fourth-order vessels in the mucosa or the crypt orifice pattern (Figs 2, 3). There is no universally agreed classification system specifically for mucosal lesions using narrow band imaging but most have used magnifying videoendoscopes to examine the superficial vessel networks and crypt openings in the lower esophagus or colon (Table 1).

image

Figure 1 (A) NBI (×115) of squamous esophageal mucosa showing normal IPCL and obliquely running vessels. (B) NBI (×115) image of distal esophagus in a patient with Barrett’s. No crypt pattern can be observed but long, thin, regular vessels are noted, consistent with intestinal metaplasia but without dysplasia.

image

Figure 2 (A) NBI (×115) showing crowded, thickened and irregular IPCLs in a patient with high grade squamous esophageal dysplasia. (B) NBI image of early squamous esophageal carcinoma. Abnormal IPCL vessel pattern and an irregular raised lesion are seen.

image

Figure 3 Barrett’s esophagus seen at NBI. (A) Type 1–2 round and oval pits. (B) Regular round and oval pits. (C) Type 3 villous/ridged pits.

Table 1 Classification used in narrow band imaging endoscopy or electronic, optical chromoendoscopy (without staining)

Narrow band imaging endoscopy of the esophagus
Squamous cancer of the esophagus
According to Kumagai et al 2002:
IPCL: intrapapillary capillary loops, from fourth-order branching vessels (×80) in the lamina propria of comparable homogeneous appearance.
Spread of squamous cancers of the esophagus.
m1: Thick, irregular pattern, intertwined with the IPCL.
m2: As m1 but with thicker and longer IPCL.
m3: Partial disappearance of the IPCL, partly replaced by thick, dilated vessels.
sm: IPCL entirely absent.

According to Yoshida et al 2004: IPCL anomaly: (1) dilation or (2) tortuosity or (3) bead-like variation of diameter or (4) of variable appearance and heterogeneous form. Inflammation and dysplasia of the esophageal mucosa.
Type 1: Normal IPCL (lugol + = normal mucosa).
Type 2: Stretching and moderate elongation of the IPCL (lugol + = esophagitis).
Type 3: 3 of the 4 IPCL anomalies (lugol − = low-grade dysplasia).
Type 4: 4 IPCL anomalies (lugol − = high-grade dysplasia)..

Barrett’s esophagus and dysplasia According to Kara et al 2005:
Type 1: Crypts showing a villous and gyrus-shaped pattern, homogeneous in size and distribution (= intestinal metaplasia).
Type 2: Rounded, circular or oval crypts with regular distribution (= columnar mucosa).
Type 3: Crypts showing a gyrus-shaped pattern, unequal in size and with irregular distribution (= high-grade dysplasia).

According to modified classification of Kara et al 2005:
Mucosal crypt pattern: regular or irregular.
Vascular pattern: regular or irregular.
Abnormal vessels: present/absent (likelihood of early neoplasia increases with increasing number of abnormalities present).
According to modified classification based on Singh et al 2008:
(A) Round pits and regular microvasculature (= columnar mucosa, no intestinal metaplasia).
(B) Villous/ridge pits with regular microvasculature (= intestinal metaplasia).
(C) Absent pits with regular microvasculature (= intestinal metaplasia).
(D) Distorted pits with irregular microvasculature (= HGD)..
Narrow band imaging endoscopy of the stomach Gastritis According to Yagi et al 2002: (see Fig. 11)
Z–0: Regular hexagonal capillary network surrounding the crypts and collecting veins spaced and distributed homogeneously.
Z–1: Irregular capillary network and disappearance of collecting veins.
Z–2: Disappearance of the capillary network and presence of pale dilated, elongated crypts.
Z–3: As Z–2, with whitish, dilated crypts surrounded by an erythematous halo.
According to Yao and Oishi 2001:
R: Regular polygonal capillary network surrounding the necks of crypts distributed homogeneously and in the antral region, capillaries resembling springs at the top of islands of mucosa separated by grooves.
I: Irregular capillary network, corkscrew or twig pattern, distributed heterogeneously.
D: Disappearance of the capillary network and a few collecting veins.
According to Sakaki et al 1978:
Stages – FP: Foveolar pattern with round crypts.
FIP: Foveolar intermediate pattern with round, oval crypts.
FSP: Foveolar/sulcus pattern with horseshoe- or doughnut-shaped crypts.
SP: Sulcus pattern with crypts in a groove or convoluted.
MP: Mesh pattern.
Stage distribution.
SP, MP: Pyloric gland area.
FP, FSP: Fundic gland and intermediate area.
FIP: Intermediate area and gastritis with intense cell infiltration.
SP: Severe atrophic gastritis.
Gastric carcinoma According to Yao et al 2002; Endo et al 2005: (see Fig. 12) Differentiated mucosal carcinoma: Hypervascularized capillary network, irregular in size and with a trellis pattern, combining branched and loop patterns. Undifferentiated mucosal carcinoma: Few, short capillaries without interconnections, twig pattern. According to Nakayoshi et al 2004:
Differentiated depressed early cancer (type IIc): fine, dense capillary network.
Undifferentiated depressed early cancer (type IIc): capillary network that is not particularly dense, with a twig or corkscrew pattern.
Narrow band imaging endoscopy of the colon Colon polyps According to Machida et al 2004, based on Kudo et al 1994, 2001: (see Fig. 6) Crypt patterns
Type I: Round crypts, homogeneous in distribution.
Type II: Stellar crypts, homogeneous in distribution.
Type III–L: Tubular, enlarged, curved crypts.
Type III–S: Small round, curved crypts, with dense distribution.
Type IV: Gyrus-shaped convoluted crypts.
Type V: Absence of any classifiable crypt structure.
According to type I and II patterns = normal mucosa or hyperplastic polyp, type III–L or IV = tubular or tubulovillous adenoma, type III–S and V = adenoma with high-grade dysplasia or carcinoma. According to Machida et al 2004, based on Konerding et al 2001; and Sano et al 2006: Vascular network pattern (see Fig. 9). Normal and hyperplastic polyps: regular, hexagonal, honeycomb vascular network around the mucosal glands and crypts with visible first- to fourth-order branching. Adenomatous polyp: part of the hexagonal vascular network is associated with a denser, shorter capillary pattern, without third- or fourth-order branches or with interrupted blind branches distributed heterogeneously. Carcinoma: increased density of disorganized vessels with nodular clusters of capillaries.

Note: there is no universally agreed or validated classification specifically for narrow band imaging using FICE or NBI. Most of the classifications described are based on using magnifying videoendoscopes.

image Clinical Tip

While technical details differ among manufacturers of narrow band imaging systems, all rely on the principle of restricting the spectral bandwidths used for imaging to enhance visualization of surface structures – mucosal crypt patterns and superficial vessel networks.

1.2 Principle of confocal laser endomicroscopy and endocytoscopy

Confocal laser endomicroscopy is discussed in Chapter 6.1. Endocytoscopy is a contact microscopy technique. After dye spraying with methylene blue, a probe is passed through the operating channel of a standard videoendoscope, with approximately ×1100 magnification and this allows cytological analysis and visualization of the density of cell nuclei.

1.3 Principles of optical coherence tomography

Optical coherence tomography is based on the principle of interferometry, which uses a light beam of a specific wavelength and a defined spectral width. This spectral band is split so that it can be simultaneously directed at the tissue target and at a reference mirror. The two beams thus reflected are recombined and form an interference wave when the distances covered between the source and these two targets are identical. By moving the reference mirror, the reflection of the tissue target can thus be received at variable distances or depths. The wider the spectral band used, the greater the interference wavelength that defines the axial resolution, and the better the definition. Only photons in the light beam from a plane in the tissue target will thus interfere and the intensity of the interference signal will then correspond to a slice image (tomography). If there is a difference in the refractive index between two environments or types of tissue, in this section located equidistantly from the reference mirror, the reflection will be greater and interference intense between the bundle of photons reflected by the slice plane and by the mirror located at the same distance. This measurement, repeated for different reference mirror positions, can be used to obtain an image at the depth of the tissue target analysed. With a source wavelength of 1270 nm and a spectral width of 210 nm, the lateral resolution is approximately 4 µm, but the axial resolution varies between 5 and 15 µm. This wavelength is chosen in the near infrared range so that the light beam penetrates the tissue target deeply enough, to approximately 2 mm.

Optical coherence tomography has an advantage over high-resolution endoscopic ultrasound, since it does not require contact with the tissue target, and it has a resolution of approximately 10 µm compared with 110 µm for 20–30 MHz probes; it nevertheless has the drawback of examining the tissue target to a depth of 2 mm, whereas high-frequency endoscopic ultrasound can examine it to about 20 mm depth. Several optical coherence tomography probes with a diameter of 2.0 and 2.4 mm have been developed using longitudinal or circular scanning. These two methods have a comparable lateral resolution of 10 µm and a field of view of 5.5 × 2.5 mm for the former and 7 mm in diameter for the latter.

1.4 Principle of autofluorescence imaging

Most fluorescence studies originally consisted of point spectral analysis focused on a lesion or a mucosal irregularity detected by other means. It involved the measurement, after laser excitation, of a difference in spectral amplitude for a given wavelength (500 or 630 nm), or of the time taken to observe a reduction in the intensity of the fluorescence emitted (relaxation time). It is only subsequently that autofluorescence has been used for a full inspection of the tissue surface (esophagus or colon), in particular by means of the LIFE-GI (Light-induced Fluorescence Endoscopy for the GastroIntestinal tract) system developed by Xillix Technologies.

Autofluorescence is based on the stimulation of endogenous fluorophores (e.g. NADPH, flavones and collagen) with a short wavelength or ultraviolet light beam that is reflected by fluorophores with a longer wavelength. Some biological processes and changes in tissue composition are associated with specific autofluorescence, with mucosal and submucosal collagen showing green autofluorescence, while dysplastic or neoplastic changes show red or purple autofluorescence (Fig. 4). Early studies with autofluorescence used an excitation probe through the operating channel of a fiberoptic endoscope, using a spectral filter, to emit and receive the fluorescent beams. This approach has been replaced more recently by endoscopic detection of the autofluorescence, using a CCD detector with a simultaneous increase in image resolution and, above all, detection of fluorescence emitted in proximity to its reflection. In this way a good signal : noise ratio can be obtained and signal intensity loss due to photon transmission by the optical fibers can be prevented. In videoendoscopy, by using a single CCD, the conventional image can first be visualized in white light, then detected in autofluorescence, whereas the use of an optical fiber probe requires a filter upstream of the fibers as well as two separate CCDs to capture a conventional image and an autofluorescence image. The only advantage of using optical fibers and spectral filters is that a choice can be made from a larger sample of filters. This is currently more of a theoretical than clinical advantage.

image

Figure 4 Autofluorescence. (A) Green autofluorescence appearance of normal esophagus (Olympus AFI). (B) Abnormal pale-pink/purple signal can be seen at the top right and bottom left of the image. High-grade dysplasia was confirmed on biopsy of these areas. (C) White light image of squamous carcinoma in situ. (D) AFI image demonstrate the lesion as an extensive area of pink signal.

Two autofluorescence detection systems have been developed and tested: the LIFE-GI system and a system from Olympus incorporating two CCDs at the endoscope tip, one for white light and one for autofluorescence. In autofluorescent mode, the excitation light beam emitted by a xenon lamp and monochromatic illumination for the green and red light (550 and 610 nm, respectively) are selected from a rotating filter. For detection, the CCD is connected to a filter, which allows only wavelengths between 490 and 625 nm to pass when the excitation light beam is in autofluorescence, and wavelengths of between 395 and 475 nm for monochromatic illuminations. During detection, the reflection following excitation with blue light is eliminated and the sequential detection of images in autofluorescent mode or from green and red monochromatic excitation beams are integrated to reconstruct an image composed from these three modes of illumination. Clinically, in autofluorescent mode, normal squamous mucosa and non-dysplastic Barrett’s esophagus appear green, while tissues containing dysplastic areas or early carcinoma appear purple. Tissue contents rich in hemoglobin appear purple because absorption of a light beam with a wavelength characterizing green light (550 nm) is greater than that of a light beam characterized by the wavelength of red light (610 nm).

image Clinical Tip

Autofluorescence systems offer the possibility of acting as a ‘red-flag’ system for screening wide areas of mucosa for abnormalities. Inflammation and non-specific tissue thickening are responsible for high false-positivity rates for the detection of neoplasia – use of magnifying narrow band imaging of AFI-positive lesions can significantly improve its positive predictive value.

2 Clinical applications of new imaging techniques

These new imaging techniques have been investigated by ‘open-label’ studies and case series with few published randomized controlled studies.

2.1 Clinical studies (FICE or NBI system)

Most clinical studies relate to Barrett’s esophagus or characterization of colonic polyps. Narrow band imaging in the esophagus examines the vascular network of the lower esophagus and the appearance of mucosal crypts based on descriptions of glands seen during studies of chromoendoscopy. This method was better able to visualize the gastroesophageal junction than standard endoscopy (58% and 17% good quality images, respectively) and was more powerful for detecting areas of intestinal metaplasia with sensitivities of 56% and 24%, and specificities of 95% and 67%, respectively. Numerous other studies have shown that, in Barrett’s esophagus, NBI endoscopy can define intestinal metaplasia and detect low- or high-grade dysplasia or early cancer (Fig. 5) with comparable accuracy to chromoendoscopy. For squamous esophageal neoplasia, NBI can detect high-grade dysplasia (Fig. 2) and differentiate mucosal from submucosal involvement as accurately as high resolution magnifying endoscopy. These studies suggest that narrow band imaging endoscopy is an alternative to systematic four-quadrant biopsy protocols for Barrett’s surveillance; targeted biopsies of abnormal areas may increase the yield of dysplasia with fewer biopsies.

image

Figure 5 NBI images of early Barrett’s neoplasia. (A) Intramucosal carcinoma – irregular pits and irregular and thickened vessels. (B) Magnified image showing absence of crypts and thickened irregular vessel pattern (×115). (C) Irregular crypts and vessel pattern in a patient with low-grade dysplasia (×115). (D) Small intramucosal carcinoma. Absent crypts and thick, irregular vessels can be seen.

In the colon, narrow band imaging endoscopy analyses the crypt pattern (Figs 6–8) in a manner similar to chromoendoscopy but also allows definition of vascular network changes (Fig. 9). It has been compared with conventional colonoscopy with chromoendoscopy using 0.2% indigo carmine in 34 patients with 43 polyps to distinguish hyperplastic polyps from adenomas. These two methods had equivalent sensitivity and specificity (100% and 75%, respectively) for diagnosing colonic neoplasia. Both techniques were superior to conventional endoscopy alone, with sensitivity and specificity of 83% and 44%, compared with histological examination. In two further studies, including 43 and 30 patients with 32 and 30 polyps, narrow band imaging endoscopy had a sensitivity and a positive predictive value (PPV) of 94% and 83%, respectively, for the diagnosis of adenoma, whereas the PPV and NPV were 74% and 81% in a study of 31 patients, eight of whom had 18 adenomas.

image

Figure 6 Colonic polyps Crypts pattern. Type I, evenly distributed, small round crypts; Type II, evenly distributed, star-shaped crypts; Type III–L, tubular crypts, enlarged and curved; Type III–S, round, curved, densely packed crypts with small tails; Type IV, convoluted, cerebriform crypts; Type V, absence of classifiable crypt structures.

image

Figure 7 Type III–L pit pattern on the surface of a colonic tubulovillous adenoma.

image

Figure 8 Cerebriform pattern of type IV pits in a villous adenoma.

image

Figure 9 Microvascular network of colonic mucosa and polyps at narrow band imaging (NBI).

(Modified from Sano Y, Horimatsu T, Fu KI, Katagiri A, Muto M, Ishikawa H. Magnifying observation of microvascular architecture of colorectal lesions using a narrow-band imaging system. Digestive Endoscopy 2006; 18 (Suppl. 1): S44-S51.)

In ulcerative colitis (UC), NBI with targeted biopsies was compared with a systematic biopsy protocol in 11 patients (7 and 42 biopsies on average performed by the two strategies). Both strategies were equivalent and found no dysplasia in seven patients, an ‘indefinite dysplasia’ lesion in one patient and dysplasia or carcinoma in three patients, suggesting that NBI with targeted biopsies was an alternative to systematic biopsy protocols that require 33–56 biopsies per patient.

In the stomach, NBI can recognize normal crypts (Fig. 10A), vascular changes in gastritis (Fig. 11) but also well- or poorly-differentiated gastric carcinomas (Figs 12, 10B). Few studies have been published but NBI is used mainly by experts in assessment of lesions prior to endoscopic mucosal resection or submucosal dissection of early gastric cancers.

image

Figure 10 (A) Low magnification NBI image of normal gastric pits. (B) Paris type 0–IIa+c early gastric cancer. (C) The pit pattern is irregular and distorted.

image

Figure 11 Gastritis. Irregular capillary network and disappearance of collecting veins (type Z–1 or D), presence of pale, dilated and elongated crypts at the level of the gastric mucosa (type Z–2).

image

Figure 12 Gastric carcinoma. Normal mucosa (left panel). Well-differentiated early carcinoma: hypervascular capillary network with an irregular mesh pattern (middle panel). Poorly-differentiated early carcinoma sparse, short twig-like capillaries without branching (right panel).

These studies show that for the diagnosis of high-grade dysplasia or early cancer in Barrett’s esophagus, NBI is more than simply a clinical practice aid and could be an alternative to the Seattle protocol of systematic four-quadrant biopsies every 1–2 cm. For the detection of dysplasia in UC, emerging data could also support this method as an alternative to multiple random biopsies every 10 cm. For the characterization of polyps, particularly adenomas, NBI is equivalent to chromoendoscopy but, like the latter, its NPV is too low to replace pathological analysis. Recently, a group of international experts has reached a consensus on the relevance of NBI or FICE in daily endoscopic practice (Table 2).

Table 2 Statement regarding the usefulness of narrow band imaging endoscopy technology (NBI or FICE)

image

2.2 Clinical application of endoscopy with autofluorescence

Most studies have been conducted with the first-generation LIFE-I system for the examination of the esophagus. In an initial study of 34 patients with short-segment Barrett’s esophagus, the yield of 136 biopsies performed after standard esophageal fiberoptic endoscopy was compared with that of 109 targeted biopsies after location by autofluorescence using an optical probe (excitation at 442 nm) through the operating channel of a fiberoptic endoscope. High-grade dysplasia was detected in these two groups in one and seven patients (3% vs 21%), respectively. Per-sample analysis found low-grade dysplasia in 19 and 27% (significant difference) of the samples and high-grade dysplasia in 0.7 and 8.3% (significant difference). A second study compared AFI via an optical probe used through an operating channel with methylene blue chromoendoscopy during fiberoptic videoendoscopy and videoendoscopy with four-quadrant staged biopsies. PPVs for the diagnosis of any grade of dysplasia or cancer were 49% and 58% for AFI and chromoendoscopy, respectively, whereas their NPVs were 69% and 72%, respectively. Per-patient analysis showed that the sensitivity and specificity for this diagnosis were 59% and 78% using AFI, and 71% and 50% using methylene blue chromoendoscopy. A later study tested the second generation LIFE-II system which uses a fiberoptic endoscope with two CCDs in the optical fiber to detect green (490–550 nm) and red (>590 nm) fluorescence. An ‘intra-patient’ comparison in 50 patients with Barrett’s esophagus between LIFE-II autofluorescence and systematic four-quadrant biopsies shows that the sensitivity for the diagnosis of high-grade dysplasia or early cancer was comparable, at 62%. The PPVs for the diagnosis of high-grade dysplasia or early cancer were 41% and 28%, respectively.

These studies show that for the diagnosis of high-grade dysplasia or early cancer in Barrett’s esophagus, the LIFE-I or LIFE-II system cannot replace the Seattle protocol of systematic four-quadrant biopsies in clinical practice. The OncoLife system, the latest version of LIFE-II (excluding reflectance interference), is undergoing trials and data are awaited.

In the colon, first-generation LIFE-I system autofluorescence has been compared with standard fiberoptic colonoscopy in 20 patients, six of whom had chronic inflammatory bowel disease. A total of 22 of the 42 samples showed flat dysplasia or a polyp with a PPV for AFI and for standard endoscopy, 91% and 85%, respectively, and a NPV of 90% and 100%. The principle of AFI with image reconstitution has been developed more recently using a videoendoscope in the esophagus and colon (Fig. 13). The CCD detected the various fluorescences, while the filter was positioned at the tip of the videoendoscope (prototype developed by Olympus).

image

Figure 13 View of dilated, curved tubular crypts (type III–L) in a colonic tubulovillous adenoma. The left-hand panel shows the magenta colour of the polyp with autofluorescence.

Compared with a standard videoendoscopy in the examination of 23 patients with high-grade dysplasia or early cancer and 18 patients after endoscopic treatment of these lesions, the PPV and NPV of videoendoscopy with AFI were 49% and 89%, respectively. If low-grade dysplasia lesions were included, the PPV increased to 59% and the NPV remained the same. The false positives responsible for a low PPV resulted from acute inflammation. A final study used a prototype Olympus videocolonoscope with AFI to characterize 168 colon polyps as hyperplastic or adenomatous. The sensitivity and specificity of AFI were 89% and 81%, with the adenomas appearing magenta against a green colonic mucosa (Fig. 13), whereas hyperplastic polyps appeared pink: 37 of the 168 polyps were examined using the LIFE-II system with a sensitivity and specificity for the diagnosis of adenoma of 87% and 71%. Color and contrast intensity were better with the videoendoscopy AFI system, compared with optical fibers, accounting for the difference in specificity of 10%.

Overall, AFI by videoendoscopy has a positive and negative predictive value for the diagnosis of dysplasia or early cancer complicating Barrett’s esophagus that is comparable with that of systematic four-quadrant biopsy protocols, but it should probably be carried out after antisecretory treatment to minimize false positive results related to acute inflammation and to obtain a NPV applicable in clinical practice. Using magnification with NBI to examine AFI-positive areas can reduce the number of false-positive results considerably and this ‘trimodality’ imaging may offer significant advantages in the evaluation of Barrett’s esophagus. The image contrast and its ease of use make it a technique for the future to reduce the miss-rate for colonic adenomas or to characterize the nature of polyps; the first published results indicate a sensitivity of 90%.

2.3 Clinical application of confocal laser endoscopy (CLE) or endocytoscopy

See Chapter 6.1 for a discussion on the results of confocal laser endomicroscopy studies. This technique will probably have more of a future for CLE probes used through the operating channel of a videoendoscope, additionally equipped with a detection system such as autofluorescence or narrow band imaging endoscopy. Endocytoscopy, even although it uses a vital stain (methylene blue) instead of a fluorochrome injection, can be likened to confocal laser endoscopy. This technique has been tested in 87 patients with neoplasia (38 of the esophagus, 18 of the stomach, and 35 of the colon). Visualization of cell nucleus size and the nuclear-cytoplasmic ratio was of very good quality in 95% of cases. There are currently no clinical or comparative studies that define its positive and negative predictive value in comparison with chromoendoscopy or standard histology.

2.4 Clinical application of optical coherence tomography (OCT)

As regards the esophagus, OCT succeeded in diagnosing intestinal metaplasia in 121 patients with Barrett’s esophagus with a sensitivity and specificity of 97% and 92%, respectively, and a PPV of 84%. Another study has reported a PPV and NPV for the diagnosis of dysplasia in Barrett’s esophagus, of 53% and 89%, respectively. The sensitivity and specificity for the diagnosis of dysplasia were 68 and 82%, and 50 and 72% for high-grade dysplasia only and 58 and 71% for carcinoma. There was, however, significant inter-observer variation among the endoscopists in their ability to detect dysplasia or early cancer. The technique of optical coherence tomography with longitudinal scanning has also been used to characterize the mucosa of 46 patients with Barrett’s esophagus, assigning a score between 0 and 2 to describe reflected wave intensity, mucosal gland irregularity and epithelial layer thickness; by correlating 177 sites biopsied and examined by OCT, a multifactorial score was determined based on the signal intensity of the surface, and on the regularity and dilation of the mucosal glands. By using an integrated score, it was possible to diagnose intramucosal carcinoma or high-grade dysplasias versus other metaplastic lesions or normal mucosa with a sensitivity and specificity of 83% and 75%, respectively.

Examination of the colon by optical coherence tomography using a radial probe has been used to determine criteria in order to characterize and differentiate them. This technology seems promising, particularly when the incident beam is produced by high-power lasers with a resolution, not of 10 µm, but of 1 µm. This technique achieves good visualization of the mucosa with a correlation of 0.84 between measurement of mucosal thickness by histology and by optical coherence tomography with a mean overestimation of 9%. There are, however, no clinical studies in the literature to recommend its use.

2.5 Other methods

Finally, other new endoscopic imaging methods are undergoing validation ex vivo or in vivo using prototypes which are mainly methods for the focal or point characterization (spectroscopy) of lesions detected by other means. For example, fluorescence with spectral measurement and analysis has yielded useful results for differentiating between neoplastic polyps and hyperplastic polyps in the colon using a short-wavelength monochromatic light for excitation, but other methods such as measurement of the RAMAN effect using a long-wavelength light beam (near infrared) can already characterize in vitro the composition and nature of intermolecular bonds in tissue samples and differentiate between hyperplastic polyps and adenomas. Measurement of the scattering of a light beam with a wavelength belonging to the visible spectrum (400–700 nm) with an identical wavelength (elastic scattering) or an increased wavelength (non-elastic scattering) has also been used alone or combined with reflecting measures to characterize cell nucleus density and size in the mucosa or submucosa in previously identified lesions or areas of mucosal irregularity.

Conclusion

Narrow band imaging endoscopy with the FICE or NBI system could be an alternative to systematic four-quadrant biopsy protocols for the diagnosis of high-grade dysplasia or early cancer in Barrett’s esophagus. This method could also be effective as an alternative to multiple random biopsies to detect dysplasia in UC. It cannot, however, replace chromoendoscopy for detecting or characterizing polyps. Autofluorescence cannot replace systematic biopsies in Barrett’s esophagus and is no better than iodine staining for detecting squamous esophageal carcinomas, but it should prove useful in the future for reducing the number of adenomas missed at colonoscopy or for characterizing the nature of polyps with 90% sensitivity. Confocal laser endomicroscopy is a histological approach, which has the drawback of requiring intravenous injection of contrast medium and previous location of the lesion. If combined with NBI and AFI, it could replace chromoendoscopy and biopsy for the diagnosis of hyperplastic polyps or low-grade dysplasia in Barrett’s esophagus.

Further Reading

Adler A, Aschenbeck J, Yenerim T, et al. Narrow-band versus white-light high definition television endoscopic imaging for screening colonoscopy: a prospective randomised trial. Gastroenterology. 2009;136:410-416.

Curvers W, Baak L, Kiesslich R, et al. Chromoendoscopy and narrow-band imaging compared with high-resolution magnification endoscopy in Barrett’s esophagus. Gastroenterology. 2008;134:670-679.

Curvers WL, van den Broek FJ, Reitsma JB, et al. Systematic review of narrow-band imaging for the detection and differentiation of abnormalities in the esophagus and stomach. Gastrointest Endosc. 2009;69:307-317.

East JE, Suzuki N, Bassett P, et al. Narrow band imaging with magnification for the characterization of small and diminutive colonic polyps: pit pattern and vascular pattern intensity. Endoscopy. 2008;40:811-817.

East JE, Tan EK, Bergman JJ, et al. Meta-analysis: narrow band imaging for lesion characterization in the colon, esophagus, duodenal ampulla and lung. Aliment Pharmacol Ther. 2008;28:854-867.

Endo T, Nosho K, Arimura Y, et al. Study of the tumor vessels in depressed-type early gastric cancers using narrow band imaging magnifying endoscopy and cDNA array analysis. Digest Endosc. 2005;17:210-217.

Evans JA, Poneros JM, Bouma BE, et al. Optical coherence tomography to identify intramucosal carcinoma and high-grade dysplasia in Barrett’s esophagus. Clin Gastroenterol Hepatol. 2006;4:38-43.

Haringsma J, Tytgat GN, Yano H, et al. Autofluorescence endoscopy: feasibility of detection of GI neoplasms unapparent to white light endoscopy with an evolving technology. Gastrointest Endosc. 2001;53:642-650.

Inoue H, Cho JY, Satodate H, et al. Development of virtual histology and virtual biopsy using laser-scanning confocal microscopy. Scand J Gastroenterol. 2003;38:37-39.

Kara MA, Peters FP, Rosmolen WD, et al. High-resolution endoscopy plus chromoendoscopy or narrow-band imaging in Barrett’s esophagus: a prospective randomised crossover study. Endoscopy. 2005;37:929-936.

Kara MA, Peters FP, Ten Kate FJ, et al. Endoscopic video autofluorescence imaging may improve the detection of early neoplasia in patients with Barrett’s esophagus. Gastrointest Endosc. 2005;61:679-685.

Kara MA, Smits ME, Rosmolen WD, et al. A randomised crossover study comparing light-induced fluorescence endoscopy with standard videoendoscopy for the detection of early neoplasia in Barrett’s esophagus. Gastrointest Endosc. 2005;61:671-678.

Kiesslich R, Burg J, Vieth M, et al. Confocal laser endoscopy for diagnosing intraepithelial neoplasias and colorectal cancer in vivo. Gastroenterology. 2004;127:706-713.

Konerding MA, Fait E, Gaumann A. 3D microvascular architecture of pre-cancerous lesions and invasive carcinomas of the colon. Br J Cancer. 2001;84:1354-1362.

Kudo S, Hirota S, Nakajima T, et al. Colorectal tumors and pit-pattern. J Clin Pathol. 1994;47(10):880-885.

Kudo S, Rubio CA, Teixeira CR, et al. Pit pattern in colorectal neoplasia: endoscopic magnifying view. Endoscopy. 2001;33:367-373.

Kumagai Y, Inoue H, Nagai K, et al. Magnifying endoscopy, stereoscopic microscopy, and the microvascular architecture of superficial esophageal carcinoma. Endoscopy. 2002;45:369-375.

Machida H, Sano Y, Hamamoto Y, et al. Narrow-band imaging in the diagnosis of colorectal mucosal lesions: a pilot study. Endoscopy. 2004;36:1094-1098.

Nakayoshi T, Tajiri H, Matsuda K, et al. Magnifying endoscopy combined with narrow band imaging system for early gastric cancer: correlation of vascular pattern with histopathology. Endoscopy. 2004;36:1080-1084.

Poneros JM, Brand S, Bouma BE, et al. Diagnosis of specialized intestinal metaplasia by optical coherence tomography. Gastroenterology. 2001;120:7-12.

Sakaki N, Iida Y, Okazaki Y, et al. Magnifying endoscopic observation of the gastric mucosa, particularly in patients with atrophic gastritis. Endoscopy. 1978;10:269-274.

Sakashita M, Inoue H, Kashida H, et al. Virtual histology of colorectal lesions using laser-scanning confocal microscopy. Endoscopy. 2003;35:1033-1038.

Sano Y, Horimatsu T, Fu KI, et al. Magnifying observation of microvascular architecture of colorectal lesions using a narrow-band imaging system. Dig Endosc. 2006;18(Suppl. 1):S44-S51.

Sharma P, Weston AP, Topalovski M, et al. Magnification chromoendoscopy for the detection of intestinal metaplasia and dysplasia in Barrett’s esophagus. Gut. 2003;52:24-27.

Singh R, Anagnostopoulos GK, Yao K, et al. Narrow-band imaging with magnification in Barrett’s esophagus: validation of a simplified grading system of mucosal morphology patterns against histology. Endoscopy. 2008;40:457-463.

Sivak MVJr, Kobayashi K, Izatt JA, et al. Narrow-band imaging with magnification in Barrett’s esophagus: validation of a simplified grading system of mucosal morphology patterns against histology. Gastrointest Endosc. 2000;51:474-479.

Song LM, Adler DG, Conway JD, et al. Narrow band imaging and multiband imaging. ASGE Technology Committee. Gastrointest Endosc. 2008;67:581-589.

Tischendorf JJ, Wasmuth HE, Koch A, et al. Value of magnifying chromoendoscopy and narrow band imaging (NBI) in classifying colorectal polyps: a prospective controlled study. Endoscopy. 2007;39:1092-1096.

Uedo N, Iishi H, Tatsuta M, et al. A novel videoendoscopy system by using autofluorescence and reflectance imaging for diagnosis of oesophagogastric cancers. Gastrointest Endosc. 2005;62:521-528.

van den Broek FJ, Fockens P, Dekker E. Review article. New developments in colonic imaging. Aliment Pharmacol Ther. 2007;26(Suppl 2):91-99.

van den Broek FJ, Fockens P, van Eeden S, et al. Endoscopic tri-modal imaging for surveillance in ulcerative colitis: randomised comparison of high-resolution endoscopy and autofluorescence imaging for neoplasia detection; and evaluation of narrow-band imaging for classification of lesions. Gut. 2008;57(8):1083-1089.

van den Broek FJ, Reitsma JL, Curvers WL, et al. Systematic review of narrow-band imaging for detection and differentiation of neoplastic and non neoplastic lesion in the colon. Gastrointest Endosc. 2009;69(1):124-135.

Wolfsen HC, Crook JE, Krishna M, et al. Prospective, controlled tandem endoscopy study of narrow band imaging for dysplasia detection in Barrett’s esophagus. Gastroenterology. 2008;135:24-31.

Yagi K, Nakamura A, Sekine A. Comparison between magnifying endoscopy and histological, culture and urease test findings from the gastric mucosa of the corpus. Endoscopy. 2002;34:376-381.

Yao K, Oishi T. Microgastroscopic findings of mucosal microvascular architecture as visualized by magnifying endoscopy. Digest Endosc. 2001;13:S27-S33.

Yao K, Oishi T, Matsui T, et al. Novel magnified endoscopic findings of microvascular architecture in intramucosal gastric cancer. Gastrointest Endosc. 56, 2002. 279–278

Yoshida T, Inoue H, Usui S, et al. Narrow-band imaging system with magnifying endoscopy for superficial esophageal lesions. Gastrointest Endosc. 2004;59:288-295.

Related posts:

Introduction to endoscopy Diagnostic upper endoscopy Preparation for endoscopy Diagnostic colonoscopy Interventional endoscopy Endosonography