High-resolution endoscopic imaging of the GI tract: a comparative study of optical coherence tomography versus high-frequency catheter probe EUS

Correlation of endoscopic optical coherence tomography with histology in the lower-GI tract

BACKGROUND

Optical coherence tomography (OCT), a noninvasive optical imaging technique, provides high-resolution cross-sectional images of tissue microstructure. We developed a system for real-time endoscopic OCT (EOCT) of the human GI tract. During clinical trials, the structure of mucosa and submucosa, glands, blood vessels, pits, villi, and crypts was observed in a range of GI organs. Although EOCT images are thought to accurately depict actual histologic features, there are few data to support this assumption. Therefore, the present study correlated images acquired with an EOCT imaging system in vitro to corresponding histologic sections.

METHODS

EOCT images were obtained of fresh specimens of ileum, colon, and rectum that then were fixed in formalin and were processed for microscopic evaluation by using standard methods. The thickness of mucosa and of submucosa was determined for both EOCT images and histologic slides.

RESULTS

The first hyper-reflective layer in the EOCT images was identified as mucosa. A close correlation (R 2=0.84) was observed between EOCT and histology. Furthermore, the submucosa and the muscularis propria could be identified as the next deepest hyporeflective band and a hyper-reflective layer, respectively, in EOCT images. The submucosa was found to be more compressible than mucosa, and its EOCT appearance was dependent on its content of adipose tissue.

CONCLUSIONS

EOCT provides images that precisely correlate with the histologic structure of the mucosa and the submucosa of the GI tract.

In vivo colonoscopic optical coherence tomography for transmural inflammation in inflammatory bowel disease

BACKGROUND & AIMS

Transmural inflammation, a distinguishing feature of Crohn's disease (CD), cannot be assessed by conventional colonoscopy with mucosal biopsy. Our previous ex vivo study of histology-correlated optical coherence tomography (OCT) imaging on colectomy specimens of CD and ulcerative colitis (UC) showed that disruption of the layered structure of colon wall on OCT is an accurate marker for transmural inflammation of CD. We performed an in vivo colonoscopic OCT in patients with a clinical diagnosis of CD or UC using the previously established, histology-correlated OCT imaging criterion.

METHODS

OCT was performed in 40 patients with CD (309 images) and 30 patients with UC (292 images). Corresponding endoscopic features of mucosal inflammation were documented. Two gastroenterologists blinded to endoscopic and clinical data scored the OCT images independently to assess the feature of disrupted layered structure.

RESULTS

Thirty-six CD patients (90.0%) had disrupted layered structure, whereas 5 UC patients (16.7%) had disrupted layered structure (P < .001). Using the clinical diagnosis of CD or UC as the gold standard, the disrupted layered structure on OCT indicative of transmural inflammation had a diagnostic sensitivity and specificity of 90.0% (95% CI: 78.0%, 96.5%) and 83.3% (95% CI: 67.3%, 93.3%) for CD, respectively. The kappa coefficient in the interpretation of OCT images was 0.80 (95% CI: 0.75, 0.86, P < .001).

CONCLUSIONS

In vivo colonoscopic OCT is feasible and accurate to detect disrupted layered structure of the colon wall indicative of transmural inflammation, providing a valuable tool to distinguish CD from UC.

Ex vivo histology-correlated optical coherence tomography in the detection of transmural inflammation in Crohn's disease

BACKGROUND AND AIMS

Distinguishing Crohn's disease (CD) from ulcerative colitis (UC) can be difficult. Transmural inflammation, a key feature of CD, cannot be assessed by conventional colonoscopy with biopsy. Optical coherence tomography (OCT) provides high-resolution, cross-sectional images of the gut wall and might become a new diagnostic tool. The aims of this study were to perform histology-correlated OCT on surgical specimens of CD and UC and to determine its diagnostic accuracy.

METHODS

Colectomy specimens from patients with a preoperative diagnosis of CD (N = 24) or UC (N = 24) were studied with OCT in the operating room. OCT and histopathology were assessed blindly, and diagnostic accuracy of OCT was assessed.

RESULTS

Eight preoperatively identified UC patients (33%) with transmural inflammation on postoperative histology were diagnosed with CD, and all 8 had a disrupted layered structure on OCT, a characteristic feature of transmural disease. Sixteen UC patients (67%) had superficial inflammation on histology; of them, 13 (81%) had an intact layered structure on OCT. All 24 preoperative CD patients had transmural inflammation on histology, and 23 (96%) had a disrupted layered structure on OCT. Of 585 histology-OCT image sets from the 48 patients, 152 sets (26%) had transmural inflammation on histology. The sensitivity and specificity for OCT to detect transmural disease were 86% and 91%, respectively.

CONCLUSIONS

Transmural inflammation, as characterized by disruption of the layered structure of colon wall on OCT, is an accurate marker for the diagnosis of CD. Ex vivo OCT predicted transmural inflammation on postoperative histopathology.

Individual variations in mucosa and total wall thickness in the stomach and rectum assessed via endoscopic ultrasound

Endoscopic ultrasound is a unique tool to acquire in vivo data on alimentary tract wall thicknesses of sufficient resolution needed in radiation dosimetry studies. Through their different echo texture and intensity, five layers of differing echo patterns for superficial mucosa, deep mucosa, submucosa, muscularis externa and serosa/adventitia exist within the walls of organs composing the alimentary tract. In this study, retrospective image analyses of patient video data were made for ten examinations of the stomach and eight examinations of the rectum covering a range of patient ages. Thicknesses for stomach mucosa ranged from 1030 +/- 130 microm to 1640 +/- 80 microm (total stomach wall thicknesses from 2.80 +/- 0.12 to 4.23 +/- 0.03 mm). Measurements made for the rectal images revealed rectal mucosal thicknesses from 660 +/- 50 microm to 1130 +/- 250 microm (total rectal wall thicknesses from 2.28 +/- 0.05 to 3.55 +/- 0.43 mm). The mucosa accounted for approximately 32 +/- 7% and approximately 32 +/- 8% of the total thickness of the stomach and rectal wall, respectively. These values can thus be utilized to investigate uncertainties in alimentary tract dosimetry that are based upon fixed reference individual definitions of organ wall structure.

Optical coherence tomography in the gastrointestinal tract

Conventional gastrointestinal endoscopic instruments have provided ready access to the mucosal surface of the esophagus, stomach,small intestinal, colon, bile duct, and pancreatic duct. The evolution of endoscopic ultrasonography has provided an additional dimension to the clinical application of modern endoscopy and imaging technology.

Optical coherence tomography for ultrahigh resolution in vivo imaging

Optical coherence tomography (OCT) is an emerging biomedical optical imaging technique that performs high-resolution, cross-sectional tomographic imaging of microstructure in biological systems. OCT can achieve image resolutions of 1-15 microm, one to two orders of magnitude finer than standard ultrasound. The image penetration depth of OCT is determined by the optical scattering and is up to 2-3 mm in tissue. OCT functions as a type of 'optical biopsy' to provide cross-sectional images of tissue structure on the micron scale. It is a promising imaging technology because it can provide images of tissue in situ and in real time, without the need for excision and processing of specimens.

Dual modality instrument for simultaneous optical coherence tomography imaging and fluorescence spectroscopy

We develop a dual-modality device that combines the anatomical imaging capabilities of optical coherence tomography (OCT) with the functional capabilities of laser-induced fluorescence (LIF) spectroscopy. OCT provides cross-sectional images of tissue structure to a depth of up to 2 mm with approximately 10-microm resolution. LIF spectroscopy provides histochemical information in the form of emission spectra from a given tissue location. The OCT subsystem utilizes a superluminescent diode with a center wavelength of 1300 nm, whereas a helium cadmium laser provides the LIF excitation source at wavelengths of 325 and 442 nm. Preliminary data are obtained on eight postmortem aorta samples, each 10 mm in length. OCT images and LIF spectra give complementary information from normal and atherosclerotic portions of aorta wall. OCT images show structures such as intima, media, internal elastic lamina, and fibrotic regions. Emission spectra ratios of 520/490 (325-nm excitation) and 595/635 (442-nm excitation) could be used to identify normal and plaque regions with 97 and 91% correct classification rates, respectively. With miniaturization of the delivery probe and improvements in system speed, this dual-modality device could provide a valuable tool for identification and characterization of atherosclerotic plaques.

Real-Time Digital Signal Processing-Based Optical Coherence Tomography and Doppler Optical Coherence Tomography

We present the development and use of a real-time digital signal processing (DSP)-based optical coherence tomography (OCT) and Doppler OCT system. Images of microstructure and transient fluid-flow profiles are acquired using the DSP architecture for real-time processing of computationally intensive calculations. This acquisition system is readily configurable for a wide range of real-time signal processing and image processing applications in OCT.

Federal funding of endoscopic research in the United States: 1972-2002

BACKGROUND

Funding for research is critical to the determination of appropriate applications for endoscopy in clinical practice. We sought to evaluate trends in funding provided by the National Institutes of Health (NIH) for endoscopic research from 1972 through 2002.

METHODS

The NIH database of funded biomedical projects for the years 1972 through 2002 was searched using the Computerized Retrieval of Information on Scientific Projects (CRISP) and the keyword "endoscopy." Grants were included if a start date, title, and/or specific aims were available. Grants were classified as primary endoscopy if the title or specific aim had an endoscopy focus. Endoscopy funding was compared with other nonendoscopic funding for the same period.

RESULTS

From 1972 through 2002, 133 endoscopy-related grant applications were funded and 98 met inclusion criteria. Funding for endoscopic research increased from one grant (1972-1982) to 4 grants (1983-1992) to 93 grants (1993-2002), a 2325% increase for the 1993-2002 decade alone. Despite this increase, there were substantially fewer funded endoscopy-related applications compared with liver disease (61,804 grants), Helicobacter pylori (866 grants), and cardiac catheterization (1547 grants). Among endoscopic grants, colorectal cancer projects accounted for the largest portion (34%), followed by advanced optical technologies (18%) and Barrett's esophagus (17%).

CONCLUSIONS

Funding for endoscopic research by the NIH has increased dramatically over the past 30 years, but it still lags behind funding in other fields. Projects focused on colorectal cancer, Barrett's esophagus, and optical technologies were most common among those funded, and the National Cancer Institute was the primary source of funding.

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Optical coherence tomography: Technology and applications for neuroimaging

Optical coherence tomography (OCT) is an emerging imaging technology with applications in biology, medicine, and materials investigations. Attractive features include high cellular-level resolution, real-time acquisition rates, and spectroscopic feature extraction in a compact noninvasive instrument. OCT can perform "optical biopsies" of tissue, producing images approaching the resolution of histology without having to resect and histologically process tissue specimens for characterization and diagnosis. This article will review several of the current technological developments in OCT. To illustrate the potential of this technology for neuroimaging, applications for imaging neural development, the neural retina, tumors of the central nervous system, and the microsurgical repair of peripheral nerves will be presented. This technology offers a potential investigative tool for addressing many of the present challenges in neuroimaging.

Speckle reduction in optical coherence tomography by "path length encoded" angular compounding

Speckle, the dominant factor reducing image quality in optical coherence tomography (OCT), limits the ability to identify cellular structures that are essential for diagnosis of a variety of diseases. We describe a new high-speed method for implementing angular compounding by path length encoding (ACPE) for reducing speckle in OCT images. By averaging images obtained at different incident angles, with each image encoded by path length, ACPE maintains high-speed image acquisition and requires minimal modifications to OCT probe optics. ACPE images obtained from tissue phantoms and human skin in vivo demonstrate a qualitative improvement over traditional OCT and an increased SNR that correlates well with theory.

Diagnostic potential of near-infrared Raman spectroscopy in the colon: differentiating adenomatous from hyperplastic polyps

BACKGROUND

Near-infrared Raman spectroscopy is a promising optical technique for GI tissue diagnosis. This study assessed the diagnostic potential of near-infrared Raman spectroscopy in the colon by evaluating its ability to distinguish between adenomatous and hyperplastic polyps.

METHODS

Ex vivo and in vivo Raman spectra of colon polyps were collected by using a custom-built, fiber-optic, near-infrared Raman spectroscopic system. Multivariate statistical techniques, including principal component analysis and linear discriminant analysis, were used to develop diagnostic algorithms for classifying colon polyps based on their spectral characteristics. With the number of samples available, spectral classification of polyps was tested by using a leave-one-out, cross-validation method.

RESULTS

Fifty-four ex vivo Raman spectra were analyzed (20 hyperplastic, 34 adenomatous). The spectral-based diagnostic algorithms identified adenomatous polyps with 91% sensitivity, 95% specificity, and 93% accuracy. In vivo, adenomas (n = 10) were distinguished from hyperplastic polyps (n = 9) with 100% sensitivity, 89% specificity, and 95% accuracy.

CONCLUSIONS

Near-infrared Raman spectroscopy differentiated adenomatous from hyperplastic polyps with high diagnostic accuracy. To our knowledge, this is the first demonstration of the potential of near-infrared Raman spectroscopy for differentiation of colonic polyps during GI endoscopy.

Usefulness of endoscopic ultrasonography in the diagnosis of congenital esophageal stenosis

BACKGROUND/PURPOSE

Endoscopic ultrasonography (EUS) is considered a potentially useful tool to investigate structural abnormalities of the esophagus in pediatric patients, as in adults. The aim of this study was to evaluate the usefulness of EUS for the diagnosis of congenital esophageal stenosis.

METHODS

High-frequency catheter probe EUS was performed under general anesthesia in 2 patients who had congenital esophageal stenosis.

RESULTS

A 4-year-old boy with anorectal anomaly showed tapered narrowing in the distal esophagus, which was not ameliorated with balloon dilatation. High-frequency catheter probe EUS showed hypertrophy of the muscular layer in the esophageal wall at the narrowed portion, but no images suggested the presence of tracheobronchial remnants. The histologic diagnosis of fibromuscular hypertrophy was confirmed at esophagoplasty. A 5-month-old boy with Gross C-type esophageal atresia and symptomatic gastroesophageal reflux showed tapered narrowing in the middle esophagus on esophagography. The symptoms of stenosis were not ameliorated by balloon dilatation performed 4 times. High-frequency catheter probe EUS showed hyperechoic lesions suggesting cartilage at the esophageal narrowing. The diagnosis of tracheobronchial remnants was confirmed by the finding of 2 pieces of cartilage in the specimen obtained at the time of esophageal resection.

CONCLUSION

EUS can be applied to show structural abnormalities of the esophageal wall even in pediatric patients with congenital esophageal stenosis and is useful for planning the therapeutic strategy.

Future developments in endoscopic imaging

Flexible gastrointestinal endoscopy was introduced more than 30 years ago; this chapter will try to look into its future. Developments are expected in five different categories. We will see better with the use of high-resolution magnification endoscopy as well as by using other light-tissue interactions (such as spectroscopy). We will also be able to look just below the surface with laser-scanning microscopy and optical coherence tomography with a resolution of 1 microm (in vivo histology). Computers will assist with the interpretation of what we see, and the availability of broadband networks all around the world will allow real-time consultation globally. Invisible areas of the gastrointestinal tract will be seen with the help of improved endoscopy capsules and virtual endoscopy. Finally, we will treat endoscopically, with the help of new instruments and accessories, more of the lesions that we see.

Interventional endoscopy

Technologic milestones have been achieved in the field of interventional endoscopy. These have resulted in improved hemostasis, more accurate cancer staging, safer and less invasive methods of removing gastric neoplasms, and endoscopic palliation of malignant gastric outlet obstruction via stenting. However, just as these milestones are achieved, new challenges emerge: (1) How much sedation can one use safely? (2) What is the risk of transmitting infection and how can that be prevented? (3) Can scopes be made smaller and more comfortable? (4) Can optics be improved? (5) Can endoscopic repair of gastric perforations be safely performed? In this section, we review some of these issues. First, we will provide an update on the most recent concepts in the field of light sedation and infection control. Then, a review of the most commonly used interventional endoscopy procedures, including hemostasis, endosonography, endoscopic mucosal resection, stenting, and percutaneous gastrostomy tube placements. Finally, an overview of the ongoing research and development in the field of interventional endoscopy and how it can improve patient comfort, diagnostic accuracy, therapeutic efficacy, and training in the future.

Interventional endoscopy in the diagnosis and staging of upper gastrointestinal malignancy

Increased population longevity as well as an emphasis on earlier diagnosis and more effective treatment of cancer have created an environment for new technologies and techniques to flourish. Some of the endoscopic entities discussed in this article have not been fully validated in clinical practice. Innovative spectroscopic modalities hold a great deal of promise, but are years away from general applicability. In contrast, many interventional endoscopic techniques are currently available and confer heightened levels of diagnostic and staging accuracy for gastric and esophageal malignancies. Earlier diagnosis can identify patients who may be eligible for less-invasive treatment options such as EMR. Minimally invasive treatment options and maximum staging accuracy are more important for patients who are marginal surgical candidates and for accurate comparison of clinical trials studying treatment options. Our challenge for the future is to properly integrate these technologic advances with the science of good medical practice.