Tethered capsule endomicroscopy for microscopic imaging of the esophagus, stomach, and duodenum without sedation in humans (with video)

A look inside the gut as a clue to nutritional status

PURPOSE OF REVIEW

Malabsorption and malnutrition are common gastrointestinal manifestations clinicians face, requiring diagnostic workup for effective diagnosis and management of the underlying cause. This review discusses recent advances in diagnostic approaches to malabsorption and maldigestion of macronutrients - lipids, proteins, and carbohydrates. We highlight underrecognized causes, available testing modalities, and ongoing diagnostic unmet needs.

RECENT FINDINGS

Innovations in the diagnostic landscape are enhancing our understanding of malabsorption syndromes. Stool collection and handling is uncomfortable and commonly avoided. The objective quantification of stool lipids, bile acids, and gut enzymes is therefore underused in the diagnosis and management of common disorders such as exocrine pancreatic insufficiency, bile acid diarrhea, protein-losing enteropathy, and more. We review the recent advancements in spot quantification of stool fat and bile acid content, endoscopic imaging techniques such as endocytoscopy, confocal laser endomicroscopy, and optical coherence tomography and the future place in clinical practice.

SUMMARY

Malabsorption and maldigestion represent significant challenges in clinical nutrition and gastroenterology. Through the integration of advanced diagnostic techniques, clinicians will be better equipped to tailor therapy and monitor treatment response, ultimately improving patient health outcomes. This review underscores the critical role of innovative diagnostic tools in accurately detecting and effectively managing gastrointestinal disorders linked to nutritional status.

Advances in Screening for Barrett Esophagus and Esophageal Adenocarcinoma

Esophageal adenocarcinoma (EAC), the primary form of esophageal cancer in the United States, is a lethal cancer with exponentially increasing incidence. Screening for Barrett esophagus (BE), the only known precursor to EAC, followed by endoscopic surveillance to detect dysplasia and early-stage EAC and subsequent endoscopic treatment (to prevent progression of dysplasia to EAC and to treat early-stage EAC effectively) is recommended by several society guidelines. Sedated endoscopy (the primary current tool for BE screening) is both invasive and expensive, limiting its widespread use. In this review, we aim to provide a comprehensive review of recent innovations in the nonendoscopic detection of BE and EAC. These include swallowable cell sampling devices combined with protein and epigenetic biomarkers (which are now guideline endorsed as alternatives to sedated endoscopy), tethered capsule endomicroscopy, emerging peripheral blood-sampled molecular biomarkers, and exhaled volatile organic compounds. We also summarize progress and challenges in assessing BE and EAC risk, which is an important complementary component of the process for the clinical implementation of these innovative nonendoscopic tools, and propose a new paradigm for the strategy to reduce EAC incidence and mortality.

Advanced endoscopic imaging for detection of Barrett's esophagus

Barrett's esophagus (BE) is the precursor to esophageal adenocarcinoma (EAC), and is caused by chronic gastroesophageal reflux. BE can progress over time from metaplasia to dysplasia, and eventually to EAC. EAC is associated with a poor prognosis, often due to advanced disease at the time of diagnosis. However, if BE is diagnosed early, pharmacologic and endoscopic treatments can prevent progression to EAC. The current standard of care for BE surveillance utilizes the Seattle protocol. Unfortunately, a sizable proportion of early EAC and BE-related high-grade dysplasia (HGD) are missed due to poor adherence to the Seattle protocol and sampling errors. New modalities using artificial intelligence (AI) have been proposed to improve the detection of early EAC and BE-related HGD. This review will focus on AI technology and its application to various endoscopic modalities such as high-definition white light endoscopy, narrow-band imaging, and volumetric laser endomicroscopy.

Endoscope Capsules: The Present Situation and Future Outlooks

This paper presents new perspectives on photonic technologies for capsule endoscopy. It first presents a review of conventional endoscopy (upper endoscopy and colonoscopy), followed by capsule endoscopy (CE), as well as their techniques, advantages, and drawbacks. The technologies for CEs presented in this paper include integration with the existing endoscopic systems that are commercially available. Such technologies include narrow-band imaging (NBI), photodynamic therapy (PDT), confocal laser endomicroscopy (CLE), optical coherence tomography (OCT), and spectroscopy in order to improve the performance of the gastrointestinal (GI) tract examination. In the context of NBI, two optical filters were designed and fabricated for integration into endoscopic capsules, allowing for the visualization of light centered at the 415 nm and 540 nm wavelengths. These optical filters are based on the principle of Fabry-Perot and were made of thin films of titanium dioxide (TiO2) and silicon dioxide (SiO2). Moreover, strategies and solutions for the adaptation of ECs for PDT are also discussed.

New US capsule endoscopy for superficial and submucosal imaging of the esophagus: the first-in-human study

BACKGROUND AND AIMS

EUS is essential in diagnosing and staging of esophageal subepithelial lesions and tumors. However, EUS is invasive, relies on highly trained endoscopists, and typically requires sedation. The newly developed US capsule endoscopy (USCE), which incorporates both white-light and US imaging modalities into a tethered capsule, is a minimally invasive method for obtaining superficial and submucosal information of the esophagus. This study aimed to assess the feasibility and safety of this USCE system.

METHODS

Twenty participants were enrolled: 10 healthy volunteers and 10 patients with esophageal lesions indicated for EUS. Participants first underwent USCE and subsequently EUS within 48 hours. The primary outcome was the technical success rate of USCE. Secondary outcomes were safety, visualization of the esophagus, and comfort assessment.

RESULTS

The technical success rate of USCE was 95% because 1 patient failed to swallow the capsule. No adverse events were observed. The esophagus was well visualized, and all lesions were detected under USCE optical mode in 19 participants. For healthy volunteers, the US images of normal esophageal walls were all characterized by differentiated 7-layer architecture under both USCE and EUS. For 9 patients, the features of esophageal lesions were recognized clearly under USCE, and presumptive diagnoses derived from USCE were all consistent with those from EUS. Most participants preferred USCE to EUS.

CONCLUSIONS

The novel USCE is feasible and safe to observe the esophageal mucosa and acquire submucosal information, which has the potential to be widely used in the clinic. (Clinical trial registration number: NCT05054933.).

Passively scanned, single-fiber optical coherence tomography probes for gastrointestinal devices

BACKGROUND/OBJECTIVES

Optical coherence tomography (OCT) uses low coherence interferometry to obtain depth-resolved tissue reflectivity profiles (M-mode) and transverse beam scanning to create images of two-dimensional tissue morphology (B-mode). Endoscopic OCT imaging probes typically employ proximal or distal mechanical beam scanning mechanisms that increase cost, complexity, and size. Here, we demonstrate in the gastrointestinal (GI) tracts of unsedated human patients, that a passive, single-fiber probe can be used to guide device placement, conduct device-tissue physical contact sensing, and obtain two-dimensional OCT images via M-to-B-mode conversion.

MATERIALS AND METHODS

We designed and developed ultrasmall, manually scannable, side- and forward-viewing single fiber-optic probes that can capture M-mode OCT data. Side-viewing M-mode OCT probes were incorporated into brush biopsy devices designed to harvest the microbiome and forward-viewing M-mode OCT probes were integrated into devices that measure intestinal potential difference (IPD). The M-mode OCT probe-coupled devices were utilized in the GI tract in six unsedated patients in vivo. M-mode data were converted into B-mode images using an M-to-B-mode conversion algorithm. The effectiveness of physical contact sensing by the M-mode OCT probes was assessed by comparing the variances of the IPD values when the probe was in physical contact with the tissue versus when it was not. The capacity of forward- and side-viewing M-mode OCT probes to produce high-quality B-mode images was compared by computing the percentages of the M-to-B-mode images that showed close contact between the probe and the luminal surface. Passively scanned M-to-B-mode images were qualitatively compared to B-mode images obtained by mechanical scanning OCT tethered capsule endomicroscopy (TCE) imaging devices.

RESULTS

The incorporation of M-mode OCT probes in these nonendoscopic GI devices safely and effectively enabled M-mode OCT imaging, facilitating real-time device placement guidance and contact sensing in vivo. Results showed that M-mode OCT contact sensing improved the variance of IPD measurements threefold and side-viewing probes increased M-to-B-mode image visibility by 10%. Images of the esophagus, stomach, and duodenum generated by the passively scanned probes and M-to-B-mode conversion were qualitatively superior to B-mode images obtained by mechanically scanning OCT TCE devices.

CONCLUSION

These results show that passive, single optical fiber OCT probes can be effectively utilized for nonendoscopic device placement guidance, device contact sensing, and two-dimensional morphologic imaging in the human GI tract in vivo. Due to their small size, lower cost, and reduced complexity, these M-mode OCT probes may provide an easier avenue for the incorporation of OCT functionality into endoscopic/nonendoscopic devices.

Expanding beyond endoscopy: A review of non-invasive modalities in Barrett’s esophagus screening and surveillance

Barrett’s esophagus (BE) is a condition that results from replacement of the damaged normal squamous esophageal mucosa to intestinal columnar mucosa and is the most significant predisposing factor for development of esophageal adenocarcinoma. Current guidelines recommend endoscopic evaluation for screening and surveillance based on various risk factors which has limitations such as invasiveness, availability of a trained specialist, patient logistics and cost. Trans-nasal endoscopy is a less invasive modality but still has similar limitations such as limited availability of trained specialist and costs. Non-endoscopic modalities, in comparison, require minimal intervention, can be done in an office visit and has the potential to be a more ideal choice for mass public screening and surveillance, particularly in patents at low risk for BE. These include newer generations of esophageal capsule endoscopy which provides direct visualization of BE, and tethered capsule endomicroscopy which can obtain high-resolution images of the esophagus. Various cell collection devices coupled with biomarkers have been used for BE screening. Cytosponge, in combination with TFF3, as well as EsophaCap and EsoCheck have shown promising results in various studies when used with various biomarkers. Other modalities including circulatory microRNAs and volatile organic compounds that have demonstrated favorable outcomes. Use of these cell collection methods for BE surveillance is a potential area of future research.

Human colorectal cancer tissue assessment using optical coherence tomography catheter and deep learning

Optical coherence tomography (OCT) can differentiate normal colonic mucosa from neoplasia, potentially offering a new mechanism of endoscopic tissue assessment and biopsy targeting, with a high optical resolution and an imaging depth of ~1 mm. Recent advances in convolutional neural networks (CNN) have enabled application in ophthalmology, cardiology, and gastroenterology malignancy detection with high sensitivity and specificity. Here, we describe a miniaturized OCT catheter and a residual neural network (ResNet)-based deep learning model manufactured and trained to perform automatic image processing and real-time diagnosis of the OCT images. The OCT catheter has an outer diameter of 3.8 mm, a lateral resolution of ~7 μm, and an axial resolution of ~6 μm. A customized ResNet is utilized to classify OCT catheter colorectal images. An area under the receiver operating characteristic (ROC) curve (AUC) of 0.975 is achieved to distinguish between normal and cancerous colorectal tissue images.

Feasibility and Safety of Tethered Capsule Endomicroscopy in Patients With Barrett's Esophagus in a Multi-Center Study

BACKGROUND & AIMS

Tethered capsule endomicroscopy (TCE) involves swallowing a small tethered pill that implements optical coherence tomography (OCT) imaging, procuring high resolution images of the whole esophagus. Here, we demonstrate and evaluate the feasibility and safety of TCE and a portable OCT imaging system in patients with Barrett's esophagus (BE) in a multi-center (5-site) clinical study.

METHODS

Untreated patients with BE as per endoscopic biopsy diagnosis were eligible to participate in the study. TCE procedures were performed in unsedated patients by either doctors or nurses. After the capsule was swallowed, the device continuously obtained 10-μm-resolution cross-sectional images as it traversed the esophagus. Following imaging, the device was withdrawn through mouth, and disinfected for subsequent reuse. BE lengths were compared to endoscopy findings when available. OCT-TCE images were compared to volumetric laser endomicroscopy (VLE) images from a patient who had undergone VLE on the same day as TCE.

RESULTS

147 patients with BE were enrolled across all sites. 116 swallowed the capsule (79%), 95/114 (83.3%) men and 21/33 (63.6%) women (P = .01). High-quality OCT images were obtained in 104/111 swallowers (93.7%) who completed the procedure. The average imaging duration was 5.55 ± 1.92 minutes. The mean length of esophagus imaged per patient was 21.69 ± 5.90 cm. A blinded comparison of maximum extent of BE measured by OCT-TCE and EGD showed a strong correlation (r = 0.77-0.79). OCT-TCE images were of similar quality to those obtained by OCT-VLE.

CONCLUSIONS

The capabilities of TCE to be used across multiple sites, be administered to unsedated patients by either physicians or nurses who are not expert in OCT-TCE, and to rapidly and safely evaluate the microscopic structure of the esophagus make it an emerging tool for screening and surveillance of BE patients. Clinical trial registry website and trial number: NCT02994693 and NCT03459339.

Optical coherence tomography

Optical coherence tomography (OCT) is a non-contact method for imaging the topological and internal microstructure of samples in three dimensions. OCT can be configured as a conventional microscope, as an ophthalmic scanner, or using endoscopes and small diameter catheters for accessing internal biological organs. In this Primer, we describe the principles underpinning the different instrument configurations that are tailored to distinct imaging applications and explain the origin of signal, based on light scattering and propagation. Although OCT has been used for imaging inanimate objects, we focus our discussion on biological and medical imaging. We examine the signal processing methods and algorithms that make OCT exquisitely sensitive to reflections as weak as just a few photons and that reveal functional information in addition to structure. Image processing, display and interpretation, which are all critical for effective biomedical imaging, are discussed in the context of specific applications. Finally, we consider image artifacts and limitations that commonly arise and reflect on future advances and opportunities.

Barrett's Esophagus: Diagnosis, Management, and Key Updates

Barrett's esophagus (BE) is the precursor lesion for esophageal adenocarcinoma (EAC) development. Unfortunately, BE screening/surveillance has not provided the anticipated EAC reduction benefit. Noninvasive techniques are increasingly available or undergoing testing to screen for BE among those with/without known risk factors, and the use of artificial intelligence platforms to aid endoscopic screening and surveillance will likely become routine, minimizing missed cases or lesions. Management of high-grade dysplasia and intramucosal EAC is clear with endoscopic eradication therapy preferred to surgery. BE with low-grade dysplasia can be managed with removal of visible lesions combined with endoscopic eradication therapy or endoscopic surveillance at present.

Innovations in Screening Tools for Barrett's Esophagus and Esophageal Adenocarcinoma

PURPOSE OF REVIEW

Esophageal adenocarcinoma (EAC) is a lethal disease with rapidly rising incidence. Screening for EAC and its metaplastic precursor, Barrett's esophagus (BE), followed by endoscopic surveillance and endoscopic treatment of dysplasia or early EAC are promising approaches to decreasing EAC incidence and EAC mortality. Historically, screening for EAC has been completed with a traditional per-oral esophagogastroduodenoscopy (EGD); however, this method has limitations including cost, tolerability, and accessibility. For this reason, much effort has been put forward to develop more effective, minimally invasive, and accessible BE and EAC screening tools. The purpose of this review is to describe recent developments of these novel tools.

RECENT FINDINGS

While endoscopic alternatives such as transnasal endoscopy are cheaper and well tolerated, they have not gained acceptance. Non-endoscopic modalities namely, swallowable cell collection devices coupled with biomarker analysis have been found to have excellent performance characteristics, tolerability, and cost effectiveness. In this article, we provide an update on innovative developments in EAC/BE screening modalities including transnasal endoscopy, capsule endomicroscopy, swallowable cell collection devices, and exhaled volatile organic compound analyses.

Minimally Invasive Image-Guided Gut Transport Function Measurement Probe

INTRODUCTION

Diseases such as celiac disease, environmental enteric dysfunction, infectious gastroenteritis, type II diabetes and inflammatory bowel disease are associated with increased gut permeability. Dual sugar absorption tests, such as the lactulose to rhamnose ratio (L:R) test, are the current standard for measuring gut permeability. Although easy to administer in adults, the L:R test has a number of drawbacks. These include an inability to assess for spatial heterogeneity in gut permeability that may distinguish different disease severity or pathology, additional sample collection for immunoassays, and challenges in carrying out the test in certain populations such as infants and small children. Here, we demonstrate a minimally invasive probe for real-time localized gut permeability evaluation through gut potential difference (GPD) measurement.

MATERIALS AND METHODS

The probe has an outer diameter of 1.2 mm diameter and can be deployed in the gut of unsedated subjects via a transnasal introduction tube (TNIT) that is akin to an intestinal feeding tube. The GPD probe consists of an Ag/AgCl electrode, an optical probe and a perfusion channel all housed within a transparent sheath. Lactated Ringer's (LR) solution is pumped through the perfusion channel to provide ionic contact between the electrodes and the gut lining. The optical probe captures non-scanning (M-mode) OCT images to confirm electrode contact with the gut lining. A separate skin patch probe is placed over an abraded skin area to provide reference for the GPD measurements. Swine studies were conducted to validate the GPD probe. GPD in the duodenum was modulated by perfusing 45 ml of 45 mM glucose.

RESULTS

GPD values of -13.1 ± 2.8 mV were measured in the duodenum across four swine studies. The change in GPD in the duodenum with the addition of glucose was -10.5 ± 2.4 mV (p < 0.001). M-mode OCT images provided electrode-tissue contact information, which was vital in ascertaining the probe's proximity to the gut mucosa.

CONCLUSION

We developed and demonstrated a minimally invasive method for investigating gastrointestinal permeability consisting of an image guided GPD probe that can be used in unsedated subjects.

Examination of Entire Gastrointestinal Tract: A Perspective of Mouth to Anus (M2A) Capsule Endoscopy

Capsule endoscopy (CE) is the only non-invasive diagnostic tool that enables the direct visualization of the gastrointestinal (GI) tract. Even though CE was initially developed for small-bowel investigation, its clinical application is expanding, and technological advances continue. The final iteration of CE will be a mouth to anus (M2A) capsule that investigates the entire GI tract by the ingestion of a single capsule. This narrative review describes the current developmental status of CE and discusses the possibility of realizing an M2A capsule and what needs to be overcome in the future.

Tethered capsule en face optical coherence tomography for imaging Barrett's oesophagus in unsedated patients

Objective

Barrett’s oesophagus (BE) screening outside the endoscopy suite can identify patients for surveillance and reduce mortality. Tethered capsule optical coherence tomography (OCT) can volumetrically image oesophageal mucosa in unsedated patients and detect features of BE. We investigated ultrahigh-speed tethered capsule swept-source OCT (SS-OCT), improved device design, developed procedural techniques and measured capsule contact, longitudinal pullback non-uniformity and patient toleration.

Design

OCT was performed in 16 patients prior to endoscopic surveillance/treatment. Unsedated patients swallowed the capsule with sips of water and the tether was pulled back to image the oesophagus. SS-OCT at 1 000 000 A-scans/s enabled imaging 10 cm oesophageal lengths in 10 s with 30 µm transverse and 8 µm axial resolution. Capsule contact, longitudinal image coverage and patient toleration were assessed.

Results

Nine patients had non-dysplastic BE, three had ablative treatment-naïve neoplasia and four had prior ablation for dysplasia. Dry swallows facilitated capsule transit through the lower oesophageal sphincter (LES), and waiting 10 s before pullback reduced swallow induced LES relaxation. Slow nasal inhalation facilitated capsule retrieval and minimised gag reflex. The procedure was well tolerated. Ultrahigh-speed SS-OCT generated cross-sectional and subsurface en face images showing BE features, while subsurface en face images were required to assess the gastro-oesophageal junction. Candidate features of dysplasia were also identified which could inform follow-up endoscopy/biopsy. BE features were seen in all patients with histologically confirmed BE. Mean capsule contact over BE was 75%±27% for all patients and better in short segment BE. Mean longitudinal image coverage over BE was 59%±34% and better for long segment BE.

Conclusions

Ultrahigh-speed tethered capsule SS-OCT can image en face and cross-sectional mucosal features over wide areas. Device and procedure optimisation improved performance. BE features could be identified in all patients, but limited capsule contact and longitudinal coverage could cause sampling errors for focal pathologies.

Dual-modality optical coherence tomography and fluorescence tethered capsule endomicroscopy

OCT tethered capsule endomicroscopy (TCE) is an emerging noninvasive diagnostic imaging technology for gastrointestinal (GI) tract disorders. OCT measures tissue reflectivity that provides morphologic image contrast, and thus is incapable of ascertaining molecular information that can be useful for improving diagnostic accuracy. Here, we introduce an extension to OCT TCE that includes a fluorescence (FL) imaging channel for attaining complementary, co-registered molecular contrast. We present the development of an OCT-FL TCE capsule and a portable, plug-and-play OCT-FL imaging system. The technology is validated in phantom experiments and feasibility is demonstrated in a methylene blue (MB)-stained swine esophageal injury model, ex vivo and in vivo.

A review of low-cost and portable optical coherence tomography

Optical coherence tomography (OCT) is a powerful optical imaging technique capable of visualizing the internal structure of biological tissues at near cellular resolution. For years, OCT has been regarded as the standard of care in ophthalmology, acting as an invaluable tool for the assessment of retinal pathology. However, the costly nature of most current commercial OCT systems has limited its general accessibility, especially in low-resource environments. It is therefore timely to review the development of low-cost OCT systems as a route for applying this technology to population-scale disease screening. Low-cost, portable and easy to use OCT systems will be essential to facilitate widespread use at point of care settings while ensuring that they offer the necessary imaging performances needed for clinical detection of retinal pathology. The development of low-cost OCT also offers the potential to enable application in fields outside ophthalmology by lowering the barrier to entry. In this paper, we review the current development and applications of low-cost, portable and handheld OCT in both translational and research settings. Design and cost-reduction techniques are described for general low-cost OCT systems, including considerations regarding spectrometer-based detection, scanning optics, system control, signal processing, and the role of 3D printing technology. Lastly, a review of clinical applications enabled by low-cost OCT is presented, along with a detailed discussion of current limitations and outlook.

Understanding the role of the gut in undernutrition: what can technology tell us?

Gut function remains largely underinvestigated in undernutrition, despite its critical role in essential nutrient digestion, absorption and assimilation. In areas of high enteropathogen burden, alterations in gut barrier function and subsequent inflammatory effects are observable but remain poorly characterised. Environmental enteropathy (EE)-a condition that affects both gut morphology and function and is characterised by blunted villi, inflammation and increased permeability-is thought to play a role in impaired linear growth (stunting) and severe acute malnutrition. However, the lack of tools to quantitatively characterise gut functional capacity has hampered both our understanding of gut pathogenesis in undernutrition and evaluation of gut-targeted therapies to accelerate nutritional recovery. Here we survey the technology landscape for potential solutions to improve assessment of gut function, focussing on devices that could be deployed at point-of-care in low-income and middle-income countries (LMICs). We assess the potential for technological innovation to assess gut morphology, function, barrier integrity and immune response in undernutrition, and highlight the approaches that are currently most suitable for deployment and development. This article focuses on EE and undernutrition in LMICs, but many of these technologies may also become useful in monitoring of other gut pathologies.

Smartphone-based multimodal tethered capsule endoscopic platform for white-light, narrow-band, and fluorescence/autofluorescence imaging

Multimodal low-cost endoscopy is highly desirable in poor resource settings such as in developing nations. In this work, we developed a smartphone-based low-cost, reusable tethered capsule endoscopic platform that allows white-light, narrowband, and fluorescence/autofluorescence imaging of the esophagus. The ex-vivo studies of swine esophagus were performed and compared with a commercial endoscope to test the white-light imaging capabilities of the endoscope. The efficacy of the capsule for narrow-band imaging was tested by imaging the vascularization of the tongue. To determine the autofluorescence/fluorescence capability of the endoscope, fluorescein dye with different concentrations was imaged. Furthermore, swine esophagus injected with fluorescein dye was imaged using the fluorescence/autofluorescence and the white-light imaging modules, ex-vivo. The overall cost of the capsules is approximately 12 €, 15 €, and 42 € for the white light imaging, the narrow-band imaging, and the fluorescence/autofluorescence imaging respectively. In addition, the cost of the laser source module required for the narrow-band imaging and the fluorescence/autofluorescence imaging is approximately 218 €. This device will open the possibility of imaging the esophagus in underprivileged areas.

Correction of circumferential and longitudinal motion distortion in high-speed catheter/endoscope-based optical coherence tomography

Catheter/endoscope-based optical coherence tomography (OCT) is a powerful modality that visualizes structural information in luminal organs. Increases in OCT speed have reduced motion artifacts by enabling acquisition faster than or comparable to the time scales of physiological motion. However motion distortion remains a challenge because catheter/endoscope OCT imaging involves both circumferential and longitudinal scanning of tissue. This paper presents a novel image processing method to estimate and correct motion distortion in both the circumferential and longitudinal directions using a single en face image from a volumetric data set. The circumferential motion distortion is estimated and corrected using the en face image. Then longitudinal motion distortion is estimated and corrected using diversity of image features along the catheter pullback direction. Finally, the OCT volume is resampled and motion corrected. Results are presented on synthetic images and clinical OCT images of the human esophagus.

Advanced Imaging and Sampling in Barrett's Esophagus: Artificial Intelligence to the Rescue?

Because the current Barrett's esophagus (BE) surveillance protocol suffers from sampling error of random biopsies and a high miss-rate of early neoplastic lesions, many new endoscopic imaging and sampling techniques have been developed. None of these techniques, however, have significantly increased the diagnostic yield of BE neoplasia. In fact, these techniques have led to an increase in the amount of visible information, yet endoscopists and pathologists inevitably suffer from variations in intra- and interobserver agreement. Artificial intelligence systems have the potential to overcome these endoscopist-dependent limitations.

Progress in Screening for Barrett's Esophagus: Beyond Standard Upper Endoscopy

The rapid increase in the incidence of esophageal adenocarcinoma in Western populations over the past 4 decades and its associated poor prognosis, unless detected early has generated great interest in screening for the precursor lesion Barrett's esophagus (BE). Recently, there have been significant developments in imaging-based modalities and esophageal cell-sampling devices coupled with biomarker assays. In this review, the authors discuss the rationale for screening for BE and the factors to consider for targeting the at-risk population. They also explore future avenues for research in this area.

Advanced endoscopic imaging for detecting and guiding therapy of early neoplasias of the esophagus

Esophageal cancers, largely adenocarcinoma in Western countries and squamous cell cancer in Asia, present a significant burden of disease and remain one of the most lethal of cancers. Key to improving survival is the development and adoption of new imaging modalities to identify early neoplastic lesions, which may be small, multifocal, subsurface, and difficult to detect by standard endoscopy. Such advanced imaging is particularly relevant with the emergence of ablative techniques that often require multiple endoscopic sessions and may be complicated by bleeding, pain, strictures, and recurrences. Assessing the specific location, depth of involvement, and features correlated with neoplastic progression or incomplete treatment may optimize treatments. While not comprehensive of all endoscopic imaging modalities, we review here some of the recent advances in endoscopic luminal imaging, particularly with surface contrast enhancement using virtual chromoendoscopy, highly magnified subsurface imaging with confocal endomicroscopy, optical coherence tomography, elastic scattering spectroscopy, angle-resolved low-coherence interferometry, and light scattering spectroscopy. While there is no single ideal imaging modality, various multimodal instruments are also being investigated. The future of combining computer-aided assessments, molecular markers, and improved imaging technologies to help localize and ablate early neoplastic lesions shed hope for improved disease outcome.

Real-time colorectal cancer diagnosis using PR-OCT with deep learning

Prior reports have shown optical coherence tomography (OCT) can differentiate normal colonic mucosa from neoplasia, potentially offering an alternative technique to endoscopic biopsy - the current gold-standard colorectal cancer screening and surveillance modality. To help clinical translation limited by processing the large volume of generated data, we designed a deep learning-based pattern recognition (PR) OCT system that automates image processing and provides accurate diagnosis potentially in real-time. Method: OCT is an emerging imaging technique to obtain 3-dimensional (3D) "optical biopsies" of biological samples with high resolution. We designed a convolutional neural network to capture the structure patterns in human colon OCT images. The network is trained and tested using around 26,000 OCT images acquired from 20 tumor areas, 16 benign areas, and 6 other abnormal areas. Results: The trained network successfully detected patterns that identify normal and neoplastic colorectal tissue. Experimental diagnoses predicted by the PR-OCT system were compared to the known histologic findings and quantitatively evaluated. A sensitivity of 100% and specificity of 99.7% can be reached. Further, the area under the receiver operating characteristic (ROC) curves (AUC) of 0.998 is achieved. Conclusions: Our results demonstrate that PR-OCT can be used to give an accurate real-time computer-aided diagnosis of colonic neoplastic mucosa. Future development of this system as an "optical biopsy" tool to assist doctors in real-time for early mucosal neoplasms screening and treatment evaluation following initial oncologic therapy is planned.

Understanding optical reflectance contrast for real-time characterization of epithelial precursor lesions

Detecting early-stage epithelial cancers and their precursor lesions are challenging as lesions could be subtle and focally or heterogeneously distributed over large mucosal areas. Optical coherence tomography (OCT) that enables wide-field imaging of subsurface microstructures in vivo is a promising screening tool for epithelial diseases. However, its diagnostic capability has not been fully appreciated since the optical reflectance contrast is poorly understood. We investigated the back-scattered intensities from clustered or packed nanometer scale intracellular scatterers using finite-difference time-domain method and 1-μm resolution form of OCT, and uncovered that there existed correlations between the reflectance contrasts and the ultrastructural clustering or packing states of these scatterers, which allows us to interpret the physiological state of the cells. Specifically, both polarized goblet cells and foveolar cells exhibited asymmetric reflectance contrast, but they could be differentiated by the optical intensity of the mucin cup due to the different ultrastructural make-ups of the mucin granules; keratinocytes could demonstrate varied cytoplasmic intensity and their cytoplasmic contrast was closely correlated with the packing state of keratin filaments. Further preliminary study demonstrated that these new understandings of OCT image contrast enables the characterization of precancerous lesions, which could complement the current morphology-based criteria in realizing "virtual histology" and would have a profound impact for the screening and surveillance of epithelial cancers.

Contrast of nuclei in stratified squamous epithelium in optical coherence tomography images at 800 nm

Imaging nuclei of keratinocytes in the stratified squamous epithelium has been a subject of intense research since nucleus associated cellular atypia is the key criteria for the screening and diagnosis of epithelial cancers and their precursors. However, keratinocyte nuclei have been reported to be either low scattering or high scattering, so that these inconsistent reports might have led to misinterpretations of optical images, and more importantly, hindered the establishment of optical diagnostic criteria. We disclose that they are generally low scattering in the core using Micro-optical coherence tomography (μOCT) of 1.28-μm axial resolution in vivo; those previously reported "high scattering" or "bright" signals from nuclei are likely from the nucleocytoplasmic boundary, and the low-scattering nuclear cores were missed possibly due to insufficient axial resolutions (~4μm). It is further demonstrated that the high scattering signals may be associated with flattening of nuclei and cytoplasmic glycogen accumulation, which are valuable cytologic hallmarks of cell maturation.

Novel Screening Tests for Barrett's Esophagus

PURPOSE OF REVIEW

There has been an exponential increase in the incidence of esophageal adenocarcinoma (EAC) over the last half century. Barrett's esophagus (BE) is the only known precursor lesion of EAC. Screening for BE in high-risk populations has been advocated with the aim of identifying BE, followed by endoscopic surveillance to detect dysplasia and early stage cancer, with the intent that treatment can improve outcomes. We aimed to review BE screening methodologies currently recommended and in development.

RECENT FINDINGS

Unsedated transnasal endoscopy allows for visualization of the distal esophagus, with potential for biopsy acquisition, and can be done in the office setting. Non-endoscopic screening methods being developed couple the use of swallowable esophageal cell sampling devices with BE specific biomarkers, as well as trefoil factor 3, methylated DNA markers, and microRNAs. This approach has promising accuracy. Circulating and exhaled volatile organic compounds and the foregut microbiome are also being explored as means of detecting EAC and BE in a non-invasive manner. Non-invasive diagnostic techniques have shown promise in the detection of BE and may be effective methods of screening high-risk patients.

Evolving screening and surveillance techniques for Barrett's esophagus

Barrett’s esophagus (BE) is a change in the esophageal lining and is known to be the major precursor lesion for most cases of esophageal adenocarcinoma (EAC). Despite an understanding of its association with BE for many years and the falling incidence rates of squamous cell carcinoma of the esophagus, the incidence for EAC continues to rise exponentially. In association with this rising incidence, if the delay in diagnosis of EAC occurs after the onset of symptoms, then the mortality at 5 years is greater than 80%. Appropriate diagnosis and surveillance strategies are therefore vital for BE. Multiple novel optical technologies and other advanced approaches are being utilized to assist in making screening and surveillance more cost effective. We review the current guidelines and evolving techniques that are currently being evaluated.

Optical coherence tomography-guided laser marking with tethered capsule endomicroscopy in unsedated patients

Tethered capsule endomicroscopy (TCE) is an emerging screening technology that comprehensively obtains microstructural OCT images of the gastrointestinal (GI) tract in unsedated patients. To advance clinical adoption of this imaging technique, it will be important to validate TCE images with co-localized histology, the current diagnostic gold standard. One method for co-localizing OCT images with histology is image-targeted laser marking, which has previously been implemented using a driveshaft-based, balloon OCT catheter, deployed during endoscopy. In this paper, we present a TCE device that scans and targets the imaging beam using a low-cost stepper motor that is integrated inside the capsule. In combination with a 4-laser-diode, high power 1430/1450 nm marking laser system (800 mW on the sample and 1s pulse duration), this technology generated clearly visible marks, with a spatial targeting accuracy of better than 0.5 mm. A laser safety study was done on swine esophagus ex vivo, showing that these exposure parameters did not alter the submucosa, with a large, 4-5x safety margin. The technology was demonstrated in living human subjects and shown to be effective for co-localizing OCT TCE images to biopsies obtained during subsequent endoscopy.

Application of optical coherence tomography in clinical diagnosis

BACKGROUND

Optical coherence tomography (OCT) is a non-invasive diagnosing tool used in clinics. Due to its high resolution (<10um), it is appropriate for the early detection of tiny infections. It has been widely used in diagnosis and treatment of diseases, evaluation of therapeutic efficacy, and monitoring of various physiological and pathological processes.

OBJECTIVE

To systemically review literature to summarize the clinic application of OCT in recent years.

METHODS

For clinic applications that OCT has been applied, we selected studies that describe the most relevant works. The discussion included: 1) which tissue could be used in the OCT detection, 2) which character of different tissue could be used as diagnosing criteria, 3) which diseases and pathological process have been diagnosed or monitored using OCT imaging, and 4) the recent development of clinic OCT diagnosing.

RESULTS

The literature showed that the OCT had been listed as a routine test choice for ophthalmic diseases, while the first commercial product for cardiovascular OCT detection had gotten clearance. Meanwhile, as the development of commercial benchtop OCT equipment and tiny fiber probe, the commercial application of OCT in dermatology, dentistry, gastroenterology and urology also had great potential in the near future.

CONCLUSIONS

The analysis and discussions showed that OCT, as an optical diagnosing method, has been used successfully in many clinical fields, and has the potential to be a standard inspection method in several clinic fields, such as dermatology, dentistry and cardiovascular.