High-resolution cross-sectional imaging of the gastrointestinal tract using optical coherence tomography: preliminary results

Simultaneous photoacoustic and ultrasound imaging: A review

Photoacoustic imaging (PAI) is an emerging biomedical imaging technique that combines the advantages of optical and ultrasound imaging, enabling the generation of images with both optical resolution and acoustic penetration depth. By leveraging similar signal acquisition and processing methods, the integration of photoacoustic and ultrasound imaging has introduced a novel hybrid imaging modality suitable for clinical applications. Photoacoustic-ultrasound imaging allows for non-invasive, high-resolution, and deep-penetrating imaging, providing a wealth of image information. In recent years, with the deepening research and the expanding biomedical application scenarios of photoacoustic-ultrasound bimodal systems, the immense potential of photoacoustic-ultrasound bimodal imaging in basic research and clinical applications has been demonstrated, with some research achievements already commercialized. In this review, we introduce the principles, technical advantages, and biomedical applications of photoacoustic-ultrasound bimodal imaging techniques, specifically focusing on tomographic, microscopic, and endoscopic imaging modalities. Furthermore, we discuss the future directions of photoacoustic-ultrasound bimodal imaging technology.

First interobserver agreement of optical coherence tomography in the bile duct: A multicenter collaborative study

Background and study aims  Optical coherence tomography (OCT) is a new technology available for evaluation of indeterminate biliary strictures. It allows under-the-surface visualization and preliminary studies have confirmed standardized characteristics associated with malignancy. The aim of this study is to evaluate the first interobserver agreement in identifying previously agreed upon OCT criteria and diagnosing of malignant versus benign disease. Patients and methods  Fourteen endoscopists were asked to review an atlas of reference clips and images of eight criteria derived from expert consensus A total of 35 de-identified video clips were then evaluated for presence of the eight criteria and for final diagnosis of malignant versus benign using the atlas as reference Intraclass correlation (ICC) analysis was done to evaluate interrater agreement. Results  Clips of 23 malignant lesions and 12 benign lesions were scored. Excellent interobserver agreement was seen with dilated hypo-reflective structures (0.85) and layering effacement (0.89); hyper-glandular mucosa (0.76), intact layering (0.81), and onion-skin layering (0.77); fair agreement was seen with scalloping (0.58), and thickened epithelium (0.4); poor agreement was seen with hyper-reflective surface (0.36). The diagnostic ICC for both neoplastic (0.8) and non-neoplastic (0.8) was excellent interobserver agreement. The overall diagnostic accuracy was 51 %, ranging from 43 % to 60 %. Conclusions  Biliary OCT is a promising new modality for evaluation of indeterminate biliary strictures. Interobserver agreement ranged from fair to almost perfect on eight previously identified criteria. Interobserver agreement for malignancy diagnosis was substantial (0.8). Further studies are needed to validate this data.

Automatic correction of the initial rotation angle error improves 3D reconstruction in endoscopic airway optical coherence tomography

Endoscopic airway optical coherence tomography (OCT) is an advanced imaging modality capable of capturing the internal anatomy and geometry of the airway. Due to fiber-optic catheter bending and friction, the rotation speed of the endoscopic probe is usually non-uniform: at each B-scan image, the initial rotation angle of the probe is easily misaligned with that of the previous slices. During the pullback operation, this initial rotation angle error (IRAE) will be accumulated and will result in distortion and deformation of the reconstructed 3D airway structure. Previous attempts to correct this error were mainly manual corrections, which are time-consuming and suffered from observer variation. In this paper, we present a method to correct the IRAE for anatomically improved visualization of the airway. Our method derived the rotation angular difference of adjacent B-scans by measuring their contour similarity and then tracks the IRAE by formulating its continuous drift as a graph-based problem. The algorithm was tested on a simulated airway contour dataset, and also on experimental datasets acquired by two different long range endoscopic airway OCT platforms. Effective and smooth compensation of the frame-by-frame initial angle difference was achieved. Our method has real-time capability and thus has the potential to improve clinical imaging efficiency.

Optical coherence tomography of small intestine allograft biopsies using a handheld surgical probe

SIGNIFICANCE

The current gold standard for monitoring small intestinal transplant (IT) rejection is endoscopic visual assessment and biopsy of suspicious lesions; however, these lesions are only superficially visualized by endoscopy. Invasive biopsies provide a coarse sampling of tissue health without depicting the true presence and extent of any pathology. Optical coherence tomography (OCT) presents a potential alternative approach with significant advantages over traditional white-light endoscopy.

AIM

The aim of our investigation was to evaluate OCT performance in distinguishing clinically relevant morphological features associated with IT graft failure.

APPROACH

OCT was applied to evaluate the small bowel tissues of two rhesus macaques that had undergone IT of the ileum. The traditional assessment from routine histological observation was compared with OCT captured using a handheld surgical probe during the days post-transplant and subsequently was compared with histophaology.

RESULTS

The reported OCT system was capable of identifying major biological landmarks in healthy intestinal tissue. Following IT, one nonhuman primate (NHP) model suffered a severe graft ischemia, and the second NHP graft failed due to acute cellular rejection. OCT images show visual evidence of correspondence with histological signs of IT rejection.

CONCLUSIONS

Results suggest that OCT imaging has significant potential to reveal morphological changes associated with IT rejection and to improve patient outcomes overall.

Optical coherence tomography for the early detection of colorectal dysplasia and cancer: validation in a murine model

BACKGROUND

There is an urgent need to develop a non-invasive imaging technique for detecting colorectal dysplasia and cancer. Technology for early and real-time microscopic assessments to select the most representative biopsy sites would also be of clinical value. In this study, we explored the sensitivity of optical coherence tomography (OCT) in detecting local lesions to demonstrate its potential for the early detection of colorectal dysplasia and cancer.

METHODS

An azoxymethane/dextran sodium sulfate mouse model of colorectal carcinogenesis was utilized. Mice were imaged by OCT, and colorectal tissue sections were observed with hematoxylin and eosin staining. The results of the parallel analyses were compared to evaluate the performance of OCT in imaging and early screening of colorectal lesions.

RESULTS

Dysplasia and cancer could be distinguished from normal colon tissues based on the OCT images. However, simple morphological changes observed in the OCT images were not sufficient to distinguish different degrees of dysplasia or distinguish dysplasia from cancerous tissues. The Youden index and diagnostic efficiency of OCT for colorectal dysplasia and cancer were 62.50% and 82.14%, respectively, while the sensitivity and specificity were 87.50% and 75.00%, respectively. Further, the positive and negative predictive values were 82.35% and 81.82%, respectively.

CONCLUSIONS

Based on our findings, we predict that OCT is a promising non-invasive imaging technique that can offer excellent positive detection rates and diagnostic accuracy for early colorectal dysplasia and cancer. This technique is expected to be valuable in realizing real-time qualitative analysis and guided targeted biopsy.

Towards an Optical Biopsy during Visceral Surgical Interventions

Background

Cancer will replace cardiovascular diseases as the most frequent cause of death. Therefore, the goals of cancer treatment are prevention strategies and early detection by cancer screening and ideal stage therapy. From an oncological point of view, complete tumor resection is a significant prognostic factor. Optical coherence tomography (OCT) and confocal laser microscopy (CLM) are two techniques that have the potential to complement intraoperative frozen section analysis as in vivo and real-time optical biopsies.

Summary

In this review we present both procedures and review the progress of evaluation for intraoperative application in visceral surgery. For visceral surgery, there are promising studies evaluating OCT and CLM; however, application during routine visceral surgical interventions is still lacking.

Key Message

OCT and CLM are not competing but complementary approaches of tissue analysis to intraoperative frozen section analysis. Although intraoperative application of OCT and CLM is at an early stage, they are two promising techniques of intraoperative in vivo and real-time tissue examination. Additionally, deep learning strategies provide a significant supplement for automated tissue detection.

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

BACKGROUND AND AIMS

Patients with many different digestive diseases undergo repeated EGDs throughout their lives. Tethered capsule endomicroscopy (TCE) is a less-invasive method for obtaining high-resolution images of the GI mucosa for diagnosis and treatment planning of GI tract diseases. In this article, we present our results from a single-center study aimed at testing the safety and feasibility of TCE for imaging the esophagus, stomach, and duodenum.

METHODS

After being swallowed by a participant without sedation, the tethered capsule obtains cross-sectional, 10 μm-resolution, optical coherence tomography images as the device traverses the alimentary tract. After imaging, the device is withdrawn through the mouth, disinfected, and reused. Safety and feasibility of TCE were tested, focusing on imaging the esophagus of healthy volunteers and patients with Barrett's esophagus (BE) and the duodenum of healthy volunteers. Images were compared with endoscopy and histopathology findings when available.

RESULTS

Thirty-eight patients were enrolled. No adverse effects were reported. The TCE device swallowing rate was 34 of 38 (89%). The appearance of a physiologic upper GI wall, including its microscopic pathology, was visualized with a tissue coverage of 85.4% ± 14.9% and 90.3% ± 6.8% in the esophagus of BE patients with and without endoscopic evidence of a hiatal hernia, respectively, as well as 84.8% ± 7.4% in the duodenum. A blinded comparison of TCE and endoscopic BE measurements showed a strong to very strong correlation (r = 0.7-0.83; P < .05) for circumferential extent and a strong correlation (r = 0.77-0.78; P < .01) for maximum extent (Prague classification). TCE interobserver correlation was very strong, at r = 0.92 and r = 0.84 (P < .01), for Prague classification circumferential (C) and maximal (M) length measurements, respectively.

CONCLUSIONS

TCE is a safe and feasible procedure for obtaining high-resolution microscopic images of the upper GI tract without endoscopic assistance or sedation.

Feasibility of using optical coherence tomography to detect radiation-induced fibrosis and residual cancer extent after neoadjuvant chemo-radiation therapy: an ex vivo study

Treatment of resectable esophageal cancer includes neoadjuvant chemo-radiation therapy (nCRT) followed by esophagectomy in operable patients. High-risk surgery may have been avoided in patients with a pathological complete response (pCR). We investigated the feasibility of optical coherence tomography (OCT) to detect residual cancer and radiation-induced fibrosis in 10 esophageal cancer patients that underwent nCRT followed by esophagectomy. We compared our OCT findings with histopathology. Overall, OCT was able to differentiate between healthy tissue, fibrotic tissue, and residual cancer with a sensitivity and specificity of 79% and 67%, respectively. Hence, OCT has the potential to add to the assessment of a pCR.

Review of optical coherence tomography in oncology

The application of optical coherence tomography (OCT) in the field of oncology has been prospering over the past decade. OCT imaging has been used to image a broad spectrum of malignancies, including those arising in the breast, brain, bladder, the gastrointestinal, respiratory, and reproductive tracts, the skin, and oral cavity, among others. OCT imaging has initially been applied for guiding biopsies, for intraoperatively evaluating tumor margins and lymph nodes, and for the early detection of small lesions that would often not be visible on gross examination, tasks that align well with the clinical emphasis on early detection and intervention. Recently, OCT imaging has been explored for imaging tumor cells and their dynamics, and for the monitoring of tumor responses to treatments. This paper reviews the evolution of OCT technologies for the clinical application of OCT in surgical and noninvasive interventional oncology procedures and concludes with a discussion of the future directions for OCT technologies, with particular emphasis on their applications in oncology.

Clinical applications of optical coherence tomography in urology

Since optical coherence tomography (OCT) was first demonstrated in 1991, it has advanced significantly in technical aspects such as imaging speed and resolution, and has been clinically demonstrated in a diverse set of medical and surgical applications, including ophthalmology, cardiology, gastroenterology, dermatology, oncology, among others. This work reviews current clinical applications in urology, particularly in bladder, urether, and kidney. Clinical applications in bladder and urether mainly focus on cancer detection and staging based on tissue morphology, image contrast, and OCT backscattering. The application in kidney includes kidney cancer detection based on OCT backscattering attenuation and non-destructive evaluation of transplant kidney viability or acute tubular necrosis based on both tissue morphology from OCT images and function from Doppler OCT (DOCT) images. OCT holds the promise to positively impact the future clinical practices in urology.

Barrett's esophagus: review of diagnosis and treatment

Barrett's esophagus (BE) is an acquired condition characterized by replacement of stratified squamous epithelium by a cancer predisposing metaplastic columnar epithelium. Endoscopy with systemic biopsy protocols plays a vital role in diagnosis. Technological advancements in dysplasia detection improves outcomes in surveillance and treatment of patients with BE and dysplasia. These advances in endoscopic technology radically changed the treatment for dysplastic BE and early cancer from being surgical to organ-sparing endoscopic therapy. A multimodal treatment approach combining endoscopic resection of visible and/or raised lesions with ablation techniques for flat BE mucosa, followed by long-term surveillance improves the outcomes of BE. Safe and effective endoscopic treatment can be either tissue acquiring as in endoscopic mucosal resection and endoscopic submucosal dissection or tissue ablative as with photodynamic therapy, radiofrequency ablation and cryotherapy. Debatable issues such as durability of response, recognition and management of sub-squamous BE and optimal management strategy in patients with low-grade dysplasia and non-dysplastic BE need to be studied further. Development of safer wide field resection techniques, which would effectively remove all BE and obviate the need for long-term surveillance, is another research goal. Shared decision making between the patient and physician is important while considering treatment for dysplasia in BE.

Barrett's esophagus: A review of diagnostic criteria, clinical surveillance practices and new developments

Barrett's esophagus is defined by metaplastic glandular changes to the distal esophagus and is linked to an increased risk of esophageal adenocarcinoma. Controversy exists whether the definition should be limited to intestinal type glands with goblet cells or should be expanded to include non-goblet cell columnar epithelium. Barrett's esophagus may be asymptomatic in a large proportion of the population but screening should be considered for those with certain clinical findings. The diagnosis of Barrett's should be based on the combination of careful endoscopic evaluation and histologic review of the biopsy material. Continued surveillance biopsies may be necessary in cases of indeterminate or low grade dysplasia. Clinical follow-up of patients with high grade dysplasia should be tailored to the individual patient. Development of newer endoscopy techniques including chemoendoscopy, chromoendoscopy and use of biomarkers on frozen tissue have shown some promise of identifying patients at risk for malignancy.

Endoscopic retrograde cholangioscopy and advanced biliary imaging

Developments in endoscopic retrograde cholangioscopy provide multiple new advanced methods of biliary imaging. Cholangioscopy provides direct visualization of epithelium with white light as well as advanced modalities, such as narrow band imaging and autofluorescence. In vivo histologic images can be achieved with confocal endomicroscopy. Cross-sectional imaging is also possible with intraductal ultrasonography and optical coherence tomography. This article describes these advanced imaging techniques, which can be used together to assist in the diagnosis of biliary strictures and lesions.

Optical coherence tomography-based freeze-drying microscopy

A new type of freeze-drying microscope based upon time-domain optical coherence tomography is presented here (OCT-FDM). The microscope allows for real-time, in situ 3D imaging of pharmaceutical formulations in vials relevant for manufacturing processes with a lateral resolution of <7 μm and an axial resolution of <5 μm. Correlation of volumetric structural imaging with product temperature measured during the freeze-drying cycle allowed investigation of structural changes in the product and determination of the temperature at which the freeze-dried cake collapses. This critical temperature is the most important parameter in designing freeze-drying processes of pharmaceutical products.

Endoscopic management of Barrett esophagus

Endoscopy has a vital role in the diagnosis, screening, surveillance and treatment of Barrett esophagus. Over the past few decades, tremendous advances have been made in endoscopic technology, and the management of dysplasia and early cancer in Barrett esophagus has changed radically from being surgical to organ-sparing endoscopic therapy. Proper endoscopic techniques and systematic biopsy protocols improve dysplasia detection, and endoscopic surveillance improves outcomes in patients with Barrett esophagus and dysplasia. Endoscopic treatment can be tissue acquiring (as in endoscopic mucosal resection and endoscopic submucosal dissection) or ablative (as with photodynamic therapy, radiofrequency ablation and cryotherapy). Treatment is usually multimodal, combining endoscopic resection of visible lesions with one or more mucosal ablation techniques, followed by long-term surveillance. Such treatment is safe and effective. Shared decision-making between the patient and physician is important while considering treatment for dysplasia in Barrett esophagus. Issues such as durability of response, importance of subsquamous Barrett epithelium and the optimal management strategy in patients with low-grade dysplasia and nondysplastic Barrett esophagus need to be studied further. Development of safer wide-field resection techniques, which would effectively remove all Barrett esophagus and obviate the need for long-term surveillance, is needed.

Optical coherence tomography: fundamental principles, instrumental designs and biomedical applications

The advances made in the last two decades in interference technologies, optical instrumentation, catheter technology, optical detectors, speed of data acquisition and processing as well as light sources have facilitated the transformation of optical coherence tomography from an optical method used mainly in research laboratories into a valuable tool applied in various areas of medicine and health sciences. This review paper highlights the place occupied by optical coherence tomography in relation to other imaging methods that are used in medical and life science areas such as ophthalmology, cardiology, dentistry and gastrointestinal endoscopy. Together with the basic principles that lay behind the imaging method itself, this review provides a summary of the functional differences between time-domain, spectral-domain and full-field optical coherence tomography, a presentation of specific methods for processing the data acquired by these systems, an introduction to the noise sources that plague the detected signal and the progress made in optical coherence tomography catheter technology over the last decade.

Multimodality approach to optical early detection and mapping of oral neoplasia

Early detection of cancer remains the best way to ensure patient survival and quality of life. Squamous cell carcinoma is usually preceded by dysplasia presenting as white, red, or mixed red and white epithelial lesions on the oral mucosa (leukoplakia, erythroplakia). Dysplastic lesions in the form of erythroplakia can carry a risk for malignant conversion of 90%. A noninvasive diagnostic modality would enable monitoring of these lesions at regular intervals and detection of treatment needs at a very early, relatively harmless stage. The specific aim of this work was to test a multimodality approach [three-dimensional optical coherence tomography (OCT) and polarimetry] to noninvasive diagnosis of oral premalignancy and malignancy using the hamster cheek pouch model (nine hamsters). The results were compared to tissue histopathology. During carcinogenesis, epithelial down grow, eventual loss of basement membrane integrity, and subepithelial invasion were clearly visible with OCT. Polarimetry techniques identified a four to five times increased retardance in sites with squamous cell carcinoma, and two to three times greater retardance in dysplastic sites than in normal tissues. These techniques were particularly useful for mapping areas of field cancerization with multiple lesions, as well as lesion margins.

Endoscopically guided spectral-domain OCT with double-balloon catheters

Fourier-domain optical coherence tomography (OCT) and balloon-based catheters have furthered the potential of OCT as a real-time surveillance tool for Barrett's esophagus (BE). However, a balloon catheter, which expands the esophagus and centers the catheter, applies direct pressure on the esophagus. This may affect the tissue appearance and the ability to detect dysplasia in BE. To study this effect, we propose a double-balloon catheter to allow imaging with and without balloon-tissue contact. A system design based on a spectral-domain OCT platform is reported and validated by acquisition of high quality, volumetric images of swine esophagus in vivo.

Potential of optical coherence tomography for early diagnosis of oral malignancies

With nearly 1,500,000 new patients diagnosed every year in the USA, cancer poses a considerable challenge to healthcare today. Oral cancer is responsible for a sizeable portion of deaths due to cancer, primarily because it is diagnosed at a late stage when the prognosis is poor. Current methods for diagnosing oral cancer need to be augmented by better early detection, monitoring and screening modalities. A new approach is needed that provides real-time, accurate, noninvasive diagnosis. The results of early clinical trials using in vivo optical coherence tomography for the diagnosis of oral dysplasia and malignancy are encouraging.

Imaging of subsquamous Barrett's epithelium with ultrahigh-resolution optical coherence tomography: a histologic correlation study

BACKGROUND

Optical coherence tomography (OCT) is being developed as a potentially valuable method for high-resolution cross-sectional imaging of the esophageal mucosal and submucosal layers. One potential application of OCT imaging is to identify subsquamous Barrett's epithelium in patients who have undergone ablative therapy, which is not visible on standard endoscopic examination. However, histologic correlation confirming the ability of OCT to image subsquamous Barrett's epithelium has yet to be performed.

DESIGN

Histologic correlation study.

OBJECTIVE

To perform histologic correlation of ultrahigh-resolution optical coherence tomography (UHR-OCT) imaging for identification of subsquamous Barrett's epithelium.

SETTING

Academic Medical Center (University of Washington, Seattle, WA).

PATIENTS

Fourteen patients with pathologic biopsy specimens, proven to be high-grade dysplasia or adenocarcinoma underwent esophagectomy.

INTERVENTIONS

UHR-OCT imaging was performed on ex vivo esophagectomy specimens immediately after resection.

MAIN OUTCOME MEASUREMENTS

Correlation of UHR-OCT images with histologic images.

RESULTS

Subsquamous Barrett's epithelium was clearly identified by using UHR-OCT images and was confirmed by corresponding histology.

LIMITATIONS

Difficulty distinguishing some subsquamous Barrett's glands from blood vessels in ex vivo tissue (because of the lack of blood flow) in some cases. Imaging was performed with a bench-top system.

CONCLUSIONS

Results from this study demonstrate that UHR-OCT imaging is capable of identifying subsquamous Barrett's epithelium.

In vivo imaging of human labial glands using advanced optical coherence tomography

OBJECTIVE

Optical coherence tomography (OCT) has emerged as a high-resolution noninvasive clinical imaging application. The purpose of this study was to show OCT images of human labial glands obtained using a swept-source (SS) OCT system.

STUDY DESIGN

Labial gland OCT imaging was carried out using our new SS-OCT system for 5 healthy volunteers using a hand-held in vivo OCT scanning probe. The labial tissue was scanned in a superior to inferior direction in 2 and 3 dimensions.

RESULTS

The resulting 2- and 3-dimensional ultrahigh-resolution images of in vivo OCT human labial minor salivary glands revealed the epithelium, connective tissue, lobes, and duct. OCT was capable of providing simultaneous and noninvasive structural information with high resolution.

CONCLUSION

This clinical imaging modality promises to have clinical impact in the diagnosis of such conditions as Sjögren syndrome and xerostomia.

Investigation of Oddi sphincter structure by optical coherence tomography in patients with biliary-type 1 dysfunction: a pilot in vivo study

BACKGROUND

Type 1 sphincter of Oddi dysfunction is a clinical entity characterised by biliary-type pain, elevated liver biochemical tests, and common bile duct dilation. Sphincter fibrosis is a common finding in this type of dysfunction and may require in some cases a differential diagnosis with a malignant intra-papillary disease. Optical coherence tomography permits high-resolution, real-time imaging of the sphincter of Oddi microstructure by a probe inserted into the common bile duct through an ERCP catheter. No data exist on the evaluation of sphincter of Oddi fibrosis by optical coherence tomography during ERCP in vivo.

OBJECTIVE

To assess the feasibility of optical coherence tomography investigation of the sphincter of Oddi structure and assess its potential for diagnosing type 1 sphincter of Oddi dysfunction.

PATIENTS

Ten consecutive patients, five with biliary-type 1 sphincter of Oddi dysfunction and five with pancreatic head/mid-body adenocarcinoma not involving the papillary region, who underwent both endoscopic ultrasound and therapeutic ERCP, were investigated by optical coherence tomography immediately before biliary sphincterotomy or stenting.

RESULTS

In all sphincter of Oddi dysfunction patients optical coherence tomography recognised a hyper-reflective intermediate, fibro-muscular layer, significantly thicker than in patients with non-pathological sphincter of Oddi (p<0.0001).

CONCLUSIONS

Optical coherence tomography imaging recognised an increased thickness and reflectance of the fibro-muscular layer of the sphincter of Oddi, very likely determined by fibrosis, and was not time-consuming; it can be safely used during ERCP to confirm the diagnosis in difficult cases. Its use in clinical practice has one important limitation since it requires magnification in the post-procedure computer analysis to obtain images useful for diagnosis.

Optical coherence tomography for bile and pancreatic duct imaging

Optical coherence tomography (OCT) is an optical imaging modality introduced in 1991 that performs high-resolution, cross-sectional, subsurface tomographic imaging of the microstructure in materials and biologic systems by measuring backscattered or backreflected infrared light. OCT has been used for biomedical applications where many factors affect the feasibility and effectiveness of any imaging technique. The highly scattering and absorbing living tissues greatly limit the application of optical imaging modalities. In the last decade, OCT technology has evolved from an experimental laboratory tool to a new diagnostic imaging modality with a wide spectrum of clinical applications in medical practice, including the gastrointestinal (GI) tract and pancreaticobiliary ductal system.

Identification of the layered morphology of the esophageal wall by optical coherence tomography

AIM: To assess each layer of the optical coherence tomography (OCT) image of the esophageal wall with reference to the histological structure.

METHODS: Resected specimens of fresh pig esophagus was used as a model for the esophageal wall. We injected cyanoacrylate adhesive into the specimens to create a marker, and scanned them using a miniature OCT probe. The localization of these markers was assessed in the OCT images. Then we compared the OCT-imaged morphology with the corresponding histological section, guided by the cyanoacrylate adhesive markers. We prepared a second set of experiments using nylon sutures as markers.

RESULTS: The OCT image of the esophageal specimen has a clear five-layered morphology. First, it consisted of a relatively less reflective layer; second, a more reflective layer; third, a less reflective layer; fourth, a more reflective layer; and fifth, a less reflective layer. Comparing the OCT images with marked histological sections showed that the first layer corresponded to stratified squamous epithelium; the second to lamina propria; the third to muscularis mucosa; fourth, submucosa; and fifth, muscularis propria with deeper structures of the esophageal wall.

CONCLUSION: We demonstrated that the OCT image of the normal esophageal wall showed a five-layered morphology, which corresponds to histological esophageal wall components.

Control of optical contrast using gold nanoshells for optical coherence tomography imaging of mouse xenograft tumor model in vivo

The control of image contrast is essential toward optimizing a contrast enhancement procedure in optical coherence tomography (OCT). In this study, the in vivo control of optical contrast in a mouse tumor model with gold nanoshells as a contrast agent is examined. Gold nanoshells are administered into mice, with the injected dosage and particle surface parameters varied and its concentration in the tumor under each condition is determined using a noninvasive theoretical OCT modeling technique. The results show that too high a concentration of gold nanoshells in the tumor only enhances the OCT signal near the tissue surface, while significantly attenuating the signal deeper into the tissue. With an appropriate dosage, IV delivery of gold nanoshells allows a moderate concentration of 6.2 x 10(9) particles/ml in tumor to achieve a good OCT signal enhancement with minimal signal attenuation with depth. An increase in the IV dosage of gold nanoshells reveals a corresponding nonlinear increase in their tumor concentration, as well as a nonlinear reduction in the fractional concentration of injected gold nanoshells. Furthermore, this fractional concentration is improved with the use of antiepodermal growth factor receptor (EGFR) surface functionalization, which also reduces the time required for tumor delivery from 6 to 2 h.

Gastrointestinal optical coherence tomography: clinical applications, limitations, and research priorities

Optical coherence tomography provides the highest resolution available of any of the technologies currently used in endoscopic imaging. There are several potential clinical applications for optical coherence tomography, particularly with precancerous conditions of the gastrointestinal tract. The future of optical coherence tomography is discussed.

Optical coherence tomography in detection of dysplasia and cancer of the gastrointestinal tract and bilio-pancreatic ductal system

Optical coherence tomography (OCT) is an optical imaging modality that performs high-resolution, cross-sectional, subsurface tomographic imaging of the microstructure of tissues. The physical principle of OCT is similar to that of B-mode ultrasound imaging, except that it uses infrared light waves rather than acoustic waves. The in vivo resolution is 10-25 times better (about 10 μm) than with high-frequency ultrasound imaging, but the depth of penetration is limited to 1-3 mm, depending upon tissue structure, depth of focus of the probe used, and pressure applied to the tissue surface. In the last decade, OCT technology has evolved from an experimental laboratory tool to a new diagnostic imaging modality with a wide spectrum of clinical applications in medical practice, including the gastrointestinal (GI) tract and pancreatic-biliary ductal system. OCT imaging from the GI tract can be done in humans by using narrow-diameter, catheter-based probes that can be inserted through the accessory channel of either a conventional front-view endoscope, for investigating the epithelial structure of the GI tract, or a side-view endoscope, inside a standard transparent ERCP catheter, for investigating the pancreatico-biliary ductal system. Esophagus and the esophago-gastric junction has been the most widely investigated organ so far; more recently, also duodenum, colon and pancreatico-biliary ductal system have been extensively investigated. OCT imaging of the gastro-intestinal wall structure is characterized by a multiple-layer architecture that permits an accurate evaluation of the mucosa, lamina propria, muscularis mucosae, and part of the submucosa. The technique may be, therefore, used to identify pre-neoplastic conditions of the GI tract, such as Barrett's epithelium and dysplasia, and evaluate the depth of penetration of early-stage neoplastic lesions. OCT imaging of the pancreatic and biliary ductal system could improve the diagnostic accuracy for ductal epithelial changes and the differential diagnosis between neoplastic and non-neoplastic lesions.

Near-infrared resonant nanoshells for combined optical imaging and photothermal cancer therapy

Metal nanoshells are core/shell nanoparticles that can be designed to either strongly absorb or scatter within the near-infrared (NIR) wavelength region ( approximately 650-950 nm). Nanoshells were designed that possess both absorption and scattering properties in the NIR to provide optical contrast for improved diagnostic imaging and, at higher light intensity, rapid heating for photothermal therapy. Using these in a mouse model, we have demonstrated dramatic contrast enhancement for optical coherence tomography (OCT) and effective photothermal ablation of tumors.

Optical adjuncts for enhanced colonoscopic diagnosis

Background

Optical techniques using previously unexploited properties of light interaction with tissue may be valuable in the detection, diagnosis and staging of colorectal neoplasia.

Methods

A Medline search (1990 to present) was conducted on optical diagnostics in the detection of colorectal neoplasia. The reference list of each identified article was reviewed for further relevant papers.

Results and conclusion

Chromoendoscopy is the only optical adjunct to colonoscopy that has been tested in large randomized clinical trials. It improves the detection of small and flat colorectal adenomas, and of neoplasia in chronic ulcerative colitis and hereditary non-polyposis colorectal cancer. All other techniques are the subject of ongoing research and the practicality of population screening with any of the methods has yet to be established. Optical techniques may, however, permit immediate clinical diagnosis, removing the need for histological analysis. They may also improve the diagnosis of early colonic neoplasia.

Optical coherence tomography evaluation of ulcerative colitis: the patterns and the comparison with histology

HYPOTHESIS

The optical coherence tomography (OCT) is an imaging modality based on infrared light backscattering properties of tissues. OCT studies documented the disappearance of crypts and the alteration in light backscattering as features of ulcerative colitis (UC) in human colon. This technique should be more and more able to identify tissue microstructures with a resolution that is nearly that of histology (optical biopsy).

AIM

To evaluate whether there are OCT patterns specific for UC and to compare the overall technique performance with the histology.

METHODS

A total of 27 patients (20-76 yr) with UC underwent OCT imaging during a total colonoscopy. The OCT images were collected both from affected and normal sites in active UC or disease in remission. Two biopsies of the same sites were acquired. The OCT images were separately scored. Two pathologists blinded to the endoscopic and OCT patterns scored the samples.

RESULTS

Three OCT patterns were identified: the mucosal backscattering alteration (MBA), the delimited dark areas (DDA), and the layered colonic wall (LCW). In colon affected segments of active and UC in remission, these patterns showed a good correspondence with the histology. Moreover, in 14/25 (56%) normal sites above the affected segment, the OCT documented the pathological features, confirmed only in 10/14 by the histology. Thus, the assessed sensitivity and specificity of OCT in normal segments of UC patients have been 100% and 69%, respectively.

CONCLUSIONS

The in vivo OCT correctly detected disease features in endoscopically affected colon segments, but even in apparently normal segments of UC patients.

Comprehensive volumetric optical microscopy in vivo

Comprehensive volumetric microscopy of epithelial, mucosal and endothelial tissues in living human patients would have a profound impact in medicine by enabling diagnostic imaging at the cellular level over large surface areas. Considering the vast area of these tissues with respect to the desired sampling interval, achieving this goal requires rapid sampling. Although noninvasive diagnostic technologies are preferred, many applications could be served by minimally invasive instruments capable of accessing remote locations within the body. We have developed a fiber-optic imaging technique termed optical frequency-domain imaging (OFDI) that satisfies these requirements by rapidly acquiring high-resolution, cross-sectional images through flexible, narrow-diameter catheters. Using a prototype system, we show comprehensive microscopy of esophageal mucosa and of coronary arteries in vivo. Our pilot study results suggest that this technology may be a useful clinical tool for comprehensive diagnostic imaging for epithelial disease and for evaluating coronary pathology and iatrogenic effects.

Optical coherence tomography compared with histology of the main pancreatic duct structure in normal and pathological conditions: an 'ex vivo study'

BACKGROUND AND STUDY AIMS

Optical coherence tomography permits high-resolution imaging of tissue microstructures by a probe inserted into the main pancreatic duct through a standard ERCP catheter. The aim of this study was to compare optical coherence tomography images of the main pancreatic duct with histology and identify the optical coherence tomography pattern of the normal and pathological structure of the main pancreatic duct.

PATIENTS AND METHODS

Multiple sections of neoplastic and non-neoplastic segments of 10 consecutive surgical pancreatic specimens obtained from patients with pancreatic head adenocarcinoma were investigated by optical coherence tomography scanning within 1h of resection. One hundred optical coherence tomography findings were then compared with the corresponding histopathological diagnoses.

RESULTS

Main pancreatic duct wall architecture appeared at optical coherence tomography investigation as a three-layer structure with a different back-scattered signal from each layer. Optical coherence tomography imaging was concordant with histology in 81.8% and 18.75% of sections with normal tissue and chronic inflammatory changes. The K statistic between the two procedures was equal to 0.059 for non-neoplastic main pancreatic duct wall appearance. In all neoplastic sections optical coherence tomography showed a subverted layer architecture with heterogeneous back-scattering of the signal and was concordant with histology.

CONCLUSIONS

Optical coherence tomography provided images of main pancreatic duct wall structure that were concordant with histology in 100% of cases in presence of neoplastic ductal changes and did not have false-positive or negative results. Optical coherence tomography images were also concordant with histology in about 80% of cases with normal main pancreatic duct structure; however, the differential diagnosis between normal tissue and chronic pancreatitis or dysplastic changes appeared very difficult.

Main pancreatic duct, common bile duct and sphincter of Oddi structure visualized by optical coherence tomography: An ex vivo study compared with histology

BACKGROUND

Optical coherence tomography has been proposed to obtain high-resolution imaging of tissue structure of GI tract. Up till now, the optical coherence tomography appearance of the common bile duct, main pancreatic duct and sphincter of Oddi wall structure has not yet been defined.

AIMS

To compare, in a prospective study, optical coherence tomography images of pancreato-biliary ductal system with histology and identify the optical coherence tomography pattern of the normal wall structure of the ducts.

METHODS

Multiple sections of non-neoplastic segments of five consecutive ex vivo human pancreatic specimens were investigated by optical coherence tomography scanning within 1h of resection. Sixty optical coherence tomography images were compared with the corresponding histological findings.

RESULTS

Optical coherence tomography appearance of normal common bile duct, main pancreatic duct and sphincter of Oddi is characterized by a differentiated three-layer architecture with a regular surface and a homogeneous back-scattered signal, corresponding to the single layer of epithelial cells, the connective-muscular layer and the muscular or acinar structure, respectively. Optical coherence tomography and histology findings were concordant in all cases.

CONCLUSIONS

Optical coherence tomography was able to provide in real-time images of wall structure of the normal common bile duct, main pancreatic duct and sphincter of Oddi that are similar to those obtained by histology. These results suggest that optical coherence tomography could enable high-resolution images to be obtained from the pancreato-biliary system during an ERCP procedure.

Optical Coherence Tomography: Real-time Imaging of Bronchial Airways Microstructure and Detection of Inflammatory/Neoplastic Morphologic Changes

PURPOSE

Current diagnostic imaging modalities for human bronchial airways do not possess sufficient resolution and tissue penetration depth to detect early morphologic changes and to differentiate in real-time neoplastic pathology from nonspecific aberrations. Optical coherence tomography (OCT) possesses the requisite high spatial resolution for reproducible delineation of endobronchial wall profiling.

EXPERIMENTAL DESIGN

To establish whether OCT could differentiate between the composite microstructural layers of the human airways and simultaneously determine in situ morphologic changes, using a bench-top OCT system, we obtained cross-sectional images of bronchi from 15 patients undergoing lung resections for cancer. All scanned sections underwent subsequent detailed histologic analysis, allowing direct comparisons to be made.

RESULTS

OCT imaging enables characterization of the multilayered microstructural anatomy of the airways, with a maximum penetration depth up to 2 to 3 mm and 10-microm spatial resolution. The epithelium, subepithelial components, and cartilage are individually defined. The acquired OCT images closely match histologically defined patterns in terms of structural profiles. Furthermore, OCT identifies in situ morphologic changes associated with inflammatory infiltrates, squamous metaplasia, and tumor presence.

CONCLUSIONS

Our results confirm that OCT is a highly feasible optical tool for real-time near-histologic imaging of endobronchial pathology, with potential for lung cancer surveillance applications in diagnosis and treatment.

Optical coherence tomography to detect epithelial lesions of the main pancreatic duct: an Ex Vivo study

BACKGROUND

Optical coherence tomography (OCT) permits high-resolution, real-time, infrared-generated imaging of tissue microstructures by a probe inserted through the endoscope operative channel. Resolution is approximately 10 microm and the penetration depth of the near-focus probe is about 1 mm. The probe can be inserted into the main pancreatic duct (MPD) through a standard endoscopic retrograde cholangiopancreatography catheter.

AIMS AND METHODS

To assess the ability of OCT to identify the structure of the MPD, to distinguish normal and malignant MPD epithelium, and to assess intra- and interobserver reproducibility of OCT images. Multiple sections of neoplastic and non-neoplastic segments of 10 consecutive surgical pancreatic specimens were obtained from patients with pancreatic head adenocarcinoma who had undergone Whipple resection, and repeated OCT radial and longitudinal scanning was done within 1 h of resection and before pathological examination. We compared 249 good-quality images with 100 histopathological sections.

RESULTS

OCT recognized a definite, different pattern in 82.9% of tumor-free and in 97.6% of tumor-involved specimens; sensitivity and specificity for discrimination between adenocarcinoma and normal tissue were 78.6% and 88.9%, respectively. Inflammatory and dysplastic changes of the MPD showed an OCT pattern similar to that of the normal tissue in 53.3% of images. Overall, intraobserver reproducibility ranged from 85.1% to 100% and interobserver reproducibility ranged from 69.9% to 100% and from 89.7% to 100% for tumor-free and tumor-involved segments, respectively.

CONCLUSIONS

OCT identified the neoplastic and non-neoplastic MPD layer structure and appeared to be a reproducible technique. In non-neoplastic conditions, OCT appeared unable to differentiate between normal and abnormal tissues in about half of the cases.

In vivo optical coherence tomography imaging of the pancreatic and biliary ductal system

BACKGROUND

In vivo optical coherence tomography (OCT) imaging has not yet been applied to the pancreatic ductal system. The aim of this study was to obtain in vivo OCT images of dog pancreatic and biliary ducts, and to correlate the images with histology.

METHODS

Images of dog pancreatic and biliary ducts were obtained by using an in vivo OCT probe introduced through the respective papillary orifices. Each duct was imaged in multiple locations, and the site of imaging was marked with injected India ink. After imaging, the dogs were euthanized, and the pancreaticobiliary system was harvested. Histologic cross sections were correlated with in vivo OCT images by measuring the structures seen on in vivo OCT images and correlating them with structures seen on corresponding histology slides that contained India ink.

OBSERVATIONS

Eighteen pairs of in vivo OCT images and histology slides from the bile duct and the pancreatic duct were obtained from 5 dogs. The entire duct wall could be visualized. A low reflective in vivo OCT layer corresponding to the epithelium could be discerned on many images. The bile duct showed a more complex architecture and had greater variations within the reflective OCT layers, possibly because of greater cellularity within the lamina propria. Nuclei within cells could not be identified, and structures adjacent to the ducts could not be imaged.

CONCLUSIONS

In vivo OCT is capable of imaging the pancreaticobiliary ductal system and of identifying the epithelial layer. Because of limited depth of imaging (320-845 micron), OCT is unlikely to serve the purpose of tumor staging.

Effect of tissue preservation on imaging using ultrahigh resolution optical coherence tomography

Ultrahigh resolution optical coherence tomography (OCT) is an emerging imaging modality that enables noninvasive imaging of tissue with 1- to 3-microm resolutions. Initial OCT studies have typically been performed using harvested tissue specimens (ex vivo). No reports have investigated postexcision tissue degradation on OCT image quality. We investigate the effects of formalin fixation and commonly used cell culture media on tissue optical scattering characteristics in OCT images at different times postexcision compared to in vivo conditions. OCT imaging at 800-nm wavelength with 1.5-mum axial resolution is used to image the hamster cheek pouch in vivo, followed by excision and imaging during preservation in phosphate-buffered saline (PBS), Dulbecco's Modified Eagle's Media (DMEM), and 10% neutral-buffered formalin. Imaging is performed in vivo and at sequential time points postexcision from 15 min to 10 to 18 h. Formalin fixation results in increases in scattering intensity from the muscle layers, as well as shrinkage of the epithelium, muscle, and connective tissue of approximately 50%. PBS preservation shows loss of optical contrast within two hours, occurring predominantly in deep muscle and connective tissue. DMEM maintains tissue structure and optical scattering characteristics close to in vivo conditions up to 4 to 6 h after excision and best preserved tissue optical properties when compared to in vivo imaging.

Ultrahigh-resolution and 3-dimensional optical coherence tomography ex vivo imaging of the large and small intestines

BACKGROUND

Ultrahigh-resolution optical coherence tomography (OCT) has an axial resolution of <5 microm, 2 to 3 times finer than standard OCT. This study investigates ultrahigh-resolution and three-dimensional OCT for ex vivo imaging of the large and small intestines and correlates images with histology.

METHODS

Ultrahigh-resolution OCT imaging was performed on fresh surgical specimens from the large and small intestines in the pathology laboratory, and images were correlated with histology. OCT was performed at 1.3-microm wavelength with 4.5-microm axial x 11-microm transverse resolution and at 1.1-microm wavelength with 3.5-microm axial x 6-microm transverse resolution. Three-dimensional OCT also was investigated.

RESULTS

Normal and pathologic areas from 23 surgical specimens of the large and small intestines were imaged. Ultrahigh-resolution OCT distinguished the epithelial layer of the mucosa and visualized individual villi, glands, and crypts. Finer transverse resolutions improved visualization of features, e.g., the epithelium, but reduced the depth of field. Architectural distortion of glands from inflammatory and neoplastic processes was observed. Three-dimensional rendering enabled visualization of surface pit pattern and mucosal folds as well as subsurface crypt microstructure.

CONCLUSIONS

This study evaluates new OCT technology and can provide a baseline for interpreting future ultrahigh-resolution endoscopic OCT studies.

Evaluation of Tracheal Imaging by Optical Coherence Tomography

BACKGROUND

Optical coherence tomography (OCT) is a new technology capable of generating high resolution cross-sectional images of complex tissue in real time. Analogous to ultrasound, OCT measures backscattered light intensity using coherence interferometery to construct topographical images of complex tissue. Since OCT uses infrared light rather than acoustic waves, its spatial resolution is exceptionally high (2-10 microm). Recent advances in data acquisition, analysis, and processing enable real-time imaging, and make OCT a potentially valuable tool for pulmonary airway diagnostic applications, including assisting directed airway biopsies.

OBJECTIVE

This study evaluates feasibility of OCT for delineating proximal airway microstructures in various animal as well as human tracheas.

METHODS

Excised trachea samples from New Zealand white rabbits, Duroc pigs, and human trachea were imaged using a compact, 1,300-nm broad-band superluminescent-diode-based prototype fiber OCT device we constructed. The resulting structural OCT images were compared to conventional hematoxilin and eosin (HE) stained histological sections from the same samples.

RESULTS

OCT was able to delineate microstructures such as the epithelium, mucosa, cartilage, and glands in all samples.

CONCLUSION

These findings suggest that integration of OCT with flexible fiberoptic bronchoscopy could enhance pulmonary diagnostic medicine and detection of pathologic tissue changes in various respiratory diseases.

New frontiers in endoscopic imaging

Gastrointestinal (GI) tract malignancies have a tremendous impact on society. Colorectal cancer is the second leading cause of cancer death in the United States and accounts for 10% of all cancer deaths. Significant research efforts are being directed toward using the interaction of light and tissue to detect pre-cancerous lesions of the GI tract. This article reviews the current status of various experimental optical technologies to detect pre-cancerous changes in the GI tract and focuses on the clinical applications of these technologies for the practicing gastroenterologist.

Optical coherence tomography imaging of the pancreas: a needle-based approach

A novel, high-resolution, needle-based optical coherence tomography (OCT) device for improving the ability to detect early epithelial dysplasia in solid tissues/organs in vivo is currently in development. An instrument capable of real-time imaging of tissue microstructures in vivo could improve the ability to detect pathologic conditions such as dysplasia, and consequently improve patient outcomes. OCT is an emerging technology that can perform real-time cross-sectional imaging of tissue structures at micron-scale resolution in vivo. OCT has been shown to be effective in the imaging of luminal epithelium, capable of detecting epithelial dysplasia in Barrett's esophagus, and colonic polyps. However, OCT imaging depth with conventional probes is limited to the luminal surface (approximately 1-2 mm). The development of a technology and device that enables high-resolution, real-time imaging of solid tissues beyond 1- to 2-mm deep at or near the cellular level in vivo could improve the diagnosis of diseases of the pancreas and other solid organs.

Dysplasia in Barrett's esophagus: limitations of current management strategies

Dysplasia is a very imperfect biomarker for malignancy in Barrett's esophagus. Invasive cancer has been found in 30-40% of esophagi resected because preoperative endoscopic examinations had shown high-grade dysplasia. Reports on the natural history of this disorder are sometimes contradictory, but suggest that 10-30% of patients with high-grade dysplasia in Barrett's esophagus will develop a demonstrable malignancy within 5 yr of the initial diagnosis. Proposed management strategies for high-grade dysplasia include esophagectomy, endoscopic ablative therapies, endoscopic mucosal resection (EMR), and intensive endoscopic surveillance. Endoscopic ablative therapies and EMR may not be effective if neoplastic cells have invaded the submucosa or disseminated through mucosal lymphatic channels, and a number of studies suggest that the endoscopic therapies usually leave metaplastic or neoplastic epithelium with malignant potential behind. Limited data suggest that intensive endoscopic surveillance might be a reasonable approach for elderly or infirm patients, but some patients managed in this fashion have developed incurable esophageal cancers. The fundamental question of what is the appropriate length of follow-up for studies on dysplasia treatments has not been resolved. Although 5 yr might be considered the absolute minimum duration for a meaningful follow-up on dysplasia therapy, the follow-up duration in most studies is substantially less than 5 yr. Specific recommendations for management based on these considerations are proposed at the end of this report.