Endoscopic optical coherence tomography (OCT) angiography enables volumetric coregistered architectural and microvasculature imaging of the human gastrointestinal tract in vivo. In this talk, we will discuss technical advances and clinical gastroenterology applications with the endoscopic OCT angiography technique.
Optical coherence tomography (OCT) is an imaging technique optically analogous to ultrasound that can generate depth-resolved images with micrometer-scale resolution. Advances in fiber optics and miniaturized actuation technologies allow OCT imaging of the human body and further expand OCT utilization in applications including but not limited to cardiology and gastroenterology. This review article provides an overview of current OCT development and its clinical utility in the gastrointestinal tract, including disease detection/differentiation and endoscopic therapy guidance, as well as a discussion of its future applications.
Radiofrequency ablation (RFA) is widely used for the eradication of dysplasia and the treatment of early stage esophageal carcinoma in patients with Barrett’s esophagus (BE). However, there are several factors, such as variation of BE epithelium (EP) thickness among individual patients and varying RFA catheter-tissue contact, which may compromise RFA efficacy. We used a high-speed optical coherence tomography (OCT) system to identify and monitor changes in the esophageal tissue architecture from RFA. Two different OCT imaging/RFA application protocols were performed using an ex vivo swine esophagus model: (1) post-RFA volumetric OCT imaging for quantitative analysis of the coagulum formation using RFA applications with different energy settings, and (2) M-mode OCT imaging for monitoring the dynamics of tissue architectural changes in real time during RFA application. Post-RFA volumetric OCT measurements showed an increase in the coagulum thickness with respect to the increasing RFA energies. Using a subset of the specimens, OCT measurements of coagulum and coagulum + residual EP thickness were shown to agree with histology, which accounted for specimen shrinkage during histological processing. In addition, we demonstrated the feasibility of OCT for real-time visualization of the architectural changes during RFA application with different energy settings. Results suggest feasibility of using OCT for RFA treatment planning and guidance.
We developed an ultrahigh speed endoscopic swept source optical coherence tomography (OCT) system for clinical
gastroenterology using a vertical-cavity surface-emitting laser (VCSEL) and micromotor based imaging catheter, which
provided an imaging speed of 600 kHz axial scan rate and 8 μm axial resolution in tissue. The micromotor catheter was
3.2 mm in diameter and could be introduced through the 3.7 mm accessory port of an endoscope. Imaging was
performed at 400 frames per second with an 8 μm spot size using a pullback to generate volumetric data over 16 mm
with a pixel spacing of 5 μm in the longitudinal direction. Three-dimensional OCT (3D-OCT) imaging was performed in
patients with a cross section of pathologies undergoing standard upper and lower endoscopy at the Veterans Affairs
Boston Healthcare System (VABHS). Patients with Barrett’s esophagus, dysplasia, and inflammatory bowel disease
were imaged. The use of distally actuated imaging catheters allowed OCT imaging with more flexibility such as
volumetric imaging in the terminal ileum and the assessment of the hiatal hernia using retroflex imaging. The high
rotational stability of the micromotor enabled 3D volumetric imaging with micron scale volumetric accuracy for both en
face and cross-sectional imaging. The ability to perform 3D OCT imaging in the GI tract with microscopic accuracy
should enable a wide range of studies to investigate the ability of OCT to detect pathology as well as assess treatment
response.
KEYWORDS: Optical coherence tomography, Vertical cavity surface emitting lasers, Endoscopy, Imaging systems, Data acquisition, In vivo imaging, 3D acquisition, Colon, Image resolution, 3D image processing
We developed a micro-motor based miniature catheter with an outer diameter of 3mm for ultrahigh speed endoscopic optical coherence tomography (OCT) using vertical cavity surface-emitting laser (VCSEL) at a 1MHz axial scan rate. The micro-motor can rotate a micro-prism at 1,200-72,000rpm (corresponding to 20- 1,200fps) with less than 5V driving voltage to provide fast and stable scanning, which is not sensitive to the bending of the catheter. The side-viewing probe can be pulled back for a long distance to acquire three-dimensional (3D) dataset covering a large area on the specimen. VCSEL provides high a-line rate to support dense sampling under high frame rate operation. With the use of a C++ based high speed data acquisition (DAQ) system, in vivo three-dimensional OCT imaging in rabbit GI tract with 1.6mm depth range, 11μm axial resolution, 8μm lateral resolution, and frame rate of 400fps is demonstrated.
Barrett's esophagus (BE) with high-grade dysplasia is generally treated by endoscopic mucosal resection or
esophagectomy. Radiofrequency ablation (RFA) is a recent treatment that allows broad and superficial
ablation for BE. Endoscopic three-dimensional optical coherence tomography (3D-OCT) is a volumetric
imaging technique that is uniquely suited for follow-up surveillance of RFA treatment. 3D-OCT uses a thin
fiberoptic imaging catheter placed down the working channel of a conventional endoscope. 3D-OCT enables
en face and cross-sectional evaluation of the esophagus for detection of residual BE, neo-squamous mucosa,
or buried BE glands. Patients who had undergone RFA treatment with the BARRX HALO90 system were
recruited and imaged with endoscopic 3D-OCT before and after (3-25 months) RFA treatment. 3D-OCT
findings were compared to pinch biopsy to confirm the presence or absence of squamous epithelium or buried
BE glands following RFA. Gastric, BE, and squamous epithelium were readily distinguished from 3D-OCT
over a large volumetric field of view (8mmx20mmx1.6 mm) with ~5μm axial resolution. In all patients, neosquamous
epithelium (NSE) was observed in regions previously treated with RFA. A small number of
isolated glands were found buried beneath the regenerated NSE and lamina propria. NSE is a marker of
successful ablative therapy, while buried glands may have malignant potential and are difficult to detect using
conventional video endoscopy and random biopsy. Buried glands were not observed with pinch biopsy due to
their extremely sparse distribution. These results indicate a potential benefit of endoscopic 3D-OCT for
follow-up assessment of ablative treatments for BE.
Optical coherence microscopy (OCM) combines confocal microscopy and optical coherence tomography (OCT) to improve imaging depth and contrast, enabling cellular imaging in human tissues. We aim to investigate OCM for ex vivo imaging of upper and lower gastrointestinal tract tissues, to establish correlations between OCM imaging and histology, and to provide a baseline for future endoscopic studies. Co-registered OCM and OCT imaging were performed on fresh surgical specimens and endoscopic biopsy specimens, and images were correlated with histology. Imaging was performed at 1.06-µm wavelength with <2-µm transverse and <4-µm axial resolution for OCM, and at 14-µm transverse and <3-µm axial resolution for OCT. Multiple sites on 75 tissue samples from 39 patients were imaged. OCM enabled cellular imaging of specimens from the upper and lower gastrointestinal tracts over a smaller field of view compared to OCT. Squamous cells and their nuclei, goblet cells in Barrett's esophagus, gastric pits and colonic crypts, and fine structures in adenocarcinomas were visualized. OCT provided complementary information through assessment of tissue architectural features over a larger field of view. OCM may provide a complementary imaging modality to standard OCT approaches for endoscopic microscopy.
Optical coherence tomography (OCT) is an emerging medical imaging technology which can generate high resolution, cross-sectional images of tissue in situ and in real time, without the removal of tissue specimen. Although endoscopic OCT has been used successfully to identify certain pathologies in the gastrointestinal tract, the resolution of current endoscopic OCT systems has been limited to 10-15 um for clinical procedures. In this study, in vivo imaging of the gastrointestinal tract is demonstrated at a three-fold higher axial resolution (<5 um), using a portable, broadband, Cr4+:Forsterite laser as the optical light source. Images acquired from the esophagus and colon on animal model display tissue microstructures and architectural details at ultrahigh resolution, and the features observed in the OCT images are well-matched with histology. The clinical feasibility study is conducted through delivering OCT imaging catheter using the standard endoscope. OCT images of normal esophagus and Barrett's esophagus are demonstrated with distinct features.
Early detection of gastrointestinal cancer is essential for the patient treatment and medical care. Endoscopically guided biopsy is currently the gold standard for the diagnosis of early esophageal cancer, but can suffer from high false negative rates due to sampling errors. Optical coherence tomography (OCT) is an emerging medical imaging technology which can generate high resolution, cross-sectional images of tissue in situ and in real time, without the removal of tissue specimen. Although endoscopic OCT has been used successfully to identify certain pathologies in the gastrointestinal tract, the resolution of current endoscopic OCT systems has been limited to 10 - 15 m for clinical procedures. In this study, in vivo imaging of the gastrointestinal tract is demonstrated at a three-fold higher resolution (< 5 m), using a portable, broadband, Cr4+:Forsterite laser as the optical light source. Images acquired from the esophagus, gastro-esophageal junction and colon on animal model display tissue microstructures and architectural details at high resolution, and the features observed in the OCT images are well-matched with histology. The clinical feasibility study is conducted through delivering OCT imaging catheter using standard endoscope. OCT images of normal esophagus, Barrett's esophagus, and esophageal cancers are demonstrated with distinct features. The ability of high resolution endoscopic OCT to image tissue morphology at an unprecedented resolution in vivo would facilitate the development of OCT as a potential imaging modality for early detection of neoplastic changes.
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