In vivo Human Colorectal Polyp Evaluation Using an Optical Coherence Tomography Catheter – A Pilot Study

Introduction:: Colorectal cancer (CRC) has the third highest estimated new cases and death rates in the United States. CRC typically arises from benign polyps, which are abnormal tissue growth in the colon mucosal layer. There are no readily available classification tools with adequate sensitivity or specificity to differentiate complex colon polyps “in the gray area”; this is, lesions with neoplasms confined to superficial submucosa from lesions with early CRC. Endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD) of colorectal neoplasms with < 1 mm of submucosal invasion offers a curative treatment. However, lesions with deeply invasive CRC ( >1 mm) should be referred for surgical resection. Polyps with irregular vessel and surface patterns (Japan NBI Expert Team classification Type 2B) may indicate submucosal invasion. In this case, magnifying chromoendoscopy to evaluate pit pattern is recommended. However, magnifying chromoendoscopy has an accuracy of < 80% for lesions with superficial submucosal invasion.

Optical coherence tomography (OCT) uses backscattered light to acquire depth resolved images of tissue and has been shown to accurately differentiate abnormal from normal tissue in multiple organs as an “optical biopsy” tool. Ex-vivo evaluation of rectal cancer and in-vivo imaging of the normal human colon and ulcerative colitis have previously been reported. To date, there are no studies that have used OCT in an in-vivo setting for the evaluation of colorectal polyps.


Materials and Methods:: A single-arm, non-blinded study to investigate the feasibility of a novel OCT/machine learning catheter probe for patients undergoing routine screening or surveillance colonoscopy (NCT05179837). The study population consists of 36 adults in a single center. The primary objective is to demonstrate the procedural feasibility of OCT during colonoscopy using time added to the length of overall procedure as a surrogate endpoint. Secondary objectives include safety of the OCT probe, quality of OCT images, and diagnosis agreement between OCT imaging and pathology.

The custom-built OCT catheter is 2.5 meters long with a 3.1 mm outer diameter. This allows the probe to fit through the working channel of an adult colonoscopy and reach the cecum (the distal end of the colon). The theoretical axial resolution is 6 µm, while the measured lateral resolution is 8.5 µm and 11 µm in the x and y directions respectively. The probe uses a single mode optical fiber with a light focusing assembly consisting of a gradient refractive index (GRIN) lens, an epoxy spacer, and a right-angle prism for side-view imaging. The probe is rotated at the proximal end with a DC motor and rotary joint, and a torque coil transmits the rotation to the probe tip. A 20 kHz swept source laser is used, while data acquisition is realized with a balanced detector and high speed DAQ card. The whole system is packaged into an endoscopy cart. (Fig. 1)


Results, Conclusions, and Discussions:: 36 participants have consented and enrolled to date. Co-morbidities include heart failure, lung disease, diabetes, and stroke. All procedures were done in the outpatient setting by five different interventional endoscopy attendings using an adult colonoscope. Four participants were excluded: one did not have polyps, one due to probe malfunction, and two due to low image quality. No participants had immediate or late complications after colonoscopy with OCT. Preliminary qualitative results of OCT imaging show a submucosal invasion depth of approximately 800 μm and distinct features that correlate well with H&E histology images and clearly differentiate tubular adenoma (TA), tubulovillous adenoma (TVA), sessile serrated polyps (SSP), and colorectal cancer. TA shows vertical teeth-like patterns corresponding to the “tubular” structures. TVA, compared to TA, has higher contrast and longer “villous” structures that extend in all directions. SSP shows a thinner mucosa layer with visible submucosa. Invasive moderately-differentiated adenocarcinoma does not have teeth or layered structures and low contrast irregular shapes are observed, corresponding to malignant growth disturbing the normally defined tissue layers.

We note three factors affecting practical in vivo OCT imaging in the human colon. 1. Tissue structures in OCT images vary with pressure applied on the probe. Higher pressure leads to more compression and better optical coupling, thereby increasing the effective imaging depth and image quality. 2. Better bowel prep leads to less fecal matter that degrades image quality. 3. Even though the subject is under general anesthesia, respiration and bowel contractions lead to motion artifacts that prohibit 3D image reconstruction. This may be overcome in the future with faster imaging.

This is the first study using OCT in an in vivo setting for the real time evaluation of colon polyps. Preliminary results show that the novel OCT probe is a safe and feasible instrument that does not significantly impact the endoscopy workflow. Qualitative results of OCT imaging show clear differences in types of colon polyps. In addition to increasing the imaging depth of OCT, we aim to optimize a deep learning algorithm using in vivo OCT images with a target accuracy of >95% for the detection of submucosal invasion.


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