Su2037 Detecting Bowel Wall Fibrosis With Photoacoustic Imaging in an Animal Model of Crohn's Disease

Background/Aims: Optical coherence tomography (OCT) enables three-dimensional (3D) examination of the tissue architecture with micrometer resolution. In previous studies, endoscopic OCT was used to provide structural information correlated with histology for gastrointestinal pathologies. However, the utility of endoscopic OCT for investigating the pathology of the terminal ileum (TI) in patients with symptoms of inflammatory bowel disease (IBD), for example, has been very limited. Endoscopically, reaching the TI entails advancing the colonoscope through multiple sharp bends of the colon, which prevents smooth rotation of previous generations of proximally actuated probes. Recently, our group has developed ultrahigh speed endoscopic OCT technology with a micromotor imaging probe, which enables precise volumetric imaging by avoiding the non-uniform rotational distortion inherent in proximally actuated probes. In this study, we reported structural and vascular changes of TI with chronic inflammation using endoscopic OCT and OCT angiography (OCTA). Methods: This prototype endoscopic OCT system achieves an imaging speed of 600,000 A-scans per second and a frame rate of 400 frames per second. The diameter of the imaging probe was small enough to pass through the accessory port of the colonoscope, enabling coregistered biopsies. OCTA visualized microvasculature by measuring decorrelation between sequential OCT images to generate motion contrast from blood flow. The study was performed at the Veterans Affairs Boston Healthcare System (VABHS) with the approval from the institutional review boards from VABHS, Harvard Medical School, and MIT. Results: Figure 1 shows OCT images of a normal TI (Figs. 1(A, B)) and TI with chronic inflammation (Figs. 1(C, D)) as well as the coregistered en face OCTA (Fig. 1(E)) at the same depth as Fig. 1(C). Typical villous structure of normal TI can be observed in Fig. 1(A) at 100 μm depth, which was consistent with the colonoscopy findings (inset, Fig. 1(A)). The slight tilted orientation of the villi was caused by the gentle pressing of the imaging probe, which was observed along the cross-sectional OCT image as well (Fig. 1(B)). On the contrary, a loss of villous structure and nodular mucosal appearance were identified in Fig. 1(C) of TI with chronic inflammation, which was confirmed by the coregistered biopsy. In addition, a decreased imaging depth was observed in the cross-sectional OCT image (Fig. 1(D)). Fig 1(E) shows the coregistered en faceOCTA as Fig. 1(C) where increased vasculature with abnormal vascular branching was observed. Conclusions: This study demonstrates that ultrahigh speed endoscopic OCT technology and OCTA allows the visualization structural and vascular features of the TI with chronic inflammation. Acknowledgment: NIH R01CA075289-17, R44-CA101067-07, AFOSR FA9550-10-1-0551 and FA9550-12-1-0499.