The aim of the study was to evaluate the performance of trans-serosal multimodal OCT (MM OCT) in in vivo detecting of changes in microstructure and blood circulation of the small intestine wall caused by arteriovenous ischemia resulted from intestine strangulation. Materials and Methods. In experiments on Wistar rats (n=22), we examined the small intestine wall in vivo using MM OCT; the access to the intestine was reached through laparotomy. The microvasculature and microstructure of the wall were studied before and after acute arteriovenous ischemia created by ligation of a small bowel segment. The results were then added with data obtained from histological and intravital microscopic examination. Results. Trans-serous MM OCT allowed us to visualize the bowel wall to its entire thickness, distinguish between the serous-muscular and mucous-submucosal layers, and detect the villi and functioning blood vessels. The structures were best seen after a fat emulsion had been administered into the bowel lumen. In OCT images made in the optical coherent angiography (OCA) mode, large paired vessels (arteries and veins) and micro-vessels with a diameter of >15 μm could be seen. Most of the blood vessels were imaged in the depth range of 80-300 μm from the surface. Capillaries with a diameter of 7-10 μm were not seen, but they produced an overall bright background. In the OCA images reconstructed from a volume of 2.4×2.4×1.8 mm, the total length of the vascular bed before ischemia was 18.3 [16.6; 19.8] mm. Strangulation of the intestinal loop was associated with changes in the CP OCT picture: the villi-associated vertical pattern and shadows of blood vessels disappeared and the depth of tissue visualization in the cross-channel decreased. The optical equivalents of the serous-muscular layer were preserved; after 180±12 min of ischemia, their proportion in the intestinal wall thickness increased from 25 [18; 32] to 42 [31; 55]% (p=0.031). At that time-point, OCA images of the strangulated bowel loop looked all similar: a uniform dark background with isolated fragmentary large vessels and no signs of blood flow in the microvascular network. Conclusion. Trans-serous MM OCT provides for in vivo visualization of microstructures critical for surgical gastroenterology: the intestinal wall layers including villi and blood vessels of each layer, as confirmed by histological analysis. Destructive processes in the intestinal wall resulting from bowel ligation bring about optical changes, which can be detected using real-time MM OCT.
Introduction: Despite the introduction of increasingly multifaceted diagnostic techniques and the general advances in emergency abdominal and vascular surgery, the outcome of treatment of patients with acute impaired intestinal circulation remains unsatisfactory. The non-invasive and high-resolution technique of optical coherence tomography (OCT) can be used intraoperatively to assess intestine viability and associated conditions that frequently emerge under conditions of impaired blood circulation. This study aims to demonstrate the effectiveness of multimodal (MM) OCT for intraoperative diagnostics of both the microstructure (cross—polarization OCT mode) and microcirculation (OCT angiography mode) of the small intestine wall in patients with acute mesenteric ischemia (AMI). Methods and Participants: A total of 18 patients were enrolled in the study. Nine of them suffered from AMI in segments II-III of the superior mesenteric artery (AMI group), whereby the ischemic segments of the intestine were examined. Nine others were operated on for adenocarcinoma of the colon (control group), thus allowing areas of their normal small intestine to be examined for comparison. Data on the microstructure and microcirculation in the walls of the small intestine were obtained intraoperatively from the side of the serous membrane using the MM OCT system (IAP RAS, Russia) before bowel resection. The MM OCT data were compared with the results of histological examination. Results: The study finds that MM OCT visualized the damage to serosa, muscularis externa, and blood vessels localized in these layers in 100% of AMI cases. It also visualized the submucosa in 33.3% of AMI cases. The MM OCT images of non-ischemic (control group), viable ischemic, and necrotic small intestines (AMI group) differed significantly across stratification of the distinguishable layers, the severity of intermuscular fluid accumulations, and the type and density of the vasculature. Conclusion: The MM OCT diagnostic procedure optimally meets the requirements of emergency surgery. Data on the microstructure and microcirculation of the intestinal wall can be obtained simultaneously in real time without requiring contrast agent injections. The depth of visualization of the intestinal wall from the side of the serous membrane is sufficient to assess the volume of the affected tissues. However, the methodology for obtaining MM OCT data needs to be improved to minimize the motion artefacts generated in actual clinical conditions.
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