Chapter 2 volume laparoscopic gastrointestinal surgery, with special emphasis on biliary tract and colorectal surgery. Deeper light penetration in tissues, by utilizing new optical imaging methods, can facilitate earlier and clearer identification of essential anatomy during surgery, for example a ureter beneath a layer of adipose or connective tissue. The assumed maximum light penetration depth in tissue varies from a few millimeters (optical coherence tomography) up to over one centimeter (NIR fluorescence imaging, optoacoustic imaging). This doubtlessly is an improvement compared to conventional laparoscopic imaging. In particular the near‐infrared light spectrum is capable of penetrating relatively deeply into tissues such as the mesenteric adipose tissue. Yet, the increased penetration depth of emerging imaging technologies is limited. Anatomy navigation at depths larger than one centimeter remains challenging. All imaging methods described in this review can be applied for the identification of anatomical structures during surgery. Infrared ray imaging and near‐infrared fluorescence imaging have been tested successfully for the intraoperative localization of blood vessels, extra‐hepatic bile ducts, ureter and lymph nodes or vessels. According to the literature optical coherence tomography can improve the visual contrast of blood vessels, nerves and lymphatics. Hyperspectral imaging has been investigated for blood vessel and extra‐hepatic bile duct imaging. Optoacoustic imaging has not yet been tested for a wide variety of applications, but should be able to detect blood vessels at larger depths (assumed penetration depth >1cm). Diffuse optical spectroscopy is not yet available for video imaging of anatomical structures, but there is potential for contrast enhancement of blood vessel and ureter. Furthermore, a better real‐time intraoperative understanding of physiology can be obtained by implementing novel optical imaging methods. The assessment of dynamic organ perfusion can be performed by using infrared ray imaging, NIR fluorescence imaging, hyperspectral imaging and optoacoustic imaging. For blood oxygen determination technologies like diffuse optical spectroscopy and hyperspectral imaging provide new opportunities. In gastrointestinal surgery the real‐time assessment of the intestinal microcirculation might, for instance, be helpful to facilitate critical decision‐making 28 whether to make an intestinal anastomosis or not. Practical advantages of the non‐invasive optical imaging modalities, discussed here, are that they neither involve radiation exposure nor extra personnel in the operating theatre, together with a negligible extension of operation duration. Only for NIR fluorescence imaging the pre‐ or peroperative administration of a fluorophore (optical dye) is required. The number of currently available optical dyes for fluorescence imaging is restricted. Indocyanine green and methylene blue are FDA
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