Advanced intraoperative imaging methods for laparoscopic anatomy navigation Fluorescence imaging Using dedicated laparoscopic fluorescence imaging systems a preoperatively or intraoperatively administered optical dye with fluorescence properties is detectable during laparoscopy (see summary in Table 2.2). Intraoperative fluorescence imaging has been widely investigated for identification of vital anatomical structures, such as blood vessels, extra‐hepatic bile ducts and ureters, but also for the detection of sentinel lymph nodes13,14. Structures are detectable at depths of one centimeter. A disadvantage of fluorescence‐guided real‐time visualization concerns the high costs of both the fluorescent dye and the required camera system. Fluorescence properties of bile acid have been investigated for enhanced visualization of the biliary tract during laparoscopic surgery in mice15 and rabbits16. Mohsen et al.17 showed that intraoperative intravenous fluorescein injection and ultraviolet excitation facilitated identification of the extra‐hepatic biliary anatomy during laparoscopic cholecystectomy. The near‐infrared fluorescence cholangiography (NIRFC) technique after local or intravenous administration of indocyanine green (ICG) has been evaluated in various animal models18‐21 and in open, laparoscopic, and single‐incision laparoscopic cholecystectomy20,22‐24. Promising results were presented for successful intraoperative identification of the common bile duct and the cystic duct, compared to conventional laparoscopic imaging. Another clinical study showed that the NIRFC technique provides significantly earlier identification of the extra‐hepatic bile ducts during dissection of Calot’s triangle25. Real‐time simultaneous imaging of the hepatic and cystic arteries can also be obtained26,27. Next to ICG, methylene blue (MB) is another clinically available contrast agent, which appeared suitable for fluorescence imaging in the aforementioned situations21,26. High sensitivity visualization of the ureters, which is desirable during laparoscopic colorectal surgery, can be provided with a near‐infrared (NIR) fluorescence imaging system after intravenous injection of MB28 or the new optical dye CW800‐CA, which is not yet FDA approved for clinical use29. Notably, CW800‐CA seems to have favorable characteristics compared to ICG30, as its fluorescence intensity is supposed to be many times stronger, resulting in better visibility in adipose tissue. In laparoscopic colorectal surgery it is shown that near‐infrared ICG fluorescence imaging can allow rapid confirmation of lymphatic drainage and sentinel node identification in the mesocolon30,31. The concept has been described earlier in a goat model32: after percutaneous injection of ICG immediate bright fluorescence visualization is obtained of the efferent draining lymph vessels in the mesocolon. 23
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