123 Quantitative analysis of intestinal perfusion with ICG and MB INTRODUCTION Anastomotic leakage (AL) is a highly concerning complication, which can occur after colorectal surgery with anastomosis formation. Impaired blood flow to the bowel is considered the primary factor contributing to AL. Consequently, bowel perfusion assessment is a critical approach to reduce the occurrence of AL 1, 2. Intraoperative near-infrared fluorescence imaging (NIRF), using administration of an optical dye, offers a convenient and versatile method to improve the assessment of anastomotic perfusion. Indocyanine green (ICG) is the dye that is most commonly used for this purpose as it provides favorable results 3-7. Recently, our research team demonstrated in an experimental study that methylene blue (MB), another widely available dye, showed promising results too 8. As it is partly cleared by the kidneys, it was previously demonstrated that it could successfully visualize the ureters intraoperatively. Less expected was the demonstration that it could also be used for intraoperative perfusion imaging, reflecting a potential benefit in comparison to ICG that is exclusively cleared by the liver and subsequently cannot visualize the ureters non-invasively. Our promising results with MB were gathered using a commercially available NIRF imaging system, which can visualize both dyes due to its bimodal properties (QUEST SPECTRUM®, Quest Medical Imaging, Middenmeer, The Netherlands). Since this NIRF imaging system uses two different wavelength modes, it solves one of the drawbacks related to the use of MB, namely its excitation characteristics. MB has an excitation peak of about 700 nm, an excitation wavelength of 668 nm, and an emission of 688 nm which can be seen with the naked eye 9. These characteristics are different from ICG that is excited at around 800nm, until recently requiring a different imaging system. So far, the majority of imaging systems used in MB studies were experimental and not commercially accessible for clinical purposes conversely to the system used in the present study. As the Federal Drug Administration (FDA) and the European Medicines Agency (EMA), have approved the clinical use of MB as well 9, this dye may be promising to use for multipurpose NIRF imaging. Our research team therefore considered it clinically relevant to investigate the use of MB for bowel perfusion assessment. The objective of the current study was to conduct a quantitative analysis of bowel perfusion assessment using a commercially available NIRF imaging system, comparing the visualization obtained with MB and ICG. MATERIALS AND METHODS This study was performed at the central animal facilities of Maastricht University (Maastricht, The Netherlands) and was approved by the local Experimental Animal Committee (DEC) (2017-021-001). All animals were used in compliance with Dutch regulations and legislation concerning animal research. 6
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