Near‐infrared fluorescence laparoscopy of the cystic duct and artery in pigs 69 Table 5.1 Overview of experimental results Experiment Injected dye Concentration of administered dye (mg/ml) Amount of dye injected (ml) Visualization of cystic artery? Visualization of cystic duct? Time to identification of cystic duct (min) 1 ICG 2.5 1.0 Y Y 20 2 ICG 2.5 1.0 Y Y 22 3 CW800‐CA 0.25 1.0 N N / 4 CW800‐CA 1.0 1.0 N N / 5 CW800‐CA 1.0 3.0 Y Y 11 6 CW800‐CA 1.0 3.0 Y Y 12 ICG = indocyanine green Quantitative fluorescence image analysis For objective assessment of the degree of fluorescence illumination in the extra‐hepatic bile ducts and artery, OsiriX 5.5.1 Imaging Software was used. The fluorescence images were analyzed by determining target‐to‐background ratio (TBR). TBR was defined as the mean fluorescence intensity (FI; in arbitrary units, A.U.) of three point regions of interest (ROIs) in the target (i.e., cystic duct, or cystic artery) minus the mean FI of three background (BG) ROIs in the liver hilum, divided by the mean FI of the three BG ROIs in the liver hilum; in formula: TBR = (FI of target ‐ FI of BG)/FI of BG. Results In the first two experiments ICG fluorescence laparoscopy for identification of the cystic artery (Figure 5.1B) and cystic duct (Figure 5.2B) was successfully conducted. CW800‐ CA dosage in experiments 3 (0.25 mg) and 4 (1.0 mg) was insufficient to obtain fluorescence delineation of these structures. Using a dose of 3 mg CW800‐CA in the last two experiments led to clear visualization of the cystic artery (Figure 5.1D) and cystic duct (Figure 5.2D) in both pigs. Observations of the six experiments are summarized in Table 5.1. Target‐to‐background ratio The target‐to‐background‐ratios (TBR) of the cystic artery versus gallbladder and cystic artery versus liver parenchyma in the arterial phase after ICG injection were ‐0.6 and 0.5 respectively (pig 2, Figure 5.1B, ±30 seconds after dye administration). These data confirm the inability of ICG based imaging to identify the cystic artery when positioned directly on the liver parenchyma. After injection of CW800‐CA, the TBRs of the cystic artery versus gallbladder and cystic artery versus liver parenchyma were 1.1 and 1.7
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