ICG is a water-soluble dye that predominantly undergoes hepatic metabolism through binding to plasma proteins [15]. The rate of ICG metabolism in the liver is determined by hepatic blood flow, hepatocellular function, and bile excretion [15]. Therefore, ICG metabolism quantification is sometimes conducted preoperatively in patients scheduled for liver resection to determine the extent of the surgical resection. On the other hand, ICG fluorescence imaging during surgery can predict liver graft function and identify perfusion defects [16].

ICG fluorescence imaging in LDLT has primarily been studied for visualizing donor-recipient biliary anastomoses and assessing donor liver quality. In 2010, Mizuno et al. [17] injected ICG through the cystic duct during open left hemihepatectomy to guide real-time visualization of the bile ducts under fluorescence. In 2017, Hong et al. [9] administered 0.05 mg/kg ICG intravenously 30 to 60 minutes prior to laparoscopic liver resection, enabling precise bile duct incisions by clearly delineating the bile duct structures. Unlike traditional angiography, ICG fluorescence offers a multi-angle perspective, enhancing understanding of the spatial relationships between the bile duct and hepatic hilar structures for more accurate incision planning.

Kawaguchi et al. [16] described a case in which ICG was injected during LDLT to detect perfusion defects and identify associated portal vein thrombosis. Dousse et al. [18] performed an analysis involving 76 patients who had undergone DDLT; ICG was administered at a dose of 0.01 mg/kg body weight, and Fluobeam was used to evaluate the correlation between FI and the three-month survival rate, as well as its association with re-transplantation.

There are very few studies that evaluate bile duct perfusion using ICG fluorescence imaging in LT. Coubeau et al. [19] utilized ICG fluorescence angiography to assess the vascularization of the bile duct by performing intraoperative fluoroscopy after administering ICG (0.25 mg/kg) via a central catheter. This technique facilitated the identification and removal of ischemic areas. Follow-up percutaneous cholangiography, conducted six months post-operation, revealed no evidence of stenosis or leakage. This study is analogous to ours in terms of observing bile duct perfusion and identifying ischemic areas with ICG fluorescence angiography. However, our study is more sophisticated: using ICG angiography, we acquired CBD perfusion images before bile duct anastomosis following HA anastomosis in engraftment, analyzed the ICG FI graph patterns, and demonstrated that these patterns vary between patients who developed BCs and those who did not. This study suggests a correlation between BCs and changes in ICG FI over time in the bile duct.

In LT and hepatobiliary surgery, most existing studies using ICG angiography have primarily focused on visualizing bile duct anatomy [20ref21-22]. Unlike these, our study represents a novel approach as it employed ICG angiography to obtain CBD perfusion images of the recipient during LDLT, analyzing the ICG FI graph over time and identifying two distinct patterns. A significant finding from this research is the correlation between extended T_1/2 max durations, lower slope, and the occurrence of BCs in patients undergoing LDLT.

Son et al. [12] demonstrated that quantitative analysis of ICG perfusion patterns using T_1/2 max, slope, and TR (T_1/2 max/T max) can accurately identify poorly perfused segments. While our study aligns with these findings in associating a lower slope and a prolonged T_1/2 max with poor perfusion and anastomosis complications, it differs in that it applied ICG angiography to bowel anastomosis in colorectal surgery and examined the correlation by measuring TR.

Study limitations include the interference from previous ICG injections in the donor, causing the graft bile duct to appear excessively bright and preventing accurate measurement of ICG FI. Furthermore, the study's small sample size of only nine LDLT recipients limits our ability to draw definitive conclusions from the data. The research methodology employs an ICG fluorescence camera and uses Image J (NIH) for measuring NIR FI, which, while sophisticated and accurate, restricts a comprehensive analysis of factors associated with BCs due to the small participant pool.

Despite such limitations, the study offers initial insights that may inform the development of new tools for predicting BCs. Verification through larger, more diverse studies is necessary to strengthen the correlations established and to enhance the predictive accuracy of ICG fluorescence imaging parameters for BCs.

In conclusion, ICG fluorescence imaging is a promising tool for assessing bile duct perfusion and predicting BCs in LDLT patients. Further studies are necessary, but the preliminary findings suggest that ICG imaging could significantly improve postoperative management and patient outcomes.