Background : Detective flow imaging (DFI) is a novel technology that evaluates low-speed blood flow signals that are difficult to visualize with conventional Doppler techniques. This technique allows for evaluating microvascular signals within tumors in endoscopic ultrasound (EUS) without using contrast agents. In this study, we aimed to investigate the usefulness of DFI for diagnosing biliary tract lesions.  

Methods : A retrospective study was conducted of patients who underwent DFI with EUS between September 2019 and December 2022 at our institution. Patients with biliary tract lesions diagnosed by either endoscopy or pathology were included. Malignant biliary tract lesions were defined as those with histopathological diagnoses of non-invasive or invasive carcinoma. To evaluate the diagnostic ability of DFI for malignant biliary tract lesions, we assessed the presence of tortuous or variable caliber vessels in DFI findings. Inter-observer agreement and the diagnostic ability of DFI in identifying malignant biliary tract lesions were also assessed. Additionally, the DFI findings of intraductal papillary neoplasms (IPNB) and cholangiocarcinoma in patients who underwent surgical resection.

Results : There were 17 cases of cholangiocarcinoma, 9 cases of IPNB, 3 cases of bile duct stone, and 3 other cases.  The sensitivity and specificity for the presence of tortuous or variable caliber vessels for the diagnosis of malignancy were 80% and 43% for tortuous vessels and 68% and 100% for variable caliber vessels, respectively. Interobserver agreement was k=0.63 for tortuous vessels and k=0.75 for variable caliber vessels. DFI identified stalk vessels in 7 of 8 cases (87.5%) of IPNB and in only 1 of 10 cases (10%) of invasive cholangiocarcinoma. The rate of concomitant stalk vessels was significantly higher in IPNB than in invasive cholangiocarcinoma (P<0.01).

Conclusions : DFI is a valuable tool for the differential diagnosis of malignant biliary tract lesions.