The convenience of contrast-enhanced intraoperative ultrasonic cholangiography in liver resection: a study protocol for a randomized, prospective, off-label trial

BACKGROUND: ) with contrast harmonic ultrasonography, enabling real-time visualization that can be repeated on demand without radiation. We hypothesize that CE-IOUSC provides superior procedural convenience while maintaining biliary visualization and safety. METHODS: administered through the cystic duct and evaluated using intraoperative ultrasonography in contrast mode. Cross-over "rescue" cholangiography with the alternative modality is allowed when the assigned method is unsuccessful or inadequate. The primary endpoint is the cumulative time required to complete intraoperative cholangiography, including any additional imaging and repeated attempts. Secondary endpoints include surgeon-rated usability (5-point Likert questionnaire completed by the primary operator immediately after surgery), detectability of biliary structures (segmental visualization rates assessed by predefined criteria), postoperative biliary complications (bile leak or stricture graded by Clavien-Dindo), cross-over rescue efficacy, and safety outcomes (procedure-related adverse events and perioperative laboratory changes). Outcomes will be analyzed primarily on an intention-to-treat basis. DISCUSSION: This trial will quantify whether CE-IOUSC improves the efficiency and usability of intraoperative biliary imaging without compromising visualization or patient safety. The results will inform evidence-based adoption of ultrasound-based cholangiography as a practical alternative to conventional radiographic IOC in liver resection. TRIAL REGISTRATION: Japan Registry of Clinical Trials (jRCT), jRCTs051230202.