The transparent cap-assisted endoscope has the function of fixing field of view and increasing visual space. It has been widely used in gastrointestinal examination and treatment. In this study, the investigators intend to apply transparent cap-assisted choledochoscopy to endoscopic biliary tract exploration and biopsy to investigate whether transparent cap-assisted choledochoscopy can improve operability, visual field clarity, and biopsy accuracy.

Recently, endoscopy has become more widely used in clinical practice. A straightforward method of improving mucosal visualization involves attachment of a transparent cap to the end of the endoscope. It has been widely used in gastrointestinal examination and treatment.This is a before-after study. In patients with suspected bile duct stricture, tandem ERCP combined with SpyGlass choledochoscopy procedures were carried out on the same day in random order, first without a transparent cap and then with a cap (without-to-with), or first with a cap and then without a cap (with-to-without). The differences in maneuverability, visual field clarity and biopsy accuracy of choledochoscopy with and without transparent cap were recorded to explore the application prospect of transparent cap assisted choledochoscopy.

Inclusion Criteria:

• The indications for ERCP.
• Written informed consent

Exclusion Criteria:

• Underlying bleeding disorder
• The platelet count less than 50×10^9/L
• Serious cardio-pulmonary, hepatic or renal disease
• Intolerance to ERCP
• Other high-risk conditions or disease (such as massive ascites, etc.)
• Pregnancy