The PDF ultrasound images interpretation is a difficult task for radiologists. The CAT PDF technique is a one of tools for PDF detection in the Cholangiocarcinoma Surveillance. This paper proposes a novel approach for Computer-aided Detection of Periductal Fibrosis in Ultrasound Images for Cholangiocarcinoma Surveillance. This technique consist of PDF image pre-processing method, PDF image edge detection mehtod, and the PDF region identification method