Abstract MRCP+ metrics are quantitative markers of the biliary tree which can be used to inform biliary tree health. These markers have shown promise as dynamic biomarkers which can be used to support disease monitoring and, by extension, support the assessment of the effects of pharmacotherapies. In this project, Perspectum Inc. seeks to complete the necessary evidence to qualify the MRCP+ metric number of strictures as a monitoring Drug Development Tool for PSC. It is envisioned that this MRCP+ metric will be used in conjunction with clinical assessments, to identify patients who are more likely to meet endpoints (including biochemical and imaging endpoints) in clinical trials signifying appropriate response to treatments. With the funding from this Drug Development Tools Research Grant, and leveraging the close collaboration with the FDA, we will perform a retrospective multi-center longitudinal observational study in 150 participants. Primary objective: 1. To collect and analyze MRCP data to generate 3D models and associated MRCP+ metrics which will be used to determine the change in the MRCP+ metric ‘number of strictures’ in relation to disease progression. Secondary Objectives: 1. To collect clinical data which can be used to determine the prognostic utility of change in the MRCP+ metric ‘number of strictures’ for predicting clinical outcomes (including cholangitis, requirement for ERCP, cirrhosis, hepatic decompensation, hepatobiliary malignancies, liver transplant or death). 2. To collect clinical data which can be used to determine whether change in predicts incidence free transplant free survival. The study will be performed in collaboration with members of the CALiD registry who will include a representative sample of their patient population. Patients must have at least two time points of interim duration of 6 months or more with associated clinical data.