Autosomal Recessive Polycystic Kidney Disease (ARPKD) is a potentially lethal genetic disorder for which there are currently no disease specific treatments. Clinical trials have been limited by the absence of robust measures of disease progression. The overall goal of this 5 year NIH-funded prospective, observational multicenter study conducted at CC (primary site) and Children's Hospital of Philadelphia (CHOP) (collaborating site) is establish a set of rapid, quantitative, and reproducible novel kidney MRI measures applicable to standard clinical MRI scanners, which could serve as potential biomarkers to measure response to therapy in patients across the disease spectrum and all ages. The investigators will recruit a total of 45 ARPKD patients and 15 healthy controls at the the two sites . All subjects will be \> or = 6yrs old with no contraindications to undergoing MRI (non contrast). ARPKD subjects will be recruited into one of 3 cohorts based on their estimated glomerular filtration rate (eGFR): early CKD (eGFR\> or =90ml/min/1.73m2), mild CKD (60-89ml/min/1.73m2) and moderate CKD (30-59ml/min/1.73m2). For ARPKD subjects, participation will last 3 years and consist of a baseline and 3 subsequent annual visits. Healthy controls will only have 1 study visit. Study visits for all participants will include collection of clinical and demographic data, clinical blood and urine tests (E.g. serum creatinine) and MRI imaging. ARPKD (but not healthy subjects) will also undergo a measured GFR test (iohexol clearance) to accurately assess their kidney function.