This is a single-center, observational cohort study aiming to validate the diagnostic value of MRI-FF in identifying osteoporosis and sarcopenia in patients with chronic kidney disease (CKD). A total of 868 participants, including 434 CKD patients and 434 non-CKD controls, will be enrolled at Beijing Jishuitan Hospital. All subjects will undergo MRI-FF scans of the lumbar spine and thigh to assess bone mineral density and muscle fat fraction. The primary objective is to evaluate the correlation between MRI-FF parameters and conventional diagnostic criteria for osteoporosis and sarcopenia, as well as to determine the optimal cut-off values for early detection. The study duration is from March 2026 to December 2028.