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.

Inclusion Criteria:

1. Age between 18 and 80 years old.
2. Able to understand and sign the informed consent form.
3. Able to complete MRI-FF scans of the lumbar spine and thigh.
4. For CKD group: Confirmed diagnosis of chronic kidney disease (eGFR < 60 mL/min/1.73m² for ≥3 months).
5. For control group: No history of chronic kidney disease and normal renal function.

Exclusion Criteria:

1. Contraindications to MRI (e.g., pacemaker, metal implants, severe claustrophobia).
2. History of primary bone metabolic disorders (e.g., osteoporosis, hyperparathyroidism) unrelated to CKD.
3. Current use of anti-osteoporotic drugs (e.g., bisphosphonates, teriparatide).
4. Severe lower limb deformity or amputation affecting thigh muscle assessment.
5. Inability to cooperate with the scan due to cognitive impairment or severe illness.

The study population consists of two groups: 434 patients with chronic kidney disease (CKD) and 434 age- and sex-matched healthy controls without CKD. All participants are adults aged 18-80 years old who are able to complete the required MRI scans.