Inclusion Criteria:  Men 18 or over years old. Patients with castration resistant prostate cancer. Evidence of bone metastases by any imaging technique. Patients due to start treatment with abiraterone or enzalutamide. In the exploratory cohorts, we will include patients due to start treatment with other systemic therapies for advanced prostate cancer (A-taxanes, B-radiopharmaceuticals, C-other therapies). Written (signed and dated) informed consent.  Exclusion Criteria:  Contraindications to MRI. Inability of patient to tolerate whole body MRI (e.g. claustrophobia). Patients who have received radiotherapy within the last three months and with no bone metastases outside the radiotherapy field.