This is a prospective, randomized, two-arm, phase II study. The purpose of this study is: * To evaluate and compare the efficacy and safety of magnetic resonance-guided focused ultrasound (MRgFUS) and radiofrequency ablation (RFA) for treatment of facet-joint osteoarthritis low back pain. * Determining the effect of the MRgFUS System and RFA for improving functional disabilities and in reducing pain resulting from facet-joint osteoarthritis low back pain. Efficacy will be determined by the level of pain relief (as measured by the Numerical Rating Scale, NRS), decrease in analgesics/opiate, improved quality of life (as measured by the Oswestry Disability Questionnaire, ODQ, and core outcome measures index questionnaire, COMI), pain interference with function (as measured by the Brief Pain Inventory-Interference scale, BPI-QoL), general health status (as measured by the EQ5D), physical exam, X-ray and MRI studies from baseline up to 12-Months post- MRgFUS and radiofrequency treatment. * Evaluate incidence and severity of adverse events associated with the MRgFUS system and RFA used for the treatment of pain resulting from facet-joint osteoarthritis low back pain.