MR Guided High Intensity Focused Ultrasound for Lumbar Back Pain

Inclusion Criteria: 1. Men and women \> 21 years of age and who are skeletally mature 2. Body mass index ≤ 30 kg/m2 3. Patients who are able to understand and willing to sign a written informed consent document and able to attend all study visits 4. Patients with at least 6 months of chronic lower back pain (LBP) localized to the midline or axial low back, with symptoms attributed to the facet joints on physical examination that have persisted despite conservative therapy. Conservative therapy is defined as systemic pain medications and anti-inflammatory medications, as well as physical therapy, such as massage, heating, hydrotherapy, and strengthening exercises. 5. Patients with Numerical Rating Scale worst lumbar back pain score of at least 4 out of 10 over the 24 hours preceding the time of rating. 6. Patients must have chronic LBP attributed to facet joints as demonstrated by MRI consistent with at least grade 2 facet joint arthritis, with corresponding abnormal activity at the facet joint on 18F-sodium fluoride PET-CT. 7. Patients must have an analgesic response to either prior local anesthetic injection to the facet joint or to radiofrequency ablation of the facet joint, with relapse of pain. 8. The targeted facet joint must be deeper than 10 mm from the skin Exclusion Criteria: 1. Patients with severe lumbar lordosis 2. Patients with contraindication for MR imaging such as implanted metallic devices that are not MRI-safe, size limitations, claustrophobia. etc 3. Patients with known intolerance or allergy to MR contrast agent (gadolinium chelates) including advanced kidney disease (GFR \<30 mL/min/1.73 m2) or on dialysis 4. Pregnant and nursing patients will be excluded from the study because of a contraindication to administering MRI contrast agents to these patients 5. Patients with known intolerance or allergy to medications used for sedation (midazolam), analgesia (fentanyl), and local and regional anesthesia (lidocaine, bupivacaine, and ropivacaine) 6. Patients with evidence of lumbosacral radiculopathy on MRI or physical exam findings, including radicular leg pain, or any neurologic deficit at or below the segmental level of the highest facet to be treated, including subjects with impaired sphincter control 7. Patients with pain at another location that 1. cannot be distinguished from lumbar back pain 2. does not rate at least 2 points less in worst pain score compared to lumbar back pain 3. requires the use of analgesics 8. Patients with gross spinal instability on imaging 9. Patients who have lumbar spinal stabilization hardware in place 10. Target is: * NOT visible by non-contrast MRI, OR * NOT accessible to ExAblate device 11. Individuals who are not able or willing to tolerate the required prolonged stationary position during treatment (can be up to 5 hrs of total table time) 12. Patients with acute medical condition (e.g. pneumonia, sepsis) that is expected to hinder them from completing this study 13. Patients with unstable cardiac status including: 1. Unstable angina pectoris on medication 2. Patients with documented myocardial infarction within six months of protocol entry 3. Congestive heart failure requiring medication (other than diuretic) 4. Patients on anti-arrhythmic drugs 14. Patients with severe hypertension (diastolic BP \> 100 on medication) 15. Patients with severe hematologic, neurologic, or other uncontrolled disease (e.g. platelets \< 50,000/microL, INR \> 1.5) 16. Patients who are taking anti-thrombotic medication 17. Severe cerebrovascular disease (multiple CVAs or CVA within 6 months) 18. Patients with inflammatory arthritides. 19. Patients unable to communicate with the investigator and staff 20. Patients seeking compensation for disability or work injury. 21. Patients who are part of another trial testing other Investigational Agents