The primary purpose of this study is to assess the safety of MRI-guided focused ultrasound (MRgFUS) in patients with chronic neuropathic pain whose medicines are not working well. The device that will be used to create and send ultrasound waves through the skull is called the ExAblate Transcranial system. The ultrasounds waves will precisely target a small part of the brain known as the thalamus. Chronic neuropathic pain is a common type of disabling pain that affects people.