Magnetic Resonance-Guided High Intensity Focused Ultrasound for Treating Movement Disorders.

Transcranial magnetic resonance-guided focused ultrasound (MRgFUS) surgery has recently gained favor as a novel, noninvasive alternative to conventional neurosurgery. In contrast to traditional ablative interventions, transcranial MRgFUS surgery is entirely imaging-guided and uses continuous temperature measurements at the target and surrounding tissue taken in real-time. Unlike Gamma Knife radiosurgery, MRgFUS surgery can make a lesion immediately and does not use ionizing radiation. Moreover, since no metallic device is implanted, MR imaging-based diagnosis is not restricted throughout life. An additional strength of transcranial MRgFUS surgery is its ability to focus acoustic energy through the intact skull onto deep-seated targets, while minimizing adjacent tissue damage. Even though the established indications of MRgFUS include bone metastases, uterine fibroids, and breast lesions, several promising preclinical and phase I clinical trials of neuropathic pain, essential tremor, Parkinson's disease (PD), and obsessive-compulsive disorder have demonstrated that the delivery of focused ultrasound energy promises to be a broadly applicable technique. For instance, this technique can be used to generate focal intracranial thermal ablative lesions of brain tumors, or to silence dysfunctional neural circuits and disrupt the blood-brain barrier for targeted drug delivery and the modulation of neural activity. Here we review the general principles of MRgFUS and its current applications, with a special focus on movement disorders such as essential tremor and PD, and discuss controversies and limitations of this technique.

Unilateral magnetic resonance guided focused ultrasound thalamotomy for essential tremor: practices and clinicoradiological outcomes.

BACKGROUND: Several options exist for surgical management of essential tremor (ET), including radiofrequency lesioning, deep brain stimulation and γ knife radiosurgery of the ventralis intermedius nucleus of the thalamus. Recently, magnetic resonance-guided focused ultrasound (MRgFUS) has been developed as a less-invasive surgical tool aimed to precisely generate focal thermal lesions in the brain. METHODS: Patients underwent tremor evaluation and neuroimaging study at baseline and up to 6 months after MRgFUS. Tremor severity and functional impairment were assessed at baseline and then at 1 week, 1 month, 3 months and 6 months after treatment. Adverse effects were also sought and ascertained by directed questions, neuroimaging results and neurological examination. RESULTS: The current feasibility study attempted MRgFUS thalamotomy in 11 patients with medication-resistant ET. Among them, eight patients completed treatment with MRgFUS, whereas three patients could not complete the treatment because of insufficient temperature. All patients who completed treatment with MRgFUS showed immediate and sustained improvements in tremors lasting for the 6-month follow-up period. Skull volume and maximum temperature rise were linearly correlated (linear regression, p=0.003). Other than one patient who had mild and delayed postoperative balance, no patient developed significant postsurgical complications; about half of the patients had bouts of dizziness during the MRgFUS. CONCLUSIONS: Our results demonstrate that MRgFUS thalamotomy is a safe, effective and less-invasive surgical method for treating medication-refractory ET. However, several issues must be resolved before clinical application of MRgFUS, including optimal patient selection and management of patients during treatment.