right-handed woman in her 90s presented with essential tremor involving bilateral arms, head, and voice. The tremors started 15 years ago and progressively became disabling. She had failed propranolol hydrochloride, primidone, and gabapentin, but she had an unremarkable medical history otherwise. Her examination revealed considerable symmetric tremor, with a Clinical Rating Scale for Tremor (score range: 0-132, with the highest score indicating severe tremor) score of 88 and scores of 38 in subscale A (at rest, posture, and action), 26 in subscale B (drawing spiral, handwriting), 24 in subscale C (quality-of-life), and 26 in subscales A and B (right-side tremor). The remainder of the neurological examina-tion results were unremarkable. Preoperative magnetic resonance imaging (MRI) revealed periventricular white-matter changes and mild age-related diffuse atrophy.After a multidisciplinary evaluation, she was not recommended for ventral intermediate nucleus (VIM) deep brain stimulation (DBS) due to her advanced age. Instead, she was offered focused ultrasound (FUS) thalamotomy. Computed tomography imaging determined that her skull was suitable for ultrasonographic treatment; her skull homogeneity was greater than 0.4, as calculated by skull density ratio (SDR, which is the median ratio of skull density between cortical and trabecular bone; higher SDR IMPORTANCE Magnetic resonance imaging-guided focused ultrasound ablation has been approved for the treatment of refractory essential tremor and is being studied for other neurological indications, including dyskinesias and tremor in Parkinson disease, dystonia, neuropathic pain, obsessive-compulsive disorder, epilepsy, and brain tumors. OBJECTIVE To review the scientific foundations of FUS technology, existing neurological applications, and future advances.EVIDENCE REVIEW PubMed was searched for the past 10 years using the terms "transcranial ultrasound," "focused ultrasound," and "neurological applications." Relevant references were selected from the author's reference collection. From the 2855 unique records, 243 publications were screened. After excluding abstracts detailing in vitro studies or non-neurological applications, 86 full texts were retrieved for qualitative review.FINDINGS Advances in the transducer design and electronic phase correction have allowed efficient focusing of ultrasounds for transcranial treatment. The mid-frequency (650 kHz) transducer can make small (4-6 mm in diameter) and precise (accuracy of <2 mm) brain lesions. The treatment monitoring is achieved via "live" anatomical thermography imaging and clinical feedback. The initial results from its clinical application in movement disorders are encouraging. Emerging applications in epilepsy and neurobehavioral and cognitive disorders are being explored. The low-frequency (220 kHz) transducer coupled with microbubbles can potentially enable targeted drug delivery for novel applications, such as Alzheimer disease and brain tumors. Finally, neuromodulation with subthreshold sonications may allow...

Backgro und: The ventral intermediate nucleus of the thalamus is not readily visible on structural magnetic resonance imaging. Therefore, a method for its visualization for stereotactic targeting is desirable. Objective: The objective of this study was to define a tractography-based methodology for the stereotactic targeting of the ventral intermediate nucleus. Methods:The lateral and posterior borders of the ventral intermediate nucleus were defined by tracking the pyramidal tract and medial lemniscus, respectively. A thalamic seed was then created 3 mm medial and anterior to these borders, and its structural connections were analyzed. The application of this method was assessed in an imaging cohort of 14 tremor patients and 15 healthy controls, in which we compared the tractography-based targeting to conventional targeting. In a separate surgical cohort (3 tremor and 3 tremor-dominant Parkinson's disease patients), we analyzed the accuracy of this method by correlating it with intraoperative neurophysiology.

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