Magnetic Resonance-Guided Focused Ultrasound in the Treatment of Essential Tremor

Abstract

Focused ultrasound (FUS) has been under investigation for neurosurgical applications since the 1940s. Early experiments demonstrated ultrasound as an effective tool for the creation of intracranial lesions; however, they were limited by the need for craniotomy to avoid trajectory damage and wave distortion by the skull, and additionally lacked effective techniques for monitoring. Since then, the development and hemispheric distribution of phased arrays has resolved the issue of the skull and allowed for a completely transcranial procedure. Similarly, advances in magnetic resonance (MR) technology have allowed for the real-time guidance of FUS procedures using MR thermometry. MR-guided FUS (MRgFUS) has primarily been investigated for its thermal lesioning capabilities and was recently approved for use in essential tremor (ET). This approval has reawakened the debate surrounding the use of thalamic deep brain stimulation (DBS) vs. thalamotomy for this indication. In Part I of this work, a contemporary comparison between DBS and MRgFUS is conducted through the comparison of two prospective controlled trials that evaluated the two technologies for the unilateral treatment of refractory ET. In context of prior literature, both DBS and MRgFUS are shown to significantly improve tremor control and QoL. The two approaches are predominantly differentiated by their adverse event (AE) profile. Additional head-to-head comparison on matched clinical populations is required to more accurately compare clinical efficacy and long-term outcomes. In part II of this work a volumetric analysis of lesion characteristics in 20 MRgFUS thalamotomy-treated ET patients is conducted. Lesion location and volume are examined in the context of clinical outcome and treatment parameters. Though accuracy and consistency of MRgFUS targeting was demonstrated, lesion location in the ACPC plane and volume were not linearly correlated with clinical efficacy. The distribution of perilesional edema was associated with reported transient AE. Maximum sonication temperature was found to be correlated with lesion volume. Ongoing work aims to expand this analysis to a larger cohort, characterization of lesion focus in 3D and elaborate on the association between accumulated thermal dose and lesion characteristics.