Echo-Focusingin Transcranial Focused Ultrasound Thalamotomy for Essential Tremor: A Feasibility Study

Background Transcranial magnetic resonance-guided focused ultrasound (TcMRgFUS) systems currently employ computed tomography (CT)-based aberration corrections, which may provide suboptimal trans-skull focusing. Objectives The objective of this study was to evaluate a contrast agent microbubble imaging-based transcranial focusing method, echo-focusing (EF), during TcMRgFUS for essential tremor. Methods A clinical trial of TcMRgFUS thalamotomy using EF for the treatment of essential tremor was conducted (NCT03935581; funded by InSightec [Tirat Carmel, Israel]). Patients (n = 12) were injected with Definity (Lantheus Medical Imaging, North Billerica, MA) microbubbles, and EF was performed using a research feature add-on to a commercial TcMRgFUS system (ExAblate Neuro, InSightec). Subablative thermal sonications carried out using (1) EF and (2) CT-based aberration corrections were compared via magnetic resonance thermometry, and the optimal focusing method for each patient was employed for TcMRgFUS thalamotomy. Results EF aberration corrections provided increased sonication efficiency, decreased focal size, and equivalent targeting accuracy relative to CT-based focusing. EF aberration corrections were employed successfully for lesion formation in all 12 patients, 3 of whom had previously undergone unsuccessful TcMRgFUS thalamotomy via CT-based focusing. There were no adverse events related directly to the EF procedure. Conclusions EF is feasible and appears safe during TcMRgFUS thalamotomy for essential tremor and improves on the trans-skull focal quality provided by existing CT-based focusing methods. (c) 2020 International Parkinson and Movement Disorder Society