Direct targeting for focused ultrasound thalamotomy in the treatment of movement disorders

Accurate targeting of the ventral intermediate nucleus (VIM) remains a critical challenge in thalamotomy for essential tremor (ET) and tremor-dominant Parkinson's disease (TDPD). Indirect atlas-based methods suffer from anatomical variability and poor visualization of thalamic substructures. Here, the authors evaluated the clinical impact of a direct targeting strategy enabled by fast gray matter acquisition T1 inversion recovery (FGATIR) imaging in MR-guided focused ultrasound (MRgFUS) thalamotomy.

The authors conducted a retrospective cohort study of adult patients who underwent first-time MRgFUS thalamotomy for ET or TDPD at the Oregon Health & Science University between August 2023 and January 2025. Patients treated with FGATIR-guided direct targeting (n = 64, 40 males) were matched to a cohort treated using indirect targeting combined with physiological mapping (n = 52, 36 males). Data were collected from intraoperative recordings and postprocedural imaging, as well as at 1-day, 1-month, and 3-month follow-up evaluations. Procedural efficiency, lesion and edema characteristics, tract involvement, clinical outcomes, and adverse events were assessed.

FGATIR-guided direct targeting significantly reduced the number of sonications (-22%), total sonication time (-32%), and overall procedural duration (-33%) compared with indirect targeting. Lesion volumes (-21%) and perilesional edema (-28%) were smaller in the direct targeting group with less impingement on the internal capsule and medial lemniscus. Direct targeting resulted in a lower incidence of acute balance (-31%), weakness (-25%), sensory (-34%), and speech (-12%) deficits while producing a 14% greater quantitative tremor reduction. Both groups achieved similar subjective tremor control.

FGATIR-based direct targeting improves the safety, precision, and efficiency of MRgFUS thalamotomy without compromising clinical benefit. The FGATIR sequence is widely available on 1.5T and 3T Siemens MRI systems, and this method may be adapted for use with other targets for stereotactic ablation. This direct targeting technique would also be applicable to other forms of thalamotomy, such as Gamma Knife radiosurgery and radiofrequency, further expanding its utility. Direct targeting represents a scalable and patient-centered advancement for stereotactic thalamotomy.