Direct Localization of the VIM/DRTT Using Quantitative Susceptibility Mapping in Essential Tremor: A Pilot MRI Study.

Accurate localization of the ventral intermediate nucleus (VIM) within the dentatorubrothalamic tract (DRTT) is critical for effective neurosurgical treatment of essential tremor (ET). This study evaluated the feasibility and anatomic specificity of quantitative susceptibility mapping (QSM) for direct VIM/DRTT visualization, comparing it with conventional diffusion tractography-based reconstructions. Twenty-seven participants (10 healthy controls, 17 patients with ET) were enrolled across 2 institutions and imaged on 3T MRI systems. QSM-defined VIM/DRTT regions were manually segmented on the basis of characteristic hypointense susceptibility contrast. Whole-brain diffusion tractography was performed to reconstruct the DRTT, pyramidal tract (PT), and medial lemniscus (ML) tracts. Spatial overlap between QSM- and tractography-defined VIM/DRTT regions was calculated, as well as overlap with neighboring PT and ML tracts to assess specificity. Two participants were excluded due to insufficient VIM/DRTT streamlines in tractography reconstruction. In healthy controls, QSM- and tractography-defined VIM/DRTT showed high spatial correspondence (left: 87.6% [SD, 5.1%]; right: 85.3% [SD, 6.5%]). Patients with ET had slightly lower overlap (mean range: 71.5%-85.1%). Overlap with neighboring PT and ML tracts was minimal (<3.3%), confirming high anatomic specificity of QSM-derived VIM/DRTT regions. QSM enables direct visualization of the VIM/DRTT with high spatial agreement with conventional tractography-based approaches while demonstrating minimal overlap with adjacent tracts. These findings support QSM as a complementary or stand-alone imaging technique for improved, patient-specific neurosurgical targeting in ET.