CT-based MRI distortion correction reveals systematic coordinate discrepancies in subthalamic nucleus deep brain stimulation planning

Abstract

Background: Accurate subthalamic nucleus (STN) targeting for deep brain stimulation depends on magnetic resonance imaging (MRI) geometric fidelity, yet the impact of MRI distortion correction on STN coordinates remains unclear. We evaluated whether CT-based MRI distortion correction systematically alters anatomically defined STN target coordinates. Methods: This retrospective study included 30 adults with normal intracranial imaging who underwent 1-mm axial T2-weighted MRI and 1-mm brain CT within 2 days. MRI datasets were processed in BrainLab Elements to generate corrected and uncorrected image sets. Bilateral STN targets were independently identified on both datasets by two blinded raters using the intersection of the Bejjani line and the medial STN border. Analyses used per-patient means of bilateral measurements. The primary outcome was the three-dimensional Euclidean distance between corrected and uncorrected coordinates. Results: Mean Euclidean distance was 1.655 +/- 0.299 mm and exceeded the prespecified 1.0 mm threshold in all patients (30/30, 100%p < 0.001). Absolute shifts were greatest along the lateral and anteroposterior axes, with mean |Delta x| of 1.062 +/- 0.274 mm, mean |Delta y| of 1.013 +/- 0.194 mm, and mean |Delta z| of 0.732 +/- 0.135 mm. Signed differences showed a consistent directional pattern, indicating lateral, posterior, and inferior displacement of uncorrected targets relative to corrected targets. Distortion was nonuniform across axes (Friedman chi & sup2= 33.97, p < 0.001), with X approximate to Y > Z. Conclusions: CT-based MRI distortion correction produced substantial, systematic shifts in STN target coordinates. Corrected and uncorrected workflows should not be considered interchangeable in STN deep brain stimulation planning.