A generalized workflow for conducting electric field-optimized, fMRI-guided, transcranial magnetic stimulation

Area of Science:

• Neuroscience
• Medical Imaging
• Biophysics

Background:

• Transcranial Magnetic Stimulation (TMS) is a noninvasive brain stimulation technique with therapeutic applications in psychiatry.
• Current TMS targeting methods often lack personalization, failing to account for individual anatomical variations and limiting generalizability.
• Optimizing TMS targeting is crucial for enhancing treatment efficacy and reducing variability.

Purpose of the Study:

• To develop and validate a generalized, subject-specific TMS targeting protocol.
• To combine functional magnetic resonance imaging (fMRI) with iterative electric-field (E-field) modeling for precise coil placement and orientation.
• To improve the accuracy and consistency of TMS application across different individuals and target sites.

Main Methods:

• The protocol involves defining a region of interest (ROI), generating subject-specific head models from structural MRI, and preprocessing fMRI data.
• Functional MRI data is used to identify the precise single-subject stimulation site within the ROI.
• Iterative E-field modeling is employed to determine the optimal TMS coil orientation for the identified site.

Main Results:

• The proposed method significantly reduces variability in the stimulation site across subjects compared to standard techniques.
• It achieves a reduced scalp-to-cortical-target distance, enhancing signal focality.
• The protocol demonstrates reduced variability in the optimal coil orientation, leading to more consistent stimulation.

Conclusions:

• Constrained fMRI targeting coupled with iterative E-field modeling offers a generalized approach for optimizing TMS.
• This method enhances the precision and reliability of TMS targeting by accounting for individual neuroanatomy.
• The protocol has the potential to improve the clinical application of TMS for psychiatric and neurological disorders.