Use of High Angular Resolution Diffusion Imaging to Predict Optimal Coil Orientation in TMS

Motivation: Transcranial magnetic stimulation (TMS) is clinically applied for modulation of brain activity. However, stimulation is rarely individualized to subject-specific brain structure, leading to suboptimal stimulation results. Goal(s): We investigated whether high angular resolution diffusion imaging (HARDI) can be employed to predict optimal coil orientation in TMS. Approach: We generated a total of 420 motor-evoked potentials (MEPs) spread across 7 different coil orientations in 19 healthy volunteers. We analyzed the relationship of coil direction, HARDI-derived fiber orientation distribution functions (FODs), and MEP amplitudes. Results: Conditional expectations of the MEP amplitudes dependent on the angular deviations between TMS coil and FOD peaks were derived. Impact: The ability to predict optimal coil orientation based on microstructural tissue properties could help to tailor therapeutic TMS to the individual patient, thus improving clinical TMS applications.