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Concordance between BeamF3 and MRI-neuronavigated target sites for repetitive transcranial magnetic stimulation of the left dorsolateral prefrontal cortex

Concordance between BeamF3 and MRI-neuronavigated target sites for repetitive transcranial magnetic stimulation of the left dorsolateral prefrontal cortex

Authors: 
Arsalan Mir-Moghtadaei, Ruth Caballero, Peter Fried, Michael D. Fox, Katherine Lee, Peter Giacobbe, Z. Jeff Daskalakis, Daniel M. Blumberger, Jonathan Downar
Year: 
2015
Journal: 
Brain Stimulation
Abstract: 

Background
The dorsolateral prefrontal cortex (DLPFC) is a common target for repetitive transcranial magnetic stimulation (rTMS) in major depression, but the conventional "5 cm rule" misses DLPFC in >1/3 cases. Another heuristic, BeamF3, locates the F3 EEG site from scalp measurements. MRI-guided neuronavigation is more onerous, but can target a specific DLPFC stereotaxic coordinate directly. The concordance between these two approaches has not previously been assessed.

Objective
To quantify the discrepancy in scalp site between BeamF3 vs. MRI-guided neuronavigation for left DLPFC.

Methods
Using 100 pre-treatment MRIs from subjects undergoing left DLPFC-rTMS, we localized the scalp site at minimum Euclidean distance from a target MNI coordinate (X-38 Y+44 Z+26) derived from our previous work. We performed nasion-inion, tragus-tragus, and head-circumference measurements on the same subjects' MRIs, and applied the BeamF3 heuristic. We then compared the distance between Beam-F3 and MRI-guided scalp sites.

Results
BeamF3-to-MRI-guided discrepancies were <0.65cm in 50% of subjects, <0.99cm in 75% of subjects, and <1.36cm in 95% of subjects. The angle from midline to the scalp site did not differ significantly using MRI-guided versus BeamF3 methods. However, the length of the radial arc from vertex to target site was slightly but significantly longer (mean 0.35 cm) with MRI-guidance versus BeamF3.

Conclusions
The BeamF3 heuristic may provide a reasonable approximation to MRI-guided neuronavigation for locating left DLPFC in a majority of subjects. A minor optimization of the heuristic may yield additional concordance.

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