Reliability of targeting methods in TMS for depression: Beam F3 vs. 5.5 cm

Abstract

Background: No consensus exists in the clinical transcranial magnetic stimulation (TMS) field as to the best method for targeting the left dorsolateral prefrontal cortex (DLPFC) for depression treatment. Two common targeting methods are the Beam F3 method and the 5.5 cm rule.

Objective: Evaluate the anatomical reliability of technician-identified DLPFC targets and obtain consensus average brain and scalp MNI152 coordinates.

Methods: Three trained TMS technicians performed repeated targeting using both the Beam F3 method and 5.5 cm rule in ten healthy subjects (n = 162). Average target locations were plotted on 7T structural MRIs to compare inter- and intra-rater reliability, respectively.

Results: (1) Beam F3 inter- and intra-rater reliability was superior to 5.5 cm targeting (p = 0.0005 and 0.0035). (2) The average Beam F3 location was 2.6±1.0 cm anterolateral to the 5.5 cm method.

Conclusions: Beam F3 targeting demonstrates greater precision and reliability than the 5.5 cm method and identifies a different anatomical target.

Keywords: Depression; F3; Neuroimaging; Neuronavigation; Prefrontal; TMS; Targeting.

Figure 1.. Comparing targeting reliability between Beam F3 method and 5.5 cm rule techniques (A,B) and comparing the group mean centroids to other published transcranial magnetic stimulation targets (C,D).

(A) Scatter plot of all 162 technician measurements plotted on an MNI composite scalp for Beam F3 (red) and 5.5 cm rule (green). The black circles demonstrate the group average centroids for each targeting method. (B) Box and whisker plot showing the inter-rater and intra-rater reliability between methods, represented by the median distance from each individual measure to the group average centroid. The horizontal black lines on each plot represent the median Euclidean distance for each measurement method, and the colored boxes represent the interquartile range. The whiskers represent the maximum and minimum values as defined by the extension of the upper or lower quartile value by 1.5 times the interquartile range. Outliers denoted as open circles. The Beam F3 technique demonstrated less variability both within and across technicians (*p = 0.0035, **p = 0.0005). (C,D) Variability in DLPFC coordinates depicted on the cortical surface (C) and the scalp surface (D). In addition to the 5.5 cm rule (green) and Beam F3 (red) group centroids derived from this study, we also show a dorsolateral prefrontal cortex target associated with antidepressant response as published in Herbsman et al. (2009, magenta)^; a prefrontal cortex target proposed based on Brodmann areas and working memory task activation in Rusjan et al. (2010, purple)^; a target activated by working memory tasks on functional MRI in Fried et al. (2014, blue)^; a prefrontal target anti-correlated with the subgenual cingulate cortex based on group average resting-state functional connectivity MRI in Fox et al. (2012, orange)^; and a stimulation target proposed for neuronavigated TMS in Fitzgerald et al. (2009, cyan)^. All targets are plotted on MNI152 atlas cortical and scalp surfaces. Our Beam F3 target most closely approximates with the Fried et. al. (2014) dorsolateral prefrontal cortex target. ^Reference details are listed in Supplemental Tables 1 & 2.