Easy methods to make the neuronavigated targeting of DLPFC accurate and routinely accessible for rTMS

Dorsolateral prefrontal cortex (DLPFC) is the main stimulation target for rTMS treatment of depression. DLPFC is located in the middle frontal gyrus and corresponds to the lateral part of Brodmann Areas 9 and 46. Current methods to locate the DLPFC are either based on head landmarks that are inaccurate, or based on MRI-neuronavigation. Neuronavigated-methods are based either on standardized stereotactic coordinates translated to the individual patient or on brain landmarks requiring neuroanatomical skills for their identification. We developed a script automating the inclusion of already validated targets into patients' MRI, and also a new method to target DLPFC based on neuroanatomical landmarks. The present study aims to assess this new approach.

Four targets were compared on 40 hemispheres: three previously validated methods (2 using superimposition of standardized targets on patient MRI and 1 using neuroanatomical landmarks) and the new one presented here. Resulting targets were presented in the individual space and in stereotactic spaces (MNI and Talairach) with the main objective being to reach the middle frontal gyrus and BA9/46. Target dispersion and distances between targets were assessed.

All targets were located in the middle frontal gyrus. Our proposed neuro-anatomical target was equivalent to or even better than the previously existing one if we consider the criteria of BA46 achievement and dispersion.

The proposed neuroanatomical method and automation of the stereotactic method allow simple and reliable targeting of DLPFC for rTMS treatment.