Methodology for Focality Homogenization in Magnetic Stimulation of Biological Tissues

Transcranial Magnetic Stimulation (TMS) is a type of neuromodulation used to regulate the neuronal activity to treat several brain disorders. In TMS, E-fields are induced by time-varying B-fields using coils from outside the head. Different definitions are found in the literature for the E-field focality in TMS [1-5], most of them with different measurement methodologies. Another common finding is definitions of “focality” without target area and/or focal distance, which are intrinsically related. Furthermore, to evaluate the degree of magnetic stimulation, a criterion indicating how well the stimulated area overlaps the targeted area is required. This work proposes a function and methodology for focality quantification considering target area, focal distance, peak value and stimulation threshold. New definitions describe the suitability of coils for specific stimulation applications and offer a general framework for comparison under homogeneous methodology, parameters and nomenclature.

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