Perturbing Effect of Stroke on Electric and Magnetic Fields Generated by Transcranial Magnetic Stimulation

Transcranial magnetic stimulation (TMS) is a non-invasive and painless technique, used as a tool in medical therapeutic and diagnostic in neurology. Recently, TMS started to be used in the treatment of stroke post-conditions such as half paralysis and difficulties of pronunciation. The main objective of this paper was to study the effect of stroke on the distribution of magnetic field and current density generated from TMS. Two head models were created: healthy and with stroke. TMS coil was designed and both head models were placed 7 mm below the TMS coil. The finite element analysis was used to calculate the magnitude and spatial distribution of magnetic field and induced currents on head tissues that generated by TMS coil. The results showed that the presence of stroke changed the magnitude and spatial distribution of magnetic field and current density. The value of current density was greater in the stroke in comparison to the gray matter, where stroke is placed. The vector distribution of the magnetic field showed that the stroke changed the distribution by attracting the magnetic vectors to the center of the stroke.

I. Introduction

Methods of non-invasive brain stimulation are increasingly being used in the study of cognitive functions and considered as a promising adjunct therapy in many psychological and neurological disorders [1]. Transcranial magnetic stimulation (TMS) is considered a promising noninvasive, painless brain stimulation modality that used in psychiatry and neurology [2]. TMS involves passing of current through one or more coils positioned above the head to generate a magnetic field that generate induced current. The generated current can be of sufficient magnitude to depolarize neurons and therefore