Electricfield estimation in deep transcranial magneticstimulation

Background:

Literature studies [Bersani et al., 2013] showed theability to treat different neuropsychiatric disorders using H1 coil,one of the coils belongs to the Hesed (H) coils, which have beendeveloped specifically for the Deep Transcranial Magnetic Stimulation(dTMS). Despite the clinical trials have obtained positive results, the electricfield distributions inside different cerebralstructures induced by these coils are not yet completely clear.

Objective:

Thisstudy aims to explore the electricfield characteristics induced bythe H1 coils in two realistic head models.

Methods:

The authorsused two human models of the Virtual Family [Christet al., 2010] based on high resolution MRI of healthy volunteers (a26-years-old female and a 34-years-old male). TheH1 coil wasmodelled as current paths according to its real complex windingpatterns and placed 5.5 cm anteriorly the left hemisphere motorcortex of the right-hand abductor pollicis brevis. Moreover, thefigure-of-8 coil was placed alternatively on the right and the leftdorsolateral prefrontal cortex to compare the effect of the stimulation with the H1 coil in both hemispheres. For all simulations,weused a current pulse with a frequency content of 5 kHz and a current intensity adjusted to obtain 120% of the hand motor threshold.Simulations were conducted using the magneto quasi-static low-frequency solver of the simulation platform SEMCAD X.

Results:

The H1 coil induced electricfield with higher amplitudeand a more widespread distribution in both the dorsolateral andmedial prefrontal cortex than thefigure-of-8 coil. Moreover, thepenetration depth of the H1 coil was much higher than thefigure-of-8 coil, particularly in the amygdala and nucleus accumbens, evenif the inducedfields were below theneural threshold.

Conclusions:

This work highlightsthe importance to know thefield distribution to evaluate the experimental results and to optimize the therapeutic treatments.

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