LEICI   25638
INSTITUTO DE INVESTIGACIONES EN ELECTRONICA, CONTROL Y PROCESAMIENTO DE SEÑALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Study of the Focality of the Electric Field Induced by TMS and its Correlation with the Coil Orientation in Three Regions of Interest: pre-SMA, IFG and PPC
Autor/es:
MIR, PABLO; FERNANDEZ CORAZZA, MARIANO; GOMEZ-FERIA FERREIRO, JOSE; MARTIN-RODRIGUEZ, JUAN FRANCISCO
Lugar:
Baden Baden
Reunión:
Conferencia; 7th International Conference on Non-Invasive Brain Stimulation; 2020
Resumen:
IntroductionThere are certain regions of the brain that play an important role in different pathologies of the brain, and these can be study using TMS. We focus our study on finding the best coil orientation to stimulate three different brain regions: pre supplementary motor area (pre-SMA), inferior frontal gyrus (IFG), and posterior parietal cortex (PPC). The effectiveness of this technique relies on the coil orientation relative to the subject´s head. To better understand the optimal coil orientation, a further analysis must be done studying the anatomy of the brain stimulated regions regarding the coil orientation and the direction of the electric field.ObjectivesIn this study, we examined whether there is an optimal coil orientation for our three volume of interest (VOI) based on the focality of the electric field at different percentiles and the relation with its anatomical properties, including grey matter (GM) volume, cerebrospinal fluid (CSF) volume, and mean gyrus slope.Materials and MethodsThis study was done in 10 different subjects. The effect of switching the coil orientation was studied in three different VOIs: pre-SMA, IFG and CPP. These regions were selected based on published brain atlas; thus, being able to ensure non inter-individual errors (figure 1). We used a finite element model to calculate the induced electric field for eight coils orientations (each 45 degrees), simulating a 70mm and a 40mm coil. In order to obtain the best stimulation angle, we studied the focality of the electric field, examining the module, normal and tangential components (figure 2). This focality showed the ratio of the electric field induced in the brain vs the electric field induced in our VOI, studying this focality at different percentiles: 0%, 10%, 50% and 70%.ResultsOur results indicate that there is not a best coil orientation for any of our volume of interest. There are some orientations that seems to be better than others, but there is a big error for all of them, indicating a big variability depending on the subject. These results seem rational, since the effect of the electric field is highly related to the individual?s brain anatomy. Thus, we completed the study by analyzing the correlation between the CSF volume and the induced electric field. Since the CSF has the highest conductivity value, it will be a determinant factor in the way the field reaches the neurons. The other approach to explain the results was to study the variance of the normal and tangential component of the signal for each individual. To do that we examined the mean angle of the gyrus, providing the mean slope of the GM within or VOI.ConclusionsThe results suggest that there is not a best coil orientation for stimulating these volumes. These are, in fact, highly related to the anatomy of the gyrus and its CSF volume. Thus, to better stimulate these regions, an individual simulation study is recommended prior the brain stimulation.