Evaluation of Transcranial Direct Current Stimulation (TDCS) of the Brain by Finite Element Method and its Effect in Alzheimer's Patients

Abstract

Transcranial Direct Current Stimulation (TDCS) is a noninvasive technique that utilizes surface electrodes to provide a low amplitude of current density (CD) to the scalp. Numerous neurological diseases are being studied as potential candidates for therapy with this method. The spatial distribution of current density in cerebral areas is determined by both logical parameter selection and subject-specific anatomical variance. Finit components modeling has been proposed as a dependable and beneficial approach for assessing the current flow pattern during TDCS in recent years.The thesis’s objective was to make exploration of mentioned factors on current density distribution. Hence, head models of three different subjects were reconstructed from corresponding structural Magnetic Resonanc Imaging (MRI) scans; a healthy young subject, an elder healthy man and Alzheimer’s patient. There were three main goals in this thesis. The first goal was to develop a new layout for electrods in order to enhance of neural efficiency of neural stimulation. Optimized electrod geometries enhance the "edging" of the electode surface, increasing the variance of the current density across the electrod surface. The current density in the suggested electrodes' human lead was determined using finite element models. The research demonstrates that the fractal electrode's form has an effect on the magnitude of the current density. When fractal electrodes were utilized instead of conventional electrodes, the peak current density for the equivalent inwared stimulus was raised by 1/3. As a result, fractal structures may be considered an excellent way for boosting the penetration of current density throughout the human brain. The second goal was to examine the distortion of current density peresence of atrophy. Numerical simulation results showed that in presence of atrophy the extent of current density value shifted, which reaches the cortical areas was reduced, and peak current density value shifted in comparisonwith healthy head model. The result suggest that current TDCS treatment protocol must be modified for Alzheimer patients. The third goal was investigated through cerebellum stimulation. Surface maps of current density demonstrated that current predominantly flow laterally and passessthrough anterior parts of the cerebellum duo to curvature of scalp and place of the cerebellum in this part. Hence, to compensate dissipation of current density on its way to the cerebellar cortex, applying 2mA Current density could meet the predicted expectations in compare with 1mA.