Electrical Modeling of Deep Brain Stimulation
Permanent address of the item is
Aivojen syvästimulaation sähköinen mallintaminen
Deep brain stimulation (DBS) is a relatively new and effective method for treating patients suffering from severe and refractory neurological disorders, such as Parkinson’s disease and epilepsy. In a DBS treatment, stimulation electrode is implanted into the patient’s deep brain structures, which is commonly the subthalamic nucleus in the Parkinson’s disease treatment and the anterior nuclear group of thalamus in the epileptic treatment. Major challenges in the procedure are the correct electrode placement and the proper stimulation parameters. Failure in either one may provoke adverse effects or prevent the effective treatment from occurring. The objective of this thesis was to create a model that could be used to observe the electrical behavior of the deep brain stimulation. Stimulation response was measured with the concept of volume of tissue activated (VTA), which describes the level of neuronal activation. 3D uniform and 2D anatomical models were created for the task. Model included encapsulation, inhomogeneous tissue and anisotropy to give a proper estimate on the electrical behavior. Misplaced electrodes are one of the major concerns in DBS surgeries and 1/3 mm misplacement may correspond to a few volts in amplitude increase. Encapsulation had an impact of requiring stimulation amplitudes to be increased by over 100% of the initial value. Anisotropic fiber tracts and conductivity variations significantly altered the shape of the VTA. In some cases, changing the electrode configuration or active electrode in a DBS lead proved to be more effective alternative than attempting to increase VTA by increasing the stimulation amplitude.