Elin Diczfalusy

Relationship between Neural Activation and Electric Field Distribution during Deep Brain Stimulation

Models and simulations are commonly used to study deep brain stimulation (DBS). Simulated stimulation fields are often defined and visualized by electric held isolevels or volumes of tissue activated (VTA). The aim of the present study was to evaluate the relationship between stimulation held strength as defined by the electric potential V, the electric held E, and the divergence of the electric held ∇²V, and neural activation. Axon cable models were developed and coupled to finite-element DBS models in three-dimensional (3-D). Field thresholds (V_T, E_T, and ∇² V_T) were derived at the location of activation for various stimulation amplitudes (1 to 5 V), pulse widths (30 to 120 μs), and axon diameters (2.0 to 7.5 μm). Results showed that thresholds for V_T and ∇² V_T were highly dependent on the stimulation amplitude while E_T were approximately independent of the amplitude for large axons. The activation held strength thresholds presented in this study may be used in future studies to approximate the VTA during model-based investigations of DBS without the need of computational axon models.

Deep Brain Stimulation of the Pallidum Internum for Gilles de la Tourette Syndrome: A Patient‐Specific Model‐Based Simulation Study of the Electric Field

The aim of this study was to investigate the deep brain stimulation (DBS) electric field distribution in proton‐density MRI scans visualizing the globus pallidus internus (GPi) of patients with Gilles de la Tourette syndrome (GTS), along with its relation to the anatomy.

Patient-Specific Modeling and Simulation of Deep Brain Stimulation

Deep brain stimulation (DBS) is widely used for reduction of symptoms caused by movement disorders. In this chapter a patient-specific finite element method for modeling and simulation of DBS electric parameters is presented. The individual’s stereotactic preoperative MR-batch of images is used as input to the model in order to classify tissue type and allot electrical conductivity for cerebrospinal fluid, blood and grey as well as white matter. With patient-specific positioning of the DBS electrodes the method allows for investigation of the relative electric field changes in relation to anatomy and DBS-settings. Examples of visualization of the patient-specific electric entities together with the surrounding anatomy are given. The use of the method is exemplified on patients with Parkinson’s disease. Future applications including multiphysics simulations and applicability for new DBS targets and symptoms are discussed.

A diffusion tensor-based finite element model of microdialysis in the deep brain.

Microdialysis of the basal ganglia was recently used to study neurotransmitter levels in relation to deep brain stimulation. In order to estimate the anatomical origin of the obtained data, the maximum tissue volume of influence (TVImax) for a microdialysis catheter was simulated using the finite element method. This study investigates the impact of brain heterogeneity and anisotropy on the TVImax using diffusion tensor imaging (DTI) to create a second-order tensor model of the basal ganglia. Descriptive statistics showed that the maximum migration distance for neurotransmitters varied by up to 55% (n = 98,444) for DTI-based simulations compared with an isotropic reference model, and the anisotropy differed between different targets in accordance with theory. The size of the TVImax was relevant in relation to the size of the anatomical structures of interest, and local tissue properties should be accounted for when relating microdialysis data to their anatomical targets.

Neurotransmitter levels in basal ganglia during levodopa and deep brain stimulation treatment in Parkinson's disease

The mechanism by which deep brain stimulation of the nucleus subthalamicus improves Parkinsons disease symptoms remains unclear. In a previous perioperative study, we showed that there might be alterations of neurotransmitter levels in the globus pallidum interna during deep brain stimulation of the nucleus subthalamicus.

Simulations and visualizations for interpretation of brain microdialysis data during deep brain stimulation

Microdialysis of the basal ganglia was used in parallel to deep brain stimulation (DBS) for patients with Parkinsons disease. The aim of this study was to patient-specifically simulate and visualize the maximum tissue volume of influence (TVImax) for each microdialysis catheter and the electric field generated around each DBS electrode. The finite element method (FEM) was used for the simulations. The method allowed mapping of the anatomical origin of the microdialysis data and the electric stimulation for each patient. It was seen that the sampling and stimulation targets differed among the patients, and the results will therefore be used in the future interpretation of the biochemical data.