Current density distributions, field distributions and impedance analysis of segmented deep brain stimulation electrodes

Abstract

Deep brain stimulation (DBS) electrodes are designed to stimulate specific areas of the brain. The most widely used DBS electrode has a linear array of 4 cylindrical contacts that can be selectively turned on depending on the placement of the electrode and the specific area of the brain to be stimulated. The efficacy of DBS therapy can be improved by localizing the current delivery into specific populations of neurons and by increasing the power efficiency through a suitable choice of electrode geometrical characteristics. We investigated segmented electrode designs created by sectioning each cylindrical contact into multiple rings. Prototypes of these designs, made with different materials and larger dimensions than those of clinical DBS electrodes, were evaluated in vitro and in simulation. A finite element model was developed to study the effects of varying the electrode characteristics on the current density and field distributions in an idealized electrolytic medium and in vitro experiments were conducted to measure the electrode impedance. The current density over the electrode surface increased towards the edges of the electrode, and multiple edges increased the non-uniformity of the current density profile. The edge effects were more pronounced over the end segments than over the central segments. Segmented electrodes generated larger magnitudes of the second spatial difference of the extracellular potentials, and thus required lower stimulation intensities to achieve the same level of neuronal activation as solid electrodes. For a fixed electrode conductive area, increasing the number of segments (edges) decreased the impedance compared to a single solid electrode, because the average current density over the segments increased. Edge effects played a critical role in determining the current density distributions, neuronal excitation patterns, and impedance of cylindrical electrodes, and segmented electrodes provide a means to increase the efficiency of DBS.

Influence of heterogeneous and anisotropic tissue conductivity on electric field distribution in deep brain stimulation

“…Wei and Grill [41], used finite element models to study the effects of varying electrode characteristics on the current density and field distributions in an idealized electrolytic medium. Yousif et al [26] DTI is performed in some institutions in order to analyse white matter fascicles when planning trajectories during primary anatomical targeting during DBS [44].…”

Mechanisms of Deep Brain Stimulation in Movement Disorders as Revealed by Changes in Stimulus Frequency

“…Improved systems may include segmented electrodes to increase spatial selectivity. 87 Finally, DBS systems can only produce periodic stimulus trains with constant interpulse intervals. If one of the mechanisms of DBS is to change the pattern of activity in the stimulated nucleus, then the temporal pattern of DBS may play an important role in the efficacy of DBS.…”

Method for patient-specific finite element modeling and simulation of deep brain stimulation

“…The distribution of the electric potential in the vicinity of a DBS electrode has previously been modelled using isotropic homogenous tissue [8][9][10][11][12][13][14][15][16]. More recently, Butson et al [17] presented a three dimensional (3D) patient-specific method to predict the volume of tissue activated by DBS based on diffusion tensor images (DTI).…”