A method to estimate the spatial extent of activation in thalamic deep brain stimulation

Abstract

Objective-The goal of this study was to develop, evaluate, and apply a method to quantify the unknown spatial extent of activation in deep brain stimulation (DBS) of the ventral intermedius nucleus (Vim) of the thalamus.Methods-The amplitude-distance relationship and the threshold amplitudes to elicit clinical responses were combined to estimate the unknown amplitude-distance constant and the distance between the electrode and the border between the Vim and the ventrocaudal nucleus (Vc) of the thalamus. We tested the sensitivity of the method to errors in the input parameters, and subsequently, applied the method to estimate the amplitude-distance constant from clinicallymeasured threshold amplitudes.Results-The method enabled estimation of the amplitude-distance constant with a median squared error of 0.07-0.23 V/mm 2 and provided an estimate of the distance between the electrode and the Vc/Vim border with a median squared error of 0.01-0.04 mm. Application of the method to clinically-measured threshold amplitudes to elicit paresthesias estimated the amplitude-distance constant to be 0.22 V/mm 2 .Conclusions-The method enabled robust quantification of the spatial extent of activation in thalamic DBS and predicted that stimulation amplitudes of 1-3.5 V would produce a mean effective radius of activation of 2.0-3.9 mm.Significance-Knowing the spatial extent of activation may improve methods of electrode placement and stimulation parameter selection in DBS.

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

“…Although the exact volume of neural tissue influenced during DBS is not known, the radial distance to the outer isolevel is considered to be outside the region where the major effect is taking place during stimulation at -3 V [27,28]. The distance to the inner isolevel, however, may be regarded as within or at the border of the region of influence during standard DBS settings [29].…”

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

“…In order to optimize gL, computed chronaxies were matched to strength-duration data for stimulation in ventral intermedius nucleus of thalamus and the internal segment of the globus pallidus (GPi) [32,33]. Relevant fiber-diameter range for clinical DBS was estimated by matching simulation results to threshold-distance data for thalamic DBS [34].…”

Explaining Clinical Effects of Deep Brain Stimulation through Simplified Target-Specific Modeling of the Volume of Activated Tissue

“…17 (In contradiction to various references, we establish "volume of activated tissue" as VAT instead of VTA to differentiate the term from the ventral tegmental area, a very important anatomic region of the brain in neurosurgery and DBS.) From work of various authors, notably the fundamental progress made by Kuncel, Grill, McIntyre, Butson, Yousif, and others, [8][9][10][11][12][13][14][15][16] we adopted a simple model to estimate the VAT, based on a monopolar stimulation design of a DBS electrode commonly used for PD, tremor, and dystonia. Previous work on axonal modeling 18 and experiments on large neurons as models for white matter 19 show behavior of the VAT lateral distance over the stimulus voltage that can be accurately fitted with a second-order polynomial of the general form:…”

“…While mentionable progress has been made in improving the optimal anatomic target areas for DBS, only a few groups have devoted their effort to the specific aim of modeling and predicting the electromagnetic field of an activated DBS electrode and understanding its interaction with the electromagnetic properties of the surrounding tissue by building volume-conductor electric field models. [8][9][10][11][12][13][14][15][16] Because the size and shape of the volume of VAT depend not only on electrode design and generator settings but more precisely on individual spatially varying tissue parameters and electromagnetic interaction at the electrode-tissue interface, it is impossible to derive a universal model based only on electrode design and stimulation voltage.…”