Analysis of patient-specific stimulation with segmented leads in the subthalamic nucleus

Abstract

Objective Segmented deep brain stimulation leads in the subthalamic nucleus have shown to increase therapeutic window using directional stimulation. However, it is not fully understood how these segmented leads with reduced electrode size modify the volume of tissue activated (VTA) and how this in turn relates with clinically observed therapeutic and side effect currents. Here, we investigated the differences between directional and omnidirectional stimulation and associated VTAs with patient-specific therapeutic and side effect currents for the two stimulation modes. Approach Nine patients with Parkinson’s disease underwent DBS implantation in the subthalamic nucleus. Therapeutic and side effect currents were identified intraoperatively with a segmented lead using directional and omnidirectional stimulation (these current thresholds were assessed in a blinded fashion). The electric field around the lead was simulated with a finite-element model for a range of stimulation currents for both stimulation modes. VTAs were estimated from the electric field by numerical differentiation and thresholding. Then for each patient, the VTAs for given therapeutic and side effect currents were projected onto the patient-specific subthalamic nucleus and lead position. Results Stimulation with segmented leads with reduced electrode size was associated with a significant reduction of VTA and a significant increase of radial distance in the best direction of stimulation. While beneficial effects were associated with activation volumes confined within the anatomical boundaries of the subthalamic nucleus at therapeutic currents, side effects were associated with activation volumes spreading beyond the nucleus’ boundaries. Significance The clinical benefits of segmented leads are likely to be obtained by a VTA confined within the subthalamic nucleus and a larger radial distance in the best stimulation direction, while steering the VTA away from unwanted fiber tracts outside the nucleus. Applying the same concepts at a larger scale and in chronically implanted patients may help to predict the best stimulation area.

Neural selectivity, efficiency, and dose equivalence in deep brain stimulation through pulse width tuning and segmented electrodes

“…In the context of directionally segmented electrodes, it is particularly important to consider biophysical dose-equivalence parameters when changing the number of active segmented contacts, rather than modulating amplitude through equivalence in measures like energy. As recently well established, segmenting contacts significantly alters the VTA shape and size [37]. Applying the same amplitude from ring mode on only one portion of a segmented electrode can result in overshooting stimulation in the direction of the segmented contact and spillover of stimulation around the back of the electrode in the unintended direction, reducing the utility of the directional electrode.…”

Lateralized Effect of Thalamic Deep Brain Stimulation Location on Verbal Abstraction

“…An anatomical structure in the DISTAL atlas was considered activated if its intersection volume with VTA was greater than 1 mm 3 , as DBS effects have be observed with a minimum stimulated volume of $1 mm 3 for the nuclei of interest. 20,21 The geometric center of each such VTA was used to represent the active stimulation location for every subject (Fig. 1B).…”

Deep-Brain Stimulation for Essential Tremor and Other Tremor Syndromes: A Narrative Review of Current Targets and Clinical Outcomes

“…When the DBS lead is not directly at the ideal stimulation target, however, more current is required to reach the target. This results in a larger volume of tissue activated which can involve adjacent structures (e.g., Vc nucleus, medial lemniscus and internal capsule) and generate side-effects [67]. Directional leads have been developed to allow eccentric stimulation around the lead's axis and On a standard Vim approach using an entry point 2.5 cm lateral to the midline and 1 cm anterior to the coronal suture, a single lead can often simultaneously traverse the Vim (on proximal contacts) and the Raprl (on distal contacts).…”