Lead-DBS: A toolbox for deep brain stimulation electrode localizations and visualizations

Highlights

• Localization of DBS-electrode contact placements

• Semi-automatic reconstruction method

• Open source Matlab toolbox

• Reconstructions of volumes of activated tissue

Abstract

To determine placement of electrodes after deep brain stimulation (DBS) surgery, a novel toolbox that facilitates both reconstruction of the lead electrode trajectory and the contact placement is introduced. Using the toolbox, electrode placement can be reconstructed and visualized based on the electrode-induced artifacts on post-operative magnetic resonance (MR) or computed tomography (CT) images.

Correct electrode placement is essential for efficacious treatment with DBS. Post-operative knowledge about the placement of DBS electrode contacts and trajectories is a promising tool for clinical evaluation of DBS effects and adverse effects. It may help clinicians in identifying the best stimulation contacts based on anatomical target areas and may even shorten test stimulation protocols in the future.

Fifty patients that underwent DBS surgery were analyzed in this study. After normalizing the post-operative MR/CT volumes into standard Montreal Neurological Institute (MNI)-stereotactic space, electrode leads (n = 104) were detected by a novel algorithm that iteratively thresholds each axial slice and isolates the centroids of the electrode artifacts within the MR/CT-images (MR only n = 32, CT only n = 10, MR and CT n = 8). Two patients received four, the others received two quadripolar DBS leads bilaterally, summing up to a total of 120 lead localizations. In a second reconstruction step, electrode contacts along the lead trajectories were reconstructed by using templates of electrode tips that had been manually created beforehand. Reconstructions that were made by the algorithm were finally compared to manual surveys of contact localizations.

The algorithm was able to robustly accomplish lead reconstructions in an automated manner in 98% of electrodes and contact reconstructions in 69% of electrodes. Using additional subsequent manual refinement of the reconstructed contact positions, 118 of 120 electrode lead and contact reconstructions could be localized using the toolbox.

Taken together, the toolbox presented here allows for a precise and fast reconstruction of DBS contacts by proposing a semi-automated procedure. Reconstruction results can be directly exported to two- and three-dimensional views that show the relationship between DBS contacts and anatomical target regions. The toolbox is made available to the public in form of an open-source MATLAB repository.

Introduction

Deep brain stimulation surgery (DBS) is a highly efficacious treatment option for patients with severe movement disorders such as Parkinson's disease (PD), dystonia and essential tremor (ET). Improvement in motor symptoms as well as quality of life have been proven in several multicenter studies for PD (Deuschl et al., 2006, Krack et al., 2003, Schupbach, 2005); for dystonia (Kupsch et al., 2006, Mueller et al., 2008, Vidailhet et al., 2005, Volkmann et al., 2012); and for ET (Hariz et al., 2008, Schuurman et al., 2000).

Additionally to the DBS stimulation parameters, the correct anatomical description of the electrode contact placements determines the area that is being stimulated and has a major influence on the clinical outcome of chronic DBS. Studies in PD patients undergoing STN DBS have shown that accuracy of electrode placement within the anatomical target region correlates with the motor improvement during DBS (for example Frankemolle et al., 2010, Welter et al., 2014, Wodarg et al., 2012). Similarly, the degree of motor improvement with DBS in dystonia was related to electrode position within the pallidum (Tisch et al., 2007, Schönecker et al., 2014). Although other factors influence the clinical outcome of DBS (Lumsden et al., 2013, Vidailhet et al., 2005), contact mislocation is considered to be the most common cause of a poor clinical response (Ellis et al., 2008, Marks et al., 2009). Accordingly, knowledge about localizations of contacts can be supportive in clinical routines to evaluate DBS effects and may help to define the best contact for chronic DBS, especially in more complex electrode designs with multiple contacts that will be available in the near future.

Moreover, information on electrode localization is crucial for various scientific approaches using depth recordings from DBS target regions of the basal ganglia (Brown and Williams, 2005) or stimulation protocols to evaluate the involvement of the anatomical DBS target region in information processing (Cavanagh et al., 2011, Frank et al., 2007, Green et al., 2013).

Evaluation of electrode placement can be achieved by postoperative magnetic resonance (MR)- or computer tomography (CT)- imaging. Depending on the DBS center, usually one imaging method is established in clinical routines. Electrode placement is most often denoted relative to the anterior commissure–posterior commissure (AC–PC) stereotactic space (in a systematic review, electrode coordinates in this notation were found in 8 of 13 studies; Caire et al., 2013) or within the standardized MNI space (e.g. see Schönecker et al., 2009, Witt et al., 2013). The former method requires manual measurements that are prone to significant inaccuracies (Pallavaram et al., 2008) and does not take anatomical inter-subject variability into account (Starr et al., 1999, Zhu et al., 2002). On the other hand, warping subject-specific anatomic images into a well-defined standard space as the MNI space makes electrode placements comparable over subjects and DBS centers. This also makes it possible to set electrode contacts into relationship with atlas data of target regions (for examples of available subcortical atlas data, e.g. see Jakab et al., 2012, Keuken et al., 2013, Keuken et al., 2014, Prodoehl et al., 2008, Sarnthein et al., 2013, Tzourio-Mazoyer et al., 2002, Yelnik et al., 2003).

After the normalization of MR-images, a time-consuming and observer-dependent manual survey of electrode contacts has usually to take place to determine their positions. This can be done by manually analyzing the terminal portion of the quadripolar DBS electrodes composed of four metallic (platinium/iridium) non-insulated contacts at equidistant intervals which generate susceptibility artifacts on the postoperative MR image (Schönecker et al., 2009). The centers of the artifacts show hypo-intense and represent the centers of the electrode contacts (Pollo et al., 2004, Yelnik et al., 2003; Fig. 1). Usually, this is performed by using a slice-based (two-dimensional, 2D) MR-viewing software, and fiducial landmarks are manually placed upon the electrode contact artifacts.

To overcome the necessity of a manual survey of electrode contacts and to increase precision in this process, we introduce a toolbox to determine the electrode contact coordinates in a semi-automated design. The primary goal is to enable the user with a tool that provides a good starting-point for fast manual fine adjustment of DBS contact localization.