Deep Brain Stimulation Electrode Contacts Research Articles

Optimizing indirect targeting of the centromedian nucleus for deep brain stimulation by incorporating third ventricular anatomy.

Deep brain stimulation (DBS) of the centromedian nucleus (CM) is used to treat diverse brain diseases including epilepsy, Tourette syndrome, and disorders of consciousness. However, the CM is challenging to visualize on routine MRI. Many surgeons use an indirect targeting method based on established stereotactic coordinates. The authors aimed to quantify how often a DBS electrode's contacts were positioned within the CM using this approach, and to identify alternative indirect coordinates that are more accurate. Indirect targeting of the CM was performed on 100 MR images obtained in healthy adults, and the resulting coordinates were warped to a common brain template. To estimate positions of DBS contacts along this trajectory, the authors developed a probable electrode location (PEL) mask, modeled on trajectory angles obtained from prior clinical cases. Euclidean and x, y, and z distances between the centroids of the PEL mask and an atlas-based CM mask were measured and defined as error. The percentage of overlaps between the PEL mask and nearby thalamic nuclei was determined. To assess the clinical utility of this methodology, the analysis was validated using 20 MR images obtained in patients with generalized epilepsy, a common clinical indication for CM-DBS. Using standard indirect coordinates, the authors found the average Euclidean error to be 4.40 ± 1.05 mm, and the x, y, and z errors were 4.19 ± 0.97 mm, 0.73 ± 0.65 mm, and 0.66 ± 0.69 mm, respectively. The PEL mask overlap was 52% with the CM and 65% with the ventral posteromedial nucleus. Variation in third ventricular width was the dominant contributor to these errors (r = -0.71). To overcome this variation, the authors developed alternative indirect coordinates: 4.5 mm lateral to the posterolateral corner of the third ventricle at the level of the posterior commissure. With this refinement, the average Euclidean error was reduced to 1.24 ± 0.5 mm, with 84% of the PEL mask within the CM. The unavailability of advanced MRI for direct targeting limits access to CM-DBS in resource-constrained neurosurgical programs. Standard indirect coordinates do not provide optimal targeting of the CM, with most contacts laterally placed in the sensory thalamus. The proposed indirect approach may therefore increase the accuracy and availability of CM-DBS, while reducing side effects.

Seeing Is Believing: Photon Counting Computed Tomography Clearly Images Directional Deep Brain Stimulation Lead Segments and Markers After Implantation

Background and ObjectivesDirectional deep brain stimulation (DBS) electrodes are increasingly used, but conventional computed tomography (CT) is unable to directly image segmented contacts owing to physics-based resolution constraints. Postoperative electrode segment orientation assessment is necessary because of the possibility of significant deviation during or immediately after insertion. Photon-counting detector (PCD) CT is a relatively novel technology that enables high resolution imaging while addressing several limitations intrinsic to CT. We show how PCD CT can enable clear in vivo imaging of DBS electrodes, including segmented contacts and markers for all major lead manufacturers. Materials and MethodsWe describe postoperative imaging and reconstruction protocols we have developed to enable optimal lead visualization. PCD CT images were obtained of directional leads from the three major manufacturers and fused with preoperative 3T magnetic resonance imaging (MRI). Radiation dosimetry also was evaluated and compared with conventional imaging controls. Orientation estimates from directly imaged leads were compared with validated software-based reconstructions (derived from standard CT imaging artifact analysis) to quantify congruence in alignment and directional orientation. ResultsHigh-fidelity images were obtained for 15 patients, clearly indicating the segmented contacts and directional markers both on CT alone and when fused to MRI. Our routine imaging protocol is described. Ionizing radiation doses were significantly lower than with conventional CT. For most leads, the directly imaged lead orientations and depths corresponded closely to those predicted by CT artifact-based reconstructions. However, unlike direct imaging, the software reconstructions were susceptible to 180° error in orientation assessment. ConclusionsHigh-resolution photon-counting CT can very clearly image segmented DBS electrode contacts and directional markers and unambiguously determine lead orientation, with lower radiation than in conventional imaging. This obviates the need for further imaging and may facilitate anatomically tailored directional programming.

Lead location as a determinant of motor benefit in subthalamic nucleus deep brain stimulation for Parkinson's disease.

BackgroundSubthalamic nucleus (STN) deep brain stimulation (DBS) is regarded as an effective treatment for patients with advanced Parkinson’s disease (PD). Clinical benefit, however, varies significantly across patients. Lead location has been hypothesized to play a critical role in determining motor outcome and may account for much of the observed variability reported among patients.ObjectiveTo retrospectively evaluate the relationship of lead location to motor outcomes in patients who had been implanted previously at another center by employing a novel visualization technology that more precisely determines the location of the DBS lead and its contacts with respect to each patient’s individually defined STN.MethodsAnatomical models were generated using novel imaging in 40 PD patients who had undergone bilateral STN DBS (80 electrodes) at another center. Patient-specific models of each STN were evaluated to determine DBS electrode contact locations with respect to anterior to posterior and medial to lateral regions of the individualized STNs and compared to the change in the contralateral hemi-body Unified Parkinson’s Disease Rating Scale Part III (UPDRS-III) motor score.ResultsThe greatest improvement in hemi-body motor function was found when active contacts were located within the posterolateral portion of the STN (71.5%). Motor benefit was 52 and 36% for central and anterior segments, respectively. Active contacts within the posterolateral portion also demonstrated the greatest reduction in levodopa dosage (77%).ConclusionThe degree of motor benefit was dependent on the location of the stimulating contact within the STN. Although other factors may play a role, we provide further evidence in support of the hypothesis that lead location is a critical factor in determining clinical outcomes in STN DBS.

Comparison of methodologies for modeling directional deep brain stimulation electrodes.

Deep brain stimulation (DBS) is an established clinical therapy, and directional DBS electrode designs are now commonly used in clinical practice. Directional DBS leads have the ability to increase the therapeutic window of stimulation, but they also increase the complexity of clinical programming. Therefore, computational models of DBS have become available in clinical software tools that are designed to assist in the identification of therapeutic settings. However, the details of how the DBS model is implemented can influence the predictions of the software. The goal of this study was to compare different methods for representing directional DBS electrodes within finite element volume conductor (VC) models. We evaluated 15 different DBS VC model variants and quantified how their differences influenced estimates on the spatial extent of axonal activation from DBS. Each DBS VC model included the same representation of the brain and head, but the details of the current source and electrode contact were different for each model variant. The more complex VC models explicitly represented the DBS electrode contacts, while the more simple VC models used boundary condition approximations. The more complex VC models required 2–3 times longer to mesh, build, and solve for the DBS voltage distribution than the more simple VC models. Differences in individual axonal activation thresholds across the VC model variants were substantial (-24% to +47%). However, when comparing total activation of an axon population, or estimates of an activation volume, the differences between model variants decreased (-7% to +8%). Nonetheless, the technical details of how the electrode contact and current source are represented in the DBS VC model can directly affect estimates of the voltage distribution and electric field in the brain tissue.

Patient-specific modeling of the volume of tissue activated (VTA) is associated with clinical outcome of DBS in patients with an obsessive-compulsive disorder.

Deep brain stimulation (DBS) promises to treat an increasing number of neurological and psychiatric disorders. DBS outcome is directly a factor of optimal targeting of the relevant brain structures. Computational models can help to interpret a patient's outcome by predicting the volume of tissue activated (VTA) around DBS electrode contacts. Here we report results of a preliminary study of DBS in two patients with obsessive-compulsive disorder and show that VTA predictions, which are based on patient-specific volume conductor models, correlate with clinical outcome. Our results suggest that patient specific VTA calculation can help inform device programing to maximize therapeutic effects and minimize side effects.Clinical Relevance- Patient-specific modeling of the volume of activated tissue can predict clinical outcomes and thus, can help to optimize DBS device programing to maximize therapeutic effects.

Development and testing of implanted carbon electrodes for electromagnetic field mapping during neuromodulation.

Deep brain stimulation electrodes composed of carbon fibers were tested as a means of administering and imaging magnetic resonance electrical impedance tomography (MREIT) currents. Artifacts and heating properties of custom carbon-fiber deep brain stimulation (DBS) electrodes were compared with those produced with standard DBS electrodes. Electrodes were constructed from multiple strands of 7-μm carbon-fiber stock. The insulated carbon electrodes were matched to DBS electrode diameter and contact areas. Images of DBS and carbon electrodes were collected with and without current flow and were compared in terms of artifact and thermal effects in phantoms or tissue samples in 7T imaging conditions. Effects on magnetic flux density and current density distributions were also assessed. Carbon electrodes produced magnitude artifacts with smaller FWHM values compared to the magnitude artifacts around DBS electrodes in spin echo and gradient echo imaging protocols. DBS electrodes appeared 269% larger than actual size in gradient echo images, in sharp contrast to the negligible artifact observed in diameter-matched carbon electrodes. As expected, larger temperature changes were observed near DBS electrodes during extended RF excitations compared with carbon electrodes in the same phantom. Magnitudes and distribution of magnetic flux density and current density reconstructions were comparable for carbon and DBS electrodes. Carbon electrodes may offer a safer, MR-compatible method for administering neuromodulation currents. Use of carbon-fiber electrodes should allow imaging of structures close to electrodes, potentially allowing better targeting, electrode position revision, and the facilitation of functional imaging near electrodes during neuromodulation.

Identification of Somatotopic Organization and Optimal Stimulation Site Within the Subthalamic Nucleus for Parkinson's Disease.

Details of the somatotopy within the subthalamic nucleus (STN) are still poorly understood; however, the STN is a common target of deep brain stimulation (DBS) for Parkinson disease. To examine somatotopic organization within the STN and identify optimal stimulation sites from 77 surgical cases with microelectrode recording. STN-DBS was performed for 77 patients with Parkinson disease between 2010 and 2014. We performed passive movements of each joint and captured single neuronal activities to identify movement-related cells (MRCs). The sites of MRCs and active contacts were determined by measuring their distances from the first contact of DBS electrode. Their positional correlations were directly and indirectly analyzed. The number of obtained MRCs was 264, of which 151 responded to multiple joints. The average x-, y-, and z-coordinates of the cells of the upper and lower limbs from the midcommisural point were 13.1±1.1 and 12.7±1.2, 0.22±1.3 and -0.45±1.5, and -2.5±1.1 and -3.0±1.4 mm, respectively. Most MRCs were distributed in the upper third of the STN, in its superior, lateral, and posterior regions, along the DBS electrode routes. Active contacts were observed to lie slightly inferior, medial, and posterior to the average MRC position. Somatotopic organization of the STN was easier to observe in the present study than in previous studies. Optimal stimulation sites were located inferior, medial, and posterior to the average MRC location. The sites may correspond to associative or motor parts through which fibers from the supplementary motor area pass.

O-12 Different contribution of muscular and cutaneous afferents to the scalp SEPs

Background Although somatosensory evoked potentials (SEPs) represent a largely diffused neurophysiological technique, the pathways generating the short-latency scalp components are not fully known. We aimed to investigate the SEPs recorded from the scalp and deep brain stimulation (DBS) leads to selective electrical stimulation of either muscular or cutaneous afferents. Material and methods SEPs were recorded in 6 patients suffering from advanced Parkinson’s disease who underwent electrode implantation in the pedunculopontine (PPTg) nucleus area. We compared SEPs recorded from the scalp and DBS electrode contacts to electrical stimulation of: (a) the median nerve at the wrist (mixed stimulation), (b) the abductor pollicis brevis motor point (pure stimulation of the muscle afferents), and (c) the distal phalanx of the thumb (pure cutaneous stimulation). High-frequency oscillations (HFOs) subtending the low-frequency SEPs were also analysed. Results The macroelectrode contacts recorded a triphasic (P1-N1-P2) potential and the scalp electrodes recorded all the classical SEP components, including the widespread N18 response, after both median nerve and pure cutaneous stimulation. After motor point stimulation, the scalp N18 component and the PPTg N1 response were not recorded. No difference in the HFOs between the stimulation modalities was found. The scalp N20 component was recorded to stimulation of any modality, even if with different latency and amplitude. Conclusions Considering that both the scalp N18 response and PPTg N1component reflect the activity of a pre-postsynaptic neural network in the cuneatus nucleus, our data suggest that the cuneate response is specifically evoked by cutaneous inputs, while muscle afferents are processed elsewhere.

3-Tesla MRI of deep brain stimulation patients: safety assessment of coils and pulse sequences.

Physicians are more frequently encountering patients who are treated with deep brain stimulation (DBS), yet many MRI centers do not routinely perform MRI in this population. This warrants a safety assessment to improve DBS patients' accessibility to MRI, thereby improving their care while simultaneously providing a new tool for neuromodulation research. A phantom simulating a patient with a DBS neuromodulation device (DBS lead model 3387 and IPG Activa PC model 37601) was constructed and used. Temperature changes at the most ventral DBS electrode contacts, implantable pulse generator (IPG) voltages, specific absorption rate (SAR), and B1+rms were recorded during 3-T MRI scanning. Safety data were acquired with a transmit body multi-array receive and quadrature transmit-receive head coil during various pulse sequences, using numerous DBS configurations from "the worst" to "the most common."In addition, 3-T MRI scanning (T1 and fMRI) was performed on 41 patients with fully internalized and active DBS using a quadrature transmit-receive head coil. MR images, neurological examination findings, and stability of the IPG impedances were assessed. In the phantom study, temperature rises at the DBS electrodes were less than 2°C for both coils during 3D SPGR, EPI, DTI, and SWI. Sequences with intense radiofrequency pulses such as T2-weighted sequences may cause higher heating (due to their higher SAR). The IPG did not power off and kept a constant firing rate, and its average voltage output was unchanged. The 41 DBS patients underwent 3-T MRI with no adverse event. Under the experimental conditions used in this study, 3-T MRI scanning of DBS patients with selected pulse sequences appears to be safe. Generally, T2-weighted sequences (using routine protocols) should be avoided in DBS patients. Complementary 3-T MRI phantom safety data suggest that imaging conditions that are less restrictive than those used in the patients in this study, such as using transmit body multi-array receive coils, may also be safe. Given the interplay between the implanted DBS neuromodulation device and the MRI system, these findings are specific to the experimental conditions in this study.

Biophysical basis of subthalamic local field potentials recorded from deep brain stimulation electrodes.

Clinical deep brain stimulation (DBS) technology is evolving to enable chronic recording of local field potentials (LFPs) that represent electrophysiological biomarkers of the underlying disease state. However, little is known about the biophysical basis of LFPs, or how the patient's unique brain anatomy and electrode placement impact the recordings. Therefore, we developed a patient-specific computational framework to analyze LFP recordings within a clinical DBS context. We selected a subject with Parkinson's disease implanted with a Medtronic Activa PC+S DBS system and reconstructed their subthalamic nucleus (STN) and DBS electrode location using medical imaging data. The patient-specific STN volume was populated with 235,280 multicompartment STN neuron models, providing a neuron density consistent with histological measurements. Each neuron received time-varying synaptic inputs and generated transmembrane currents that gave rise to the LFP signal recorded at DBS electrode contacts residing in a finite element volume conductor model. We then used the model to study the role of synchronous beta-band inputs to the STN neurons on the recorded power spectrum. Three bipolar pairs of simultaneous clinical LFP recordings were used in combination with an optimization algorithm to customize the neural activity parameters in the model to the patient. The optimized model predicted a 2.4-mm radius of beta-synchronous neurons located in the dorsolateral STN. These theoretical results enable biophysical dissection of the LFP signal at the cellular level with direct comparison to the clinical recordings, and the model system provides a scientific platform to help guide the design of DBS technology focused on the use of subthalamic beta activity in closed-loop algorithms. NEW & NOTEWORTHY The analysis of deep brain stimulation of local field potential (LFP) data is rapidly expanding from scientific curiosity to the basis for clinical biomarkers capable of improving the therapeutic efficacy of stimulation. With this growing clinical importance comes a growing need to understand the underlying electrophysiological fundamentals of the signals and the factors contributing to their modulation. Our model reconstructs the clinical LFP from first principles and highlights the importance of patient-specific factors in dictating the signals recorded.

A Wavelet-Based Correlation Analysis Framework to Study Cerebromuscular Activity in Essential Tremor

Objective. Deep brain stimulation (DBS) provides dramatic tremor relief in patients with severe essential tremor (ET). Typically, the VIM nucleus is the most effective brain area to target for high-frequency electrical stimulation in these patients. Correlation analysis between electrical local field potential (LFP) recordings from the thalamic DBS leads and electrical muscle activity from the contralateral tremulous limb has become an attractive practical tool to interpret the LFPs and their association with the tremulous clinical manifestations. Although functional connectivity analysis between brain electrical recordings and electromyographic (EMG) signals from the tremor has been of interest to an increasing number of engineering researchers, there is no well-accepted tailored framework to consistently characterise the association between thalamic electrical recordings and the tremorogenic EMG activity. Methods. This paper proposes a novel framework to address this challenge, including an estimation of the interaction strength using wavelet cross-spectrum and phase lag index while demonstrating the statistical significance of the findings. Results. Consistent results were estimated for single and multiple trials of consecutive or partially overlapping epochs of data. The latter approach reveals a substantial increase on the range of statistically significant dynamic low-frequency interrelationships while decreasing the dynamic range of high-frequency interactions. Conclusion. Results from both simulation and real data demonstrate the feasibility and robustness of the proposed framework. Significance. This study offers the proof of principle required to implement this methodology to uncover VIM thalamic LFP-EMG interactions for (i) better understanding of the pathophysiology of tremor; (ii) objective selection of the DBS electrode contacts with the highest strength of association with the tremorogenic EMG, a particularly useful feature for the implementation of novel multicontact directional leads in clinical practice; and (iii) future research on DBS closed-loop devices.

Sensory percepts induced by microwire array and DBS microstimulation in human sensory thalamus

BackgroundMicrostimulation in human sensory thalamus (ventrocaudal, VC) results in focal sensory percepts in the hand and arm which may provide an alternative target site (to somatosensory cortex) for the input of prosthetic sensory information. Sensory feedback to facilitate motor function may require simultaneous or timed responses across separate digits to recreate perceptions of slip as well as encoding of intensity variations in pressure or touch. ObjectivesTo determine the feasibility of evoking sensory percepts on separate digits with variable intensity through either a microwire array or deep brain stimulation (DBS) electrode, recreating “natural” and scalable percepts relating to the arm and hand. MethodsWe compared microstimulation within ventrocaudal sensory thalamus through either a 16-channel microwire array (∼400 kΩ per channel) or a 4-channel DBS electrode (∼1.2 kΩ per contact) for percept location, size, intensity, and quality sensation, during thalamic DBS electrode placement in patients with essential tremor. ResultsPercepts in small hand or finger regions were evoked by microstimulation through individual microwires and in 5/6 patients sensation on different digits could be perceived from stimulation through separate microwires. Microstimulation through DBS electrode contacts evoked sensations over larger areas in 5/5 patients, and the apparent intensity of the perceived response could be modulated with stimulation amplitude. The perceived naturalness of the sensation depended both on the pattern of stimulation as well as intensity of the stimulation. ConclusionsProducing consistent evoked perceptions across separate digits within sensory thalamus is a feasible concept and a compact alternative to somatosensory cortex microstimulation for prosthetic sensory feedback. This approach will require a multi-element low impedance electrode with a sufficient stimulation range to evoke variable intensities of perception and a predictable spread of contacts to engage separate digits.

Intraoperative Microstimulation Predicts Outcome of Postoperative Macrostimulation in Subthalamic Nucleus Deep Brain Stimulation for Parkinson’s Disease

In deep brain stimulation (DBS) of the subthalamic nucleus for treatment of Parkinson's Disease, a commonly encountered stimulation side effect is involuntary muscle contractions from spread of electrical current to cortico-spinal and cortico-bulbar fibers in the internal capsule. During surgery, a variety of techniques, including microelectrode recording (MER), are used to avoid positioning the DBS electrode too close to the internal capsule. At some centers, MER includes stimulating through the microelectrode (microstimulation). To assess if intraoperative microstimulation can help avoid positioning the DBS electrode too close to the internal capsule. From clinical records, we compiled microelectrode and DBS-electrode locations, microstimulation effect thresholds and DBS side effect thresholds. We found that capsular macrostimulation thresholds were significantly lower in cases where capsular microstimulation effects were observed. In addition, we found that lower-threshold for microstimulation-induced involuntary muscle contractions from a given DBS electrode contact predicts a lower threshold for involuntary muscle contractions as a side effect of stimulation with that contact. Specifically, our results suggest that capsular macrostimulation thresholds below 2V are avoided when the product of microstimulation threshold (in µA) and distance (in mm) is greater than 500. intraoperative microstimulation can help avoid positioning the DBS electrode too close to the internal capsule.

Electrophysiologic Validation of Diffusion Tensor Imaging Tractography during Deep Brain Stimulation Surgery.

Diffusion tensor imaging fiber tractography-assisted planning of deep brain stimulation is an emerging technology. We investigated its accuracy by using electrophysiology under clinical conditions. We hypothesized that a level of concordance between electrophysiology and DTI fiber tractography can be reached, comparable with published modeling approaches for deep brain stimulation surgery. Eleven patients underwent subthalamic nucleus deep brain stimulation. DTI scans and high-resolution T1- and T2-weighted MR imaging was performed at 3T. Corticospinal tracts were traced. We studied electrode positions and current amplitudes that elicited corticospinal tract effects during the operation to determine relative corticospinal tract distance. Postoperatively, 3D deep brain stimulation electrode contact locations and stimulation patterns were applied for the same corticospinal tract distance estimation. Intraoperative electrophysiologic (n = 40) clinical effects in 11 patients were detected. The mean intraoperative electrophysiologic corticospinal tract distance was 3.0 ± 0.6 mm; the mean image-derived corticospinal tract distance (DTI fiber tractography) was 3.0 ± 1.3 mm. The 95% limits of agreement were ±2.4 mm. Postoperative electrophysiology (n = 44) corticospinal tract activation effects were encountered in 9 patients; 39 were further evaluated. Mean electrophysiologic corticospinal tract distance was 3.7 ± 0.7 mm; for DTI fiber tractography, it was 3.2 ± 1.9 mm. The 95% limits of agreement were ±2.5 mm. DTI fiber tractography depicted the medial corticospinal tract border with proved concordance. Although the overall range of measurements was relatively small and variance was high, we believe that further use of DTI fiber tractography to assist deep brain stimulation procedures is advisable if inherent limitations are respected. These results confirm our previously published electric field simulation studies.

P116. DBS electrode imaging using 3D transcranial ultrasound – A feasibility study with first quantitative results

Purpose Deep Brain Stimulation (DBS) is an established surgical treatment for neurodegenerative diseases such as Parkinson’s Disease (PD) or Dystonia. In terms of imaging, pre-operative MRI scans are used for surgical planning and post-operative CT scans for control of electrode placement. Intra-operatively, however, imaging guidance is often avoided, due to contra-indications of DBS electrode contacts with MRI and difficulty of acquiring CT scans. Ultrasound imaging could be an attractive alternative, but has not been investigated yet due to difficult positioning of the transducer in the narrow burr-holes. Recently, there has been interest in the community towards the usage of non-invasive transcranial ultrasound (TCUS) through the pre-aureal bone window. In a seminal work ( Walter, 2012 ), Walter described the intra-operative usage of TCUS for lead electrode imaging and post-operative placement assessment of DBS electrode, showing its potential and limitations. In this work, we investigate, for the first time, the feasibility of using 3D-TCUS for imaging of already implanted Deep Brain Stimulation (DBS) electrodes. As a first step towards this goal, we report electrode localization errors outside of the operating room on six previously operated DBS patients. Methods Post-operative CT scans are registered to already acquired pre-operative T1 and T2 MRI sequences to localize the actual electrode tip locations in MRI. We then acquire 3D-TCUS sweeps and co-register them to the pre-operative MRI as well, using a head-surface point-cloud registration first (using Iterative Closest Points, ICP) and a manual refinement using several pairs of corresponding points on anatomical structures (midbrain, ventricles) in TCUS and MRI. The comparison between electrode tips identified in 3D-TCUS and actual tip positions in CT are a first step towards assessing whether 3D-TCUS could provide a benefit intra-operatively in future. Results Quantitative evaluation is performed by reporting the accuracy of electrode tip localization after ICP-based registration (mean 5.62 mm, stdev 2.26 mm) and after manual registration refinement (mean 4.09 mm, stdev 1.75 mm). Additionally, we provide multiple image examples showing the dependence of 3D-TCUS quality depending on the bone window, and multiple examples of image artifacts in TCUS images and 3D reconstructions. Conclusions Intra-operative 3D ultrasound imaging has potential for electrode tip localization during DBS procedures. 3D transcranial US could be an attractive alternative to intra-cranial imaging through the narrow burr-hole. We report the first results of volumetric 3D-TCUS imaging on already operated patients in a post-operative scenario. Initial results still show a relatively high inaccuracy of electrode tip localization, e.g. due to TCUS artifacts and imperfect registration to the pre-operative MRI. Nevertheless, the potential of TCUS for DBS electrode imaging as described by Walter (2012) can be extended to 3D, allowing for electrode tip and shaft localization. This motivates further work, e.g. on improved MRI-US registration and computer-aided tip detection ( Fig. 1 , Fig. 2 ).

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

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.

Low and high-frequency somatosensory evoked potentials recorded from the human pedunculopontine nucleus

ObjectiveTo investigate the generators of the somatosensory evoked potential (SEP) components recorded from the Pedunculopontine Tegmental nucleus (PPTg). MethodsTwenty-two patients, suffering from Parkinson’s disease (PD), underwent electrode implantation in the PPTg area for deep brain stimulation (DBS). SEPs were recorded from the DBS electrode contacts to median nerve stimulation. ResultsSEPs recorded from the PPTg electrode contacts could be classified in 3 types, according to their waveforms. (1) The biphasic potential showed a positive peak (P16) whose latency (16.05±0.61ms) shifted of 0.18±0.07ms from the lower to the upper contact of the electrode. (2) The triphasic potential showed an initial positive peak (P15) whose latency (15.4±0.2ms) did not change across the DBS electrode contacts. (3) In the last SEP configuration (mixed biphasic and triphasic waveform), the positive peak was bifid including both the P15 and P16 potentials. ConclusionWhile the P16 potential is probably generated by the somatosensory volley travelling along the medial lemniscus, the P15 response represents a far-field potential probably generated at the cuneate nucleus level. SignificanceOur results show the physiological meaning of the somatosensory responses recorded from the PPTg nucleus area.

Connectivity patterns of pallidal DBS electrodes in focal dystonia: A diffusion tensor tractography study

Deep brain stimulation (DBS) of the internal pallidal segment (GPi: globus pallidus internus) is gold standard treatment for medically intractable dystonia, but detailed knowledge of mechanisms of action is still not available. There is evidence that stimulation of ventral and dorsal GPi produces opposite motor effects. The aim of this study was to analyse connectivity profiles of ventral and dorsal GPi. Probabilistic tractography was initiated from DBS electrode contacts in 8 patients with focal dystonia and connectivity patterns compared. We found a considerable difference in anterior–posterior distribution of fibres along the mesial cortical sensorimotor areas between the ventral and dorsal GPi connectivity. This finding of distinct GPi connectivity profiles further confirms the clinical evidence that the ventral and dorsal GPi belong to different functional and anatomic motor subsystems. Their involvement could play an important role in promoting clinical DBS effects in dystonia.

Evaluation of Interactive Visualization on Mobile Computing Platforms for Selection of Deep Brain Stimulation Parameters

In recent years, there has been significant growth in the use of patient-specific models to predict the effects of neuromodulation therapies such as deep brain stimulation (DBS). However, translating these models from a research environment to the everyday clinical workflow has been a challenge, primarily due to the complexity of the models and the expertise required in specialized visualization software. In this paper, we deploy the interactive visualization system ImageVis3D Mobile, which has been designed for mobile computing devices such as the iPhone or iPad, in an evaluation environment to visualize models of Parkinson's disease patients who received DBS therapy. Selection of DBS settings is a significant clinical challenge that requires repeated revisions to achieve optimal therapeutic response, and is often performed without any visual representation of the stimulation system in the patient. We used ImageVis3D Mobile to provide models to movement disorders clinicians and asked them to use the software to determine: 1) which of the four DBS electrode contacts they would select for therapy; and 2) what stimulation settings they would choose. We compared the stimulation protocol chosen from the software versus the stimulation protocol that was chosen via clinical practice (independent of the study). Lastly, we compared the amount of time required to reach these settings using the software versus the time required through standard practice. We found that the stimulation settings chosen using ImageVis3D Mobile were similar to those used in standard of care, but were selected in drastically less time. We show how our visualization system, available directly at the point of care on a device familiar to the clinician, can be used to guide clinical decision making for selection of DBS settings. In our view, the positive impact of the system could also translate to areas other than DBS.

Targeting the Pedunculopontine Nucleus

Pedunculopontine tegmental nucleus (PPTg) deep brain stimulation (DBS) has been used in patients with Parkinson disease. To verify the position of the DBS lead within the pons during PPTg targeting. In 10 Parkinson disease patients undergoing electrode implantation in the PPTg, somatosensory evoked potentials were recorded after median nerve stimulation from the 4 DBS electrode contacts and from 2 scalp leads placed in the frontal and parietal regions. The DBS electrode recorded a P16 potential (latency at contact 0, 16.33 ± 0.76 ms). There was a P16 latency shift of 0.18 ± 0.07 ms from contact 0 (lower) to contact 3 (upper). The scalp electrodes recorded the P14 far-field response (latency, 15.44 ± 0.63 ms) and the cortical N20 potential (latency, 21.58 ± 1.42 ms). The P16 potentials recorded by the intracranial electrode contacts are generated by the volley traveling along the medial lemniscus, whereas the scalp P14 potential represents a far-field response generated at the Obex level. Considering that the distance between the electrode contacts 0 and 3 is 6 mm, the distance of the electrode contact 0 from the Obex (ΔObex) was calculated by the equation: ΔObex = 6 × Δlatency P14- PPTg0/Δlatency PPTg0-PPTg3. The Obex-to-brainstem electrode distance obtained by the neurophysiological method confirmed that the electrode was located within the pons in all patients. Moreover, this distance was very similar to that issued from the individual brain magnetic resonance imaging. Somatosensory evoked potentials may be a helpful tool for calculating the macroelectrode position within the pons during PPTg targeting.