Determining the Orientation of Directional Deep Brain Stimulation Electrodes Using 3D Rotational Fluoroscopy

Detection of deep brain stimulation lead position and orientation in patients using magnetoencephalography

OBJECTIVE

Deep brain stimulation (DBS) programming in patients with directional DBS requires precise lead position and orientation knowledge. Current computed tomography (CT)-based methods expose patients to radiation. This study investigates a non-radiation-based magnetic detection approach using magnetoencephalography (MEG) in four Parkinson's disease patients.

METHODS

MEG recordings were performed under omnidirectional and directional electrode configurations. Three patients were measured with individualized head-casts to minimize head movement. Magnetic detection was applied to determine DBS lead's position and orientation, compared with those derived from postoperative CT imaging.

RESULTS

Conventional MEG recordings without head-casts achieved lead position and orientation accuracies of up to 17.3 mm and 24.1°. The use of head-casts improved accuracies to 5.8 ± 1.3 mm and 8.8 ± 2.2° at best. Higher mean errors indicate the presence of systematic biases, primarily caused by the MEG system's limited spatial precision. Reduced error variability demonstrates potential for 1-2 mm localization and 2-4° orientation accuracy.

CONCLUSIONS

While magnetic lead position detection is inferior to established approaches, DBS lead orientation could be determined with sufficient accuracy for potential clinical use. Advances in MEG technology may offer improvements in spatial precision and detection accuracy.

SIGNIFICANCE

This method may serve as a radiation-free alternative to imaging-based approaches.

Potential for reduction of radiation dose in the assessment of the lead orientation in directional deep brain stimulation electrodes

PURPOSE

Directional deep brain stimulation (dDBS) relies on electrodes steering the stimulation field in a specific direction. Post implantation, however, the intended and real orientation of the lead frequently deviates e.g. due to torque of the electrode. The orientation is assessed by postoperative imaging such as C-arm cone-beam CT (CBCT) using 3D rotational fluoroscopy and multi-slice CT (MSCT). The objective is to determine the effect of different X-ray systems such as CBCT and MSCT, and scan acquisition parameters on effective radiation doses.

MATERIAL AND METHODS

We retrospectively investigated the dose area product (DAP) and dose length product (DLP) of patients who underwent both CBCT and MSCT after dDBS surgery. These metrics were then converted into the effective dose by established conversion coefficients. For CBCT, the feasible dose optimization by collimation was virtually assessed. Univariate analysis was performed to determine differences.

RESULTS

Among 88 patients median effective dose was 0.20 ± 0.07 mSv in CBCT and 2.11 ± 0.33 mSv in MSCT (p < 0.001). The field of view (FOV) in CBCT can be collimated in craniocaudal orientation by 33.6 % and mediolaterally by 60.8 %. This optimized collimation implies an effective dose reduction of 76 % (p < 0.001). Comparison of the effective dose of MSCT vs. CBCT revealed a significant dose reduction by 90.3 % (p < 0.001), whereas optimal collimation by 97.7 % (p < 0.001).

CONCLUSIONS

For assessment of dDBS orientation, CBCT had significantly lower radiation doses compared to MSCT. Optimized collimation in CBCT allows for a further substantial dose reduction. Moreover, the proposed approach is applicable on other neuroimaging procedures such as 3D visualization of treated intracranial aneurysm.

Intraoperative 3D fluoroscopy accurately predicts final electrode position in deep brain stimulation surgery

PURPOSE

In the absence of an intraoperative CT or MRI setup, post-implantation confirmation of electrode position in deep brain stimulation (DBS) requires patient transportation to the radiology unit, prolonging surgery time. This project aims to validate intraoperative 3D fluoroscopy (3DF), a widely available tool in Neurosurgical units, as a method to determine final electrode position.

METHODS

We performed a retrospective study including 64 patients (124 electrodes) who underwent DBS at our institution. Intraoperative 3DF after electrode implantation and postoperative volumetric CT were acquired. The Euclidean coordinates of the electrode tip displayed in both imaging modalities were determined and inter-method deviations were assessed. Pneumocephalus was quantified and its potential impact in determining the electrode position analyzed. Finally, 3DF and CT-imposed exposure to radiation was compared.

RESULTS

The difference between the electrode tip estimated by 3DF and CT was 0.85 ± 0.03 mm, and not significantly different (p = 0.11 for the distance to MCP assessed by both methods), but was, instead, highly correlated (p = 0.91; p < 0.0001). Even though pneumocephalus was larger in 3DF (6.89 ± 1.76 vs 5.18 ± 1.37 mm3 in the CT group, p < 0.001), it was not correlated with the difference in electrode position measured by both techniques (p = 0.17; p = 0.06). Radiation exposure from 3DF is significantly lower than CT (0.36 ± 0.03 vs 2.08 ± 0.05 mSv; p < 0.0001).

CONCLUSIONS

Intraoperative 3DF is comparable to CT in determining the final DBS electrode position. Being a method with fewer radiation exposure, less expensive, faster and that avoids patient transportation outside the operation room, it is a valid tool to replace postoperative CT.

3D-visualization of segmented contacts of directional deep brain stimulation electrodes via registration and fusion of CT and FDCT

OBJECTIVES

3D-visualization of the segmented contacts of directional deep brain stimulation (DBS) electrodes is desirable since knowledge about the position of every segmented contact could shorten the timespan for electrode programming. CT cannot yield images fitting that purpose whereas highly resolved flat detector computed tomography (FDCT) can accurately image the inner structure of the electrode. This study aims to demonstrate the applicability of image fusion of highly resolved FDCT and CT to produce highly resolved images that preserve anatomical context for subsequent fusion to preoperative MRI for eventually displaying segmented contactswithin anatomical context in future studies.

MATERIAL AND METHODS

Retrospectively collected datasets from 15 patients who underwent bilateral directional DBS electrode implantation were used. Subsequently, after image analysis, a semi-automated 3D-registration of CT and highly resolved FDCT followed by image fusion was performed. The registration accuracy was assessed by computing the target registration error.

RESULTS

Our work demonstrated the feasibility of highly resolved FDCT to visualize segmented electrode contacts in 3D. Semiautomatic image registration to CT was successfully implemented in all cases. Qualitative evaluation by two experts revealed good alignment regarding intracranial osseous structures. Additionally, the average for the mean of the target registration error over all patients, based on the assessments of two raters, was computed to be 4.16 mm.

CONCLUSION

Our work demonstrated the applicability of image fusion of highly resolved FDCT to CT for a potential workflow regarding subsequent fusion to MRI in the future to put the electrodes in an anatomical context.

Evaluation of the Rotational Stability of Directional Deep Brain Stimulation Leads: A Case Series and Systematic Review

BACKGROUND

The rotational stability of directional deep brain stimulation leads is a major prerequisite for sustained clinical effects. Data on directional lead stability are limited and controversial.

METHODS

 We aimed to evaluate the long-term rotational stability of directional leads and define confounding factors in our own population and the current literature. We retrospectively evaluated the orientation of directional leads in patients with available postoperative computed tomography (CT; T1; day of surgery) and an additional postoperative image (T2; CT or rotational fluoroscopy) performed more than 7 days after the initial scan. The potential impact of intracranial air was assessed. We also reviewed the literature to define factors impacting stability.

RESULTS

 Thirty-six leads were evaluated. The mean follow-up between T1 and T2 was 413.3 (7-1,171) days. The difference in rotation between T1 and T2 was 2.444 ± 2.554 degrees (range: 0-9.0 degrees). The volume of intracranial air did not impact the rotation. The literature search identified one factor impacting the stability of directional leads, which is the amount of twist applied at implantation.

CONCLUSION

 Directional leads for deep brain stimulation show stable long-term orientation after implantation. Based on our literature review, large amounts of twist during implantation can lead to delayed rotation and should thus be avoided.

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

BACKGROUND AND OBJECTIVES

Directional 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 METHODS

We 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.

RESULTS

High-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.

CONCLUSIONS

High-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.

Directional electrodes in deep brain stimulation: Results of a survey by the European Association of Neurosurgical Societies (EANS)

Introduction

Directional Leads (dLeads) represent a new technical tool in Deep Brain Stimulation (DBS), and a rapidly growing population of patients receive dLeads.

Research question

The European Association of Neurosurgical Societies(EANS) functional neurosurgery Task Force on dLeads conducted a survey of DBS specialists in Europe to evaluate their use, applications, advantages, and disadvantages.

Material and methods

EANS functional neurosurgery and European Society for Stereotactic and Functional Neurosurgery (ESSFN) members were asked to complete an online survey with 50 multiple-choice and open questions on their use of dLeads in clinical practice.

Results

Forty-nine respondents from 16 countries participated in the survey (n = 38 neurosurgeons, n = 8 neurologists, n = 3 DBS nurses). Five had not used dLeads. All users reported that dLeads provided an advantage (n = 23 minor, n = 21 major). Most surgeons (n = 35) stated that trajectory planning does not differ when implanting dLeads or conventional leads. Most respondents selected dLeads for the ability to optimize stimulation parameters (n = 41). However, the majority (n = 24), regarded time-consuming programming as the main disadvantage of this technology. Innovations that were highly valued by most participants included full 3T MRI compatibility, remote programming, and closed loop technology.

Discussion and conclusion

Directional leads are widely used by European DBS specialists. Despite challenges with programming time, users report that dLeads have had a positive impact and maintain an optimistic view of future technological advances.

Visualization of volume of tissue activated modeling in a clinical planning system for deep brain stimulation

BACKGROUND

Pathway activating models try to describe stimulation spread in deep brain stimulation (DBS). Volume of tissue activated (VTA) models are simplified model variants allowing faster and easier computation. Our study aimed to investigate, how VTA visualization can be integrated into a clinical workflow applying directional electrodes using a standard clinical DBS planning system.

METHODS

Twelve patients underwent DBS, using directional electrodes for bilateral subthalamic nucleus (STN) stimulation in Parkinson's disease. Preoperative 3T magnetic resonance imaging was used for automatic visualization of the STN outline, as well as for fiber tractography. Intraoperative computed tomography was used for automatic lead detection. The Guide XT software, closely integrated into the DBS planning software environment, was used for VTA calculation and visualization.

RESULTS

VTA visualization was possible in all cases. The percentage of VTA covering the STN volume ranged from 25% to 100% (mean: 60±25%) on the left side and from 0% to 98% (51±30%) on the right side. The mean coordinate of all VTA centers was: 12.6±1.2 mm lateral, 2.1±1.2 mm posterior, and 2.3±1.4 mm inferior in relation to the midcommissural point. Stimulation effects can be compared to the VTA visualization in relation to surrounding structures, potentially facilitating programming, which might be especially beneficial in case of suboptimal lead placement.

CONCLUSIONS

VTA visualization in a clinical planning system allows an intuitive adjustment of the stimulation parameters, supports programming, and enhances understanding of effects and side effects of DBS.

General Algorithm Applicability in Determining DBS Lead Orientation: Adapting 2D and 3D X-Ray Techniques for SenSightTM Leads

INTRODUCTION

With recent advancements in deep brain stimulation (DBS), directional leads featuring segmented contacts have been introduced, allowing for targeted stimulation of specific brain regions. Given that manufacturers employ diverse markers for lead orientation, our investigation focuses on the adaptability of the 2017 techniques proposed by the Cologne research group for lead orientation determination.

METHODS

We tailored the two separate 2D and 3D X-ray-based techniques published in 2017 and originally developed for C-shaped markers, to the dual-marker of the Medtronic SenSight™ lead. In a retrospective patient study, we evaluated their feasibility and consistency by comparing the degree of agreement between the two methods.

RESULTS

The Bland-Altman plot showed favorable concordance without any noticeable systematic errors. The mean difference was 0.79°, with limits of agreement spanning from 21.4° to -19.8°. The algorithms demonstrated high reliability, evidenced by an intraclass correlation coefficient of 0.99 (p < 0.001).

CONCLUSION

The 2D and 3D algorithms, initially formulated for discerning the circular orientation of a C-shaped marker, were adapted to the marker of the Medtronic SenSight™ lead. Statistical analyses revealed a significant level of agreement between the two methods. Our findings highlight the adaptability of these algorithms to different markers, achievable through both low-dose intraoperative 2D X-ray imaging and standard CT imaging.

The Impact of Burr Hole Device and Lead Design on Deep Brain Stimulation Lead Stability in Benchtop and Ovine Models

BACKGROUND AND OBJECTIVES

A market-released deep brain stimulation (DBS) lead and burr hole device (BHD) have been used for more than ten years to provide stable DBS therapy using leads with four equally distributed cylindrical electrodes along the distal lead length. Newer directional leads cluster segmented electrodes at the center of the electrode array. This work tests the hypothesis that improved chronic translational and rotational stability through enhanced BHD design may ensure that these newer directional electrodes remain in a stable orientation near the stimulation target to maintain therapy and maximize opportunities to adjust therapy, if needed.

MATERIALS AND METHODS

A new DBS lead system (commercially available in the United States and termed "new" throughout the manuscript) has been developed, and a combination of bench testing (45 product samples tested) and chronic sheep studies (17 animals followed for 13.5 weeks on average) was conducted to test the hypothesis that design changes incorporated into the new DBS system further stabilize the position and orientation of a DBS lead tip compared with a legacy DBS system.

RESULTS

The new DBS system demonstrated a 55% relative improvement in chronic lead tip stability compared with the legacy DBS system with over a decade of clinical use. In a bench test, the new system required 79% more applied torque and 203% more lead body revolutions to rotate the lead in the BHD than the legacy system that was not designed to offer rotational stability.

CONCLUSIONS

These measurements quantitatively demonstrate that DBS system design can positively improve lead translational and rotational stability and show that system design is an important consideration for future product development.

A Novel and Simple Method Using Computed Tomography Streak Artifact to Determine the Orientation of Directional Deep Brain Stimulation Leads

BACKGROUND AND OBJECTIVES

Directional leads have garnered widespread use in deep brain stimulation (DBS) because of the ability to steer current and maximize the therapeutic window. Accurate identification of lead orientation is critical to effective programming. Although directional markers are visible on 2-dimensional imaging, precise orientation may be difficult to interpret. Recent studies have suggested methods of determining lead orientation, but these involve advanced intraoperative imaging and/or complex computational algorithms. Our objective is to develop a precise and reliable method of determining orientation of directional leads using conventional imaging techniques and readily available software.

METHODS

We examined postoperative thin-cut computed tomography (CT) scans and x-rays of patients who underwent DBS with directional leads from 3 vendors. Using commercially available stereotactic software, we localized the leads and planned new trajectories precisely overlaying the leads visualized on CT. We used trajectory view to locate the directional marker in a plane orthogonal to the lead and inspected the streak artifact. We then validated this method with a phantom CT model by acquiring thin-cut CT images orthogonal to 3 different leads in various orientations confirmed under direct visualization.

RESULTS

The directional marker creates a unique streak artifact that reflects the orientation of the directional lead. There is a hyperdense symmetric streak artifact parallel to the axis of the directional marker and a symmetric hypodense dark band orthogonal to the marker. This is often sufficient to infer the direction of the marker. If not, it at least renders 2 opposite possibilities for the direction of the marker, which can then be easily reconciled by comparison with x-ray images.

CONCLUSION

We propose a method to determine orientation of directional DBS leads in a precise manner on conventional imaging and readily available software. This method is reliable across DBS vendors, and it can simplify this process and aid in effective programming.

Technical evolution of pediatric neurosurgery: the evolution of intraoperative imaging

Imaging has always been fundamental to neurosurgery, and its evolution over the last century has made a dramatic transformation in the ability of neurosurgeons to define pathology and preserve normal tissue during their operations. In the mid-70 s, the development of computerized cross-sectional imaging with CT scan and subsequently MRI have revolutionized the practice of neurosurgery. Later, further advances in computer technology and medical engineering have allowed the combination of many modalities to bring them into the operating theater. This evolution has allowed real-time intraoperative imaging, in the hope of helping neurosurgeons achieve accuracy, maximal safe resection, and the implementation of minimally invasive techniques in brain and spine pathologies. Augmented reality and robotic technologies are also being applied as useful intra-operative techniques that will improve surgical planning and outcomes in the future. In this article, we will review imaging modalities and provide our institutional perspective on how we have integrated them into our practice.

Variations in Determining Actual Orientations of Segmented Deep Brain Stimulation Leads Using the DiODe Algorithm: A Retrospective Study Across Different Lead Designs and Medical Institutions

INTRODUCTION

Directional deep brain stimulation (DBS) leads have become widely used in the past decade. Understanding the asymmetric stimulation provided by directional leads requires precise knowledge of the exact orientation of the lead in respect to its anatomical target. Recently, the DiODe algorithm was developed to automatically determine the orientation angle of leads from the artifact on postoperative computed tomography (CT) images. However, manual DiODe results are user-dependent. This study analyzed the extent of lead rotation as well as the user agreement of DiODe calculations across the two most common DBS systems, namely, Boston Scientific's Vercise and Abbott's Infinity, and two independent medical institutions.

METHODS

Data from 104 patients who underwent an anterior-facing unilateral/bilateral directional DBS implantation at either Northwestern Memorial Hospital (NMH) or Albany Medical Center (AMC) were retrospectively analyzed. Actual orientations of the implanted leads were independently calculated by three individual users using the DiODe algorithm in Lead-DBS and patients' postoperative CT images. The deviation from the intended orientation and user agreement were assessed.

RESULTS

All leads significantly deviated from the intended 0° orientation (p < 0.001), regardless of DBS lead design (p < 0.05) or institution (p < 0.05). However, the Boston Scientific leads showed an implantation bias toward the left at both institutions (p = 0.014 at NMH, p = 0.029 at AMC). A difference of 10° between at least two users occurred in 28% (NMH) and 39% (AMC) of all Boston Scientific and 76% (NMH) and 53% (AMC) of all Abbott leads.

CONCLUSION

Our results show that there is a significant lead rotation from the intended surgical orientation across both DBS systems and both medical institutions; however, a bias toward a single direction was only seen in the Boston Scientific leads. Additionally, these results raise questions into the user error that occurs when manually refining the orientation angles calculated with DiODe.

Usage of augmented reality for interventional neuraxial procedures: A phantom-based study

BACKGROUND

Neuraxial access is necessary for an array of procedures in anaesthesia, interventional pain medicine and neurosurgery. The commonly used anatomical landmark technique is challenging and requires practical experience.

OBJECTIVE

We aimed to evaluate the technical feasibility of an augmented reality-guided approach for neuraxial access and tested the hypothesis that its use would improve success as the primary outcome. As secondary outcomes, we measured accuracy and the procedural duration compared with the classical landmark approach.

DESIGN

A randomised phantom-based study.

SETTING

The three-dimensional image of a thoracolumbar phantom spine model with the surrounding soft tissue was created with a neurosurgical planning workstation and ideal trajectories to the epidural space on the levels T10-L1 were planned using a paramedian approach. Both the three-dimensional holographic image of the spine and the trajectories were transferred to an augmented reality-headset. Four probands (two anaesthesiologists, one neuroradiologist and one stereotactic neurosurgeon) performed 20 attempts, 10 each of either conventional landmark or augmented reality-guided epidural punctures, where anatomical level, side and sequence of modality were all randomised.

OUTCOME MEASURES

Accuracy was assessed by measuring Euclidean distance and lateral deviation from the predefined target point. Success of epidural puncture on the first attempt was compared between the conventional and the augmented reality-guided approaches.

RESULTS

Success was achieved in 82.5% of the attempts using augmented reality technique, compared with 40% with the conventional approach [ P  = 0.0002, odds ratio (OR) for success: 7.07]. Euclidean distance (6.1 vs. 12 mm, P  < 0.0001) and lateral deviation (3.7 vs. 9.2 mm, P  < 0.0001) were significantly smaller using augmented reality. Augmented reality-guided puncture was significantly faster than with the conventional landmark approach (52.5 vs. 67.5 s, P  = 0.0015).

CONCLUSION

Augmented reality guidance significantly improved the accuracy and success in an experimental phantom model of epidural puncture. With further technical development, augmented reality guidance might prove helpful in anatomically challenging neuraxial procedures.

Analysis of the intended and actual orientations of directional deep brain stimulation leads across deep brain stimulation systems

Deep brain stimulation (DBS) offers therapeutic benefits to patients suffering from a variety of treatment-resistant neurological and psychiatric disorders. The newest generation of DBS devices now offer directional leads, which utilize segmented electrodes to direct current asymmetrically to the neuronal tissue. Since segmented electrodes offer a larger degree of freedom for contact positioning, it is critical to assess how well the surgically intended and the actual orientation of the lead match to facilitate programming and allow appropriate interpretation of the therapeutic outcome. Postoperative image analysis algorithms, such as DiODe, are commonly used to determine DBS leads' actual orientation. In this work, we used DiODe to compare the deviation between intended and actual orientations of DBS leads across two most commonly implanted directional DBS systems, namely, Boston Scientific Cartesia™ and St. Jude Medical Infinity. This study is the first to investigate the rotation of leads from both DBS systems in a large group of 86 patients. Clinical Relevance- Our results quantify the variability between the surgically intended and actual orientations of Boston Scientific Vercise and St. Jude Medical Infinity DBS systems thus highlighting the need to develop more precise implantation procedures.

Deviation of the orientation angle of directional deep brain stimulation leads quantified by intraoperative stereotactic X-ray imaging

Directional deep brain stimulation (dDBS) provides multiple programming options. Knowledge of the spatial lead orientation is useful for time-efficient programming. Recent studies demonstrated deviations of up to 90° from the intended orientation angle. We examined the deviation of dDBS-lead orientation for leads from two different manufacturers using intraoperative stereotactic (STX) X-ray images. Intraoperative 2D-X-ray images were acquired after implantation of the first lead (TP1) and the second lead (TP2) enabling the estimation of the spatial position of the first lead at TP1 and TP2 and of changes of the orientation for a defined time period. Two investigators retrospectively estimated the orientation of the directional marker for 64 patients. The mean deviation from intended spatial orientation was 40.8° ± 46.1° for all examined leads. The spatial orientation of the first lead did not significantly change within a period of approximately 1 h. The degree of deviation did not differ significantly between two lead manufacturers but depended on the lead fixation technique. Our results showed deviations from the intended orientation angle immediately after the insertion of dDBS leads. The initial spatial orientation remained stable for approximately 1 h and was not caused by technical properties of the implanted lead. Hence, it was most probably the result of unintended mechanical torsion during insertion and/or fixation. Because precise determination of the lead orientation is mandatory for target-oriented dDBS programming, the use of additional imaging suitable for precise 3D visualization of lead contacts and/or the positioning marker is recommended.

Sweet spots of standard and directional leads in patients with refractory essential tremor: white matter pathways associated with maximal tremor improvement

OBJECTIVE

In patients with essential tremor (ET) treated with standard deep brain stimulation (sDBS) whose ET had progressed and who no longer received optimal benefit from sDBS, directional deep brain stimulation (dDBS) may provide better tremor control. Current steering may provide better coverage of subcortical structures related to tremor control in patients with ET and significant progression without optimal response to sDBS.

METHODS

This study included 6 patients with ET initially treated with sDBS whose tremor later progressed and who then underwent reimplantation with dDBS to optimize their tremor control. To investigate the differences in the local effects of sDBS and dDBS, the authors generated the volume of tissue activation (VTA) to calculate the sweet spots associated with the best possible tremor control with no side effects. Then, to investigate the anatomical structures associated with maximal tremor control, the white matter pathways of the posterior subthalamic areas (PSAs) were generated and their involvement with the sDBS and dDBS sweet spots was calculated.

RESULTS

Tremor improvement was significantly better with dDBS (68.4%) than with sDBS (48.7%) (p = 0.017). The sDBS sweet spot was located within the ventral intermediate nucleus, whereas the sweet spot of the dDBS was mainly located within the PSA. The sweet spots of both sDBS and dDBS involved a similar portion of the cerebellothalamic pathway. However, the dDBS had greater involvement of the pallidofugal pathways than the sDBS.

CONCLUSIONS

In patients with ET treated with sDBS who later had ET progression, dDBS provided better tremor control, which was related to directionality and a more ventral position. The involvement of both the cerebellothalamic and pallidofugal pathways obtained with dDBS is associated with additional improvement over the sDBS.

Deciphering the Network Effects of Deep Brain Stimulation in Parkinson's Disease

INTRODUCTION

Deep brain stimulation of the subthalamic nucleus (STN-DBS) is an established therapy for Parkinson's disease (PD). However, a more detailed characterization of the targeted network and its grey matter (GM) terminals that drive the clinical outcome is needed. In this direction, the use of MRI after DBS surgery is now possible due to recent advances in hardware, opening a window for the clarification of the association between the affected tissue, including white matter fiber pathways and modulated GM regions, and the DBS-related clinical outcome. Therefore, we present a computational framework for reconstruction of targeted networks on postoperative MRI.

METHODS

We used a combination of preoperative whole-brain T1-weighted (T1w) and diffusion-weighted MRI data for morphometric integrity assessment and postoperative T1w MRI for electrode reconstruction and network reconstruction in 15 idiopathic PD patients. Within this framework, we made use of DBS lead artifact intensity profiles on postoperative MRI to determine DBS locations used as seeds for probabilistic tractography to cortical and subcortical targets within the motor circuitry. Lastly, we evaluated the relationship between brain microstructural characteristics of DBS-targeted brain network terminals and postoperative clinical outcomes.

RESULTS

The proposed framework showed robust performance for identifying the DBS electrode positions. Connectivity profiles between the primary motor cortex (M1), supplementary motor area (SMA), and DBS locations were strongly associated with the stimulation intensity needed for the optimal clinical outcome. Local diffusion properties of the modulated pathways were related to DBS outcomes. STN-DBS motor symptom improvement was highly associated with cortical thickness in the middle frontal and superior frontal cortices, but not with subcortical volumetry.

CONCLUSION

These data suggest that STN-DBS outcomes largely rely on the modulatory interference from cortical areas, particularly M1 and SMA, to DBS locations.

MaDoPO: Magnetic Detection of Positions and Orientations of Segmented Deep-Brain Stimulation Electrodes: A Radiation-Free Method Based on Magnetoencephalography

Background: Current approaches to detect the positions and orientations of directional deep-brain stimulation (DBS) electrodes rely on radiative imaging data. In this study, we aim to present an improved version of a radiation-free method for magnetic detection of the position and the orientation (MaDoPO) of directional electrodes based on a series of magnetoencephalography (MEG) measurements and a possible future solution for optimized results using emerging on-scalp MEG systems. Methods: A directional DBS system was positioned into a realistic head–torso phantom and placed in the MEG scanner. A total of 24 measurements of 180 s each were performed with different predefined electrode configurations. Finite element modeling and model fitting were used to determine the position and orientation of the electrode in the phantom. Related measurements were fitted simultaneously, constraining solutions to the a priori known geometry of the electrode. Results were compared with the results of the high-quality CT imaging of the phantom. Results: The accuracy in electrode localization and orientation detection depended on the number of combined measurements. The localization error was minimized to 2.02 mm by considering six measurements with different non-directional bipolar electrode configurations. Another six measurements with directional bipolar stimulations minimized the orientation error to 4°. These values are mainly limited due to the spatial resolution of the MEG. Moreover, accuracies were investigated as a function of measurement time, number of sensors, and measurement direction of the sensors in order to define an optimized MEG device for this application. Conclusion: Although MEG introduces inaccuracies in the detection of the position and orientation of the electrode, these can be accepted when evaluating the benefits of a radiation-free method. Inaccuracies can be further reduced by the use of on-scalp MEG sensor arrays, which may find their way into clinics in the foreseeable future.

Reduced Programming Time and Strong Symptom Control Even in Chronic Course Through Imaging-Based DBS Programming

Objectives: Deep brain stimulation (DBS) programming is based on clinical response testing. Our clinical pilot trial assessed the feasibility of image-guided programing using software depicting the lead location in a patient-specific anatomical model. Methods: Parkinson's disease patients with subthalamic nucleus-DBS were randomly assigned to standard clinical-based programming (CBP) or anatomical-based (imaging-guided) programming (ABP) in an 8-week crossover trial. Programming characteristics and clinical outcomes were evaluated. Results: In 10 patients, both programs led to similar motor symptom control (MDS-UPDRS III) after 4 weeks (medicationOFF/stimulationON; CPB: 18.27 ± 9.23; ABP: 18.37 ± 6.66). Stimulation settings were not significantly different, apart from higher frequency in the baseline program than CBP (p = 0.01) or ABP (p = 0.003). Time spent in a program was not significantly different (CBP: 86.1 ± 29.82%, ABP: 88.6 ± 29.0%). Programing time was significantly shorter (p = 0.039) with ABP (19.78 ± 5.86 min) than CBP (45.22 ± 18.32). Conclusion: Image-guided DBS programming in PD patients drastically reduces programming time without compromising symptom control and patient satisfaction in this small feasibility trial.

Linking immune-mediated damage to neurodegeneration in multiple sclerosis: could network-based MRI help?

Inflammatory demyelination characterizes the initial stages of multiple sclerosis, while progressive axonal and neuronal loss are coexisting and significantly contribute to the long-term physical and cognitive impairment. There is an unmet need for a conceptual shift from a dualistic view of multiple sclerosis pathology, involving either inflammatory demyelination or neurodegeneration, to integrative dynamic models of brain reorganization, where, glia-neuron interactions, synaptic alterations and grey matter pathology are longitudinally envisaged at the whole-brain level. Functional and structural MRI can delineate network hallmarks for relapses, remissions or disease progression, which can be linked to the pathophysiology behind inflammatory attacks, repair and neurodegeneration. Here, we aim to unify recent findings of grey matter circuits dynamics in multiple sclerosis within the framework of molecular and pathophysiological hallmarks combined with disease-related network reorganization, while highlighting advances from animal models (in vivo and ex vivo) and human clinical data (imaging and histological). We propose that MRI-based brain networks characterization is essential for better delineating ongoing pathology and elaboration of particular mechanisms that may serve for accurate modelling and prediction of disease courses throughout disease stages.

DiODe v2: Unambiguous and Fully-Automated Detection of Directional DBS Lead Orientation

Directional deep brain stimulation (DBS) leads are now widely used, but the orientation of directional leads needs to be taken into account when relating DBS to neuroanatomy. Methods that can reliably and unambiguously determine the orientation of directional DBS leads are needed. In this study, we provide an enhanced algorithm that determines the orientation of directional DBS leads from postoperative CT scans. To resolve the ambiguity of symmetric CT artifacts, which in the past, limited the orientation detection to two possible solutions, we retrospectively evaluated four different methods in 150 Cartesia™ directional leads, for which the true solution was known from additional X-ray images. The method based on shifts of the center of mass (COM) of the directional marker compared to its expected geometric center correctly resolved the ambiguity in 100% of cases. In conclusion, the DiODe v2 algorithm provides an open-source, fully automated solution for determining the orientation of directional DBS leads.

Surgical Strategy for Directional Deep Brain Stimulation

Deep brain stimulation (DBS) is a well-established treatment for drug-resistant involuntary movements. However, the conventional quadripole cylindrical lead creates electrical fields in all directions, and the resulting spread to adjacent eloquent structures may induce unintended effects. Novel directional leads have therefore been designed to allow directional stimulation (DS). Directional leads have the advantage of widening the therapeutic window (TW), compensating for slight misplacement of the lead and requiring less electrical power to provide the same effect as a cylindrical lead. Conversely, the increase in the number of contacts from four to eight and the addition of directional elements has made stimulation programming more complex. For these reasons, new treatment strategies are required to allow effective directional DBS. During lead implantation, the directional segment should be placed in a "sweet spot," and the orientation of the directional segment is important for programming. Trial-and-error testing of a large number of contacts is unnecessary, and efficient and systematic execution of the programmed procedure is desirable. Recent improvements in imaging technologies have enabled image-guided programming. In the future, optimal stimulations are expected to be programmed by directional recording of local field potentials.

Determining the rotational orientation of directional deep brain stimulation electrodes using magnetoencephalography

Objective.The aim of the present study was to evaluate the effect of different electrode configurations on the accuracy of determining the rotational orientation of the directional deep brain stimulation (DBS) electrode with our previously published magnetoencephalography (MEG)-based method.Approach.A directional DBS electrode, along with its implantable pulse generator, was integrated into a head phantom and placed within the MEG sensor array. Predefined bipolar electrode configurations, based on activation of different directional and omnidirectional contacts of the electrode, were set to generate a defined magnetic field during stimulation. This magnetic field was then measured with MEG. Finite element modeling and model fitting approach were used to calculate electrode orientation.Main results.The accuracy of electrode orientation detection depended on the electrode configuration: the vertical configuration (activation of two directional contacts arranged one above the other) achieved an average accuracy of only about 41 ^∘. The diagonal configuration (activation of the electrode tip and a single directional contact at the next higher level of the electrode) achieved an accuracy of 13^∘, while the horizontal electrode configuration (activation of two adjacent directional contacts at the same electrode level) achieved the best accuracy of 6^∘. The accuracy of orientation detection of the DBS electrode depends on the change in spatial distribution of the magnetic field with the rotation of the electrode along its own axis. In the vertical configuration, rotation of the electrode has a small effect on the magnetic field distribution, while in the diagonal or horizontal configuration, electrode rotation has a significant effect on the magnetic field distribution.Significance.Our work suggests that in order to determine rotational orientation of a DBS electrode using MEG, horizontal configuration should be used as it provides the most accurate results compared to other possible configurations.

Directional Deep Brain Stimulation Can Target the Thalamic "Sweet Spot" for Improving Neuropathic Dental Pain

BACKGROUND

Neuropathic dental pain (NDP) is a chronic pain condition that is notoriously difficult to treat. To date, there are no deep brain stimulation (DBS) studies on this specific pain condition and no optimal target or "sweet spot" has ever been defined.

OBJECTIVE

To determine the optimal thalamic target for improving this condition by utilizing the steering abilities of a directional DBS electrode (Vercise CartesiaTM Model DB-2202-45, Boston Scientific).

METHODS

A literature search and review of our database identified 3 potential thalamic targets. A directional lead was implanted in a patient with NDP and its current steering used to test the effects in each nucleus. The patient reported her pain after 2 wk of stimulation in a prospective randomized blinded trial of one. Quality of life measurements were performed before and after 3 mo on their best setting.

RESULTS

We identified 3 potential nuclei: the centromedian (CM), ventral posterior medial (VPM), and anterior pulvinar. The best results were during VPM stimulation (>90% reduction in pain) and CM stimulation (50% reduction). Following 3 mo of VPM-DBS in combination of lateral CM stimulation, their pain disability index dropped (from 25 to 0) and short form 36 improved (from 67.5 to 90).

CONCLUSION

VPM stimulation in combination with CM stimulation is a promising target for NDP. DBS electrode directionality can be used to test multiple targets and select a patient specific "sweet spot" for NDP treatment.

Deep brain stimulation electrodes may rotate after implantation-an animal study

Directional deep brain stimulation (dDBS) electrodes allow to steer the electrical field in a specific direction. When implanted with torque, they may rotate for a certain time after implantation. The aim of this study was to evaluate whether and to which degree leads rotate in the first 24 h after implantation using a sheep brain model. dDBS electrodes were implanted in 14 sheep heads and 3D rotational fluoroscopy (3D-RF) scans were acquired to visualize the orientation of the electrode leads. Electrode leads were clockwise rotated just above the burr holes (180° n = 6, 360° n = 6, 2 controls) and 3D-RF scans were again acquired after 3, 6, 13, 17, and 24 h, respectively. One hundred eighty degree rotated electrodes showed an initial rotation of 83.5° (range: 35.4°-128.3°) and a rotation of 114.0° (range: 57°-162°) after 24 h. With 360° torsion, mean initial rotation was 201° (range: 3.3°-321.4°) and mean rotation after 24 h 215.7° (range 31.9°-334.7°), respectively. Direct postoperative imaging may not be accurate for determining the rotation of dDBS electrodes if torque is present.

Orientation of Temporal Interference for Non-invasive Deep Brain Stimulation in Epilepsy

In patients with focal drug-resistant epilepsy, electrical stimulation from intracranial electrodes is frequently used for the localization of seizure onset zones and related pathological networks. The ability of electrically stimulated tissue to generate beta and gamma range oscillations, called rapid-discharges, is a frequent indication of an epileptogenic zone. However, a limit of intracranial stimulation is the fixed physical location and number of implanted electrodes, leaving numerous clinically and functionally relevant brain regions unexplored. Here, we demonstrate an alternative technique relying exclusively on non-penetrating surface electrodes, namely an orientation-tunable form of temporally interfering (TI) electric fields to target the CA3 of the mouse hippocampus which focally evokes seizure-like events (SLEs) having the characteristic frequencies of rapid-discharges, but without the necessity of the implanted electrodes. The orientation of the topical electrodes with respect to the orientation of the hippocampus is demonstrated to strongly control the threshold for evoking SLEs. Additionally, we demonstrate the use of Pulse-width-modulation of square waves as an alternative to sine waves for TI stimulation. An orientation-dependent analysis of classic implanted electrodes to evoke SLEs in the hippocampus is subsequently utilized to support the results of the minimally invasive temporally interfering fields. The principles of orientation-tunable TI stimulation seen here can be generally applicable in a wide range of other excitable tissues and brain regions, overcoming several limitations of fixed electrodes which penetrate tissue and overcoming several limitations of other non-invasive stimulation methods in epilepsy, such as transcranial magnetic stimulation (TMS).

3D X-ray based visualization of directional deep brain stimulation lead orientation

Knowing the orientation of directional deep brain stimulation electrodes enables imaging-based adjustment of the stimulation settings. A rotational X-ray based examination was developed to determine the electrodes orientation. By identifying the patient´s 0° axis and the electrode´s rotation using the "iron sights"-sign, the exact orientation of the electrode in relation to the ACPC-line is given. The presented imaging approach offers a reliable diagnostic tool for visualization of the implanted DBS electrode orientation in clinical routine.

Investigation of Magnetoelectric Sensor Requirements for Deep Brain Stimulation Electrode Localization and Rotational Orientation Detection

Correct position and orientation of a directional deep brain stimulation (DBS) electrode in the patient’s brain must be known to fully exploit its benefit in guiding stimulation programming. Magnetoelectric (ME) sensors can play a critical role here. The aim of this study was to determine the minimum required limit of detection (LOD) of a ME sensor that can be used for this application by measuring the magnetic field induced by DBS. For this experiment, a commercial DBS system was integrated into a head phantom and placed inside of a state-of-the-art Superconducting Quantum Interference Device (SQUID)-based magnetoencephalography system. Measurements were performed and analyzed with digital signal processing. Investigations have shown that the minimum required detection limit depends on various factors such as: measurement distance to electrode, bandwidth of magnetic sensor, stimulation amplitude, stimulation pulse width, and measurement duration. For a sensor that detects only a single DBS frequency (stimulation frequency or its harmonics), a LOD of at least 0.04 pT/Hz0.5 is required for 3 mA stimulation amplitude and 60 μs pulse width. This LOD value increases by an order of magnitude to 0.4 pT/Hz0.5 for a 1 kHz, and by approximately two orders to 3 pT/Hz0.5 for a 10 kHz sensor bandwidth. By averaging, the LOD can be reduced by at least another 2 orders of magnitude with a measurement duration of a few minutes.

Influence of Virchow-Robin spaces on the electric field distribution in subthalamic nucleus deep brain stimulation

Patient MRI from DBS implantations in the subthalamic nucleus (STN) were reviewed and it was found that around 10% had Virchow-Robin spaces (VRS). Patient-specific models were developed to evaluate changes in the electric field (EF) around DBS leads. The patients (n = 7) were implanted bilaterally either with the standard voltage-controlled lead 3389 or with the directional current-controlled lead 6180. The EF distribution was evaluated by comparing simulations using patient-specific models with homogeneous models without VRS. The EF, depicted with an isocontour of 0.2 V/mm, showed a deformation in the presence of the VRS around the DBS lead. For patient-specific models, the radial extension of the EF isocontours was enlarged regardless of the operating mode or the DBS lead used. The location of the VRS in relation to the active contact and the stimulation amplitude, determined the changes in the shape and extension of the EF. It is concluded that it is important to take the patients' brain anatomy into account as the high conductivity in VRS will alter the electric field if close to the DBS lead. This can be a cause of unexpected side effects.

SPECTRE-A novel dMRI visualization technique for the display of cerebral connectivity

The visualization of diffusion MRI related properties in a comprehensive way is still a challenging problem. We propose a simple visualization technique to give neuroradiologists and neurosurgeons a more direct and personalized view of relevant connectivity patterns estimated from clinically feasible diffusion MRI. The approach, named SPECTRE (Subject sPEcific brain Connectivity display in the Target REgion), is based on tract‐weighted imaging, where diffusion MRI streamlines are used to aggregate information from a different MRI contrast. Instead of using native MRI contrasts, we propose to use continuous template information as the underlying contrast for aggregation. In this respect, the SPECTRE approach is complementary to normative approaches where connectivity information is warped from the group level to subject space by anatomical registration. For the purpose of demonstration, we focus the presentation of the SPECTRE approach on the visualization of connectivity patterns in the midbrain regions at the level of subthalamic nucleus due to its importance for deep brain stimulation. The proposed SPECTRE maps are investigated with respect to plausibility, robustness, and test–retest reproducibility. Clear dependencies of reliability measures with respect to the underlying tracking algorithms are observed.

DBS electrode localization and rotational orientation detection using SQUID-based magnetoencephalography

The aim of the present study was to investigate the accuracy of localization and rotational orientation detection of a directional deep brain stimulation (DBS) electrode using a state-of-the-art magnetoencephalography (MEG) scanner. A directional DBS electrode along with its stimulator was integrated into a head phantom and placed inside the MEG sensor array. The electrode was comprised of six directional and two omnidirectional contacts. Measurements were performed while stimulating with different contacts and parameters in the phantom. Finite element modeling and fitting approach were used to compute electrode position and orientation. The electrode was localized with a mean accuracy of 2.2 mm while orientation was determined with a mean accuracy of 11°. The limitation in detection accuracy was due to the lower measurement precision of the MEG system. Considering an ideal measurement condition, these values represent the lower bound of accuracy that can be achieved in patients. However, a future magnetic measuring system with higher precision will potentially detect location and orientation of a DBS electrode with an even increased accuracy.

Do directional deep brain stimulation leads rotate after implantation?

BACKGROUND

The two middle contacts of directional leads (d-leads) for deep brain stimulation are split into three segments, allowing current steering toward desired axial directions. To facilitate programming, their final orientation needs to be reliably determined. However, it is currently unclear whether d-leads rotate after implantation. Our objective was to assess the degree of d-lead rotation after implantation.

METHODS

We retrospectively analyzed d-lead orientation on intraoperative X-rays, postoperative CT scans (latencies to surgery: 108-189 min postoperatively), and rotational fluoroscopies (4-9 days postoperatively) for a consecutive series of 32 implanted d-leads. For five d-leads, a CT scan with a mean follow-up of 57 days (range 28-182) was available. All d-leads were implanted with the marker facing anterior and the intention to hit an "iron sight" (ISi) on the X-ray, indicating anterior orientation (i.e., 0° ± 6°).

RESULTS

In nine d-leads, an ISi was visible on the final X-ray; median orientation was 1.5° (range 0.5-6.0°) at the first follow-up CT, confirming anterior orientation. In d-leads without ISi or where ISi was not evaluable, the median rotation was 15.5° (9.5-35.0°) and 26.5° (5.5-62.0°), respectively. The orientation of the initial CT was comparable with the orientation determined by the postoperative rotational fluoroscopy and second CT in all d-lead groups.

CONCLUSION

D-lead orientation does not change within the first week after implantation. We provide first indications that d-lead orientation remains stable for several weeks after surgery. Determination of lead orientation using marker-based X-ray alone seems too imprecise; adding the ISi method can increase determination of intraoperative orientation.

Structure-function relationship of the posterior subthalamic area with directional deep brain stimulation for essential tremor

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Directional DBS of the DRTT and the zona incerta is correlated with tremor suppression.

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Activation patterns for tremor suppression and side effects involve mostly the dentato-rubro-thalamic tract and the zona incerta.

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Concomitant side effects often limit the therapeutic window of directional deep brain stimulation.

Deep Brain Stimulation of the posterior subthalamic area is an emergent target for the treatment of Essential Tremor. Due to the heterogeneous and complex anatomy of the posterior subthalamic area, it remains unclear which specific structures mediate tremor suppression and different side effects. The objective of the current work was to yield a better understanding of what anatomical structures mediate the different clinical effects observed during directional deep brain stimulation of that area.

We analysed a consecutive series of 12 essential tremor patients. Imaging analysis and systematic clinical testing performed 4–6 months postoperatively yielded location, clinical efficacy and corresponding therapeutic windows for 160 directional contacts. Overlap ratios between individual activation volumes and neighbouring thalamic and subthalamic nuclei as well as individual fiber tracts were calculated. Further, we generated stimulation heatmaps to assess the area of activity and structures stimulated during tremor suppression and occurrence of side effects.

Stimulation of the dentato-rubro-thalamic tract and the zona incerta was most consistently correlated with tremor suppression. Both individual and group analysis demonstrated a similar pattern of activation for tremor suppression and different sorts of side-effects. Unlike current clinical concepts, induction of spasms and paresthesia were not correlated with stimulation of the corticospinal tract and the medial lemniscus. Furthermore, we noticed a significant difference in the therapeutic window between the best and worst directional contacts. The best directional contacts did not provide significantly larger therapeutic windows than omnidirectional stimulation at the same level.

Deep brain stimulation of the posterior subthalamic area effectively suppresses all aspects of ET but can be associated with concomitant side effects limiting the therapeutic window. Activation patterns for tremor suppression and side effects were similar and predominantly involved the dentato-rubro-thalamic tract and the zona incerta. We found no different activation patterns between different types of side effects and no clear correlation between structure and function. Future studies with use of more sophisticated modelling of activation volumes taking into account fiber heterogeneity and orientation may eventually better delineate these different clusters, which may allow for a refined targeting and programming within this area.

Tremor and Quality of Life in Patients With Advanced Essential Tremor Before and After Replacing Their Standard Deep Brain Stimulation With a Directional System

OBJECTIVES

Patients with essential tremor treated with thalamic deep brain stimulation may experience increased tremor with the progression of their disease. Initially, this can be counteracted with increased stimulation. Eventually, this may cause unwanted side-effects as the circumferential stimulation from a standard ring contact spreads into adjacent regions. Directional leads may offer a solution to this clinical problem. We aimed to compare the ability of a standard and a directional system to reduce tremor without side-effects and to improve the quality of life for patients with advanced essential tremor.

MATERIALS AND METHODS

Six advanced essential tremor patients with bilateral thalamic deep brain stimulation had their standard system replaced with a directional system. Tremor rating scale scores were prospectively evaluated before and after the replacement surgery. Secondary analyses of quality of life related to tremor, voice, and general health were assessed.

RESULTS

There was a significantly greater reduction in tremor without side-effects (p = 0.017) when using the directional system. There were improvements in tremor (p = 0.031) and voice (p = 0.037) related quality of life but not in general health for patients using optimized stimulation settings with the directional system compared to the standard system.

CONCLUSIONS

In this cohort of advanced essential tremor patients who no longer had ideal tremor reduction with a standard system, replacing their deep brain stimulation with a directional system significantly improved their tremor and quality of life. Up-front implantation of directional deep brain stimulation leads may provide better tremor control in those patients who progress at a later time point.

Potentials and Limitations of Directional Deep Brain Stimulation: A Simulation Approach

BACKGROUND

Directional leads are increasingly used in deep brain stimulation. They allow shaping the electrical field in the axial plane. These new possibilities increase the complexity of programming. Thus, optimized programming approaches are needed to assist clinical testing and to obtain full clinical benefit.

OBJECTIVES

This simulation study investigates to what extent the electrical field can be shaped by directional steering to compensate for lead malposition.

METHOD

Binary volumes of tissue activated (VTA) were simulated, by using a finite element method approach, for different amplitude distributions on the three directional electrodes. VTAs were shifted from 0 to 2 mm at different shift angles with respect to the lead orientation, to determine the best compensation of a target volume.

RESULTS

Malpositions of 1 mm can be compensated with the highest gain of overlap with directional leads. For larger shifts, an improvement of overlap of 10-30% is possible, depending on the stimulation amplitude and shift angle of the lead. Lead orientation and shift determine the amplitude distribution of the electrodes.

CONCLUSION

To get full benefit from directional leads, both the shift angle as well as the shift to target volume are required to choose the correct amplitude distribution on the electrodes. Current directional leads have limitations when compensating malpositions >1 mm; however, they still outperform conventional leads in reducing overstimulation. Further, their main advantage probably lies in the reduction of side effects. Databases like the one from this simulation could serve for optimized lead programming algorithms in the future.

Temporal Stability of Lead Orientation in Directional Deep Brain Stimulation

BACKGROUND

Directional deep brain stimulation (DBS) enlarges the therapeutic window by increasing side-effect thresholds and improving clinical benefits. To determine the optimal stimulation settings and interpret clinical observations, knowledge of the lead orientation in relation to the patient's anatomy is required.

OBJECTIVE

To determine if directional leads remain in a fixed orientation after implantation or whether orientation changes over time.

METHOD

Clinical records of 187 patients with directional DBS electrodes were screened for CT scans in addition to the routine postoperative CT. The orientation angle of each electrode at a specific point in time was reconstructed from CT artifacts using the DiODe algorithm implemented in Lead-DBS. The orientation angles over time were compared with the originally measured orientations from the routine postoperative CT.

RESULTS

Multiple CT scans were identified in 18 patients and the constancy of the orientation angle was determined for 29 leads at 48 points in time. The median time difference between the observations and the routine postoperative CT scan was 82 (range 1-811) days. The mean difference of the orientation angles compared to the initial measurement was -1.1 ± 3.9° (range -7.6 to 8.7°). Linear regression showed no relevant drift of the absolute value of the orientation angle over time (0.8°/year, adjusted R2: 0.040, p = 0.093).

CONCLUSION

The orientation of directional leads was stable and showed no clinically relevant changes either in the first weeks after implantation or over longer periods of time.

Longitudinal Assessment of Rotation Angles after Implantation of Directional Deep Brain Stimulation Leads

PURPOSE

The risk/benefit-ratio of deep brain stimulation (DBS) depends on focusing the electrical field onto the target volume, excluding side-effect eliciting structures. Directional leads limiting radial current diffusion can target stimulation but add a spatial degree of freedom that requires control to align multimodal imaging datasets and for anatomical interpretation of stimulation. Unpredictable postoperative lead rotations have been reported. The extent and timing of rotation from the surgically intended alignment remain uncertain, as does the time point at which directional stimulation can be safely initiated without risking unexpected shifts in stimulation volume. We present a retrospective analysis of clinically indicated, repeated neuroimaging controls postimplantation in patients with directional DBS systems, which allow estimation of the amount and timing of postoperative lead rotation.

METHODS

Data from 67 patients with directional leads and multiple cranial computer tomographies (CCT) and/or rotation fluoroscopies at different postoperative time points were included. Rotation angles were detected based on CCT artifacts (n = 56) or direct visualization of lead segments on rotation fluoroscopies (n = 52). Cross-validation of both methods was conducted in patients who received both imaging modalities (n = 51).

RESULTS

Rotation angles deviated significantly (∼30°) from their intended 0° anterior/posterior orientation. Rotation was firmly established within the first postoperative day, with no additional torque in subsequent scans. The two methods highly correlated (right hemisphere: R2 = 0.94, left hemisphere: R2 = 0.91).

CONCLUSION

Both methods for measuring rotation angles led to comparable results and can be used interchangeably. Directional stimulation settings can safely be initiated after the first postoperative day, without risking subsequent lead rotation-related anatomical shifts.

Evaluation of Automatic Segmentation of Thalamic Nuclei through Clinical Effects Using Directional Deep Brain Stimulation Leads: A Technical Note

Automatic anatomical segmentation of patients’ anatomical structures and modeling of the volume of tissue activated (VTA) can potentially facilitate trajectory planning and post-operative programming in deep brain stimulation (DBS). We demonstrate an approach to evaluate the accuracy of such software for the ventral intermediate nucleus (VIM) using directional leads. In an essential tremor patient with asymmetrical brain anatomy, lead placement was adjusted according to the suggested segmentation made by the software (Brainlab). Postoperatively, we used directionality to assess lead placement using side effect testing (internal capsule and sensory thalamus). Clinical effects were then compared to the patient-specific visualization and VTA simulation in the GUIDE™ XT software (Boston Scientific). The patient’s asymmetrical anatomy was correctly recognized by the software and matched the clinical results. VTA models matched best for dysarthria (6 out of 6 cases) and sensory hand side effects (5/6), but least for facial side effects (1/6). Best concordance was observed for the modeled current anterior and back spread of the VTA, worst for the current side spread. Automatic anatomical segmentation and VTA models can be valuable tools for DBS planning and programming. Directional DBS leads allow detailed postoperative assessment of the concordance of such image-based simulation and visualization with clinical effects.

Modeling of Electric Fields in Individual Imaging Atlas for Capsular Threshold Prediction of Deep Brain Stimulation in Parkinson's Disease: A Pilot Study

Background: Modeling of deep brain stimulation electric fields and anatomy-based software might improve post-operative management of patients with Parkinson's disease (PD) who have benefitted from subthalamic nucleus deep brain stimulation (STN-DBS).

Objective: We compared clinical and software-guided determination of the thresholds for current diffusion to the pyramidal tract, the most frequent limiting side effect in post-operative management of STN-DBS PD patients.

Methods: We assessed monopolar reviews in 16 consecutive STN-DBS PD patients and retrospectively compared clinical capsular thresholds, which had been assessed according to standard clinical practice, to those predicted by volume of tissue activated (VTA) model software. All the modeling steps were performed blinded from patients' clinical evaluations.

Results: At the group level, we found a significant correlation (p = 0.0001) when performing statistical analysis on the z-scored capsular thresholds, but with a low regression coefficient (r = 0.2445). When considering intra-patient analysis, we found significant correlations (p < 0.05) between capsular threshold as modeled with the software and capsular threshold as determined clinically in five patients (31.2%).

Conclusions: In this pilot study, the VTA model software was of limited assistance in identifying capsular thresholds for the whole cohort due to a large inter-patient variability. Clinical testing remains the gold standard in selecting stimulation parameters for STN-DBS in PD.

High resolution transcranial acoustoelectric imaging of current densities from a directional deep brain stimulator

OBJECTIVE

New innovations in deep brain stimulation (DBS) enable directional current steering-allowing more precise electrical stimulation of the targeted brain structures for Parkinson's disease, essential tremor and other neurological disorders. While intra-operative navigation through MRI or CT approaches millimeter accuracy for placing the DBS leads, no existing modality provides feedback of the currents as they spread from the contacts through the brain tissue. In this study, we investigate transcranial acoustoelectric imaging (tAEI) as a new modality to non-invasively image and characterize current produced from a directional DBS lead. tAEI uses ultrasound (US) to modulate tissue resistivity to generate detectable voltage signals proportional to the local currents.

APPROACH

An 8-channel directional DBS lead (Infinity 6172ANS, Abbott Inc) was inserted inside three adult human skulls submerged in 0.9% NaCl. A 2.5 MHz linear array delivered US pulses through the transtemporal window and focused near the contacts on the lead, while a custom amplifier and acquisition system recorded the acoustoelectric (AE) interaction used to generate images.

MAIN RESULTS

tAEI detected monopolar current with stimulation pulses as short as 100 µs with an SNR ranging from 10-27 dB when using safe US pressure (mechanical indices  <0.78) and injected current of ~2 mA peak amplitude. Adjacent contacts were discernable along the length and within each ring of the lead with a mean radial separation between contacts of 2.10 and 1.34 mm, respectively.

SIGNIFICANCE

These results demonstrate the feasibility of tAEI for high resolution mapping of directional DBS currents using clinically-relevant stimulation parameters. This new modality may improve the accuracy for placing the DBS leads, guide calibration and programming, and monitor long-term performance of DBS for treatment of Parkinson's disease.

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

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.

Directional stimulation of subthalamic nucleus sweet spot predicts clinical efficacy: Proof of concept

BACKGROUND

Directional deep brain stimulation (dDBS) of the subthalamic nucleus for Parkinson's disease (PD) increases the therapeutic window. However, empirical programming of the neurostimulator becomes more complex given the increasing number of stimulation parameters. A better understanding of dDBS is needed to improve therapy and help guide postoperative programming.

OBJECTIVE

To determine whether clinical effects of dDBS can be predicted in individual patients based on lead location and volume of tissue activated (VTA) modelling.

METHODS

We analysed a prospective series of 28 PD patients. Imaging analysis and systematic clinical testing performed 4-6 months postoperatively yielded location, clinical efficacy and corresponding therapeutic windows for 272 directional contacts. We calculated the corresponding VTAs to build a probabilistic stimulation map using voxel-wise statistical analysis.

RESULTS

We found a positive and statistically significant correlation between the overlap ratio of a patient's individual stimulation volume and the probabilistic map's sweet spot -defined as the 10% voxels with the highest clinical efficacy values (average Spearman's rho = 0.43, average p ≤ 0.036). Patients who had a larger therapeutic window with directional compared to omnidirectional stimulation had a larger distance between the electrode and the sweet spot centroid (average distances 2.3 vs. 1.5 mm, p = 0.0019).

CONCLUSION

Our analysis provides new insights into how the definition of a probabilistic sweet spot based on directional stimulation data and individual VTA modelling can be applied to predict clinically effective directional stimulation and help guide clinicians with the intricate postoperative DBS programming.

Directional Deep Brain Stimulation

Over the last years, deep brain stimulation has seen many technological innovations. New electrode designs allowing to direct the current flow not only in the vertical but also in the horizontal plane are the most recent. We summarize the concept of "directional deep brain stimulation" with its opportunities and challenges and the available study data and discuss the use of imaging techniques to assist programming deep brain stimulation devices.

Multi-objective particle swarm optimization for postoperative deep brain stimulation targeting of subthalamic nucleus pathways

OBJECTIVE

The effectiveness of deep brain stimulation (DBS) therapy strongly depends on precise surgical targeting of intracranial leads and on clinical optimization of stimulation settings. Recent advances in surgical targeting, multi-electrode designs, and multi-channel independent current-controlled stimulation are poised to enable finer control in modulating pathways within the brain. However, the large stimulation parameter space enabled by these technologies also poses significant challenges for efficiently identifying the most therapeutic DBS setting for a given patient. Here, we present a computational approach for programming directional DBS leads that is based on a non-convex optimization framework for neural pathway targeting.

APPROACH

The algorithm integrates patient-specific pre-operative 7 T MR imaging, post-operative CT scans, and multi-objective particle swarm optimization (MOPSO) methods using dominance based-criteria and incorporating multiple neural pathways simultaneously. The algorithm was evaluated on eight patient-specific models of subthalamic nucleus (STN) DBS to identify electrode configurations and stimulation amplitudes to optimally activate or avoid six clinically relevant pathways: motor territory of STN, non-motor territory of STN, internal capsule, superior cerebellar peduncle, thalamic fasciculus, and hyperdirect pathway.

MAIN RESULTS

Across the patient-specific models, single-electrode stimulation showed significant correlations across modeled pathways, particularly for motor and non-motor STN efferents. The MOPSO approach was able to identify multi-electrode configurations that achieved improved targeting of motor STN efferents and hyperdirect pathway afferents than that achieved by any single-electrode monopolar setting at equivalent power levels.

SIGNIFICANCE

These results suggest that pathway targeting with patient-specific model-based optimization algorithms can efficiently identify non-trivial electrode configurations for enhancing activation of clinically relevant pathways. However, the results also indicate that inter-pathway correlations can limit selectivity for certain pathways even with directional DBS leads.

Understanding the Effects and Adverse Reactions of Deep Brain Stimulation: Is It Time for a Paradigm Shift Toward a Focus on Heterogenous Biophysical Tissue Properties Instead of Electrode Design Only?

Deep brain stimulation (DBS) has been proven to be an effective treatment modality for various late-stage neurological and psychiatric disorders. However, knowledge on the electrical field distribution in the brain tissue is still scarce. Most recent attempts to understand electric field spread were primarily focused on the effect of different electrodes on rather simple tissue models. The influence of microanatomic, biophysical tissue properties in particular has not been investigated in depth. Ethical concerns restrict thorough research on field distribution in human in vivo brain tissue. By means of a simplified model, we investigated the electric field distribution in a broader area of the subthalamic nucleus (STN). Pivotal biophysical parameters including conductivity, permittivity and permeability of brain tissue were incorporated in the model. A brain tissue model was created with the finite element method (FEM). Stimulation was mimicked with parameters used for monopolar stimulation of patients suffering from Parkinson's disease. Our results were visualized with omnidirectional and segmented electrodes. The stimulated electric field was visualized with superimpositions on a stereotactic atlas (Morel). Owing to the effects of regional tissue properties near the stimulating electrode, marked field distortions occur. Such effects include, for example, isolating effects of heavily myelinated neighboring structures, e.g., the internal capsule. In particular, this may be illustrated through the analysis of a larger coronal area. While omnidirectional stimulation has been associated with vast current leakage, higher targeting precision was obtained with segmented electrodes. Finally, targeting was improved when the influence of microanatomic structures on the electric spread was considered. Our results confirm that lead design is not the sole influence on current spread. An omnidirectional lead configuration does not automatically result in an omnidirectional spread of current. In turn, segmented electrodes do not automatically imply an improved steering of current. Our findings may provide an explanation for side-effects secondary to current leakage. Furthermore, a possible explanation for divergent results in the comparison of the intraoperative awake patient and the postoperative setting is given. Due to the major influence of biophysical tissue properties on electric field shape, the local microanatomy should be considered for precise surgical targeting and optimal hardware implantation.