One-pass deep brain stimulation of dentato-rubro-thalamic tract and subthalamic nucleus for tremor-dominant or equivalent type Parkinson's disease

Deep brain stimulation for Parkinson's disease: bibliometric analysis of the top 100 cited literature

Background

Deep Brain Stimulation (DBS) has been widely applied and accepted in the treatment of neurological and psychiatric disorders. Despite numerous studies exploring the effects of DBS on the progression of neurodegenerative diseases and the treatment of advanced Parkinson's disease (PD), there is a limited number of articles summarizing this research. The purpose of this study is to investigate the current trends, hot topics, and potential in research surrounding DBS therapy for PD, as well as to anticipate the challenges of such research.

Methods

We searched the Web of Science Core Collection database (WoSCC) for DBS research literature related to PD published from January 2014 to January 2024, utilized CiteSpace, VOS viewer, the bibliometric online analysis platform, Scimago Graphica, Microsoft Excel 2021, and R software version 4.2.3 for data analysis. And we conducted quantitative research on publications, citations, journals, authors, countries, institutions, keywords, and references, visualized the results in network graphs.

Results

From 2014 to 2024, papers from 39 journals from 11 countries were among the top 100 cited. Most papers were published in Neurology, with the highest average citations per paper in Nature Neuroscience. The United States (US) contributed the most publications, followed by the United Kingdom (UK) and Germany. In terms of total publications, University College London (UCL) contributed the most papers. The primary classifications of articles were Clinical Neurology, Neurosciences, and Surgery. The top five keywords were subthalamic nucleus, DBS, PD, medical therapy, and basal ganglia. Cluster analysis indicates that DBS research focus on improving quality of life and applying computational models.

Conclusion

Through bibliometric analysis, researchers could quickly and clearly understand the hotspots and boundaries of their research field, thus guiding their research direction and scope to improve research efficiency and the quality of outcomes. Although studies indicate that DBS is currently a crucial method for treating advanced PD, in the long run, creating a personalized, low-cost treatment regimen with precise targeting and long-term efficacy poses a challenge.

One-pass deep brain stimulation of subthalamic nucleus and ventral intermediate nucleus for levodopa-resistant tremor-dominant Parkinson's disease

Objective

Tremor-dominant Parkinson's disease (TD-PD) can be further separated into levodopa-responsive and levodopa-resistant types, the latter being considered to have a different pathogenesis. Previous studies indicated that deep brain stimulation (DBS) of the subthalamic nucleus (STN) or the globus pallidus internus (GPi) individually was not sufficient for tremor control, especially for the levodopa-resistant TD-PD (LRTD-PD). The thalamic ventral intermediate nucleus (VIM) has been regarded as a potent DBS target for different kinds of tremors. Therefore, we focused on the LRTD-PD subgroup and performed one-pass combined DBSs of STN and VIM to treat refractory tremors, aiming to investigate the safety and effectiveness of this one-trajectory dual-target DBS scheme.

Methods

We retrospectively collected five LRTD-PD patients who underwent a one-pass combined DBS of STN and VIM via a trans-frontal approach. The targeting of VIM was achieved by probabilistic tractography. Changes in severity of symptoms (measured by the Unified Parkinson Disease Rating Scale part III, UPDRS-III), levodopa equivalent daily doses (LEDD), and disease-specific quality of life (measured by the 39-item Parkinson's Disease Questionnaire, PDQ-39) were evaluated.

Results

Three-dimensional reconstruction of electrodes illustrated that all leads were successfully implanted into predefined positions. The mean improvement rates (%) were 53 ± 6.2 (UPDRS-III), 82.6 ± 11.4 (tremor-related items of UPDRS), and 52.1 ± 11.4 (PDQ-39), respectively, with a mean follow-up of 11.4 months.

Conclusion

One-pass combined DBS of STN and VIM via the trans-frontal approach is an effective and safe strategy to alleviate symptoms for LRTD-PD patients.

Radiofrequency ablation of the pallidothalamic tract and ventral intermediate nucleus for dystonic tremor through the parietal approach

Background

The thalamic ventral intermediate nucleus (Vim) and globus pallidus internus are far apart and cannot be captured using a single electrode.

Case Description

We describe our experience with a patient with dystonic tremors of the head and upper and lower extremities who showed symptomatic improvement after radiofrequency (RF) ablation using a parietal lobe approach with a single trajectory to capture the pallidothalamic tract and Vim. A 46-year-old man developed head tremors at 41 and a right-sided neck tilt three years later. Five years after the onset of the head tremors, tightness of the larynx during speech and tremors in both the upper and lower limbs also appeared. The Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) score was 24, and the Fahn-Tolosa-Marin Tremor Rating Scale (FTM) score was 48. We captured the pallidothalamic tract and Vim along a single trajectory by locating the entry point in the inferior parietal lobule. One week after treatment, the TWSTRS and FTM scale scores were 9 (62.5%) and 30 (37.5%), respectively. No adverse events were observed.

Conclusion

This case suggests that in dystonic tremors involving abnormalities of the basal ganglia-thalamo-cortical and cerebello-thalamo-cortical circuits, a single electrode can be used to approach both circuits through the parietal lobe approach.

Insights and opportunities for deep brain stimulation as a brain circuit intervention

Deep brain stimulation (DBS) is an effective treatment and has provided unique insights into the dynamic circuit architecture of brain disorders. This Review illustrates our current understanding of the pathophysiology of movement disorders and their underlying brain circuits that are modulated with DBS. It proposes principles of pathological network synchronization patterns like beta activity (13-35 Hz) in Parkinson's disease. We describe alterations from microscale including local synaptic activity via modulation of mesoscale hypersynchronization to changes in whole-brain macroscale connectivity. Finally, an outlook on advances for clinical innovations in next-generation neurotechnology is provided: from preoperative connectomic targeting to feedback controlled closed-loop adaptive DBS as individualized network-specific brain circuit interventions.

A case report: Dual-lead deep brain stimulation of the posterior subthalamic area and the thalamus was effective for Holmes tremor after unsuccessful focused ultrasound thalamotomy

Holmes tremor is a symptomatic tremor that develops secondary to central nervous system disorders. Stereotactic neuromodulation is considered when the tremors are intractable. Targeting the ventral intermediate nucleus (Vim) is common; however, the outcome is often unsatisfactory, and the posterior subthalamic area (PSA) is expected as alternative target. In this study, we report the case of a patient with intractable Holmes tremor who underwent dual-lead deep brain stimulation (DBS) to stimulate multiple locations in the PSA and thalamus. The patient was a 77-year-old female who complained of severe tremor in her left upper extremity that developed one year after her right thalamic infarction. Vim-thalamotomy using focused ultrasound therapy (FUS) was initially performed but failed to control tremor. Subsequently, we performed DBS using two leads to stimulate four different structures. Accordingly, one lead was implanted with the aim of targeting the ventral oralis nucleus (Vo)/zona incerta (Zi), and the other with the aim of targeting the Vim/prelemniscal radiation (Raprl). Electrode stimulation revealed that Raprl and Zi had obvious effects. Postoperatively, the patient achieved good tremor control without any side effects, which was maintained for two years. Considering that she demonstrated resting, postural, and intention/action tremor, and Vim-thalamotomy by FUS was insufficient for tremor control, complicated pathogenesis was presumed in her symptoms including both the cerebellothalamic and the pallidothalamic pathways. Using the dual-lead DBS technique, we have more choices to adjust the stimulation at multiple sites, where different functional networks are connected. Intractable tremors, such as Holmes tremor, may have complicated pathology, therefore, modulating multiple pathological networks is necessary. We suggest that the dual-lead DBS (Vo/Raprl and Vim/Zi) presented here is safe, technically feasible, and possibly effective for the control of Holmes tremor.

Closing the loop: Novel quantitative fMRI approach for manipulation of the sensorimotor loop in tremor

Tremor is thought to be an effect of oscillatory activity within the sensorimotor network. To date, the underlying pathological brain networks are not fully understood. Disentangling tremor activity from voluntary motor output and sensorimotor feedback systems is challenging. To better understand the intrinsic sensorimotor fingerprint underlying tremor, we aimed to disentangle the sensorimotor system into driving (motor) and feedback/compensatory (sensory) neuronal involvement, and aimed to pinpoint tremor activity in essential tremor (ET) and tremor-dominant Parkinson's disease (PD) with a novel closed-loop approach. Eighteen ET patients, 14 tremor-dominant PD patients, and 18 healthy controls were included. An MR-compatible wrist manipulator was employed during functional MRI (fMRI) while muscle activity during (in)voluntary movements was concurrently recorded using electromyography (EMG). Tremor was quantified based on EMG and correlated to brain activity. Participants performed three tasks: an active wrist motor task, a passive wrist movement task, and rest (no wrist movement). The results in healthy controls proved that our experimental paradigm activated the expected motor and sensory networks separately using the active (motor) and passive (sensory) task. ET patients showed similar patterns of activation within the motor and sensory networks. PD patients had less activity during the active motor task in the cerebellum and basal ganglia compared to ET and healthy controls. EMG showed that in ET, tremor fluctuations correlated positively with activity in the inferior olive region, and that in PD tremor fluctuations correlated positively with cerebellar activity. Our novel approach with an MR-compatible wrist manipulator, allowed to investigate the involvement of the motor and sensory networks separately, and as such to better understand tremor pathophysiology. In ET sensorimotor network function did not differ from healthy controls. PD showed less motor-related activity. Focusing on tremor, our results indicate involvement of the inferior olive in ET tremor modulation, and cerebellar involvement in PD tremor modulation.

Toward personalized medicine in connectomic deep brain stimulation

At the group-level, deep brain stimulation leads to significant therapeutic benefit in a multitude of neurological and neuropsychiatric disorders. At the single-patient level, however, symptoms may sometimes persist despite "optimal" electrode placement at established treatment coordinates. This may be partly explained by limitations of disease-centric strategies that are unable to account for heterogeneous phenotypes and comorbidities observed in clinical practice. Instead, tailoring electrode placement and programming to individual patients' symptom profiles may increase the fraction of top-responding patients. Here, we propose a three-step, circuit-based framework with the aim of developing patient-specific treatment targets that address the unique symptom constellation prevalent in each patient. First, we describe how a symptom network target library could be established by mapping beneficial or undesirable DBS effects to distinct circuits based on (retrospective) group-level data. Second, we suggest ways of matching the resulting symptom networks to circuits defined in the individual patient (template matching). Third, we introduce network blending as a strategy to calculate optimal stimulation targets and parameters by selecting and weighting a set of symptom-specific networks based on the symptom profile and subjective priorities of the individual patient. We integrate the approach with published literature and conclude by discussing limitations and future challenges.

Connectivity correlates to predict essential tremor deep brain stimulation outcome: Evidence for a common treatment pathway

BACKGROUND AND PURPOSE

Deep brain stimulation (DBS) is the most common surgical treatment for essential tremor (ET), yet there is variation in outcome and stimulation targets. This study seeks to consolidate proposed stimulation "sweet spots," as well as assess the value of structural connectivity in predicting treatment outcomes.

MATERIALS AND METHODS

Ninety-seven ET individuals with unilateral thalamic DBS were retrospectively included. Using normative brain connectomes, structural connectivity measures were correlated with the percentage improvement in contralateral tremor, based on the Fahn-Tolosa-Marin tremor rating scale (TRS), after parameter optimization (range 3.1-12.9 months) using a leave-one-out cross-validation in 83 individuals. The predictive feature map was used for cross-validation in a separate cohort of 14 ET individuals treated at another center. Lastly, estimated volumes of tissue activated (VTA) were used to assess a treatment "sweet spot," which was compared to seven previously reported stimulation sweet spots and their relationship to the tract identified by the predictive feature map.

RESULTS

In the training cohort, structural connectivity between the VTA and dentato-rubro-thalamic tract (DRTT) correlated with contralateral tremor improvement (R = 0.41; p < 0.0001). The same connectivity profile predicted outcomes in a separate validation cohort (R = 0.59; p = 0.028). The predictive feature map represented the anatomical course of the DRTT, and all seven analyzed sweet spots overlapped the predictive tract (DRTT).

CONCLUSIONS

Our results strongly support the possibility that structural connectivity is a predictor of contralateral tremor improvement in ET DBS. The results suggest the future potential for a patient-specific functionally based surgical target. Finally, the results showed convergence in "sweet spots" suggesting the importance of the DRTT to the outcome.

DBS targeting for essential tremor using intersectional dentato-rubro-thalamic tractography and direct proton density visualization of the VIM: technical note on 2 cases

OBJECTIVE

Direct visualization of the ventral intermediate nucleus (VIM) of the thalamus on standard MRI sequences remains elusive. Therefore, deep brain stimulation (DBS) surgery for essential tremor (ET) indirectly targets the VIM using atlas-derived consensus coordinates and requires awake intraoperative testing to confirm clinical benefits. The objective of this study was to evaluate the utility of proton density (PD)-weighted MRI and tractography of the intersecting dentato-rubro-thalamic tract (DRTT) for direct "intersectional" targeting of the VIM in ET.

METHODS

DBS targets were selected by identifying the VIM on PD-weighted images relative to the DRTT in 2 patients with ET. Tremor reduction was confirmed with intraoperative clinical testing. Intended target coordinates based on the direct intersectional targeting technique were compared with consensus coordinates obtained with indirect targeting. Pre- and postoperative tremor scores were assessed using the Fahn-Tolosa-Marin tremor rating scale (TRS).

RESULTS

Planned DBS coordinates based on direct versus indirect targeting of the VIM differed in both the anteroposterior (range 0 to 2.3) and lateral (range -0.7 to 1) directions. For 1 patient, indirect targeting-without PD-weighted visualization of the VIM and DRTT-would have likely resulted in suboptimal electrode placement within the VIM. At the 3-month follow-up, both patients demonstrated significant improvement in tremor symptoms subjectively and according to the TRS (case 1: 68%, case 2: 72%).

CONCLUSIONS

Direct intersectional targeting of the VIM using PD-weighted imaging and DRTT tractography is a feasible method for DBS placement in patients with ET. These advanced targeting techniques can supplement awake intraoperative testing or be used independently in asleep cases to improve surgical efficiency and confidence.

DTI for brain targeting: Diffusion weighted imaging fiber tractography-Assisted deep brain stimulation

Fiber tractography assisted Deep Brain Stimulation (DBS) has been performed by different groups for more than 10 years to now. Groups around the world have adapted initial approaches to currently embrace the fiber tractography technology mainly for treating tremor (DBS and lesions), psychiatric indications (OCD and major depression) and pain (DBS). Despite the advantages of directly visualizing the target structure, the technology is demanding and is vulnerable to inaccuracies especially since it is performed on individual level. In this contribution, we will focus on tremor and psychiatric indications, and will show future applications of sophisticated tractography applications for subthalamic nucleus (STN) DBS surgery and stimulation steering as an example.

Directed stimulation of the dentato-rubro-thalamic tract for deep brain stimulation in essential tremor: a blinded clinical trial

OBJECTIVE

Observational studies utilising diffusion tractography have suggested a common mechanism for tremor alleviation in deep brain stimulation for essential tremor: the decussating portion of the dentato-rubro-thalamic tract. We hypothesised that directional stimulation of the dentato-rubro-thalamic tract would result in greater tremor improvement compared to sham programming, as well as comparable improvement as more tedious standard-of-care programming.

METHODS

A prospective, blinded crossover trial was performed to assess the feasibility, safety and outcomes of programming based solely on dentato-rubro-thalamic tract anatomy. Using magnetic resonance imaging diffusion-tractography, the dentato-rubro-thalamic tract was identified and a connectivity-based treatment setting was derived by modelling a volume of tissue activated using directional current steering oriented towards the dentato-rubro-thalamic tract centre. A sham setting was created at approximately 180° opposite the connectivity-based treatment. Standard-of-care programming at 3 months was compared to connectivity-based treatment and sham settings that were blinded to the programmer. The primary outcome measure was percentage improvement in the Fahn-Tolosa-Marín tremor rating score compared to the preoperative baseline.

RESULTS

Among the six patients, tremor rating scores differed significantly among the three experimental conditions (P=0.030). The mean tremor rating score improvement was greater with the connectivity-based treatment settings (64.6% ± 14.3%) than with sham (44.8% ± 18.6%; P=0.031) and standard-of-care programming (50.7% ± 19.2%; P=0.062). The distance between the centre of the dentato-rubro-thalamic tract and the volume of tissue activated inversely correlated with the percentage improvement in the tremor rating score (R²=0.24; P=0.04). No significant adverse events were encountered.

CONCLUSIONS

Using a blinded, crossover trial design, we have shown the technical feasibility, safety and potential efficacy of connectivity-based stimulation settings in deep brain stimulation for treatment of essential tremor.

Sign-specific stimulation 'hot' and 'cold' spots in Parkinson's disease validated with machine learning

Deep brain stimulation of the subthalamic nucleus has become a standard therapy for Parkinson’s disease. Despite extensive experience, however, the precise target of optimal stimulation and the relationship between site of stimulation and alleviation of individual signs remains unclear. We examined whether machine learning could predict the benefits in specific Parkinsonian signs when informed by precise locations of stimulation. We studied 275 Parkinson’s disease patients who underwent subthalamic nucleus deep brain stimulation between 2003 and 2018. We selected pre-deep brain stimulation and best available post-deep brain stimulation scores from motor items of the Unified Parkinson's Disease Rating Scale (UPDRS-III) to discern sign-specific changes attributable to deep brain stimulation. Volumes of tissue activated were computed and weighted by (i) tremor, (ii) rigidity, (iii) bradykinesia and (iv) axial signs changes. Then, sign-specific sites of optimal (‘hot spots’) and suboptimal efficacy (‘cold spots’) were defined. These areas were subsequently validated using machine learning prediction of sign-specific outcomes with in-sample and out-of-sample data (n = 51 subthalamic nucleus deep brain stimulation patients from another institution). Tremor and rigidity hot spots were largely located outside and dorsolateral to the subthalamic nucleus whereas hot spots for bradykinesia and axial signs had larger overlap with the subthalamic nucleus. Using volume of tissue activated overlap with sign-specific hot and cold spots, support vector machine classified patients into quartiles of efficacy with ≥92% accuracy. The accuracy remained high (68–98%) when only considering volume of tissue activated overlap with hot spots but was markedly lower (41–72%) when only using cold spots. The model also performed poorly (44–48%) when using only stimulation voltage, irrespective of stimulation location. Out-of-sample validation accuracy was ≥96% when using volume of tissue activated overlap with the sign-specific hot and cold spots. In two independent datasets, distinct brain areas could predict sign-specific clinical changes in Parkinson’s disease patients with subthalamic nucleus deep brain stimulation. With future prospective validation, these findings could individualize stimulation delivery to optimize quality of life improvement.

Combination targeting of subthalamic nucleus and ventral intermediate thalamic nucleus with a single trajectory in deep brain stimulation for tremor-dominant Parkinson's disease

Deep brain stimulation (DBS) has traditionally been used to target the subthalamic nucleus (STN) or globus pallidus internus (GPi) to treat Parkinson's disease (PD) and the ventral intermediate thalamic nucleus (VIM) to treat essential tremor (ET). Recent case reports have described targeting both the STN and VIM with a single trajectory and electrode to treat patients with tremor-dominant PD, yet outcome data for this procedure remains sparse. Our objective is to determine the safety and efficacy of combination STN-VIM DBS. We conducted a single-center retrospective case series of all patients who underwent combined STN-VIM DBS. Demographic, perioperative, and outcome data, including Unified Parkinson Disease Rating Scale-III (UPDRS) and tremor scores (OFF-medication), and levodopa equivalent daily dose (LEDD), were collected and analyzed. Nineteen patients underwent this procedure. Patients were 89% male and 11% female, with a mean age of 63.6 years. Mean preoperative UPDRS was 24.1, and LEDD was 811.8. At a mean follow-up of 33.8 months, UPDRS and LEDD decreased by an average of 9.2 (38.2%) and 326.3 (40.2%), respectively. Tremor scores decreased by 4.9 (59.0%), and 58% were able to decrease total medication burden. One patient developed transient left-sided weakness, yielding a complication rate of 5.3%. Combined targeting of STN and VIM thalamus via a single frontal trajectory for tremor-dominant Parkinson's Disease results in similar UPDRS outcomes to STN DBS and improved control of tremor symptoms. Larger multicenter studies are necessary to validate this as the optimal DBS target for tremor-dominant PD.

Neuromodulation of the subthalamic nucleus in Parkinson's disease: the effect of fiber tract stimulation on tremor control

Background

Therapeutic effects of deep brain stimulation (DBS) of the subthalamic nucleus (STN) in Parkinson’s disease (PD) may in parts be attributed to the stimulation of white matter near the targeted structure. The dentato-rubro-thalamic (DRT) tract supposed to improve tremor control in patients with essential tremor could be one candidate structure. The aim of this study was to investigate the effect of stimulation proximity to the DRT on tremor control in PD patients treated with STN-DBS.

Methods

For this retrospective analysis, we included 36 consecutive patients (median age 65.5 years) treated with STN-DBS for disabling motor symptoms including tremor. Stereotactic implantation of DBS electrodes into the motor area of the STN was performed using direct MRI-based targeting and intraoperative microelectrode recording. Tremor severity was assessed preoperatively and at regular intervals postoperatively (Unified Parkinson’s Disease Rating Scale III). The DRT was visualized in 60 hemispheres after probabilistic fiber tracking (3-T MRI). The position of active electrode contacts was verified on intraoperative stereotactic X-rays and postoperative CT images after co-registration with 3D treatment planning MRI/CT images. We determined the shortest distance of active contacts to the ipsilateral DRT tracts on perpendicular view slices and correlated this value with tremor change percentage.

Results

Twelve patients had unilateral tremor only, and accordingly, 12 hemispheres were excluded from further imaging analysis. The remaining 60 hemispheres were associated with contralateral resting tremor. Active brain electrode contacts leading to resting tremor improvement (46 hemispheres) had a significantly shorter distance to the DRT (1.6 mm (0.9–2.1) [median (25th–75th percentiles)]) compared with contacts of non-responders (14 hemispheres, distance: 2.8 mm (2–4.6), p < 0.001).

Conclusion

This retrospective analysis suggests that in STN-DBS, better tremor control in PD patients correlates with the distance of active electrode contacts to the DRT. Tractography may optimize both individually DBS targeting and postoperative adjustment of stimulation parameters.

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

Tremor is a prevalent symptom associated with multiple conditions, including essential tremor (ET), Parkinson's disease (PD), multiple sclerosis (MS), stroke and trauma. The surgical management of tremor evolved from stereotactic lesions to deep-brain stimulation (DBS), which allowed safe and reversible interference with specific neural networks. This paper reviews the current literature on DBS for tremor, starting with a detailed discussion of current tremor targets (ventral intermediate nucleus of the thalamus (Vim), prelemniscal radiations (Raprl), caudal zona incerta (Zi), thalamus (Vo) and subthalamic nucleus (STN)) and continuing with a discussion of results obtained when performing DBS in the various aforementioned tremor syndromes. Future directions for DBS research are then briefly discussed.

Opportunities of connectomic neuromodulation

The process of altering neural activity - neuromodulation - has long been used to treat patients with brain disorders and answer scientific questions. Deep brain stimulation in particular has provided clinical benefit to over 150,000 patients. However, our understanding of how neuromodulation impacts the brain is evolving. Instead of focusing on the local impact at the stimulation site itself, we are considering the remote impact on brain regions connected to the stimulation site. Brain connectivity information derived from advanced magnetic resonance imaging data can be used to identify these connections and better understand clinical and behavioral effects of neuromodulation. In this article, we review studies combining neuromodulation and brain connectomics, highlighting opportunities where this approach may prove particularly valuable. We focus on deep brain stimulation, but show that the same principles can be applied to other forms of neuromodulation, such as transcranial magnetic stimulation and MRI-guided focused ultrasound. We outline future perspectives and provide testable hypotheses for future work.

Multimodal MRI for MRgFUS in essential tremor: post-treatment radiological markers of clinical outcome

BACKGROUND

MRI-guided focused ultrasound (MRgFUS) thalamotomy is a promising non-invasive treatment option for medication-resistant essential tremor. However, it has been associated with variable efficacy and a relatively high incidence of adverse effects.

OBJECTIVES

To assess the evolution of radiological findings after MRgFUS thalamotomy and to evaluate their significance for clinical outcomes.

METHODS

Ninety-four patients who underwent MRgFUS between 2012 and 2017 were retrospectively evaluated. Lesion characteristics were assessed on routine MRI sequences, as well as with tractography. Relationships between imaging appearance, extent of white matter tract lesioning (59/94, on a 4-point scale) and clinical outcome were investigated. Recurrence was defined as >33% loss of tremor suppression at 3 months relative to day 7.

RESULTS

Acute lesions demonstrated blood products, surrounding oedema and peripheral diffusion restriction. The extent of dentatorubrothalamic tract (DRTT) lesioning was significantly associated with clinical improvement at 1 year (t=4.32, p=0.001). Lesion size decreased over time (180.8±91.5 mm³ at day 1 vs 19.5±19.3 mm³ at 1-year post-treatment). Higher post-treatment oedema (t=3.59, p<0.001) was associated with larger lesions at 3 months. Patients with larger lesions at day 1 demonstrated reduced rates of tremor recurrence (t=2.67, p=0.019); however, lesions over 170 mm³ trended towards greater incidence of adverse effects (sensitivity=0.60, specificity=0.63). Lesion encroachment on the medial lemniscus (Sn=1.00, Sp=0.32) and pyramidal tract (Sn=1.00, Sp=0.12) were also associated with increased adverse effects incidence.

CONCLUSION

Lesion size at day 1 predicts symptom recurrence, with fewer recurrences seen with larger lesions. Greater DRTT lesioning is associated with treatment efficacy. These findings may have implications for lesion targeting and extent.

TRIAL REGISTRATION NUMBER

NCT02252380.

Distance to white matter tracts is associated with deep brain stimulation motor outcome in Parkinson's disease

OBJECTIVE

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) alleviates motor symptoms in patients with Parkinson's disease (PD). However, the underlying mechanism of tremor suppression is not well understood. Stimulation of white matter tracts, such as the dentatorubrothalamic tract (DRT), might be involved. Also, side effects, including dysarthria, might result from (unwanted) stimulation of white matter tracts in proximity to the STN. The aim of this study was to establish an association between stimulation effect on tremor and dysarthria and stimulation location relative to relevant white matter tracts.

METHODS

In 35 PD patients in whom a bilateral STN DBS system was implanted, the authors established clinical outcome measures per electrode contact. The distance from each stimulation location to the center of the DRT, corticopontocerebellar tract, pyramidal tract (PT), and medial lemniscus was determined using diffusion-weighted MRI data. Clinical outcome measures were subsequently related to the distances to the white matter tracts.

RESULTS

Patients with activated contacts closer to the DRT showed increased tremor improvement. Proximity of activated contacts to the PT was associated with dysarthria.

CONCLUSIONS

Proximity to specific white matter tracts is associated with tremor outcome and side effects in DBS. This knowledge can help to optimize both electrode placement and postsurgical electrode contact selection. Presurgical white matter tract visualization may improve targeting and DBS outcome. These findings are of interest not only for treatment in PD, but potentially also for other (movement) disorders.

The dentato-rubro-thalamic tract as the potential common deep brain stimulation target for tremor of various origin: an observational case series

INTRODUCTION

Deep brain stimulation alleviates tremor of various origins. The dentato-rubro-thalamic tract (DRT) has been suspected as a common tremor-reducing structure. Statistical evidence has not been obtained. We here report the results of an uncontrolled case series of patients with refractory tremor who underwent deep brain stimulation under tractographic assistance.

METHODS

A total of 36 patients were enrolled (essential tremor (17), Parkinson's tremor (8), multiple sclerosis (7), dystonic head tremor (3), tardive dystonia (1)) and received 62 DBS electrodes (26 bilateral; 10 unilateral). Preoperatively, diffusion tensor magnetic resonance imaging sequences were acquired together with high-resolution anatomical T1W and T2W sequences. The DRT was individually tracked and used as a direct thalamic or subthalamic target. Intraoperative tremor reduction was graded on a 4-point scale (0 = no tremor reduction to 3 = full tremor control) and recorded together with the current amplitude, respectively. Stimulation point coordinates were recorded and compared to DRT. The relation of the current amplitude needed to reduce tremor was expressed as TiCR (tremor improvement per current ratio).

RESULTS

Stimulation points of 241 were available for analysis. A total of 68 trajectories were tested (62 dB leads, 1.1 trajectories tested per implanted lead). Tremor improvement was significantly decreasing (p < 0.01) if the distance to both the border and the center of the DRT was increasing. On the initial trajectory, 56 leads (90.3%) were finally placed. Long-term outcomes were not part of this analysis.

DISCUSSION

Tremor of various origins was acutely alleviated at different points along the DRT fiber tract (above and below the MCP plane) despite different tremor diseases. DRT is potentially a common tremor-reducing structure. Individual targeting helps to reduce brain penetrating tracts. TiCR characterizes stimulation efficacy and might help to identify an optimal stimulation point.

White matter tracts involved by deep brain stimulation of the subthalamic nucleus in Parkinson's disease: a connectivity study based on preoperative diffusion tensor imaging tractography

Purpose: To depict the specific brain networks that are modulated by deep brain stimulation (DBS) of the subthalamic nucleus (STN) in Parkinson's disease (PD), using diffusion tensor imaging-based fibre tractography (DTI-FT).Materials and methods: Nine patients who received bilateral STN-DBS for PD were included. Electrodes were localized by co-registering preoperative magnetic resonance imaging and postoperative computed tomography. The volume of tissue activated (VTA) was estimated as an isotropic, spherical electric field distribution centred at each effective electrode contact's centroid coordinates, taking into account individual stimulation parameters (i.e. voltage, impedance). Brain connectivity analysis was undertaken using a deterministic DTI-FT method, seeded from a single region of interest corresponding to the VTA. The labelling of the reconstructed white matter fibre tracts relied on their path and (sub)cortical termination territories.Results: Six months after surgery, we observed a statistically significant reduction in both the Unified Parkinson Disease Rating Scale part III and L-dopa equivalent daily dose. Areas consistently connected to the VTA included the brainstem (100%), cerebellum (94%), dorsal (i.e. supplementary motor area) and lateral premotor cortex (94%), and primary motor cortex (72%). An involvement of the hyperdirect pathway (HDP) connecting the STN and the (pre)motor cortex was demonstrated.Conclusions: The connectivity patterns observed in this study suggest that the therapeutic effects of STN-DBS are mediated through the modulation of distributed, large-scale motor networks. Specifically, the depiction of projection neurons connecting the stimulated area/STN to the (pre)motor cortex, reinforce the growing evidence that the HDP might be a potential therapeutic target in PD. If further replicated, these findings could raise the possibility that DTI-FT reconstruction of the HDP may critically improve DBS targeting and stimulation parameters selection, through the development of programming tools that incorporate VTA modelling and patient-specific DTI-FT data.

Automatic Segmentation of the Subthalamic Nucleus: A Viable Option to Support Planning and Visualization of Patient-Specific Targeting in Deep Brain Stimulation

BACKGROUND

Automatic segmentation is gaining relevancy in image-based targeting of neural structures.

OBJECTIVE

To evaluate its feasibility, we retrospectively analyzed the concordance of magnetic resonance imaging (MRI)-based automatic segmentation of the subthalamic nucleus (STN) and intraoperative microelectrode recordings (MERs).

METHODS

Electrodes (n = 60) for deep brain stimulation were implanted in the STN of patients (n = 30; median age 57 yr) with Parkinson disease (n = 29) or rapid-onset dystonia parkinsonism (n = 1). Elements (Brainlab, Munich, Germany) were used to segment the STN, using 2 volumetric T1 (±contrast) and volumetric T2 images as input. The stereotactic computed tomography was coregistered with the imaging, and the original stereotactic coordinates were imported. MERs (0.5-1 mm steps) along the anterior, central, and lateral trajectories were used to determine differences between the image-segmented STN boundary and MER-based STN entry and exit.

RESULTS

Of 175 trajectories, 105 penetrated or touched (≤0.7 mm) the STN. The overall median deviation between the segmented STN boundary and electrophysiological recordings was 1.1 mm for MER-based STN entry and 2.0 mm for STN exit. Regarding the entry point of the STN, there was no statistically significant difference between MRI-based automatic segmentation and the electrophysiological trajectories analyzed with intraoperative MER. The exit point was significantly different between both methods in the central and lateral trajectories.

CONCLUSION

MRI-based automatic segmentation of the STN is a viable, patient-specific targeting approach that can be used alongside traditional targeting methods in deep brain stimulation to support preoperative planning and visualization of target structures and aid postoperative optimization of programming.

Deep Brain Stimulation for Parkinson Disease

Parkinson disease (PD) is the second most common neurodegenerative disorder and affects more than 1 million individuals in the United States. Deep brain stimulation (DBS) is one form of treatment of PD. DBS treatment is still evolving due to technological innovations that shape how this therapy is used.

A retrospective evaluation of thalamic targeting for tremor deep brain stimulation using high-resolution anatomical imaging with supplementary fiber tractography

OBJECTIVES

Deep brain stimulation (DBS) of the ventral intermediate (Vim) thalamic nucleus is used to treat tremors. Here, we identified the Vim nucleus on fast gray matter acquisition T1 inversion recovery (FGATIR) images and delineated the dentate-rubrothalamic tract (DRT) to determine the DBS target. We evaluated whether this method could consistently identify the Vim nucleus by anatomical imaging and fiber tractography.

METHODS

We retrospectively reviewed clinical data of patients who underwent unilateral thalamic DBS for severe tremor disorders. We evaluated outcomes at baseline, 6 months and 1 year following intervention, and annually thereafter. We reviewed preoperative planning to determine whether our tractography technique could consistently depict the DRT, and evaluated implanted electrode position by fusing postoperative CT scans to preoperative MR images.

RESULTS

Seven patients (three men and four women) were included; preoperative diagnoses included essential tremor (n = 3), Parkinson's (n = 2), and Holmes tremor (n = 2). All patients responded to DBS therapy; motor scores improved at 6-month and last follow-up. The Vim nucleus was successfully identified, as the DRT was depicted in all cases. Of ten active DBS contacts in seven leads, four contacts were located outside of the depicted DRT, and these contacts tended to require higher stimulation intensity.

CONCLUSIONS

The Vim nucleus was successfully identified with FGATIR. Our methods may be useful to determine optimal DBS trajectory, and potentially improve outcomes.

Structural connectivity-based segmentation of the thalamus and prediction of tremor improvement following thalamic deep brain stimulation of the ventral intermediate nucleus

Objectives

Traditional targeting methods for thalamic deep brain stimulation (DBS) performed to address tremor have predominantly relied on indirect atlas-based methods that focus on the ventral intermediate nucleus despite known variability in thalamic functional anatomy. Improvements in preoperative targeting may help maximize outcomes and reduce thalamic DBS–related complications. In this study, we evaluated the ability of thalamic parcellation with structural connectivity–based segmentation (SCBS) to predict tremor improvement following thalamic DBS.

Methods

In this retrospective analysis of 40 patients with essential tremor, hard segmentation of the thalamus was performed by using probabilistic tractography to assess structural connectivity to 7 cortical targets. The volume of tissue activated (VTA) was modeled in each patient on the basis of the DBS settings. The volume of overlap between the VTA and the 7 thalamic segments was determined and correlated with changes in preoperative and postoperative Fahn-Tolosa-Marin Tremor Rating Scale (TRS) scores by using multivariable linear regression models.

Results

A significant association was observed between greater VTA in the supplementary motor area (SMA) and premotor cortex (PMC) thalamic segment and greater improvement in TRS score when considering both the raw change (P = .001) and percentage change (P = .011). In contrast, no association was observed between change in TRS score and VTA in the primary motor cortex thalamic segment (P ≥ .19).

Conclusions

Our data suggest that greater VTA in the thalamic SMA/PMC segment during thalamic DBS was associated with significant improvement in TRS score in patients with tremor. These findings support the potential role of thalamic SCBS as an independent predictor of tremor improvement in patients who receive thalamic DBS.

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Pre-operative connectivity data may improve thalamic DBS targeting for tremor.

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Tremor control was positively correlated with connectivity-based thalamic segmentation.

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Stimulation of the SMA/PMC connected thalamic region correlated with tremor control.

Comparison of tractography-assisted to atlas-based targeting for deep brain stimulation in essential tremor

BACKGROUND

Direct targeting of the dentato-rubro-thalamic tract is efficacious in DBS for tremor suppression.

OBJECTIVES

We sought to compare outcomes and optimal stimulation parameters for tremor control using the technique of directly targeting the dentato-rubro-thalamic tract to those who underwent indirect targeting of the ventral intermediate nucleus thalamus.

METHODS

Twenty consecutive essential tremor patients obtained preoperative diffusion MRIs, where the dentato-rubro-thalamic tract was individually drawn and used to directly target the ventral intermediate nucleus of the thalamus during surgery. These patients were compared to an earlier cohort of 20 consecutive patients who underwent surgery using atlas-based coordinates. Baseline and 1-year postsurgery tremor amplitude using The Essential Tremor Rating Assessment Scale was recorded, as were the parameters needed for successful tremor control.

RESULTS

The indirectly targeted group had greater baseline and postop tremor severity relative to those directly targeted (baseline, 2.9 vs. 2.6; P = 0.02; postop, 1.1 vs. 0.8; P = 0.03). Mean voltage, pulse width, and frequency for optimal tremor control in the directly targeted group (38 electrodes) = 2.8 V, 80 μs, 153 Hz; the parameters for the indirectly targeted group (38 electrodes) = 2.9 V, 86 µs, 179 Hz (significantly greater, P < 0.001). Both groups had significant improvement in arm tremor amplitude from baseline (P < 0.001) without sustained side effects.

CONCLUSION

Direct targeting of the dentato-rubro-thalamic tract provides excellent tremor control, comparable to indirectly targeting the ventral intermediate nucleus of the thalamus. Use of lower stimulation parameters, especially frequency, to control tremor in the directly targeted group suggests that it is a more efficient targeting methodology, which may minimize battery depletion. © 2018 International Parkinson and Movement Disorder Society.

The oscillatory boundary conditions of different frequency bands in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease that is common in the elderly population. The most important pathological change in PD is the degeneration and death of dopaminergic neurons in the substantia nigra of the midbrain, which results in a decrease in the dopamine (DA) content of the striatum. The exact cause of this pathological change is still unknown. Numerous studies have shown that the evolution of PD is associated with abnormal oscillatory activities in the basal ganglia, with different oscillation frequency ranges, such as the typical beta band (13-30 Hz), the alpha band (8-12 Hz), the theta band (4-7 Hz) and the delta band (1-3 Hz). Although some studies have implied that abnormal interactions between the subthalamic nucleus (STN) and globus pallidus (GP) neurons may be a key factor required to induce these oscillations, the relative mechanism is still unclear. The effects of other nerve nuclei in the basal ganglia, such as the striatum, on these oscillations are still unknown. The thalamus and cortex both have close input and output relationships with the basal ganglia, and many previous studies have indicated that they may also exert effects on Parkinson's disease oscillation, but the mechanisms involved are unclear. In this paper, we built a corticothalamic-basal ganglia (CTBG) mean firing-rate model to explore the onset mechanisms of these different oscillation phenomena. We found that, in addition to the STN-GP network, Parkinson's disease oscillations may also be induced by changing the coupling strength and delays in other pathways. Different frequency bands appear in the oscillating region, and various boundary conditions are depicted in parameter diagrams. The onset mechanism is well explained both by the model and by the numerical simulation results. Therefore, this model provides a unifying framework for studying the mechanism of Parkinson's disease oscillations, and we hope that the results obtained in this work can inspire future experimental studies.

One Pass Thalamic and Subthalamic Stimulation for Patients with Tremor-Dominant Idiopathic Parkinson Syndrome (OPINION): Protocol for a Randomized, Active-Controlled, Double-Blinded Pilot Trial

Background

Besides fluctuations, therapy refractory tremor is one of the main indications of deep brain stimulation (DBS) in patients with idiopathic Parkinson syndrome (IPS). Although thalamic DBS (ventral intermediate nucleus [Vim] of thalamus) has been shown to reduce tremor in 85-95% of patients, bradykinesia and rigidity often are not well controlled. The dentato-rubro-thalamic tract (DRT) that can directly be targeted with special diffusion tensor magnetic resonance imaging sequences has been shown as an efficient target for thalamic DBS. The subthalamic nucleus (STN) is typically chosen in younger patients as the target for dopamine-responsive motor symptoms. This study investigates a one-path thalamic (Vim/DRT) and subthalamic implantation of DBS electrodes and possibly a combined stimulation strategy for both target regions.

Objective

This study investigates a one path thalamic (Vim/DRT) and subthalamic implantation of DBS electrodes and a possibly combined stimulation strategy for both target regions.

Methods

This is a randomized, active-controlled, double-blinded (patient- and observer-blinded), monocentric trial with three treatments, three periods and six treatment sequences allocated according to a Williams design. Eighteen patients will undergo one-path thalamic (Vim/DRT) and STN implantation of DBS electrodes. After one month, a double-blinded and randomly-assigned stimulation of the thalamic target (Vim/DRT), the STN and a combined stimulation of both target regions will be performed for a period of three months each. The primary objective is to assess the quality of life obtained by the Parkinson’s Disease Questionnaire (39 items) for each stimulation modality. Secondary objectives include tremor reduction (obtained by the Fahn-Tolosa-Marin tremor rating scale, video recordings, the Unified Parkinson’s disease rating scale, and by tremor analysis), psychiatric assessment of patients, and to assess the safety of intervention.

Results

At the moment, the recruitment is stopped and 12 patients have been randomized and treated. A futility analysis is being carried out by means of a conditional power analysis.

Conclusions

The approach of the OPINION trial planned to make, for the first time, a direct comparison of the different stimulation conditions (Vim/DRT, compared to STN, compared to Vim/DRT+STN) in a homogeneous patient population and, furthermore, will allow for intraindividual comparison of each condition with the “quality of life” outcome parameter. We hypothesize that the combined stimulation of the STN and the thalamic (Vim/DRT) target will be superior with respect to the patients’ quality of life as compared to the singular stimulation of the individual target regions. If this holds true, this work might change the standardized treatment described in the previous section.

Trial Registration

ClinicalTrials.gov: NCT02288468; https://clinicaltrials.gov/ct2/show/NCT02288468 (Archived by WebCite at http://www.webcitation.org/6wlKnt2pJ); and German Clinical Trials Register: DRKS00007526; https://www.drks.de/drks_ web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00007526 (Archived by WebCite at http://www.webcitation.org/6wlKyXZZL).

Connectivity derived thalamic segmentation in deep brain stimulation for tremor

The ventral intermediate nucleus (VIM) of the thalamus is an established surgical target for stereotactic ablation and deep brain stimulation (DBS) in the treatment of tremor in Parkinson's disease (PD) and essential tremor (ET). It is centrally placed on a cerebello-thalamo-cortical network connecting the primary motor cortex, to the dentate nucleus of the contralateral cerebellum through the dentato-rubro-thalamic tract (DRT). The VIM is not readily visible on conventional MR imaging, so identifying the surgical target traditionally involved indirect targeting that relies on atlas-defined coordinates. Unfortunately, this approach does not fully account for individual variability and requires surgery to be performed with the patient awake to allow for intraoperative targeting confirmation. The aim of this study is to identify the VIM and the DRT using probabilistic tractography in patients that will undergo thalamic DBS for tremor. Four male patients with tremor dominant PD and five patients (three female) with ET underwent high angular resolution diffusion imaging (HARDI) (128 diffusion directions, 1.5 mm isotropic voxels and b value = 1500) preoperatively. Patients received VIM-DBS using an MR image guided and MR image verified approach with indirect targeting. Postoperatively, using parallel Graphical Processing Unit (GPU) processing, thalamic areas with the highest diffusion connectivity to the primary motor area (M1), supplementary motor area (SMA), primary sensory area (S1) and contralateral dentate nucleus were identified. Additionally, volume of tissue activation (VTA) corresponding to active DBS contacts were modelled. Response to treatment was defined as 40% reduction in the total Fahn-Tolosa-Martin Tremor Rating Score (FTMTRS) with DBS-ON, one year from surgery. Three out of nine patients had a suboptimal, long-term response to treatment. The segmented thalamic areas corresponded well to anatomically known counterparts in the ventrolateral (VL) and ventroposterior (VP) thalamus. The dentate-thalamic area, lay within the M1-thalamic area in a ventral and lateral location. Streamlines corresponding to the DRT connected M1 to the contralateral dentate nucleus via the dentate-thalamic area, clearly crossing the midline in the mesencephalon. Good response was seen when the active contact VTA was in the thalamic area with highest connectivity to the contralateral dentate nucleus. Non-responders had active contact VTAs outside the dentate-thalamic area. We conclude that probabilistic tractography techniques can be used to segment the VL and VP thalamus based on cortical and cerebellar connectivity. The thalamic area, best representing the VIM, is connected to the contralateral dentate cerebellar nucleus. Connectivity based segmentation of the VIM can be achieved in individual patients in a clinically feasible timescale, using HARDI and high performance computing with parallel GPU processing. This same technique can map out the DRT tract with clear mesencephalic crossing.

Predictors of deep brain stimulation outcome in tremor patients

BACKGROUND

Deep brain stimulation of the ventro-intermedius nucleus of the thalamus is an established treatment for tremor of differing etiologies but factors that may predict the short- and especially long-term outcome of surgery are still largely unknown.

METHODS

We retrospectively investigated the clinical, pharmacological, electrophysiological and anatomical features that might predict the initial response and preservation of benefit in all patients who underwent deep brain stimulation for tremor. Data were collected at the following time points: baseline (preoperative), one-year post-surgery, and most recent visit. Tremor severity was recorded using the Fahn-Tolosa-Marin Tremor Rating Scale and/or the Unified Parkinson's Disease Rating Scale.

RESULTS

A total of 52 patients were included in the final analysis: 31 with essential tremor, 15 with cerebellar tremor of different etiologies, and 6 with Parkinson's disease. Long-term success (mean follow-up duration 34.7 months, range 1.7-121.1 months) was reported in 63.5%. Predictors of long-term benefit were: underlying tremor etiology (best outcome in Parkinson's disease, worst outcome in cerebellar tremor); age at surgery (the older the better); baseline tremor severity (the greater the better); lack of response to benzodiazepines; a more anterior electrode placement and single-unit beta power (the greater the better).

CONCLUSIONS

Specific patients' features (including single unit beta activity) and electrode locations may predict the short- and long-term benefit of thalamic stimulation for tremor. Future prospective studies enrolling a much larger sample of patients are needed to substantiate the associations detected by this retrospective study.

Improving Surgical Outcome Using Diffusion Tensor Imaging Techniques in Deep Brain Stimulation

Introduction

Recent advances in surgical imaging include the use of diffusion tensor imaging (DTI) in deep brain stimulation (DBS) and provide a detailed view of the white matter tracts and their connections which are not seen with conventional magnetic resonance imaging. Given that the efficacy of DBS depends on the precise and accurate targeting of these circuits, better surgical planning using information obtained from DTI may lead to improved surgical outcome. We aim to review the available literature to evaluate the efficacy of such a strategy.

Methods

A search of PubMed was performed to identify all articles using the search terms “(diffusion tractography OR diffusion tensor imaging OR DTI) AND (deep brain stimulation OR DBS).” Studies were included if DTI was used and clinical outcomes were reported.

Results

We identified 35 studies where the use of DTI in DBS was evaluated. The most studied pathology was movement disorders (17 studies), psychiatric disorders (11 studies), and pain (7 studies). The overall responder rates for tremor reduction was 70.0% (SD = 26.1%) in 69 patients, 36.5% (SD = 19.1%) for obsessive–compulsive disorder in 9 patients, 48.3% (SD = 40.0%) for depression in 40 patients, and 49.7% (SD = 35.1%) for chronic pain in 23 patients.

Discussion

The studies reviewed show that the use of DTI for surgical planning is feasible, provide additional information over conventional targeting methods, and can improve surgical outcome. Patients in whom the DBS electrodes were within the DTI targets experienced better outcomes than those in whom the electrodes were not. Many current studies are limited by their small sample size or retrospective nature. The use of DTI in DBS planning appears underutilized and further studies are warranted given that surgical outcome can be optimized using this non-invasive technique.

Efficacy of Fiber Tractography in the Stereotactic Surgery of the Thalamus for Patients with Essential Tremor

Several targets and targeting methods are utilized in stereotactic surgery to achieve tremor suppression for patients with intractable tremor. Recent developments in magnetic resonance imaging, including diffusion tensor imaging, have enabled the setting of appropriate targets in stereotactic surgery. In this retrospective study, the optimal target to suppress tremors in stereotactic surgery was explored using diffusion tensor image-based fiber tractography. Four tracts were focused on in this study, namely: the cerebello-thalamo-premotor cortical fiber tract, cerebello-thalamo-primary motor cortical fiber tract, spino-thalamo-somatosensory cortical fiber tract, and pyramidal tract. In 10 patients with essential tremor, we evaluated the thalamotomy lesions and active contacts of the lead in thalamic stimulation by diffusion tensor image-based fiber tractography to reveal which part of the cerebral cortex is most affected by stereotactic surgery. Tremor suppression and adverse events were also evaluated in the patients involved in this study. Consequently, the good tremor suppression was achieved in all patients. There had been no permanent adverse events 3 months after surgery. Twelve lesions in thalamotomy patients or active contacts of the lead in thalamic stimulation patients were on the cerebello-thalamo-premotor cortical fiber tract (12/14 lesions or active contacts: 86%). In conclusion, the cerebello-thalamo-premotor cortical fiber tract may be an optimal target for tremor suppression. Diffusion tensor image-based fiber tractography may enable us to both determine the optimal target to achieve strong tremor suppression and to reduce the number of adverse events by keeping lesions or electrodes away from important fiber tracts, such as the pyramidal tract and spinothalamic fibers.

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

BACKGROUND AND PURPOSE

New deep brain stimulation leads with electrode contacts that are split along their circumference allow steering of the electrical field in a predefined direction. However, imaging-assisted directional stimulation requires detailed knowledge of the exact orientation of the electrode array. The purpose of this study was to evaluate whether this information can be obtained by rotational 3D fluoroscopy.

MATERIALS AND METHODS

Two directional leads were inserted into a 3D-printed plaster skull filled with gelatin. The torsion of the lead tip versus the lead at the burr-hole level was investigated. Then, 3 blinded raters evaluated 12 3D fluoroscopies with random lead orientations. They determined the lead orientation considering the x-ray marker only and considering the overlap of the gaps between the contact segments. Intraclass correlation coefficients and an extended version of the Bland-Altman plot were used to determine interrater reliability and agreement of the measurements of the different raters.

RESULTS

Electrode torsion of up to 35° could be demonstrated. Evaluation of the lead rotation considering the x-ray marker only revealed limits of agreement of ±9.37° and an intraclass correlation coefficient of 0.9975. In addition, taking into account the lines resulting from overlapping of the gaps between the electrode segments, the limits of agreement to the mean were ±2.44° and an intraclass correlation coefficient of 0.9998.

CONCLUSIONS

In directional deep brain stimulation systems, rotational 3D fluoroscopy combined with the described evaluation method allows for determining the exact orientation of the leads, enabling the full potential of imaging-assisted personalized programming.

The "curved lead pathway" method to enable a single lead to reach any two intracranial targets

Deep brain stimulation is an effective way to treat movement disorders, and a powerful research tool for exploring brain functions. This report proposes a “curved lead pathway” method for lead implantation, such that a single lead can reach in sequence to any two intracranial targets. A new type of stereotaxic system for implanting a curved lead to the brain of human/primates was designed, the auxiliary device needed for this method to be used in rat/mouse was fabricated and verified in rat, and the Excel algorithm used for automatically calculating the necessary parameters was implemented. This “curved lead pathway” method of lead implantation may complement the current method, make lead implantation for multiple targets more convenient, and expand the experimental techniques of brain function research.

A simple method for EEG guided transcranial electrical stimulation without models

OBJECTIVE

There is longstanding interest in using EEG measurements to inform transcranial Electrical Stimulation (tES) but adoption is lacking because users need a simple and adaptable recipe. The conventional approach is to use anatomical head-models for both source localization (the EEG inverse problem) and current flow modeling (the tES forward model), but this approach is computationally demanding, requires an anatomical MRI, and strict assumptions about the target brain regions. We evaluate techniques whereby tES dose is derived from EEG without the need for an anatomical head model, target assumptions, difficult case-by-case conjecture, or many stimulation electrodes.

APPROACH

We developed a simple two-step approach to EEG-guided tES that based on the topography of the EEG: (1) selects locations to be used for stimulation; (2) determines current applied to each electrode. Each step is performed based solely on the EEG with no need for head models or source localization. Cortical dipoles represent idealized brain targets. EEG-guided tES strategies are verified using a finite element method simulation of the EEG generated by a dipole, oriented either tangential or radial to the scalp surface, and then simulating the tES-generated electric field produced by each model-free technique. These model-free approaches are compared to a 'gold standard' numerically optimized dose of tES that assumes perfect understanding of the dipole location and head anatomy. We vary the number of electrodes from a few to over three hundred, with focality or intensity as optimization criterion.

MAIN RESULTS

Model-free approaches evaluated include (1) voltage-to-voltage, (2) voltage-to-current; (3) Laplacian; and two Ad-Hoc techniques (4) dipole sink-to-sink; and (5) sink to concentric. Our results demonstrate that simple ad hoc approaches can achieve reasonable targeting for the case of a cortical dipole, remarkably with only 2-8 electrodes and no need for a model of the head.

SIGNIFICANCE

Our approach is verified directly only for a theoretically localized source, but may be potentially applied to an arbitrary EEG topography. For its simplicity and linearity, our recipe for model-free EEG guided tES lends itself to broad adoption and can be applied to static (tDCS), time-variant (e.g., tACS, tRNS, tPCS), or closed-loop tES.