Segmented Contact Research Articles

Reducing Ataxic Side Effects from Ventral Intermediate Nucleus of the Thalamus Deep Brain Stimulation Implantation in Essential Tremor: Potential Advantages of Directional Stimulation

Objective: The aim of the study was to retrospectively evaluate the effect of directional deep brain stimulation (DBS) on ataxia in an essential tremor patient population. Materials and Methods: A retrospective chart review of documented Scale for Assessment and Rating of Ataxia (SARA) scores were analyzed using a case-control design. All subjects we evaluated were treated at a single, tertiary care academic center. We reviewed 14 patients who underwent bilateral ventral intermediate nucleus of the thalamus (VIM) implantation with microelectrode recording, with electrodeposition and segmented contact orientation confirmed via postoperative computed tomography. The main outcome was to determine change in ataxia scores between directional versus monopolar circumferential stimulation. Results: Fourteen patients (9 males, median age at implantation 69 [range 63–82]) underwent surgery between October 2017 and July 2020 at the UNC Movement Disorders Center. SARA scores between directional stimulation and monopolar circumferential stimulation demonstrated a significant reduction in total scores with best possible segmented stimulation (n = 13, p < 0.0001, 95% confidence interval [CI] −3.496 to −6.789). This difference remained statistically significant even after removing the SARA tremor subscore (n = 13, p < 0.0001, 95% CI −3.155 to −6.274). In line with prior reports, SARA score changes from the preoperative state were generally worsened when applying monopolar circumferential stimulation bilaterally (n = 13, p = 0.655; 95% CI −2.836 to 4.359), but improved with directional stimulation (n = 13, p = 0.010; 95% CI −1.216 to −7.547). Conclusion: This retrospective analysis appears to show evidence for improved outcomes through directional stimulation in bilateral VIM DBS implantation with reduction of ataxic side effects that have traditionally plagued postoperative results, all while providing optimized tremor reduction via stimulation.

DEPOSITION OF Al/SnAl OHMIC CONTACT ON SILICON FROM A LIQUID PHASE

Background. Single- and multi-layer metal films are widely utilized in modern electronics and optoelectronics as ohmic contacts. As a rule, the films are deposited by thermal evaporation, ion sputtering and chemical vapour deposition. However the methods of deposition from a liquid phase are the most simple and cost-effective. Thus the ohmic contact deposition by these methods is still an actual problem. Objective. The purpose of the paper is to study the possibility of deposition of multi-layer ohmic metal films over a semiconductor wafer surface from a liquid phase, particularly by scanning liquid phase epitaxy technique. Methods. In this work we considered the influence of a long-term temperature gradient at the interface metallic solution-melt – semiconductor wafer on the possibility of deposition of multi-layer ohmic metal films on the semiconductor wafer surface during segmental contact between the solution-melt and the wafer. For this purpose we carried out the simulation of heat transport process, wafer wetting process as well as the process of wafer cleansing off the solution-melt taking into account capillary phenomena in the mask openings using the method of scanning liquid phase epitaxy. For experimental confirmation of adequacy of the model proposed we carried out the deposition of Al/SnAl layer on silicon wafer in the above mentioned conditions. Results. We have deposited the contact layer Al/SnAl on the surface of silicon wafer from Al-Sn solution-melt by scanning liquid phase epitaxy technique using supplementary heater for the wafer and mask installed in the apparatus. The contact layer is made as three identical pads located at different distance one from each other. By the analysis of current-voltage characteristic we determined that the metallic film contact with the semiconductor is a non-rectifying, i.e. ohmic contact. The specific contact resistance was determined by the Transmission Line Method using linear configuration of the contact pads (LTLM). Its value was 7.2∙10-4 Ohm·cm2. Conclusions. The principal possibility of obtaining of multi-layer ohmic contacts to the semiconductor by scanning liquid phase epitaxy technique in conditions of segmental contact between the solution-melt and the wafer as well as long-term gradient at the contact interface was shown. The conditions were realized by using extra heating of the wafer back side and the high-temperature mask through which the solution-melt contacted the wafer.

Experimental investigation on vortex-induced vibration and solid-structure impact of a near-bottom horizontal flexible pipeline in oblique shear flow

Vortex-induced vibrations and solid-structure impacts of a horizontal flexible pipeline in the vicinity of a bottom wall boundary are experimentally investigated in a water flume. A neutrally-buoyant submerged pipe, with a length-to-diameter ratio of about 87 and fixed end supports, is subject to a shear flow with an oblique angle of 30°. The initial gap-to-diameter ratio between the wall and the pipe is equal to 0.2. A non-intrusive measurement with high-speed cameras is employed to simultaneously capture the space–time varying in-line and cross-flow vibrations in the normal flow reduced velocity range of 3–15 with a maximum Reynolds number of about 2780. Experimental results highlight new pipe equilibrium profiles and modal response branches being significantly broadened due to the wall proximity. Two solid-pipe impact features are discussed, including single-segment and two-segment alternating impacts depending on the dominant oscillation mode of the flexible pipe. Both the response amplitude and frequency increase with the reduced velocity, resulting in a more frequent impact with a greater impact force. A temporal evolution from a single point contact to a segment contact is observed for the two-segment alternating impact. Nevertheless, the lengths of the two contact segments are different as a result of the asymmetric response profile. In all cases, the pipe transversely impacts the bottom wall introducing a perturbation transmission along the pipe, which leads to the multi-mode, multi-frequency and asynchronous in-line and cross-flow oscillations with a 1:1 and 2:1 resonance. Due to a momentum energy consumption, the pipe experiences a slow post-impact bouncing phenomenon, contributing to a longer temporal period of the fluid–pipe interaction with a wall impact.

Research on cutting performance of coated cutting tools by a new impact test method considering contact stress condition caused by segmented chips

The generation of segmented chip will cause unstable vibration of cutting force and produce high-frequency stress impact on the cutting tool. The segmented chip morphology and contact stress between chip and flank face of coated cutting tool were studied by cutting experiments. It was found that the average contact stress of the coated tool was 4.9 GPa and the alternating frequency reached 22 kHz. A new high-frequency impact test method was used to simulate the loading condition of coated tools in the cutting experiments. The results showed that the cutting performance of the coated tool was related to the impact fatigue resistance. In the case of a high feed rate (above 0.1 mm/rev) or high preloading depth (7.51 μm and 9 μm), TiSiN/TiAlN bilayer coating shows better performance, compared with TiSiN/TiAlN nanolayer coating. However, in the case of low feed rate (less than 0.1 mm/rev) or low preloading depth (18 μm), TiSiN/TiAlN nanolayer coating shows better performance. Cutting conditions and coating structure could match to get optimized cutting performance of coated cutting tools.

Motor Evoked Potential Recordings During Segmented Deep Brain Stimulation-A Feasibility Study.

Segmented deep brain stimulation (DBS) leads, which are capable of steering current in the direction of any 1 of 3 segments, can result in a wider therapeutic window by directing current away from unintended structures, particularly, the corticospinal tract (CST). It is unclear whether the use of motor evoked potentials (MEPs) is feasible during DBS surgery via stimulation of individual contacts/segments in order to quantify CST activation thresholds and optimal contacts/segments intraoperatively. To assess the feasibility of using MEP to identify CST thresholds for ring and individual segments of the DBS lead under general anesthesia. MEP testing was performed during pulse generator implantation under general anesthesia on subjects who underwent DBS lead implantation into the subthalamic nucleus (STN). Stimulation of each ring and segmented contacts of the directional DBS lead was performed until CST threshold was reached. Stereotactic coordinates and thresholds for each contact/segment were recorded along with the initially activated muscle group. A total of 34 hemispheres were included for analysis. MEP thresholds were recorded from 268 total contacts/segments. For segmented contacts (2 and 3, respectively), the mean highest CST thresholds were 2.33 and 2.62 mA, while the mean lowest CST thresholds were 1.7 and 1.89 mA, suggesting differential thresholds in relation to CST. First dorsal interosseous and abductor pollicis brevis (34% each) were the most commonly activated muscle groups. MEP threshold recording from segmented DBS leads is feasible. MEP recordings can identify segments with highest CST thresholds and may identify segment orientation in relation to CST.

Steering the Volume of Tissue Activated With a Directional Deep Brain Stimulation Lead in the Globus Pallidus Pars Interna: A Modeling Study With Heterogeneous Tissue Properties

Objective: To study the effect of directional deep brain stimulation (DBS) electrode configuration and vertical electrode spacing on the volume of tissue activated (VTA) in the globus pallidus, pars interna (GPi).Background: Directional DBS leads may allow clinicians to precisely direct current fields to different functional networks within traditionally targeted brain areas. Modeling the shape and size of the VTA for various monopolar or bipolar configurations can inform clinical programming strategies for GPi DBS. However, many computational models of VTA are limited by assuming tissue homogeneity.Methods: We generated a multimodal image-based detailed anatomical (MIDA) computational model with a directional DBS lead (1.5 mm or 0.5 mm vertical electrode spacing) placed with segmented contact 2 at the ventral posterolateral “sensorimotor” region of the GPi. The effect of tissue heterogeneity was examined by replacing the MIDA tissues with a homogeneous tissue of conductance 0.3 S/m. DBS pulses (amplitude: 1 mA, pulse width: 60 μs, frequency: 130 Hz) were used to produce VTAs. The following DBS contact configurations were tested: single-segment monopole (2B-/Case+), two-segment monopole (2A-/2B-/Case+ and 2B-/3B-/Case+), ring monopole (2A-/2B-/2C-/Case+), one-cathode three-anode bipole (2B-/3A+/3B+/3C+), three-cathode three-anode bipole (2A-/2B-/2C-/3A+/3B+/3C+). Additionally, certain vertical configurations were repeated with 2 mA current amplitude.Results: Using a heterogeneous tissue model affected both the size and shape of the VTA in GPi. Electrodes with both 0.5 mm and 1.5 mm vertical spacing (1 mA) modeling showed that the single segment monopolar VTA was entirely contained within the GPi when the active electrode is placed at the posterolateral “sensorimotor” GPi. Two segments in a same ring and ring settings, however, produced VTAs outside of the GPi border that spread into adjacent white matter pathways, e.g., optic tract and internal capsule. Both stacked monopolar settings and vertical bipolar settings allowed activation of structures dorsal to the GPi in addition to the GPi. Modeling of the stacked monopolar settings with the DBS lead with 0.5 mm vertical electrode spacing further restricted VTAs within the GPi, but the VTA volumes were smaller compared to the equivalent settings of 1.5 mm spacing.

Study of the Spatial and Current Dynamics of Optical Loss in Semiconductor Laser Heterostructures by Optical Probing

The spatial and temporal dynamics of the optical loss and carrier density in the heterostructure of a semiconductor laser with a segmented contact are studied using an optical pump–probe technique based on the injection of probe radiation with a wavelength of 1560 nm into a semiconductor laser chip under study that is based on an AlGaAs/InGaAs/GaAs heterostructure and emits at wavelength of 1010 nm. It is demonstrated that employing probe light at a wavelength of 1560 nm enables sensitivity in measuring an internal optical loss of no less than 1 cm–1. The segmented design of the current pumping region made it possible to estimate the absolute internal optical loss. It is shown that changing the configuration of the Fabry–Perot eigenmodes of the laser affects the carrier distribution and the internal optical loss both in the current pumping region and in the passive, current unpumped part of the laser chip.

Early Experience With New Generation Deep Brain Stimulation Leads in Parkinson’s Disease and Essential Tremor Patients

Newer generation deep brain stimulation (DBS) systems have recently become available in the United States. Data on real-life experience are limited. We present our initial experience incorporating newer generation DBS with Parkinson's disease (PD) and essential tremor (ET) patients. Newer systems allow for smart energy delivery and more intuitive programming and hardware modifications including constant current and directional segmented contacts. We compared six-month outcomes between 42 newer generation and legacy leads implanted in 28 patients. Two cohorts each included 7 PD patients with bilateral subthalamic nucleus (STN) stimulation and 7 ET patients with unilateral ventral intermediate nucleus (VIM) stimulation of the thalamus. All directional leads included 6172 Infinity 8-Channel Directional leads and Infinity internal pulse generators (Abbott Neuromodulation, Plano, TX, USA) and nondirectional leads included lead 3389 with Activa SC for VIM and PC for STN (Medtronic, Minneapolis, MN, USA). Six-month outcomes for medication reduction and motor score improvements between new and legacy DBS systems in PD and ET patients were similar. Directionality was employed in 1/3 of patients. Therapeutic window (difference between amplitude when initial symptom relief was obtained and when intolerable side effects appeared with the contact being used) was significantly greater in new DBS systems in both PD (p = 0.005) and ET (p = 0.035) patients. The windows for new and legacy systems were 3.60 V ± 0.42 and 2.00 V ± 0.32 for STN and 3.06 V ± 0.44 and 1.85 V ± 0.28 for VIM, respectively. The therapeutic window of newer systems, whether or not directionality was used, was significantly greater than that of the legacy system, which suggests increased benefit and programming options. Improvements in hardware and programming interfaces in the newer systems may also contribute to wider therapeutic windows. We expect that as we alter workflow associated with newer technology, more patients will use directionality, and amplitudes will become lower.

An improved disk discontinuous deformation analysis model for simulating particle mixing process in rotary drums

This paper develops an improved disk discontinuous deformation analysis (DDDA) model to simulate mixing particles in rotary drums. The original DDDA is improved by developing a disk-movable line segment contact model to motivate the constant movements of the disks during the mixing operation. The analytical solution of the movement of a single disk in a rotary drum is achieved by building a force analysis model, and the improved DDDA is validated by comparing this analytical solution with the proposed numerical simulation. Then, the improved DDDA is utilized to simulate mixing 8805 disks in a rotary drum, during which the influences of rotational speed and layouts of stirring blades are studies. Model performance shows that, the improved DDDA is a feasible tool to simulate the particle mixing process in rotary drums, which may optimize schemes for mixing particles and designing mixing equipment in industry.

Functional Use of Directional Local Field Potentials in the Subthalamic Nucleus Deep Brain Stimulation

BackgroundDirectional deep brain stimulation (DBS) technology aims to address the limitations, such as stimulation-induced side effects, by delivering selective, focal modulation via segmented contacts. However, DBS programming becomes more complex and time-consuming for clinical feasibility. Local field potentials (LFPs) might serve a functional role in guiding clinical programming.ObjectiveIn this pilot study, we investigated the spectral dynamics of directional LFPs in subthalamic nucleus (STN) and their relationship to motor symptoms of Parkinson’s disease (PD).MethodsWe recorded intraoperative STN-LFPs from 8-contact leads (Infinity-6172, Abbott Laboratories, Illinois, United States) in 8 PD patients at rest. Directional LFPs were referenced to their common average and time-frequency analysis was computed using a modified Welch periodogram method. The beta band (13–35 Hz) features were extracted and their correlation to preoperative UPDRS-III scores were assessed.ResultsNormalized beta power (13–20 Hz) and normalized peak power (13–35 Hz) were found to be higher in anterior direction despite lack of statistical significance (p > 0.05). Results of the Spearman correlation analysis demonstrated positive trends with bradykinesia/rigidity in dorsoanterior direction (r = 0.659, p = 0.087) and with axial scores in the dorsomedial direction (r = 0.812, p = 0.072).ConclusionGiven that testing all possible combinations of contact pairs and stimulation parameters is not feasible in a single clinic visit, spatio-spectral LFP dynamics obtained from intraoperative recordings might be used as an initial marker to select optimal contact(s).

Directional deep brain stimulation leads reveal spatially distinct oscillatory activity in the globus pallidus internus of Parkinson's disease patients

The goal of this study was to characterize the spectral characteristics and spatial topography of local field potential (LFP) activity in the internal segment of the globus pallidus (GPi) in patients with Parkinson's disease utilizing directional (segmented) deep brain stimulation (dDBS) leads. Data were collected from externalized dDBS leads of three patients with idiopathic Parkinson's disease after overnight withdrawal of parkinsonian medication at rest and during a cued reach-to-target task. Oscillatory activity across lead contacts/segments was examined in the context of lead locations and contact orientations determined using co-registered preoperative 7 Tesla (T) MRI and postoperative CT scans. Each of the three patients displayed a unique frequency spectrum of oscillatory activity in the pallidum, with prominent peaks ranging from 5 to 35 Hz, that modulated variably across subjects during volitional movement. Despite subject-specific spectral profiles, a consistent finding across patients was that oscillatory power was strongest and had the largest magnitude of modulation during movement in LFPs recorded from segments facing the postero-lateral “sensorimotor” region of GPi, whereas antero-medially-directed segmented contacts facing the internal capsule and/or anterior GPi, had relatively weaker LFP power and less modulation in the 5 to 35 Hz. In each subject, contact configurations chosen for clinically therapeutic stimulation (following data collection and blinded to physiology recordings), were in concordance with the contact pairs showing the largest amplitude of LFP oscillations in the 5–35 Hz range. Although limited to three subjects, these findings provide support for the hypothesis that the sensorimotor territory of the GPi corresponds to the site of maximal power of oscillatory activity in the 5 to 35 Hz and provides the greatest benefit in motor signs during stimulation in the GPi. Variability in oscillatory activity across patients is likely related to Parkinson's disease phenotype as well as small differences in recording location (i.e. lead location), highlighting the importance of lead location for optimizing stimulation efficacy. These data also provide compelling evidence for the use of LFP activity for the development of predictive stimulation models that may optimize patient benefits while reducing clinic time needed for programming.

Исследование пространственной и токовой динамики оптических потерь в полупроводниковых лазерных гетероструктурах методом оптического зондирования

The spatiotemporal dynamics of optical losses and carrier density in a heterostructure of a semiconductor laser with a segmented contact were studied using an optical probe technique based on the coupling of probe radiation with a wavelength of 1560 nm into a semiconductor laser chip under investigation based on an AlGaAs/ InGaAs/ GaAs heterostructure and emitting at a wavelength of 1010 nm. It has been shown that the use of a probe beam with a wavelength of 1560 nm makes it possible to ensure the sensitivity of the measurement of internal optical losses of no worse than 1 cm-1. The use of a segmented design of the current pumping region made it possible to estimate the absolute value of internal optical losses. It was shown that a change in the configuration of the Fabry-Perot eigenmodes of the laser affects the distribution of charge carriers and internal optical losses both in the current pump region and in the passive part of the laser chip that is not pumped by the current.

Virtual Surgical Planning in Subscapular System Free Flap Reconstruction of Midface Defects

ObjectivesReconstruction of the midface has many inherent challenges, including orbital support, skull base reconstruction, optimizing midface projection, separation of the nasal cavity and dental rehabilitation. Subscapular system free flaps (SF) have sufficient bone stock to support complex reconstruction and the option of separate soft tissue components. This study analyzes the effect of virtual surgical planning (VSP) in SF for midface on subsite reconstruction, bone segment contact and anatomic position. Materials and MethodsRetrospective cohort of patients with midface defects that underwent SF reconstruction at a single tertiary care institution. ResultsNine cases with VSP were compared to fourteen cases without VSP. VSP was associated with a higher number of successfully reconstructed subunits (5.9 vs 4.2, 95% CI of mean difference 0.31–3.04, p = 0.018), a higher number of successful bony contact between segments (2.2 vs 1.4, 95% CI of mean difference 0.0–1.6, p = 0.050), and a higher percent of segments in anatomic position (100% vs 71%, 95% CI of mean difference 2–55%, p = 0.035). When postoperative bone position after VSP reconstruction was compared to preoperative scans, the difference in anteroposterior, vertical and lateral projection compared to the preoperative ‘ideal’ bone position was <1 cm in 82% of measurements. There were no flap losses. ConclusionVSP may augment SF reconstruction of the midface by allowing for improved subunit reconstruction, bony segment contact and anatomically correct bone segment positioning. VSP can be a useful adjunct for complex midface reconstruction and the benefits should be weighed against cost.

A modal based reduction technique for wide loose interfaces and application to a turbine stator

Aim of this research is the prediction of the non-linear forced response of a stator bladed disk for aeronautical applications in the presence of friction contacts at the hook joints (casing – vane segment contact). Due to the large extension of the contact interfaces the use of classic node-to-node contact elements based on the Coulomb friction law becomes cumbersome. Although such approach appears convenient for problems involving small contact regions, it is computationally expensive when large contact interfaces with refined meshes are present between components. In this research, a novel modal interface reduction method is combined with a layer of Jenkins contact elements in order to efficiently predict the effects of friction on the non-linear forced response of the stator bladed disk. The wide rail/hook contact regions are therefore suitable for the application of the presented technique. The goodness of the proposed methodology is quantified both in terms of accuracy and time costs savings on the calculation of non-linear forced responses by exploiting cyclic symmetry hypotheses and the Harmonic Balance Method.

Non-Equilibrium Phase Behavior of Immiscible Polymer-Grafted Nanoparticle Blends

Preferential attraction of polymer chains to the substrate [i.e., poly(methyl methacrylate) (PMMA) on the hydroxyl-terminated Si substrate] typically results in the initial phase separation of spin-cast immiscible linear polymer blends [i.e., polystyrene (PS)/PMMA] with a characteristic interfacial microstructure depending on their molecular weight. A formation of the undesired microstructure in those blends is inevitable because of the thermodynamic force driving their phase separation combined with relatively rapid dynamics in solution. In contrast, the polymer ligands, which are grafted from nanoparticles, are capable of limited segmental interactions in the presence of segmental contacts of chemically distinct chains as well as hindered mobility by interpenetration (or entanglement) and thus exhibit a homogeneous but non-equilibrium phase behavior. Here, the microstructure of the blends consisting of immiscible polymer-grafted nanoparticles (PGNPs) was identified by their neutron reflectivity, in whic...

Reduction of Side Effects by Segmented Electrodes in Case of Subthalamic Nucleus Deep Brain Stimulation in Parkinson Disease: A Case Report.

Patients suffering treatment resistant Parkinson´s disease (PD) are potential candidates for deep brain stimulation (DBS). Commonly most implanted electrodes have a cylindrical shape with quadripolar electrode contacts and generate a symmetrical stimulation field around the lead. To reduce side effects through activation of neighboring fibers a new electrode design with segmented contacts was developed and enables a better adaption of the field of stimulation as well as a multi-target stimulation to improve therapeutic benefits. We report about a 51-year-old male patient with a 15-year history of treatment-refractory PD, who was implanted with bilateral segmented electrodes in the subthalamic nucleus (STN) with St. Jude Medical Infinity™ DBS System (Abbott/St. Jude Medical, Saint Paul, Minnesota, USA). Despite a clear mood-enhancing effect, stimulation with ring electrodes caused motor side effects including rigor and speech disorder. With segmented electrodes an effective and gentle stimulation was achieved. The stimulation of the anterior segments in the central position of the electrode in the STN showed no side-effects and allowed a reduction of initial symptoms in an low stimulation amplitude. Despite precise preoperatively planning and intraoperative trial stimulation, side effects of STN stimulation are very common. The application of segmented electrodes permits more options to reduce side effects rather than using ring electrodes. Studies with larger samples sizes are needed to establish the optional DBS electrode.

Compensation effects of high oxygen levels in semipolar AlGaN electron blocking layers and their mitigation via growth optimization

InGaN-based laser diodes (LDs) grown on the semipolar (202¯1¯) plane of GaN offer advantages arising from predicted higher gain compared to c-plane devices. However, the performance of semipolar devices has been limited by low injection efficiency. In prior work, this has been proposed to be caused by an inefficient AlGaN electron blocking layer (EBL). A high oxygen level in the EBL found in previous work could cause compensation of the p-type dopants. In this work the oxygen impurities were eliminated via optimizations during the metalorganic chemical vapor deposition (MOCVD) growth. Optimization of the V/III ratio and an increase in the growth temperature during the AlGaN growth was found to reduce the oxygen incorporation. Additionally, residual sources of oxygen were removed from the MOCVD growth process. These combined steps reduced the peak oxygen level in the AlGaN from 5 × 1018/cm3 to 6 × 1017/cm3 as measured by secondary ion mass spectroscopy. LDs were fabricated with and without these modifications to clarify the effect of the reduced oxygen. The threshold current and differential efficiency showed improvement with reduced oxygen. The internal loss and gain of these LDs were measured using the segmented contact method, confirming that the injection efficiency was boosted from 60% with high oxygen to 80% with low oxygen.

Nonlinear Mechano-Optical Behavior and Strain-Induced Structural Changes of l-Valine-Based Poly(ester urea)s

The uniaxial mechano-optical behavior of a series of amorphous l-valine-based poly(ester urea) (VAL-PEU) with varying diol lengths was studied to elucidate the molecular mechanism associated with their thermal shape memory properties. A custom, real-time measurement system was used to capture the true stress, true strain, and birefringence during the temporary shape programming at stretching temperatures above the glass transition temperature (Tg). The mechano-optical response of VAL-PEUs exhibits an initial photoelastic behavior related to enhanced segmental correlation at low temperatures above the Tg. A characteristic temperature, defined as the liquid–liquid (Tll) transition (rubbery–viscous transition), was found at about 1.05 Tg (K) (at Tg + 15 °C) at strain rate of 0.017 s–1, above which the segmental contacts largely “melt” and the initial slope of the stress-optical curves becomes temperature independent. This temperature corresponds to the temperature where mean relaxation time for the polymer i...

Thalamic short pulse stimulation diminishes adverse effects in essential tremor patients.

To investigate the effect of directional current steering and short pulse stimulation in the ventral intermediate thalamic nucleus (VIM) on stimulation-induced side effects in patients with essential tremor. We recruited 8 patients with essential tremor in a stable postoperative condition (>3 months after electrode implantation of deep brain stimulation [DBS] electrodes) with segmented contacts implanted in the VIM. Tremor severity on acute stimulation was assessed by the Fahn-Tolosa-Marin Tremor Rating Scale. Cerebellar impairment was evaluated with the International Cooperative Ataxia Rating Scale. Patients rated paresthesia intensity with a visual analog scale. In all patients, tremor was reduced to the same extent by VIM stimulation regardless of pulse width using energy dose-equivalent amplitudes. Short pulse stimulation diminished stimulation-induced ataxia of the upper extremities and paresthesia compared with conventional parameters. Directional steering with monopolar stimulation of single segments successfully suppressed tremor but also induced ataxia. No differences in adverse effects were found between single-segment stimulation conditions. These proof-of-principle findings provide evidence that acute short pulse stimulation is superior to directional steering in the subthalamic area to decrease stimulation-induced side effects while preserving tremor suppression effects in patients with tremor. This study provides Class IV evidence that for patients with tremor with thalamic DBS, acute short pulse stimulation reduces adverse effects, while directional steering does not provide a generalizable benefit regarding adverse effects.

Automatic segmentation of stereoelectroencephalography (SEEG) electrodes post-implantation considering bending

PurposeThe accurate and automatic localisation of SEEG electrodes is crucial for determining the location of epileptic seizure onset. We propose an algorithm for the automatic segmentation of electrode bolts and contacts that accounts for electrode bending in relation to regional brain anatomy.MethodsCo-registered post-implantation CT, pre-implantation MRI, and brain parcellation images are used to create regions of interest to automatically segment bolts and contacts. Contact search strategy is based on the direction of the bolt with distance and angle constraints, in addition to post-processing steps that assign remaining contacts and predict contact position. We measured the accuracy of contact position, bolt angle, and anatomical region at the tip of the electrode in 23 post-SEEG cases comprising two different surgical approaches when placing a guiding stylet close to and far from target point. Local and global bending are computed when modelling electrodes as elastic rods.ResultsOur approach executed on average in 36.17 s with a sensitivity of 98.81% and a positive predictive value (PPV) of 95.01%. Compared to manual segmentation, the position of contacts had a mean absolute error of 0.38 mm and the mean bolt angle difference of 0.59^{circ } resulted in a mean displacement error of 0.68 mm at the tip of the electrode. Anatomical regions at the tip of the electrode were in strong concordance with those selected manually by neurosurgeons, ICC(3,k)=0.76, with average distance between regions of 0.82 mm when in disagreement. Our approach performed equally in two surgical approaches regardless of the amount of electrode bending.ConclusionWe present a method robust to electrode bending that can accurately segment contact positions and bolt orientation. The techniques presented in this paper will allow further characterisation of bending within different brain regions.