| 1. |
- Glasbey, JC, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 2. |
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| 3. |
- Alonso, Fabiola, 1980-, et al.
(författare)
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Comparison of Three Deep Brain Stimulation Lead Designs under Voltage and Current Modes
- 2015
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Ingår i: WORLD CONGRESS ON MEDICAL PHYSICS AND BIOMEDICAL ENGINEERING, 2015, VOLS 1 AND 2. - Cham : Springer. - 9783319193861 - 9783319193878 ; , s. 1196-1199
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Konferensbidrag (refereegranskat)abstract
- Since the introduction of deep brain stimulation (DBS) the technique has been dominated by Medtronic sys-tems. In recent years, new DBS systems have become available for patients, and some are in clinical trials. The present study aims to evaluate three DBS leads operated in either voltage or current mode. 3D finite element method (FEM) models were built in combination with a neuron model for this purpose. The axon diameter was set to D = 5 μm and simulations performed in both voltage (0.5-5 V) and current (0.5-5 mA) mode. The evaluation was achieved based on the distance from the lead for neural activation and the electric field (EF) extension at 0.1 V/mm. The results showed that the neural activation distance agrees well between the leads with an activation distance dif-ference less than 0.5 mm. The shape of the field at the 0.1 V/mm isopotential surface in 3D is mostly spherical in shape around the activated section of the steering lead.
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| 4. |
- Alonso, Fabiola, et al.
(författare)
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Investigation into Deep Brain Stimulation Lead Designs : A Patient-Specific Simulation Study
- 2016
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Ingår i: Brain Sciences. - : MDPI. - 2076-3425. ; 6:3, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- New deep brain stimulation (DBS) electrode designs offer operation in voltage and current mode and capability to steer the electric field (EF). The aim of the study was to compare the EF distributions of four DBS leads at equivalent amplitudes (3 V and 3.4 mA). Finite element method (FEM) simulations (n = 38) around cylindrical contacts (leads 3389, 6148) or equivalent contact configurations (leads 6180, SureStim1) were performed using homogeneous and patient-specific (heterogeneous) brain tissue models. Steering effects of 6180 and SureStim1 were compared with symmetric stimulation fields. To make relative comparisons between simulations, an EF isolevel of 0.2 V/mm was chosen based on neuron model simulations (n = 832) applied before EF visualization and comparisons. The simulations show that the EF distribution is largely influenced by the heterogeneity of the tissue, and the operating mode. Equivalent contact configurations result in similar EF distributions. In steering configurations, larger EF volumes were achieved in current mode using equivalent amplitudes. The methodology was demonstrated in a patient-specific simulation around the zona incerta and a “virtual” ventral intermediate nucleus target. In conclusion, lead design differences are enhanced when using patient-specific tissue models and current stimulation mode.
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| 5. |
- Alonso, Fabiola, 1980-, et al.
(författare)
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Neural Activation Compared to Electric Field Extension of Three DBS Lead Designs
- 2015
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Konferensbidrag (refereegranskat)abstract
- SINCE the introduction of deep brain stimulation (DBS) about 20 years ago, the stimulation technique has been dominated by Medtronic DBS-system setup. In recent years, new DBS systems have become available, of which some are in clinical trials or available to patients [1]. In the present study three different lead designs are investigated via computer simulation:Medtronic 3389, St. Jude 6148 and Sapiens SureStim. The aim was to compare the neural activation distance and the electric field (EF) maximum spatial extension for each lead.A 3D finite element method model was built using COMSOL Multiphysics 4.4a (COMSOL AB, Stockholm, Sweden) to simulate the electric potential around the DBS lead. Brain tissue was modelled as a homogeneous volume of grey matter (electric conductivity of 0.09 S/m). The electrode-tissue interface was modelled with a 250μm thick peri-electrode space mimicking the fibrous tissue which covers the lead at the chronic stimulation stage (σ = 0.06S/m, equivalent to white matter electric conductivity). The stimulation amplitude was set to 1V in monopolar configuration using C1 electrode or equivalent in all cases. Each simulated electric potential distribution was exported to MatLab (The MathWorks, USA) and used as input to a cable neuron simulation.An axon cable model with 21 nodes based on the concept by Åström et al., [2] was set up in MatLab and combined with the exported field distributions. The model considered a 5 μm thick neuron, a pulse width of 60 μs and a drive potential ranging from 0.5 V to 5 V in 0.5 V steps.The SureStim lead results showed a shorter neural activation distance and EF extension. The distance to the isolevel of 0.2 V/mm is close to the neural activation distance at each stimulation amplitude, and we conclude that the electric field is a suitable predictor to visualize the stimulated regions.
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| 6. |
- Latorre, Malcolm A., et al.
(författare)
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A Physical Action Potential Generator : Design, Implementation and Evaluation
- 2015
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Ingår i: Frontiers in Neuroscience. - : Frontiers Research Foundation. - 1662-4548 .- 1662-453X. ; 9, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- The objective was to develop a physical action potential generator (Paxon) with the ability to generate a stable, repeatable, programmable, and physiological-like action potential. The Paxon has an equivalent of 40 nodes of Ranvier that were mimicked using resin embedded gold wires (Ø = 20 μm). These nodes were software controlled and the action potentials were initiated by a start trigger. Clinically used Ag-AgCl electrodes were coupled to the Paxon for functional testing. The Paxon’s action potential parameters were tunable using a second order mathematical equation to generate physiologically relevant output, which was accomplished by varying the number of nodes involved (1 to 40 in incremental steps of 1) and the node drive potential (0 to 2.8V in 0.7 mV steps), while keeping a fixed inter-nodal timing and test electrode configuration. A system noise floor of 0.07 ± 0.01 μV was calculated over 50 runs. A differential test electrode recorded a peak positive amplitude of 1.5 ± 0.05 mV (gain of 40x) at time 196.4 ± 0.06 ms, including a post trigger delay. The Paxon’s programmable action potential like signal has the possibility to be used as a validation test platform for medical surface electrodes and their attached systems.
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| 7. |
- Latorre, Malcolm A., et al.
(författare)
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Characterization of a Surface Ag-AgCl Electrode using the Paxon Test Platform
- 2015
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Evaluation of an electrode for intraelectrode differences using both a traditional gain-phase method and the Paxon test platform. The direct gain-phase measurements are useful to extract the transfer function of the electrode, as well as some other base parameters. The Paxon test platform is a complementary method that tests electrodes under conditions that are more realistic than the gel-to-gel connection used in the gain-phase method. Testing stability over time e.g. DC signal drift (worst set 6,31 ± 43,00 nV) over a one hour of measurement duration was carried out. The Paxon also lets tests be performed beyond what the gain-phase methods can measure, for example electrode rotation, which would uncover variations in the symmetry of the electrode. When tested, the symmetry properties of the electrode (test set variations, start to end, over rotations 0,90,180 and 270 degrees) resulted in a peak to peak variation in detected amplitude of 5.3 ±8.9 mV. Intraelectrode variations were detected and quantized with the Paxon test platform.
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| 8. |
- Latorre, Malcolm, 1967-, et al.
(författare)
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A comparison between single and double cable neuron models applicable to deep brain stimulation
- 2019
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Ingår i: Biomedical Engineering & Physics Express. - : Bibliopolis, Edizioni di Filosofia e Scienze. - 2057-1976. ; 5:2
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Tidskriftsartikel (refereegranskat)abstract
- Computational models for activation assessment in deep brain stimulation (DBS) are commonly based on neuronal cable equations. The aim was to systematically compare the activation distance between a single cable model implemented in MATLAB, and a well-established double cable model implemented in NEURON. Both models have previously been used for DBS studies. The field distributions generated from a point source and a 3389 DBS lead were applied to the neuron models as input stimuli. Simulations (n = 670) were performed with intersecting axon diameters (D) between the models (2.0, 3.0, 5.7, 7.3, 8.7, 10.0 μm), variation in pulse shape and amplitude settings (0 to 5 in increments of 0.5 mA or V) with the single cable model as reference. Both models responded linearly to change of input (point source: 0.93 < R2 < 0.99, DBS source: R2 > 0.98), but with a systematic extended activation distance for the single cable model. The difference for a point source ranged from −0.2 mm (D = 2.0 μm) to −1.1 mm (D = 5.7 μm). For the DBS lead a D = 3.2 μm agreed with the commonly used double cable simulations D =5.7 μm in voltage mode. Possible reasons for the deviation at larger axons are the internodal length, the ion channel selection and physiological data behind the models. The single cable model covers a continuous range of small axon diameters and calculated the internodal length for each iteration, whereas the double cable models uses fixed defined axon diameters and tabulated data for the internodal length. Despite different implementations and model complexities, both models present similar sensitivity to pulse shape, amplitude and axon diameter. With awareness of the strength and weakness both models can be used to extract activation distance used to relate a specific electric field isolevel and thus estimate the volume of tissue activated in DBS simulation studies.
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| 9. |
- Latorre, Malcolm
(författare)
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Action Potential Generator and Electrode Testing
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Design, validation and application of a test platform for electrode characterization and comparison is a problem today. Development of target specific electrodes is increasing, for example surface cloth electrodes, non-contact electrodes, and deep brain stimulation electrodes. Whenever these new designs are implemented, there is always a need for testing. How these tests should be performed to verify the function of the electrode in an environment like the one they are designed for is still not solved.In this thesis, a physical axon, the Paxon, is suggested as a possibility to overcome this issue. The intent of the Paxon was to generate an electric field that is similar to the external field created by a live axonal process when an action potential is propagating along its length, and to do this in a stable, repeatable manner. In order to meet these specifications, the Paxon was designed with a microcontroller to drive the sequence of events and control the output parameters. A chamber with gold wire nodes entering through the bottom was manufactured as a dimensional mimic to a myelinated 20 μm diameter nerve axon segment. The chamber was flooded with normal saline solution mimicking the intervening tissues and to allow ionic coupling of electrodes to the electrical field produced in the chamber.The initial validation tests demonstrated that the timing is stable (196.4 ± 0.06 ms between trigger to action potential), as is the output “detected” amplitude (1.5 ± 0.05 mV with a gain of 40).Once the Paxon test platform was verified as functional for its intended application of testing electrodes for comparison, it was then used to compare a set of six electrodes (used as a set of three differential pairs) from a single manufacturer lot and batch number.With this approach, better assessment of the stability of the manufactured electrode, as well as longer term stability, can be attained. As more electrodes of similar and differing types are tested, the data can be used for inter-electrode comparisons and eventually verification of newelectrode designed.
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| 10. |
- Latorre, Malcolm, et al.
(författare)
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Describing Measurement Behaviour of a Surface Ag-AgCl Electrode Using the Paxon Test Platform
- 2016
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Ingår i: XIV MEDITERRANEAN CONFERENCE ON MEDICAL AND BIOLOGICAL ENGINEERING AND COMPUTING 2016. - Cham : SPRINGER. - 9783319327037 - 9783319327013 ; , s. 442-445
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Konferensbidrag (refereegranskat)abstract
- A better understanding of bioelectrodes can be acquired with extended testing, which will lead to better methodology and data quality. Today electrodes are evaluated for intraelectrode differences and performance with a traditional gain-phase method, while using the physical axon action potential generator (Paxon) test platform offers extended test possibilities. The direct gain-phase measurements are useful to extract the transfer function of the electrode, as well as some other base parameters. The Paxon test platform is a complementary method that tests electrodes under conditions that are more realistic, mimicking real measurement situations in comparison to the gain-phase method. The Paxon also allows tests to be performed beyond what the gain-phase methods can measure, for example electrode rotation, which would uncover variations in the symmetry of the electrode. When tested, the symmetry properties of the electrode, where the electrodes are rotated in steps of 90 degrees, resulted in a peak to peak variation in detected amplitude of 5.3 +/- 8.9 mV. Therefore, the Paxon appears to be a feasible test platform for characterizing electrodes beyond the gain-phase tests in a semiautomatic manner.
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