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Latorre, Malcolm
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Publications (10 of 11) Show all publications
Latorre, M. & Wårdell, K. (2019). A comparison between single and double cable neuron models applicable to deep brain stimulation. Biomedical Physics & Engineering Express, 5(2)
Open this publication in new window or tab >>A comparison between single and double cable neuron models applicable to deep brain stimulation
2019 (English)In: Biomedical Physics & Engineering Express, E-ISSN 2057-1976, Vol. 5, no 2Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Medical Engineering
Identifiers
urn:nbn:se:liu:diva-155800 (URN)10.1088/2057-1976/aafdd9 (DOI)
Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-10-04
Latorre, M. (2017). The Physical Axon: Modeling, Simulation and Electrode Evaluation. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>The Physical Axon: Modeling, Simulation and Electrode Evaluation
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electrodes are used in medicine for detection of biological signals and for stimulating tissue, e.g. in deep brain stimulation (DBS). For both applications, an understanding of the functioning of the electrode, and its interface and interaction with the target tissue involved is necessary. To date, there is no standardized method for medical electrode evaluation that allows transferability of acquired data. In this thesis, a physical axon (Paxon) potential generator was developed as a device to facilitate standardized comparisons of different electrodes. The Paxon generates repeatable, tuneable and physiological-like action potentials from a peripheral nerve. It consists of a testbed comprising 40 software controlled 20 μm gold wires embedded in resin, each wire mimicking a node of Ranvier. ECG surface Ag-AgCl electrodes were systematically tested with the Paxon. The results showed small variations in orientation (rotation) and position (relative to axon position) which directly impact the acquired signal. Other electrode types including DBS electrodes can also be evaluated with the Paxon.

A theoretical comparison of a single cable neuronal model with an alternative established double cable neuron model was completed. The output with regards to DBS was implemented to comparing the models. These models were configured to investigate electrode stimulation activity, and in turn to assess the activation distance by DBS for changes in axon diameter (1.5-10 μm), pulse shape (rectangular biphasic and rectangular, triangular and sinus monophasic) and drive strength (1-5 V or mA). As both models present similar activation distances, sensitivity to input shape and computational time, the neuron model selection for DBS could be based on model complexity and axon diameter flexibility. An application of the in-house neuron model for multiple DBS lead designs, in a patient-specific simulation study, was completed. Assessments based on the electric field along multiple sample planes of axons support previous findings that a fixed electric field isolevel is sufficient for assessments of tissue activation distances for a predefined axon diameter and pulse width in DBS.

Abstract [sv]

Elektroder används inom sjukvården, både för att mäta biologiska signaler, t.ex. hjärtats aktivitet med EKG, eller för att stimulera vävnad, t.ex. vid djup hjärnstimulering (DBS). För båda användningsområdena är det viktigt med en grundläggande förståelse av elektrodens interaktion med vävnaden. Det finns ingen standardiserad metod för att utvärdera medicinsk elektroders dataöverföringsfunktion. I den här avhandlingen presenteras en metod för att underlätta elektrodtestning. En hårdvarumodell av ett axon (Paxon) har utvecklats. Paxon kan programmeras för att efterlikna repeterbara aktionspotentialer från en perifer nerv. Längs axonet finns 40 noder, vilka var och en består av en tunn (20 μm) guldtråd inbäddad i harts och därefter kopplad till elektronik. Denna testbädd har använts för att undersöka EKG elektroders egenskaper. EKG elektroderna visade på variationer i orientering och position i relation till Paxon. Detta har en direkt inverkan på den registrerade signalen. Även andra elektrotyper kan testas i Paxon, t.ex. DBS elektroder.

En teoretisk jämförelse mellan två neuronmodeller med olika komplexitet, anpassade för användning vid DBS studier, har utförts. Modellerna konfigurerades för att studera inverkan på aktiveringsavstånd från olika axondiametrar, stimulationspuls och stimulationsstyrka. Då båda modellerna visade likvärdiga aktiveringsavstånd och beräkningstid så förordas den enklare neuronmodellen för DBS simuleringar. En enklare modell kan lättare introduceras i klinisk verksamhet. Simuleringarna stöder tidigare resultat som visat att det elektriska fältet är en bra parameter för presentation av resultat vid simulering av DBS. Metoden exemplifieras vid simulering av aktiveringsavstånd och elektriska fältets utbredning för olika typer av DBS elektroder i en patient-specifik studie.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. p. 75
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1847
National Category
Medical Laboratory and Measurements Technologies Other Medical Engineering Biomedical Laboratory Science/Technology Computer Systems
Identifiers
urn:nbn:se:liu:diva-138587 (URN)10.3384/diss.diva-138587 (DOI)9789176855294 (ISBN)
Public defence
2017-08-25, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 621-2013-6078Swedish Research Council, 2016-03564Linköpings universitetSwedish Foundation for Strategic Research , BD15-0032
Available from: 2017-06-19 Created: 2017-06-19 Last updated: 2019-10-11Bibliographically approved
Latorre, M., Salerud, G. & Wårdell, K. (2016). Describing Measurement Behaviour of a Surface Ag-AgCl Electrode Using the Paxon Test Platform. In: XIV MEDITERRANEAN CONFERENCE ON MEDICAL AND BIOLOGICAL ENGINEERING AND COMPUTING 2016: . Paper presented at 14th Mediterranean Conference on Medical and Biological Engineering and Computing (MEDICON) (pp. 442-445). SPRINGER, 57
Open this publication in new window or tab >>Describing Measurement Behaviour of a Surface Ag-AgCl Electrode Using the Paxon Test Platform
2016 (English)In: XIV MEDITERRANEAN CONFERENCE ON MEDICAL AND BIOLOGICAL ENGINEERING AND COMPUTING 2016, SPRINGER , 2016, Vol. 57, p. 442-445Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
SPRINGER, 2016
Series
IFMBE Proceedings, ISSN 1680-0737
Keywords
Electrode testing; Characterization; Coupling Parameters; Stability test; Axon potential
National Category
Medical Equipment Engineering
Identifiers
urn:nbn:se:liu:diva-129510 (URN)10.1007/978-3-319-32703-7_86 (DOI)000376283000086 ()978-3-319-32703-7 (ISBN)978-3-319-32701-3 (ISBN)
Conference
14th Mediterranean Conference on Medical and Biological Engineering and Computing (MEDICON)
Available from: 2016-06-20 Created: 2016-06-20 Last updated: 2017-06-19Bibliographically approved
Latorre, M. A., Chan, A. D. .. & Wårdell, K. (2015). A Physical Action Potential Generator: Design, Implementation and Evaluation. Frontiers in Neuroscience, 9, 1-11, Article ID 371.
Open this publication in new window or tab >>A Physical Action Potential Generator: Design, Implementation and Evaluation
2015 (English)In: Frontiers in Neuroscience, ISSN 1662-4548, E-ISSN 1662-453X, Vol. 9, p. 1-11, article id 371Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Frontiers Research Foundation, 2015
Keywords
Action potential, biomedical electrode, electronic nerve model, nodes of Ranvier, ulnar nerve
National Category
Medical Engineering
Identifiers
urn:nbn:se:liu:diva-121086 (URN)10.3389/fnins.2015.00371 (DOI)
Note

Funding agencies| Linköping University; the Swedish Research Council (Grant No. 621-2013-6078)

At the time for thesis presentation publication was in status: Manuscript

Available from: 2015-09-07 Created: 2015-09-07 Last updated: 2017-12-04Bibliographically approved
Latorre, M. (2015). Action Potential Generator and Electrode Testing. (Licentiate dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Action Potential Generator and Electrode Testing
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. p. 44
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1725
National Category
Medical Engineering
Identifiers
urn:nbn:se:liu:diva-121088 (URN)978-91-7685-974-2 (ISBN)
Presentation
2015-09-25, IMT 1, Campus US, Linköpings universitet, Linköping, 13:00 (Swedish)
Opponent
Supervisors
Note

The Series name Linköping Studies in Science and Technology Licentiate Thesis in the thesis is incorrect. The correct series name is Linköping Studies in Science and Technology. Thesis.

Available from: 2015-09-07 Created: 2015-09-07 Last updated: 2017-02-13Bibliographically approved
Latorre, M. A., Salerud, E. G. & Wårdell, K. (2015). Characterization of a Surface Ag-AgCl Electrode using the Paxon Test Platform.
Open this publication in new window or tab >>Characterization of a Surface Ag-AgCl Electrode using the Paxon Test Platform
2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

Keywords
Electrode testing, Characterization, Coupling Parameters. Stability test, Axon potential
National Category
Medical Engineering
Identifiers
urn:nbn:se:liu:diva-121087 (URN)
Available from: 2015-09-07 Created: 2015-09-07 Last updated: 2017-02-03Bibliographically approved
Alonso, F., Wårdell, K. & Latorre, M. (2015). Comparison of Three Deep Brain Stimulation Lead Designs under Voltage and Current Modes. In: David A. Jaffray (Ed.), WORLD CONGRESS ON MEDICAL PHYSICS AND BIOMEDICAL ENGINEERING, 2015, VOLS 1 AND 2: . Paper presented at World congress on medical physics and biomedical engineering, Toronto, June 7-12, 2015 (pp. 1196-1199). Springer, 51
Open this publication in new window or tab >>Comparison of Three Deep Brain Stimulation Lead Designs under Voltage and Current Modes
2015 (English)In: WORLD CONGRESS ON MEDICAL PHYSICS AND BIOMEDICAL ENGINEERING, 2015, VOLS 1 AND 2 / [ed] David A. Jaffray, Springer, 2015, Vol. 51, p. 1196-1199Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
Springer, 2015
Series
IFMBE Proceedings, ISSN 1680-0737 ; 51
Keywords
deep brain stimulation (DBS), electrode design, finite element method (FEM), neuron model
National Category
Other Medical Engineering
Identifiers
urn:nbn:se:liu:diva-120637 (URN)10.1007/978-3-319-19387-8_290 (DOI)000381813000290 ()978-3-319-19386-1 (ISBN)978-3-319-19387-8 (ISBN)
Conference
World congress on medical physics and biomedical engineering, Toronto, June 7-12, 2015
Funder
Swedish Research Council, 621-2013-6078EU, FP7, Seventh Framework Programme, 305814
Available from: 2015-08-20 Created: 2015-08-20 Last updated: 2017-02-03Bibliographically approved
Alonso, F., Wårdell, K. & Latorre, M. (2015). Neural Activation Compared to Electric Field Extension of Three DBS Lead Designs. In: : . Paper presented at 7TH INTERNATIONAL IEEE/EMBS CONFERENCE ON NEURAL ENGINEERING, Montpellier, April 22-24, 2015.
Open this publication in new window or tab >>Neural Activation Compared to Electric Field Extension of Three DBS Lead Designs
2015 (English)Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

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.

Keywords
DBS leads, neural activation, steering leads, finite element model
National Category
Other Medical Engineering
Identifiers
urn:nbn:se:liu:diva-120636 (URN)
Conference
7TH INTERNATIONAL IEEE/EMBS CONFERENCE ON NEURAL ENGINEERING, Montpellier, April 22-24, 2015
Funder
Swedish Research Council, 621-2013-6078EU, FP7, Seventh Framework Programme, 305814
Available from: 2015-08-20 Created: 2015-08-20 Last updated: 2017-02-03Bibliographically approved
Wårdell, K., Latorre, M. & Chan, A. D. .. (2013). The Paxon – A Physical Axonal Mimic. In: : . Paper presented at 6th Annual International IEEE EMBS Conference on Neural Engineering, San Diego, California, USA, 6 - 8 November.
Open this publication in new window or tab >>The Paxon – A Physical Axonal Mimic
2013 (English)Conference paper, Poster (with or without abstract) (Refereed)
National Category
Other Medical Engineering
Identifiers
urn:nbn:se:liu:diva-100836 (URN)
Conference
6th Annual International IEEE EMBS Conference on Neural Engineering, San Diego, California, USA, 6 - 8 November
Available from: 2013-11-13 Created: 2013-11-13 Last updated: 2017-02-03Bibliographically approved
Latorre, M. & Wårdell, K. (2011). Evaluation of the Paxon: Electro-physical Myelinated Exon Model (poster). In: : . Paper presented at Medicinteknikdagarna 2011, 11-12 oktober 2011, Linköping, Sweden.
Open this publication in new window or tab >>Evaluation of the Paxon: Electro-physical Myelinated Exon Model (poster)
2011 (English)Conference paper, Published paper (Refereed)
National Category
Other Medical Engineering
Identifiers
urn:nbn:se:liu:diva-71969 (URN)
Conference
Medicinteknikdagarna 2011, 11-12 oktober 2011, Linköping, Sweden
Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2017-02-09Bibliographically approved
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