儀器設備銷售 | Auden Techno Corp.

RLS-2100 Satellite Radio Link Emulator

產品行銷課市場行銷部 — Mon, 21 Oct 2024 09:31:12 +0000

The RLS-2100 is the most feature-rich satellite link emulation tester available—providing fast, repeatable results. Ideal for the following applications:

Upgrade the broadband signal compatibility test bench
Verify link performance through true hardware-in-the-loop testing
Test modem performance verification under dynamic link conditions
Verify new satellite network configuration
Validate and refine next-generation satellite network concepts before deploying new satellite network configurations

The simulated signal path includes the RF characteristics of the transmitter, uplink, satellite/relay, downlink, and receiver, and can set realistic scenarios for path delay, Doppler, fading, and other characteristics.

Can be combined with a touch screen or keyboard/mouse user interface allowing real-life scenes to be mapped directly onto applicable elements in the signal path. All stations (transmitters, satellites/relays, receivers) can be in motion and dynamically update the affected simulation parameters.

RLS-2100 includes integrated real-time multi-satellite orbit calculations and displays for modeling LEO, MEO, HEO, GEO and hybrid satellite constellations. Navigation routes can be planned for mobile vehicles such as vehicles, ships, aircraft, drones, HAPs or rockets.

Dual independent integrated GNSS emulators can provide site location to user equipment. Graphical display of signal spectrum, signal power distribution, site location and characteristic parameters helps to verify the test setup and allows simple visualization of the effects of applied impairments.

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Coping with the Challenges of Designing Medical Body Area Networks

儀器設備銷售 — Fri, 15 Apr 2022 02:10:14 +0000

Coping with the Challenges of Designing Medical Body Area Networks

Problem Description

Connected nodes in a wireless body area network.

Wireless body area networks (WBAN) consist of wirelessly connected nodes of sensors or actuators, which are often enhanced with data processing. The nodes are placed in, on and around/off the human body forming a network for the continuous and unobtrusive monitoring of physiological and/or environmental signals to support medical, lifestyle and entertainment applications. Medical WBANs offer a paradigm shift from illness to wellness management, with an emphasis on early disease detection that can hopefully save some of the $4 trillion annual health care expenditure in the US. However, the design and efficient operation of WBANs bring forward several technical challenges due to the strict requirements that have to be met by the physical (PHY) layer of the applications.

Standards Addressed

The IEEE standard 802.15.6 on Wireless Body Area Networks.

Most WBANs are built around the IEEE 802.15.6 standard on Wireless Body Area Networks, which also includes channel models based on measurements. However, these models do not account for node mobility and human interaction effects. The technical specifications for WBANs operating in Europe are described in ETSI standards EN 301 839 (402-405MHz), EN 303 203 (2483.5-2500MHz) and in technical recommendation TR 101 557 (1785-2500MHz). In all cases it is mentioned that compliance to human exposure guidelines should be checked against local regulations for basic limits on the specific absorption rate (SAR; according to IEC/TR 62630, FCC OET 65c or IEC62704-1).

Methodology

1. Technical requirements

Simulation of wireless body area networks in Sim4Life.

The most critical function of a WBAN is to efficiently provide for information exchange from and to its nodes. Efficient information exchange translates to reliable, secure, fast, fault-tolerant, and interference-immune communication with low power consumption. While power consumption is outside of the scope of this document, all other aspects to achieve the desired efficiency must take into consideration many important issues closely related to the human body. Communication between implanted nodes and surface nodes (in-body and in-out communication) may experience high signal attenuation. The movements of the body parts carrying the WBAN nodes may even affect network topology by changing communication link budgets or blocking a signal. Signal propagation is highly complicated, since free space propagation is combined with diffracted, creeping and surface waves, depending on the characteristics of the source (frequency, polarization, incidence angle, body posture and shape, etc.). ZMT has developed all the necessary tools to help the designer cope with the challenges of assessing and optimizing the performance of a WBAN.

2. In-body and in-out-body RF communication

Nodes for wireless body can also comprise popular gadgets such as smart glasses and smart watches. Here they are mounted on a physical phantom for measurements, from our sister company SPEAG. Simulation allows to optimize for performance and regulatory aspects early in the design phase.

While there are simple formulas for designing free-space communications, it is impossible to characterize precisely in-body RF propagation. The latter depends on the frequency used, the position of the device, and the anatomy of the individual. Tissue inhomogeneity creates an electromagnetically complex environment, which changes with time, because of patient motion, weight variations and aging. Therefore, the use of the Virtual Population (ViP) models is the recommended solution to this challenging task. They allow for the fast placement of the BAN nodes inside any of the anatomically detailed models covering the patient population. These functionalized models naturally mimic patient movements (POSER module) and are easily morphed to extend patient population or reproduce certain pathologies. Moreover, the assignment of tissues at any frequency is straightforward with the DISFIT module. The P-EM-FDTD physics model is used to evaluate the in-body and in-out body communication performance either for narrowband or for ultra-wideband (UWB) applications.

3. Antenna design

Sim4Life stands to the challenge of simulating highly resolved CAD models with complex full-body phantoms.

Whether in or on the body, antennas used at WBAN body-nodes are usually non-resonant, due to size constraints. Therefore, the MATCH module is a valuable tool for optimizing antenna performance. Since in most cases such antennas are miniaturized, it is important to be able to model accurately their geometry (with the subgrid engine in the P-EM-FDTD model), in order to study the effects of dimensions and material properties. The impact of patient motion, node position and device orientation on the antenna characteristics (impedance, radiation pattern) is easy to assess with the posable human phantoms. Finally, with the MIMOS module the user can get a clearer picture about signal availability, since more and more hubs or base stations use antenna diversity to improve quality and reliability of the links in a WBAN.

4. Communication link budget

Electromagnetic fields generated by a body area network node in and around the human body.

Received signal strength at a node is calculated with the P-EM-FDTD model for in- and on-body nodes. In the case of large problems (hospital or home rooms) the high performance computing (HPC) framework allows for full-wave analysis of the realistic environment and the estimation of link budget between body-nodes and hubs/base-stations. If propagation data are available from other numerical techniques for sources in a complex indoor environment, the HUYGENS module offers a quick solution to establishing the link budget. The body positioning and posture of any of the ViP3.0 phantoms is easily defined in space to cover lifelike patient activity. Finally, a similar approach can be followed to investigate interference issues that arise from the coexistence of WBANs with other technologies or resolve energy detection thresholds (EDT) for clear channel assessment (CCA) protocols.

5. Regulatory compliance

CAD model of a phantom from our sister company SPEAG wearing a smart watch, simulated in Sim4Life.

Regulatory compliance of WBAN devices is complicated by the fact that the patient is free to roam across different jurisdictions in the world. However, the maximum equivalent isotropically radiated power (EIRP) to achieve desired received signal strength (RSS) levels is estimated with the highest degree of certainty with the P-EM-FDTD model and, thereafter, compared against ETSI or FCC regulations. Moreover, the peak spatial SAR distribution is generated according to the IEC62704-1 draft standard at the press of a button, to allow comparison with exposure guidelines. The MBSAR module can combine the SAR pattern from simulations at different frequency bands and compute/visualize the peak spatial SAR of the total SAR distribution. This tool is invaluable in the case the WBAN nodes are using various frequency bands.

Publications

W. Scanlon, G. Conway, and S. Cotton, “Antennas and propagation considerations for robust wireless communications in medical body area networks,” in IET Seminar on Antennas and Propagation for Body- Centric Wireless Communications, p. 37, IET, 2007.
G. A. Conway and W. G. Scanlon, “Antennas for over-body-surface communication at 2.45 GHz,” IEEE Trans. Antennas Propag., vol. 57, no. 4, pt. 1, pp. 844–855, Apr. 2009.
D. Kurup, W. Joseph, G. Vermeeren, and L. Martens “In-body Path Loss Model for Homogeneous Human Tissues,” IEEE Trans. Electromagnetic Compatibility, vol.54, no.3, pp. 556-564, June 2012

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Getting Acoustic Energy Precisely to its Target

儀器設備銷售 — Fri, 15 Apr 2022 01:46:10 +0000

Getting Acoustic Energy Precisely to its Target

Problem Description

Schematic view of tissue ablation with a sonic knife in the liver.

Focused ultrasound (FUS) and high intensity FUS (HIFU) have found valuable application in a wide range of medical treatments: tumor ablation; treatment of epilepsy, movement disorder, and chronic pain; reversible blood-brain-barrier opening (e.g., to increase uptake of Parkinson drugs); clot lysis; and neurostimulation. They offer the potential of targeting locations deep inside the human body without requiring surgical access. The mechanisms can be thermal (e.g., thermal ablation) or non-thermal. Acoustic propagation is affected by bones, air cavities, and the general anatomy within the exposed domain, which can reduce the focusing ability and produce unwanted secondary foci. Phased array transducers allow for aberration correction, provided suitable steering parameters can be identified for a specific target shape, location and patient anatomy. Modeling enables investigation and design of novel applicators and patient-specific treatment planning.

Methodology

1. Comprehensive Modeling Framework

HIFU transducer array creating a thermal hot spot deep in the brain for tissue ablation during noninvasive brain surgery.

Sim4Life offers a comprehensive environment for image-based or anatomical model-based simulation of acoustic propagation, induced heating, and resulting effect quantification: The IMG and iSEG modules add support for image integration and image-based model generation. The Virtual Population (ViP) 3.0 anatomical phantoms offer the most detailed and accurate representations of the patient population for device design or in-depth analysis. The P-THERMAL module adds a solver optimized for the modelling of thermal phenomena in living, blood-perfused tissue, while T-CEM43 adds thermal dose and effect assessment models for the quantification of thermal tissue damage and treatment efficacy. For more detail see Thermal therapies.

P-ACOUSTICS seamlessly integrates with all this functionality and permits full-wave modelling of acoustic propagation in the human body or artificial structures at unprecedented resolution and problem size. This is possible thanks to the use of high performance computing (HPC) techniques that harness the power of one or multiple graphics processing units (GPU) cards to accelerate the simulations by orders of magnitude.

2. Focusing & Treatment Planning

Focus optimization in Sim4Life.

Sim4Life has been applied to investigate ways of improving focusing, especially in the context of transcranial focused ultrasound, where applicators with over a thousand ultrasound transducers are used to target locations deep in the brain without opening the skull. Various focusing approaches have been investigated and compared. Superior results, also in comparison with clinically applied methods, were obtained by using the virtual source approach (also known as time reversal technique), where an initial simulation is performed with a source at the target location while recording the incoming pressure wave at the transducer elements. For the real sonication, these signals are then conjugated and applied.

Sim4Life allows to compensate for the impact of skull induced aberration and focus shifting and even enables considering the inhomogeneous nature of the skull bone based on computed tomography (CT) image data. The results indicate the possibility of considerably extending the envelope of treatable regions in the head.

When modeling HIFU tumor ablation in the liver, the virtual source approach was combined with a 4D animated anatomical model, where breathing motion was extracted from MRI images and applied to warp the body model. This allows to study the importance of motion tracking. Furthermore, the virtual source approach is successful in reducing collateral damage to the ribs, as assessed using the T-CEM43 model in combination with thermal modeling.

3. Volume Scanning

Focus optimization with a transducer array.

Sim4Life acoustic modeling can be used to explore strategies to cover large treatment areas, e.g., to achieve hyperthermia cancer treatment. For example, it could be demonstrated that very similar treatment outcomes can be achieved using sequential sonication (successive scanning of the tumor volume with the focus) and volumetric sonication (rapid interleaving of foci placements), but that the latter can be achieved within half the treatment time. Also, the concept of unstructured meshing-based tumor volume coverage strategies as superior alternative to the commonly applied regular placement of sonications on a rectangular grid was proposed based on modeling. In addition to reducing the number of required sonications, this approach naturally offers the possibility of improving thermal coverage near cooling vessels by using adaptive mesh refinement, as assessed using thermal modeling.

4. Device Design

CAD model of a transducer for simulation in Sim4Life..

Simulations have been used to investigate and design new acoustic transducers. This includes a novel design with an acoustic blade-like focus for mostly superficial interventions. Another applicator developed using Sim4Life uses random placement of transducer elements to reduce notorious side-lobes and produce a more localized focus. Sim4Life P-ACOUSTICS already offers templates for common applicator array designs.

5. Verification & Validation

Validation of the simulation in a measurement setup.

Sim4Life P-ACOUSTICS has undergone extensive and document verification and validation. The correctness of the implementation has been verified by identifying all relevant physical and numerical phenomena and comparing simulation results against analytical and numerical reference solutions that critically test these. To ascertain that the simulated equation captures reality, a dedicated validation setup has been built that permits 3D, robot-supported, acoustic interference field measurements in the wake of multiple obstacles with varying shape and material properties placed in and near the acoustic focus. Extensive uncertainty quantification has been performed and used to confirm the excellent agreement between measurements and simulations.

In addition, hydrophone measurements were used to compare the predicted and measured pressure distribution while designing a novel linear acoustic ablation device.

Publications

Kennedy, J. E., G. R. Ter Haar, and D. Cranston. “High intensity focused ultrasound: surgery of the future?.” The British journal of radiology (2014).
Jolesz, Ferenc A. “MRI-guided focused ultrasound surgery.” Annual review of medicine 60 (2009): 417.
Kyriakou, Adamos, et al. “A review of numerical and experimental compensation techniques for skull-induced phase aberrations in transcranial focused ultrasound.” International Journal of Hyperthermia 30.1 (2013): 36-46.
Kyriakou, Adamos, et al. “Full-wave acoustic and thermal modeling of transcranial ultrasound propagation and investigation of skull-induced aberration correction techniques: a feasibility study.” Journal of therapeutic ultrasound 3.1 (2015): 1-18.
Neufeld, Esra, et al. “Modeling, effect prediction, and planning for EM-and FUS-based thermal treatment.” Antennas and Propagation (EuCAP), 2014 8th European Conference on. IEEE, 2014.
Paulides, Margarethus M., et al. “Simulation techniques in hyperthermia treatment planning.” International Journal of Hyperthermia 29.4 (2013): 346-357.

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Exposure Assessment of Wireless Power Transfer Systems

儀器設備銷售 — Fri, 15 Apr 2022 01:23:05 +0000

Exposure Assessment of Wireless Power Transfer Systems

Problem Description

Schematic view of a wireless car charger.

Wireless power transfer (WPT) is an emerging technology and is expected to become ubiquitous in the human environment for charging electronic or household appliances, medical implants or, even, cars. Therefore, it is important for all WPT systems to operate in compliance with the guidelines that regulate exposure of the general public and professionals to electromagnetic fields.

Wireless power transfer systems use various approaches for their operation. They can be grouped according to the distance of the power receiving device from the power source. When the distance is small, wireless chargers may operate in the frequency range of 20 kHz up to 13.56 MHz. In order to transmit power to larger distances or to energy harversters (e.g., RFID tags) radiofrequencies are used. In the lower frequency range power is transferred with capacitive or inductive coupling. The latter mechanism is used more often in commercially available systems, implemented in the form of resonant coils.

Standards Addressed

The IEEE standard C95.1 for safety levels with respect to human exposure to radio frequency electromagnetic fields.

Currently, there are no standardized procedures for assessing the exposure of WPT systems and demonstrating compliance with the exposure guidelines. The most widely adopted documents on restricting human exposure from electromagnetic fields are issued by the International Commission on Nonionizing Radiation Protection (ICNIRP 1998, ICNIRP 2010) and the Institute of Electrical and Electronics Engineers (IEEE C95.1). They include basic restrictions in order to prevent tissue stimulation in the lower frequency range (up to 5 or 10 MHz) and excessive tissue heating for frequencies above 100 kHz. Since many WPT systems operate at frequencies between 100 kHz and 10 MHz both sets of basic restrictions must simultaneously apply.

Methodology

1. Single-step procedure

Electromagnetic exposure induced in hands close to coil for wireless power transfer.

In the single-step approach typical exposure scenarios are used. The Virtual Population (ViP) human models are placed next to the sources with postures obtained with the POSER tool, so as to reflect realistic exposure conditions for the intended use of the WPT system. Worst-case analysis (e.g., leaning upon or touching the system) is also possible in a straightforward manner. The induced fields in the computational phantoms are thereafter extracted and analyzed with respect to basic restrictions. In order to carry out this type of analysis it is necessary to use a full-wave technique, like finite-difference-time-domain (FDTD), implemented by the P-EM-FDTD solver, which takes into account the tissue distribution inside the human body and the loading it causes to the power source.

If the frequency of the WPT system is very low, then the High Performance Computing (HPC) framework is the solution to simulation acceleration. In this case, however, it is worth checking whether the quasistatic conditions are fulfilled, so as to use the respective low frequency solver (P-EM-QS), although the interaction of the body to the source is not considered then.

2. Two-step procedure

Magnetic fields and induced exposure of a person sitting near a wireless power charger.

The two-step approach also neglects the effects of the human body on the source. Nevertheless, it allows for reduction in the computational times. The electromagnetic field generated by the WPT system (calculated either analytically or numerically in the first step of the process) is used to excite the HUYGENS source, which, in turn, gives an assessment of the dosimetric quantities inside the ViP models. In this way, it is not necessary to simulate the resonant structures in the time domain.

3. Validation of source modeling

A wireless charging configuration (top) and a comparison of measured and simulated fields.

It is worth mentioning here, that for both procedures (single- and two-step) it is important to validate that the numerical model of the WPT system source corresponds to the physical device. This can be achieved by experimental measurements in air and close to the source, as well as in liquid-filled phantoms. All necessary validation equipment can be obtained either from us or from our sister company SPEAG (Schmid and Partner Engineering AG).

Using the robot-based DASY5 the magnetic fields generated by the actual WPT system can be measured in air with the help of the free-space probe H3DV8 and compared with the Sim4Life calculated results of the source model. A similar comparison can be performed for the specific absorption rate (SAR) distribution inside a flat phantom made of glass fiber reinforced vinylester shell. The phantom can be filled with the high conductivity liquid (HCL) produced by ZMT, which is employed also in medical implant safety assessment inside MRI scanners. The SAR measurements inside the liquid are conducted with a calibrated probe ET3DV6 mounted on the DASY5 system from SPEAG with the WPT system placed at various distances from the outer surface of the flat phantom. The validation of the source model is again achieved by comparing measured and Sim4Life computed SAR distributions, e.g., adopting the procedure described in the draft standard IEC/IEEE 62704-1.

4. Optimization of power transfer

Complex configurations and associated assessment and optimization can be performed by simulation in Sim4Life.

An optimal WPT system allows for the maximum transfer of power between the source and the device charging at the lowest human exposure. Both for short- and mid-range systems it is possible to use generic coil models and calculate the coupling efficiency between resonant coils (the most popular technology until now in WPT) as a function of frequency and distance. With the ViP models placed in realistic scenarios within the magnetic field both induced electric field and SAR can be calculated for each coil setup. The WPT system designer can then choose the configuration which results in the highest power transfer complying with exposure guidelines. In this way both time-to-market and costs can be reduced during the system’s design phase.

Procedure Overview

Publications

A. Christ, M. Douglas, J. Nadakuduti, and N. Kuster, “Assessing human exposure to electromagnetic fields from wireless power transmission systems ,” Proceedings of the IEEE, vol. 101, no. 6, pp. 1482—1493, 2013.
A. Christ, M. G. Douglas, J. M. Roman, E. B. Cooper, A. P. Sample, B. H. Waters, J. R. Smith, and N. Kuster, “Evaluation of wireless resonant power transfer systems with human electromagnetic exposure limits,” vol. 55, no. 2, pp. 265-274, 2013
X. L. Chen, A. E. Umenei, D. W. Baarman, N. Chavannes, V. De Santis, J. R. Mosig, and N. Kuster, “Human Exposure to Close-Range Resonant Wireless Power Transfer Systems as a Function of Design Parameters,” IEEE Transactions on Electromagnetic Compatibility, vol. 56, no. 5, pp. 1027-1034, 2014
X. L. Chen, V. De Santis, and A. E. Umenei, “Theoretical assessment of the maximum obtainable power in wireless power transfer constrained by human body exposure limits in a typical room scenario,” Phys. Med. Biol., vol. 59, no. 13, pp. 3453-3464, 2014
J. S. Hoa, A. J. Yeha, E. Neofytou, S. Kim, Y. Tanabe, B. Patlolla, R. E. Beygui, and A. S. Y. Poona, “Wireless power transfer to deep-tissue microimplants,” PNAS, vol. 111, no. 22, 7974-7979, 2014
J. Nadakuduti, M. Douglas, L. Lu, A. Christ, P. Guckian, and N. Kuster, “Compliance Testing Methodology for Wirelss Power Transfer Systems,”, vol. 30, no. 11, pp. 6264-6273, 2015
UL, “Safety Considerations of Wireless Charger for Electric Vehicles – A Review Paper,”, available for download [Last Accessed,7 September 2015].

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Modeling for Device Design and Personalized Treatment Planning

儀器設備銷售 — Thu, 14 Apr 2022 09:26:25 +0000

Modeling for Device Design and Personalized Treatment Planning

Problem Description

Various views of a simulation of a tumor being exposed to electro-thermal therapy. From left to right: Medical image of the problem; CAD model of the simulation set-up; cross section of the discretized model, simulation results with Sim4Life.

Hyperthermia cancer therapy (hyperthermic oncology) is used in combination with radio- and/or chemotherapy to treat a wide range of cancers. It employs electromagnetic energy to mildly heat a tumor, frequently resulting in dramatic improvement of initial response and survival rates. For deep seated tumors, phased radiofrequency (RF) arrays are typically used to target the energy to a tumor while avoiding overexposure of sensitive healthy tissues. Due to the strongly inhomogeneous nature of the human body and the impact of physiological factors such as blood perfusion and thermoregulation this is a demanding task. Simulations are required i) to personalize treatments reflecting tumor shape and location as well as the individual anatomy, and ii) to develop and investigate novel applicators capable of achieving controlled energy deposition in challenging locations such as the head and neck area.

RF and MW (microwave ) ablation use interstitial (inserted in the tissue, e.g., by catheter) applicators to locally heat tissues to high temperatures resulting in direct cell killing to treat diseases, such as cardiac arrhythmia or cancer. Alternative sources of ablation energy include ultrasound. Modeling is used to determine the impact of nearby vasculature on the achievable ablation zone, to optimize catheter placement, and to design novel applicators.

The required modeling functionality includes personalized model generation, electromagnetic and thermal simulation considering in vivo physiological factors, optimization of steering parameters, and outcome-related effect assessment.

Methodology

1. Patient Model

Generation of a personalized model from medical image data, with the iSEG module of Sim4Life.

Sim4Life supports the generation of personalized models from medical image data, e.g., for treatment planning. A wide range of image data, such as MRI and CT images, can be imported and jointly visualized with the simulation model and results (IMG module). The integrated image processing and segmentation module iSEG facilitates the rapid generation of anatomical models by offering a wide range of segmentation algorithms, ranging from highly interactive to automatic, which can be flexibly combined and are complemented by preprocessing routines to improve the image quality and measurement/analysis routines. The segmented images are then converted into surface-based body models suitable for simulation purposes using Sim4Life functionality that guarantees high quality, self-intersection-free, topologically compatible mesh creation.

When it is not necessary to employ personalized models, e.g., for mechanism investigations, applicator development, or when it is considered sufficient to personalize tumor location and shape but not anatomy, the highly detailed Virtual Population (ViP) 3.0 models, which have also been generated with, iSEG can be used instead.

2. 2. EM-Induced Tissue Heating

Simulation of electromagnetic exposure of the cancerous tissue, in Sim4Life.

Initially, the electromagnetic energy deposition is determined. In Sim4Life, the simultaneous setup of multi-antenna simulations is facilitated by the multi-port simulation feature, while flexible coherent and incoherent field combining is part of the analysis functionality. Depending on the frequency and the material properties, the full-wave P-EM-FDTD or the quasistatic P-EM-QS solver is best suited for determining the EM fields. In hyperthermic oncology, it is typically the former, while ablation modeling typically benefits from the latter. All of the EM solvers included in Sim4Life are optimized for simulation of setups comprising complex anatomical models, such as those of the ViP3.0. Sim4Life also facilitates the use of the integrated tissue properties database for assignment of dielectric properties.

Applicators and antennas can be designed with the Sim4Life modeler CAD functionality.

In vivo EM induced heating, both transient and steady state, is simulated with the P-THERMAL module. It is based on the Pennes Bioheat equation and accounts for metabolic and EM heat sources, heat diffusion, and heat transfer by tissue perfusion, with functionality to consider local thermoregulation by vasodilation as well as body core temperature increase over time. Convective surface cooling by external and internal air or a heated/cooled water-bolus in contact with the skin as well as the influence of large vessels in the treatment region can be included. Again, the Sim4Life tissue properties database includes thermal and perfusion parameters for a wide range of tissues.

3. Treatment Optimization

Model of an exposure set-up with a body model including the cancer, and a phased array applicator for electro-magnetic treatment. The treatment settings are optimized with Sim4Life.

For phased array applicators, such as in deep hyperthermia treatments or ablation treatment with multiple catheters, the phases and amplitudes of the individual antennas are optimized to achieve optimal tumor coverage while avoiding exposure of sensitive tissues. SIm4Life offers automatic and rapid treatment parameter optimization and allows the definition of multiple treatment regions as well as weighting to reflect treatment priority and tissue sensitivity. Alternatively, manual optimization is possible by means of the field combiner tool, e.g., while superposing the computed energy deposition distribution for a certain set of steering parameters over the medical image data of the patient.

Modeling can also be used to investigate and optimize the impact of other treatment parameters. For example, the impact of water-bolus temperature for surface cooling or heating is often optimized for individual treatment.

SEMCAD X / Sim4Life thermal therapy planning tools are in use in a series of leading clinical centers world-wide.

4. Effect Assessment

Assessment of the thermal treatment dose in treatment optimization with Sim4Life.

Induced in vivo effects are either predicted directly or assessed through thermal dose. A variety of tissue damage models is available in Sim4Life (T-CEM43): The Arrhenius model directly assesses tissue damage in coagulation and necrosis zones in ablation therapies. In hyperthermic oncology, the use of the CEM43 thermal dose concept is common. The CEM43 thermal dose expresses the thermal history of a tissue location in terms of minutes of heating at 43^oC that would result in an equivalent thermal effect. It offers the advantage of not depending on tissue specific material parameters, and that CEM43 thresholds for thermal damage have been experimentally determined for a wide range of tissues and biological effects. Correlations between CEM43 and treatment outcome have been established clinically.

5. Device Design

Sim4Life used in design optimization of an hyperthermic applicator.

Sim4Life and SEMCAD X have been used to investigate various aspects of hyperthermic oncology applicators and RF/MW-ablation catheters, such as:

optimal 3D arrangement and placement of antennas to achieve ideal focusing and steering potential in phased array deep hyperthermia systems
exploration of arrangements featuring multiple ablation catheters and electrodes for superior focus steering and lesion shaping
design of antennas with high efficiency and low loading dependency
design of applicator elements that permit online determination of effectively applied phase and amplitude and cross-talk between antennas, allowing high treatment administration quality and feed-back control
development of quality assurance phantoms and measurement setups

A range of novel applicators have been built and introduced into the clinic, including novel head & neck treatment applicators with superior focus control, MRI compatible applicators, waveguide-based superficial hyperthermia treatment systems, modular treatment applicator concepts for maximal usage flexibility, and applicator elements with integrated on-line monitoring and feed-back control.

6. Validation

Simulation of thermal therapies with Sim4Life has been accompanied by a range of verification and validation efforts. Experimental validation setup (top) and simulation (bottom).

Simulation of thermal therapies with Sim4Life has been accompanied by a range of verification and validation efforts. The electromagnetic and thermal solvers have been systematically verified for correct implementation of the physical and numerical phenomena of the underlying mathematical model. Dosimetric measurement setups featuring body phantoms and robotic sensor scans have ascertained correct modeling of applicator performance. Thermal measurements have been performed using a variety of methods such as infrared thermometry or invasive and non-invasive thermal catheter measurements on phantoms, volunteers, and patients. Clinical outcome has been statistically compared with simulated dose quantities and the prediction of critical hot-spots has been correlated with patient and measurement feedback.

Procedure Overview

Clinical integration of hyperthermia cancer treatment and hyperthermia treatment planning

Steps in hyperthermia treatment planning and modeling

Publications

van der Zee, Jill. “Heating the patient: a promising approach?.” Annals of oncology 13.8 (2002): 1173-1184.
Neufeld, Esra. High resolution hyperthermia treatment planning. Hartung-Gorre Verlag, 2008.
Neufeld, Esra. “Numerical modeling for simulation and treatment planning of thermal therapy.” Physics of Thermal Therapy: Fundamentals and Clinical Applications (2012): 119.
Paulides, Margarethus M., et al. “Simulation techniques in hyperthermia treatment planning.” International Journal of Hyperthermia 29.4 (2013): 346-357.
Paulides, Margarethus M., et al. “The HYPERcollar: A novel applicator for hyperthermia in the head and neck.” International Journal of Hyperthermia 23.7 (2007): 567-576.
Paulides, Margarethus M., et al. “The clinical feasibility of deep hyperthermia treatment in the head and neck: new challenges for positioning and temperature measurement.” Physics in medicine and biology 55.9 (2010): 2465.
Togni, Paolo, et al. “Electromagnetic redesign of the HYPERcollar applicator: toward improved deep local head-and-neck hyperthermia.” Physics in medicine and biology 58.17 (2013): 5997.
Verhaart, René F., et al. “Temperature simulations in hyperthermia treatment planning of the head and neck region.” Strahlentherapie und Onkologie 190.12 (2014): 1117-1124.
van Rhoon, Gerard C., et al. “CEM43° C thermal dose thresholds: a potential guide for magnetic resonance radiofrequency exposure levels?.” European radiology 23.8 (2013): 2215-2227.
Karampatzakis, Andreas, et al. “Heating characteristics of antenna arrays used in microwave ablation: A theoretical parametric study.” Computers in biology and medicine 43.10 (2013): 1321-1327.
de Bruijne, Maarten, et al. “Effects of waterbolus size, shape and configuration on the SAR distribution pattern of the Lucite cone applicator.” International journal of hyperthermia 22.1 (2006): 15-28.
de Bruijne, Maarten, et al. “Quantitative validation of the 3D SAR profile of hyperthermia applicators using the gamma method.” Physics in medicine and biology 52.11 (2007): 3075.
Paulides, Margarethus M., et al. “Laboratory prototype for experimental validation of MR-guided radiofrequency head and neck hyperthermia.” Physics in medicine and biology 59.9 (2014): 2139.
Rijnen, Zef, et al. “Clinical integration of software tool VEDO for adaptive and quantitative application of phased array hyperthermia in the head and neck.”International Journal of Hyperthermia 29.3 (2013): 181-193.

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The Most Effective Way to Demonstrating RF Active Implant Safety

儀器設備銷售 — Thu, 14 Apr 2022 08:45:06 +0000

The Most Effective Way to Demonstrating RF Active Implant Safety

Problem Description

Undesirable interactions of an active implanted medical device (AIMD) inside an MRI scanner.

Magnetic resonance imaging (MRI) is a medical imaging modality, which is indispensable in diagnosing several pathologies. Nevertheless, the presence of medical implants in some patients taking an MRI scan may lead to undesirable interactions of the implants with the radiofrequency (RF) radiation necessary for the operation of the scanner. Therefore, it is necessary to develop a comprehensive risk assessment methodology, in order to determine the specific conditions that would permit an MRI examination for implant-bearing patients.

Standards Addressed

The standard ISO/TS 10974 for assessment of the safety of magnetic resonance imaging for patients with an active implantable medical device.

The ISO Technical Specification 10974 (ISO/TS 10974) defines the procedures to assess the local power deposition (RF heating) at the electrodes and the voltage/current (EMC) at the device terminals of an active implanted medical device (AIMD). Vertical standards define the risk assessment procedures. Members of ZMT and the IT’IS Foundation have contributed in the development of the standards and have optimized a toolbox for demonstrating RF implant safety.

IMAnalytics and MRIxViP are qualified by the FDA for MRI safety evaluations.

Methodology

1. Generation of the Calibrated AIMD Response Model (piX and MITS)

The piX system is used to validate numerical results for the transfer function.

RFoF1P4MED: A miniature electrically fully isolated RF-over-Fiber (RFoF) transducer.

In the Tier 3 approach described in TS 10974 the first step towards safety evaluation is to create a response model of the AIMD, namely to create a transfer function that allows the assessment of the power deposited at the distal end of the AIMD lead or the current induced at the device terminals under known excitation.

The AIMD model can be determined either experimentally and/or with simulations. In the experimental case, a physical sample of the device under test (DUT) is measured with the piX system equipped with E1TDSz probe (RF Heating) or RFoF1P4MED probe (EMC). The photonic technology avoids crosstalk of the excitor with the DUT (E1TDSz probe) and allows measurement of voltages without modifying the devices (RFoF1P4MED). In numerical evaluation, Sim4Life electromagnetics solver and a CAD model of the DUT are used to simulate the AIMD model. The model is then calibrated to a well-defined exposure condition with a medical implant test system (MITS).

2. Validation of the AIMD Response Model for Power Deposition and for Induced Voltages or Current at the Device Terminals

The MITS 1.5/3.0 validates the power deposition distribution along a pacemaker lead.

Thereafter, the created model needs to be validated with a sufficient set of orthogonal test functions. This involves specific absorption (SAR) or temperature rise (ΔΤ) measurements in RF heating case, or measurements of the current at the terminals and/or the induced voltages inside the device for EMC with RFoF1P4MED. The MITS allows for the fast evaluation of the AIMD model under worst-case incident fields of commercial scanners, but also for specific exposures generated by varying the polarization of the B1-field which is monitored continuously with TDS B1 measurements system.

The integration of the measurement and Sim4Life results is seamless for the user, facilitating comparison and sensitivity and/or uncertainty analysis. It should be noted here that the AIMD model can be established for each operating mode of the AIMD separately.

3. Computation of the Incident Field Distributions for the Patient Population

ViP3.0 human models.

POSER tool in action.

Coil library includes E-fields of coils with varying length and diameter.

Once the AIMD response model is known and validated, the next step is to estimate typical incident field distributions with which the AIMD can be excited when implanted inside a human body (in vivo). The approach described in TS 10974 requires that the risk assessment of RF heating covers a wide range of the population.

Currently, Sim4Life is the only software platform that is based on computable anatomical phantoms functionalized for morphing and posing, enabling the user to obtain a wide and representative patient population with realistic and clinically relevant postures. The choice is not limited to standard male and female subjects in child- or adulthood, but includes an elderly male and an obese one, the latter being most important for worst-case evaluations inside an MRI volume coil.

The calculation of the incident electric fields for all the above computational models and for all the possible clinical exposure scenarios would be a challenging task in terms of human and computational resources. Instead of performing the calculations anew, the user has the option of acquiring MRIxViP, a validated library of the electric field distributions in eight human models placed at different imaging positions (according to TS 10974) inside various birdcage coils, which are carefully selected to represent the majority of commercially available ones.

IMAnalytics and MRIxViP are qualified by the FDA for MRI safety evaluations.

4. Power Deposition and Risk Assessment for RF Heating

IMAnalytics Module: automated Tier 3 analysis of implants (PiX transfer functions) with user-defined parameter ranges (e.g., normalizations, coil dimensions, shimming angles, clinical routings, subsets of the patient population and landmarks).

Tier 3 deposited power for different imaging positions.

Temperature rise at the tip of a cardiac pacemaker lead, simulated with Sim4Life.

The incident field distributions are used to assess power deposition at the distal tip of the AIMD lead when implanted inside the human body.

The safety analysis as described in Tier 3 of TS 10974 requires repeating the power deposition assessment for a wide range of computational models, for all the possible ways of clinical implantation in them, and for all possible exposure scenarios. Performed manually, this would be a very demanding task in terms of human and computational resources.

With the IMAnalytics module of Sim4Life, this becomes a simple, reliable and traceable procedure. From the AIMD response model, the incident field distributions and the implants’ routing trajectories, IMAnalytics automatically performs the statistical analysis of power deposition at the tip of the AIMD lead in all possible scenarios. The results can be exported and included in regulatory submission reports.

The industry mainly applies two approaches to translate the power deposition into risk assessment. The first one is to use animal experiments by injecting the equivalent power to the electrodes and assessing the response (e.g., change in the pacing threshold) as a function of the deposited power. The other approach is to translate the power deposition into in vivo temperature rise inside the human tissues using the Sim4Life thermal solver, which has been validated both for local and locoregional RF heating in humans.

IMAnalytics and MRIxViP are qualified by the FDA for MRI safety evaluations.

Procedure Overview

Publications

Zastrow, E., Cabot, E., Kuster, N. Assessment of local RF-induced heating of AIMDs during MR exposure (2014) 2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014, art. no. 6930111.
Cabot, E., Lloyd, T., Christ, A., Kainz, W., Douglas, M., Stenzel, G., Wedan, S., Kuster, N. Evaluation of the RF heating of a generic deep brain stimulator exposed in 1.5T magnetic resonance scanners (2013) Bioelectromagnetics, 34 (2), pp. 104-113.
Kyriakou, A., Christ, A., Neufeld, E., Kuster, N. Local tissue temperature increase of a generic implant compared to the basic restrictions defined in safety guidelines (2012) Bioelectromagnetics, 33 (5), pp. 366-374.
Neufeld, E., Kühn, S., Szekely, G., Kuster, N. Measurement, simulation and uncertainty assessment of implant heating during MRI (2009) Physics in Medicine and Biology, 54 (13), pp. 4151-4169.
Gosselin, M.-C., Neufeld, E., Moser, H., Huber, E., Farcito, S., Gerber, L., Jedensjo, M., Hilber, I., Gennaro, F.D., Lloyd, B., Cherubini, E., Szczerba, D., Kainz, W., Kuster, N. Development of a new generation of high-resolution anatomical models for medical device evaluation: The Virtual Population 3.0 (2014) Physics in Medicine and Biology, 59 (18), pp. 5287-5303.

The post The Most Effective Way to Demonstrating RF Active Implant Safety first appeared on Auden Techno Corp..

Modeling Intended and Unintended Neurostimulation by EM-fields

儀器設備銷售 — Thu, 14 Apr 2022 07:30:34 +0000

Modeling Intended and Unintended Neurostimulation by EM-fields

Problem Description

Highly resolved full body human model, with details of the nerves (top); Sim4Life simulation of exposure in an MRI examination.

Electromagnetic fields (EMF) interact with neurons. The interaction can be stimulating, inhibitory, or synchronizing, and it can be intended or unintended. Unintended stimulation by exposure to strong low frequency fields is for example occurring in magnetic resonance imaging (MRI) gradient coils, while examples of intended stimulation include therapeutic applications (transcranial stimulation, deep brain stimulation, functional electrical stimulation, etc.) or neuroprosthetic devices (artificial retina, neuroprosthetic limbs, etc.). Modeling is particularly valuable for treatment and device safety and efficacy assessment, but also to optimize medical device performance.

The prediction of safety thresholds, stimulation selectivity, spiking frequency, pulse-shape impact, etc. is complicated by the intricate structure and ion channel dynamics of the neurons, by the inhomogeneous nature of the electric field distribution in the human body, and by the complex interplay between the two. The latter is the reason, why coupled EM-neuronal dynamics modeling is required.

Related Standards

There are multiple relevant standards regulating EM exposure safety with regard to induced neuronal dynamics: The ICNIRP 2010 exposure guidelines and the IEEE C95.1 exposure standard provide thresholds for general public and occupational exposure to low frequency fields that are based on considerations dominated by the need to prevent adverse EM-neuron interaction-related effects. The IEC 60601-2-33 standard regulates specifically exposure the MRI-related fields.

An important factor in deriving safety limits for the guidelines and standards is the SENN (Spatially Extended Nonlinear Node) model of neuronal dynamics that was designed to represent myelinated axons (nerve fiber).

Methodology

1. Coupled EM-Neuronal Dynamics Modeling in Sim4Life

Detail of a simulation of a spinal neural stimulator, in Sim4Life.

The Sim4Life T-NEURO module offers comprehensive neuronal dynamics simulation, full integration and coupling to the EM modeling functionality (P-EM-FDTD and P-EM-QS) of the Sim4Life platform, as well as a range of predefined neuronal dynamics models, including the SENN model underlying the safety standards. A principal strength of Sim4Life is its ability to simulate complex neuronal dynamics models within realistic anatomical models (e.g., the Virtual Population (ViP) 3.0 or models generated from medical image data using the IMG and the iSEG modules). The T-NEURO module is powered by the NEURON solver developed at the Yale University.

Neuron models can be easily designed either by specifying trajectories as splines and then attributing them predefined behavior models, or by importing detailed neuron models from large repositories, such as the ModelDB. Functionality to automatically determine stimulation thresholds for given pulse shapes is available.

2. Application to Neuroprosthetics

Detail of a simulation of a deep brain stimulator (DBS) in Sim4Life.

Using the T-NEURO functionality of Sim4Life it is possible to investigate implantable electrodes for neuroprosthetic applications. For example, a transverse intrafascicular multichannel electrode (TIME – a neural interface that promises higher stimulation selectivity at the cost of increased invasiveness when compared, e.g., to more common cuff electrodes) design featuring five sub-electrodes to selectively stimulate different neuron groups in the sciatic nerve related to the activation of various muscles was simulated. For this, the nerve geometry, including the different fascicles was extracted from image data and transformed into a nerve model. Several hundred dynamic neuron models capturing the statistical variability of neuron properties were then placed inside the nerve model and their stimulation by the TIME electrode array modeled. Such simulations were used to compare different electrode designs with regard to muscle stimulation selectivity and placement sensitivity. The simulation predictions were confirmed by experimental measurements of muscle stimulation in rats. Sciatic nerve stimulation with TIME electrodes is being investigated with the goal of returning leg motion to paraplegic and first results in mice are very encouraging.

3. Application to Neurostimulation

Currents induced by external transcranial magnetic stimulation. Simulation with Sim4Life.

Neurostimulation using external or internal electrodes is applied for various purposes. For example, deep brain stimulation (DBS) uses implanted electrodes to treat movement disorders, depression, etc. Transcranial stimulation uses external electrodes mounted on the head surface, e.g., for stroke rehabilitation. With Sim4Life, it is possible to simulate not only the electric field distribution and currents, but also the related impact on neuronal activity. Field distributions from various transcranial stimulation electrode montages have been compared using the Sim4Life low frequency solvers in combination with the highly resolution MIDA head model and the obtained current densities through the retina could be correlated with the experimentally observed occurrence of visual phosphenes, i.e., the phenomenon of seeing light in absence of light entering the eye.

4. Application to MRI safety

Highly resolved full-body human model, undergoing an MRI examination. Simulation with Sim4Life.

Coupled EM-neuronal dynamics modeling has been applied to assess safety concerns about unintended nerve stimulation induced by MRI gradient coil switching. By integrating realistic motor neuron models along various nerve trajectories inside the human body and investigating stimulation thresholds with regard to the fields induced by a realistic gradient coil model inside the functionalized ViP 3.0 phantom, it could be demonstrated that a series of assumptions underlying current safety standards is problematic. Most importantly, it was found that i) in addition to field strength, field inhomogeneity – as present inside the human body – can be a relevant source of neurostimulation, ii) the SENN model is not always conservative, and iii) the impact of temperature on neuronal dynamics is important, such that coupled EM-neuronal dynamics modeling inside realistic anatomical models is required to properly understand low frequency exposure safety and derive suitable safety criteria. The modeling fidelity is further increased by using inhomogeneous, anisotropic conductivity maps obtained with diffusion tensor imaging. EM modeling of DBS electrode exposure of various treatment relevant thalamic and subthalamic nuclei has been combined with simulations of >100 realistic neuron models representing three different neuron populations (accurately placed using Sim4Life’s Python scripting functionality) and the predicted stimulation rates could be related to experimentally determined quantities.

5. Validation

Simulation of a neuron firing due to electrical stimulation. Simulation with the T-NEURO module in Sim4Life.

The underlying EM solvers have been extensively verified, e.g., using the method of manufactured solutions.

The coupled EM-neuronal dynamics modeling has been verified and validated on multiple levels: The correctness of the Sim4Life implementation was verified by reproducing neuron models from the ModelDB in Sim4Life and by comparing against threshold values obtained using the reference SENN model implementation available from the FDA website for a large variety of pulse durations and shapes. Experimental validation was performed by predicting and measuring i) stimulation thresholds for retinal ganglion cells and ii) muscle activation selectivity from neuroprosthetic sciatic nerve stimulation. Furthermore, qualitative validation of deep brain stimulation modeling was performed against literature data.

Publications

Reilly, J. Patrick, and Alan M. Diamant. Electrostimulation: theory, applications, and computational model. Artech House, 2011.
Neufeld, Esra, et al. “Simulation platform for coupled modeling of EM-induced neuronal dynamics and functionalized anatomical models.” Neural Engineering (NER), 2015 7th International IEEE/EMBS Conference on. IEEE, 2015.
Iacono, Maria Ida, et al. “MIDA: A Multimodal Imaging-Based Detailed Anatomical Model of the Human Head and Neck.” PloS one 10.4 (2015).
Neufeld, Esra, Ioannis V. Oikonomidis, and Niels Kuster. “Thresholds for interference with neuronal activity.” Electromagnetic Compatibility (APEMC), 2015 Asia-Pacific Symposium on. IEEE, 2015.
Neufeld, Esra, et al. “Computational platform combining detailed and precise functionalized anatomical phantoms with EM-Neuron interaction modeling.”General Assembly and Scientific Symposium (URSI GASS), 2014 XXXIth URSI. IEEE, 2014.

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Modeling Vagus Nerve Stimulation

儀器設備銷售 — Thu, 14 Apr 2022 06:17:52 +0000

Modeling Vagus Nerve Stimulation

Problem Description

Vagus nerve stimulation (VNS). Image from: http://heatherdane.com/

Computational MIDA head model [2], specifically realized for neurostimulation investigations.

Vagus nerve stimulation (VNS) was approved in 1997 by the US Food and Drug Administration (FDA) [1] as an invasive neuromodulator approach for the treatment of epilepsy in anti-epileptic drug (AED) resistant subjects. As the vagus nerve (VN) innervates many organs, it is candidate for many new potentially therapeutically relevant applications of selective neurostimulation.

The VN (like many other large nerves in the human body) is composed by multiple functional units assembling many myelinated A- and B- axons of different diameters combined with small unmyelinated C-fibers. Hereafter, VNS approaches for therapeutically relevant applications require approaches providing high fiber selectivity. Electrode arrays with optimized stimulation waveforms can be used to provide, in theory, such selectivity. Computational models that feature simplified or realistic VN models embedded in realistic human anatomical models along realistic trajectories, together with electrophysiological models of axonal fibers capturing the electric-neuronal interaction, are fundamental for the computationally assisted formulation of new VNS protocols, the design of electrode arrays, the optimization of stimulation waveforms, and the prediction of setup-specific axonal fiber recruitment.

Functionalized VN models, featuring head models, nerve trajectories with an arbitrary numbers of electrophysiological axonal models, can now be created in Sim4Life with the recently added T-NEURO feature in combination with electromagnetic (EM) simulations in the low-frequency range.

Methodology

Sim4Life, with its expanded simulative abilities of T-NEURO, permits the investigation of the mechanisms of interaction between EM fields and the electrical activity of neuronal membranes. A wide range of applications ranging from neurostimulation investigations (e.g. transcranial electric (TES) and magnetic (TMS) stimulation), safety (e.g. against peripheral nerve stimulation (PNS) in magnetic resonance imaging (MRI)), as well as the computationally assisted development of electroceuticals or neuroprostetic devices, is now possible. Anatomically realistic compartmentalized electrophysiological representations of axons and neurons modeled using NEURON [3] libraries according to Sim4Life pre-defined biophysical models or available in the web-depository databases – can be positioned within the computational human head/body models to predict the physiological response of nerve and neurons to applied electric (E-) or magnetic (M-) fields. Highly customizable solutions for modeling, execution of simulations, and post-processing analysis for numerical optimization are also provided in Sim4Life.

1. Modeling of VN Geometry, Electrodes, and EM Simulations

2D section of Helmers’s VN model [4] (top); simplified 3D model (middle); anatomically realistic VN model that follows the trajectory of the VN in the MIDA model [2,5] (bottom).

Cross-sectional 2D VN models that feature, e.g., epineurium, perineurium, and fascicles, can be created from medical images or scratched in Sim4Life (see Figure top) with the graphical user interface (GUI). 3D models of the VN can be created, for example, by extruding realistic 2D nerve cross sections along user-defined trajectories (see Figure middle), or along anatomical nerve trajectories within computational human models (see Figure bottom) Electrode geometries can be imported in Sim4life as CAD files or created as parameterized model objects even using available templates entities (helical, spiral, etc.).

Sim4Life’s electro-quasi-static current dominated (EQSCD) solver can be used to set up low frequency EM simulations for either homogeneous or anisotropic dielectric tissue parameters. Electrode voltages may be assigned as Dirichlet boundary conditions.
Sim4Life’s post-processing tools permit the analysis and visualization of exposure-related quantities such as E-field distribution, input currents at electrodes as well as neurostimulation-related quantities as Eigenvalues and Eigenvectors of the E-field Jacobian to identify regions of neurostimulation on the basis of the ‘activation function concept’ [6].

2. Creation of Axonal Trajectories and Functionalization

Fascicles populated with axonal trajectories modeled as lines.

具有神经外膜、神经外膜和束等特征的横截面 2D VN 模型可以从医学图像创建或在 Sim4Life 中使用图形用户界面 (GUI) 进行划痕（参见图顶部）。可以创建 VN 的 3D 模型，例如，通过沿用户定义的轨迹（参见图中间）或沿着计算人体模型中的解剖神经轨迹（参见图底部）挤出逼真的 2D 神经横截面，可以将电极几何形状导入 Sim4life 作为 CAD 文件或创建为参数化模型对象，甚至使用可用的模板实体（螺旋、螺旋等）。

Sim4Life 的电准静态电流主导 (EQSCD) 求解器可用于为均匀或各向异性电介质组织参数设置低频 EM 模拟。电极电压可以指定为狄利克雷边界条件。
Sim4Life 的后处理工具允许分析和可视化与暴露相关的量，例如电场分布、电极上的输入电流以及神经刺激相关量，如电场雅可比行列式的特征值和特征向量，以识别神经刺激区域 “激活函数概念”的基础[6]。

3. Execution of T-NEURO Simulation

T-Neuro simulations can be executed serially or in parallel. Each simulation can include multiple independent electric sources of neurostimulation (as in the case of electrode arrays), each with its own stimulation waveform.

Point or line sensors can be defined to record transmembrane potential or currents information, to be used for post-pro analyses. The implemented ‘titration procedure’ is fundamental to identify threshold values of E-field or stimulation related quantities (such as input currents) for initiation of action potentials (APs) within each individual axon in the model.

4. Post-processing

Visualization of the activation function along fiber trajectories (top); examples of fiber recruitment curves for three types of axons populations (bottom).

Sim4Life provides multiple options for data visualization (slice and surface view, vector field view and streamline, etc.) including the calculation of E-field related integrals (i.e., flux integrator), the visualization or animation of transmembrane voltages or current profiles. These features can be also used for the visualization of customized post-pro quantities derived from python script (e.g., compound action potentials).

The activation function, predictor of the site of neurostimulation, can be visualized along the axonal geometries (see Figure top). The titration sensor provides threshold E-fields for spike initiation, time and location of spike initiation and permits to derive fiber recruitment curves (Figure bottom).

All post-processing results can be exported for further analysis in MATLAB or Excel. Python scripts and the Sweeper tool can be used to customize optimization procedures aimed, for example, at identifying steering parameters for selective stimulation (e.g. recruitment of either A-, B-, or C- fibers) or to optimize electrodes geometry.

结论

Sim4Life T-Neuro is conceived to assist in the computational assisted investigation of neurostimulation, the design and optimization of electroceuticals and neurostimulators, and for studies about the mechanisms of electromagnetic-neuronal interaction. In this example the benefits of using T-Neuro to investigate fiber recruitment on realistic or simplified models of Vagus Nerve have been illustrated. Similar procedures can be applied to model arbitrary complex nerve stimulation in arbitrary computational human or animal bodies. Sim4Life provides unique and unprecedented features to investigate the complex domain of neurostimulation, affirming itself as the leader tool in the market for neurostimulation investigations

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Introducing the IMAnalytics Module

儀器設備銷售 — Mon, 28 Mar 2022 03:45:04 +0000

Implant Safety Evaluation at IT’IS – Episode II: Model Validation using Test Field Diversity

儀器設備銷售 — Mon, 28 Mar 2022 01:27:46 +0000