| 1. |
- Persson, Mikael, 1959, et al.
(författare)
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Advances in Neuro Diagnostic based on Microwave Technology, Transcranial Magnetic Stimulation and EEG source localization
- 2011
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Ingår i: Asia Pacific Microwave Conference, (APMC 2011;Melbourne, VIC; 5 - 8 December 2011). - 9780858259744 ; , s. 469-472
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Konferensbidrag (refereegranskat)abstract
- Advances in neuro diagnostics based on microwave antenna system in terms of a helmet including a set of broad band patch antennas is presented. It is shown that classification algorithms can be used to detect internal bleeding in stroke patients. Transcranial magnetic stimulation has traditionally been used for brain mapping and treatment of depression. In this paper we discuss the use of the method for neuro diagnostics with the help of integrated image guidance. Surgical therapy has become an important therapeutic alternative for some patients with medically intractable epilepsy. Electroencephalography and the associated model based diagnostics as a non-invasive diagnostic tool is also discussed.
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| 2. |
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| 3. |
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| 4. |
- Shirvany, Yazdan, 1980, et al.
(författare)
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Investigation of brain tissue segmentation error and its effect on EEG source localization
- 2012
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Ingår i: Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS. - 1557-170X. ; , s. 1522-1525
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Konferensbidrag (refereegranskat)abstract
- Surgical therapy has become an important therapeutic alternative for patients with medically intractable epilepsy. Correct and anatomically precise localization of the epileptic focus, preferably with non-invasive methods, is the main goal of the pre-surgical epilepsy diagnosis to decide if resection of brain tissue is possible. For evaluating the performance of the source localization algorithms in an actual clinical situation, realistic patient-specific human head models that incorporate the heterogeneity nature of brain tissues is required. In this paper, performance of two of the most widely used software packages for brain segmentation, namely FSL and FreeSurfer has been analyzed. Then a segmented head model from a package with better performance is used to investigate the effects of brain tissue segmentation in EEG source localization.
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| 5. |
- Talcoth, Oskar, 1980, et al.
(författare)
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Monolithic Multi-Scale Modeling of MR-Induced Pacemaker Lead Heating
- 2011
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Ingår i: 13th International Conference on Electromagnetics in Advanced Applications (ICEAA), 2011, Torino, 12-16 September 2011. - 9781612849768 ; , s. 599 - 602
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Konferensbidrag (refereegranskat)abstract
- Modeling of MR-induced pacemaker lead heating is complicated by, among other things, the multi-scale characteristics of the problem. In this paper, the method of moments is used to model a wide range of length scales of the problem simultaneously including the helix-shaped conducting wires present in the pacemaker lead. A cross-section area conserving meshing scheme for helices is proposed and evaluated. For a relative error of 1%, the meshing scheme reduces the number of thin wire segments needed to model a helix with a factor of roughly 3 to 6, as compared to the conventional approach. In addition, we study the relationship between the maximum induced current on the lead and the number of turns of the helices.
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| 6. |
- Talcoth, Oskar, 1980, et al.
(författare)
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MR-induced heating of pacemaker leads: A parameter study of contributing factors based on multi-scale modeling
- 2011
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Ingår i: Proceedings of Medicinteknikdagarna 2011. ; , s. 52-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Magnetic resonance imaging (MRI) is a valuable tool for diagnostic imaging inhealthcare and the number of examinations using this imaging modality increases each year.At the same time, pacemakers and other types of active implantable medical devices (AIMD)are getting increasingly common. Unfortunately, patients with an AIMD are currentlydeprived of the benefits of MRI due to the potentially harmful interactions of the implant withthe electromagnetic fields present during MRI. In particular, currents induced by the radiofrequency (RF) field can give rise to excessive heating near sharp corners and edges of theimplant. The occurrence of such heating at the electrodes of a pacemaker lead can result inreduction or loss of the pacemaker’s pacing ability.As a consequence, there is a need for MR-safe pacemaker systems. Experiments andnumerical modeling have been frequently used for investigations of the heating phenomenon.Such modeling is difficult due to the heterogeneity of the human body, the multi-scale natureof the problem, and inter-patient variations in factors like implant configuration.In this work, we model a wide range of length scales of the problem simultaneously. Themodeled MRI birdcage antenna and the human-body phantom have sizes of approximatelyone fifth of a wavelength whereas the helix-shaped conducting wires of the bi-polarpacemaker lead vary on a length scale of roughly one thousandth of a wavelength. The modelbeing entirely parameterized, we perform parameter studies to investigate how the heating isinfluenced by different factors, including the dielectric constants of the phantom material, thenumber of wire turns of the conductors, and the radii of the helices. Furthermore, implicationsof these results for the design of MR-safe pacemaker leads are discussed.
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| 7. |
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| 8. |
- Talcoth, Oskar, 1980, et al.
(författare)
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Optimal measurements in magnetic tracking for organ-positioning during radiotherapy
- 2011
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Ingår i: Proceedings of Medicinteknikdagarna 2011. ; , s. 79-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In a magnetic tracking system, the position and orientation of a coil is determined by its low frequency (LF)magnetic interactions with a coil array of known position and orientation. There are two main types of systems:(i) the coil with unknown position works as a transmitter with a receiving array of sensors, or (ii) the coil array isthe transmitter and the coil with unknown position is used as sensor. As LF magnetic fields do not interact withthe human body, magnetic tracking is particularly well-suited for tracking of objects in and around the humanbody. For example, this tracking technique has in recent years been proposed for eye tracking, tracking of tonguemovements, and organ-positioning during radiotherapy.We focus on an organ-positioning system for use during radiotherapy. The system, which is of type (i) above,consists of a transmitter that is implanted near the organ of interest and an external array of sensors. Of particularinterest is the spatial layout of the sensor array, since this strongly influences the performance of the trackingsystem. A well-designed sensor array will give good positioning accuracy whereas an ill-designed array canresult in an unsolvable positioning problem.In this work, we use Fisher-information theory from the field of optimal measurements to formulate anoptimization problem for the layout of the sensor array. Furthermore, we solve the optimization problem anddiscuss the implications of the results on the design of magnetic tracking systems.
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| 9. |
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| 10. |
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| 11. |
- Aldhubaib, Faisal, et al.
(författare)
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A Radar Target Signature based on Resonance and dual Polarization Features
- 2008
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Ingår i: 2008 Asia Pacific Microwave Conference, APMC 2008; Hong Kong; China; 16 December 2008 through 20 December 2008. - 9781424426423 ; , s. 1-4
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Konferensbidrag (refereegranskat)abstract
- A physically based radar target scattering signature is derived from observable data using a frequency domain scattering model that incorporates the backscattered radar target polarization response at the target natural resonance frequencies (NRF). Two rotationally symmetric targets of simple but similar characteristic geometry are used to demonstrate the theoretical feasibility and the ability to distinguish the two similar targets by this proposed signature.
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| 12. |
- Aldhubaib, F., et al.
(författare)
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Aspect segmentation and feature selection of radar targets based on average probability of error
- 2010
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Ingår i: IET Microwaves, Antennas and Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725 .- 1751-8733. ; 4:10, s. 1654-1664
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Tidskriftsartikel (refereegranskat)abstract
- Through statistical estimation by a non-parametric model, a fused polarimetric and resonant return from the radar target is modelled as a function of the target aspect angle. The outcome of this type of modelling is a set of non-parametric density estimates, which are then used to represent this target in a multi-dimensional probability space. These densities within this probability space can be well separated and therefore utilised to make decision rules to identify targets of interest. The return set to be modelled is the average power set associated with spectral bands centred on the target natural resonant frequencies. This return set is mapped into density set using a Gaussian kernel function; subsequently, the density set will be considered as the target radar feature set of interest. To decrease density overlapping between respective densities of different targets, a criterion based on the Bayesian error is employed; first, to bisect the aspect global range into smaller sectors, and second, to select discriminative features that can minimise the average probability of error between the targets respective features. The results show that two targets with similar resonant frequencies can be separated by the Bayesian error criterion based on the proposed features. A simple likelihood ratio test had more than 80% success down to 20 dB of signal-to-noise ratio.
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| 13. |
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| 14. |
- Dobsicek Trefna, Hana, 1979, et al.
(författare)
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Evolution of an UWB antenna for hyperthermia array applicator
- 2012
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Ingår i: Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012. Prague, 26-30 March 2012.. - 9781457709180 ; , s. 1046 - 1048
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Konferensbidrag (refereegranskat)abstract
- Designs of three UWB antennas and their suitability to be used as a basis antenna element in the hyperthermia applicator for the treatment of tumors in head and neck region are considered. The antennas with reflection coefficient less than -10 dB at frequency range 350 MHz to 1 GHz are immersed in water bolus. The evaluation of the SAR distributions was carried out by comparing the different cross-sections of muscle equivalent phantom. Numerical simulations were performed in CST Microwave studio and verified experimentally via measurements of S-parameters and SAR distributions in phantoms.
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| 15. |
- Fayazi, Seyedeh Shaghayegh, et al.
(författare)
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Microwave imaging of near-field object using ultra-wideband synthetic aperture radar algorithm
- 2012
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Ingår i: 2012 IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM (APSURSI). - 1522-3965. - 9781467304627
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Konferensbidrag (refereegranskat)abstract
- A simple procedure that suppresses artefact from ultra-wideband (UWB) synthetic aperture radar (SAR) images is proposed and verified using experimental data. The proposed imaging solution is useful for imaging small objects located in the near-field region with less ambiguity.
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| 16. |
- Fayazi, Seyedeh Shaghayegh, et al.
(författare)
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UWB SAR Imaging of Near-Field Object for Industrial Process Applications
- 2013
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Ingår i: 7th European Conference on Antennas and Propagation, EuCAP 2013, Gothenburg, Sweden, 8-12 April 2013. - 2164-3342. - 9781467321877 ; , s. 2245-2248
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Konferensbidrag (refereegranskat)abstract
- Ultra wideband technology becomes more widely used for near-field object detection. We present an aperture synthetic radar (SAR) system using ultra-wideband (UWB) signals for such applications. One of the problems with UWB time-domain SAR imaging algorithm is the artefact originated from scattered field of adjacent objects. In this paper an algorithm based on the Range Point Migration (RPM) method is used to alleviate this problem. This method estimates a possibility distribution of the optimal Direction of Arrival (DOA) of the scattered field from objects. A weighting factor based on this possibility is used to suppress the effect of artifact scattered fields. The results in the paper show that the UWB SAR accompanied with RPM can produce an image of an object with a significant suppression of undesired artifact from scattered field of adjacent objects.
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| 17. |
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| 18. |
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| 19. |
- Johansson, Markus, 1978, et al.
(författare)
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Comparison between Two Phase Retrieval Methods for Electromagnetic Source Modeling
- 2011
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Ingår i: Progress in Electromagnetics Research B. - 1937-6472. ; 30, s. 239-253
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Tidskriftsartikel (refereegranskat)abstract
- Phase-retrieval from measured phaseless field data is of interest for various applications including electromagnetic dosimetry, electromagnetic compatibility investigations, near-field to far-field transformations and antenna diagnostics. In this study two phaseretrieval methods are compared. The first method, the adjoint field method, employs a gradient-based optimization algorithm based on the adjoint fields. The second method, the phase angle gradient method, uses an optimization algorithm based on the phase angle gradients of a functional. The methods are tested with numerical test cases and the phase angle gradient method is found to retrieve the phase with the best accuracy. Moreover it gives results that agree well with correct phase.
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| 20. |
- Johansson, Markus, 1978, et al.
(författare)
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Electromagnetic Source Modeling using Phase Retrieval Methods
- 2011
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Ingår i: 30th URSI General Assembly and Scientific Symposium, URSIGASS 2011, Istanbul, 13-20 August 2011. - 9781424451173 ; , s. 1-2
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Konferensbidrag (refereegranskat)abstract
- Modeling of the field distributions from electromagnetic sources is of interest for various applications for example electromagnetic compatibility investigations, near-field to far-field transformations, antenna diagnostics and electromagnetic dosimetry. In order to determine whether exposure safety guidelines, such as the EU directive 2004/40/EC, are complied with, source modeling methods are important. Two methods for determining the total field, including phase information, when only field amplitudes have been measured on a set of planes in front of an electromagnetic source have been developed. The first method, the adjoint field method, is a gradient based optimization algorithm based on the adjoint fields. The second method, the phase angle gradient method, employs an optimization algorithm based on the phase angle gradients of a functional. Promising results have been obtained both for numerical test cases and for measured field.
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| 21. |
- Johansson, Markus, 1978, et al.
(författare)
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Performance Evaluation of Phase-Angle Gradient Method for Phase Retrieval based on Low-Frequency amplitude-Only Near-Field Data
- 2010
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Ingår i: Progress in Electromagnetics Research B. - 1937-6472. ; 25:25, s. 113-130
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Tidskriftsartikel (refereegranskat)abstract
- The Phase Angle Gradient Method (PAGM) is a recent technique developed for phase retrieval based on amplitude-only measurement data. Preliminary results have shown that the PAGM is able to perform phase retrieval at 100MHz with accurate phase information based on measured fIeld components on three planar surfaces. In this paper, a performance evaluation of the PAGM under different conFigurations is conducted. Phase retrieval based on field measurements for different plane sizes and separations between the planes are studied rigorously. In addition, the PAGM is tested for different initial phase distributions. The results show that the PAGM is capable of retrieving phase information even if the separation between the measurement planes is small in terms of wavelengths.
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| 22. |
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| 23. |
- Johansson, Markus, 1978, et al.
(författare)
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Source Modeling using Phaseless Low-Frequency Near-Field Measurements
- 2012
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Ingår i: IEEE Transactions on Electromagnetic Compatibility. - 0018-9375 .- 1558-187X. ; 54:3, s. 613-624
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Tidskriftsartikel (refereegranskat)abstract
- Field measurements of both amplitude and phase generally are more complicated and require more expensive equipment than amplitude-only measurements. Phase retrieval from measured phaseless field data is, therefore, of interest for source modeling in dosimetry applications, electromagnetic compatibility investigations, near-field to far-field transformations and antenna diagnostics. We here present a phase-retrieval method that uses an optimization algorithm based on the phase angle gradients of a functional. Numerical test cases have shown that the method is working for different initial phase distributions as well as different placements of the source. The method also works well for a test case with measured 50 Hz magnetic flux density from a transformer. The obtained phase angles on a measurement plane in front of the transformer gave calculated field amplitudes on other measurement planes that agree well with measured field. The ratios between the largest amplitude difference and the largest measured amplitude for the three Cartesian magnetic flux density components, for one of the planes, are for example 6.62%, 9.51% and 6.40%.
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| 25. |
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