| 1. |
- Candefjord, Stefan, 1981, et al.
(författare)
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Microwave technology for detecting traumatic intracranial bleedings: tests on phantom of subdural hematoma and numerical simulations
- 2017
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Ingår i: Medical and Biological Engineering and Computing. - : Springer Science and Business Media LLC. - 1741-0444 .- 0140-0118. ; 55:8, s. 1177-1188
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Tidskriftsartikel (refereegranskat)abstract
- Traumatic brain injury is the leading cause of death and severe disability for young people and a major public health problem for elderly. Many patients with intracranial bleeding are treated too late, because they initially show no symptoms of severe injury and are not transported to a trauma center. There is a need for a method to detect intracranial bleedings in the prehospital setting. In this study, we investigate whether broadband microwave technology (MWT) in conjunction with a diagnostic algorithm can detect subdural hematoma (SDH). A human cranium phantom and numerical simulations of SDH are used. Four phantoms with SDH 0, 40, 70 and 110 mL are measured with a MWT instrument. The simulated dataset consists of 1500 observations. Classification accuracy is assessed using fivefold cross-validation, and a validation dataset never used for training. The total accuracy is 100 and 82–96 % for phantom measurements and simulated data, respectively. Sensitivity and specificity for bleeding detection were 100 and 96 %, respectively, for the simulated data. SDH of different sizes is differentiated. The classifier requires training dataset size in order of 150 observations per class to achieve high accuracy. We conclude that the results indicate that MWT can detect and estimate the size of SDH. This is promising for developing MWT to be used for prehospital diagnosis of intracranial bleedings.
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| 2. |
- 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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| 3. |
- 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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| 4. |
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| 5. |
- 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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