Selecting the Optimal Subset of Antennas in Hyperthermia Treatment Planning
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Among them, increasing the frequency and the number of radiating elements has shown effective for achieving more conformal heating. However, as each radiating element requires a power amplifier to control it, increasing the number of antennas considerably impacts the overall cost and complexity of the system. Accordingly, a procedure capable of selecting an optimal patient-specific subset of antennas from an oversized phased array applicator (with more antenna elements than available amplifiers) could help improving cost-effectiveness. In this study, we present an original approach which allows improving performance by adaptively selecting the optimal subset of antennas to be activated for a given (redundant) applicator and a given patient. The proposed approach takes inspiration from the compressive sensing theory by embedding the sparsity promotion paradigm into a treatment planning procedure which casts power-deposition as a constrained convex optimization. Performance were demonstrated for the case of head and neck hyperthermia, and benchmarked against the antenna selection procedure presently used in the clinical practice.
RF Injection Network Development for Testing of Active Implantable Medical Devices Exposed to RF Fields in 1.5 T MRI Systems
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The system was developed to meet the requirements of ISO/TS 10974:2018(E). A directional lumped element coupler, power splitter, an attenuator/isolator, low pass filter and high pass filter were designed and implemented as part of the network. The RF injection network was developed in both a compact version implemented in a single PCB and discrete PCB version for use in different situations. The performance of each designed component was simulated and compared to measurement results. As an application example, a neuromodulation system was tested using the developed RF injection network for conductive emission testing.
Effects of Coaxial-lateral and Coaxial-angular Displacements on Link Efficiency of a Wirelessly Powered Optogenetic Implant: Design, Modeling and Experimental Validation
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The coupling coefficient deteriorates significantly due to the displacements thus decreasing the overall power transfer efficiency (PTE) of the system. In this paper, we present an analysis and modeling of the effects of various displacements on the efficiency and the overall performance of a miniaturized WPT system designed for an optogenetic implant. To emulate the tissue media inside a human head, skin, skull and gray matter layers are theoretically modeled using dielectric properties and simulation models are developed using the Ansys High Frequency Structure Simulator (HFSS) software. The propagation loss and link efficiency are modeled and simulated as a function of various displacement combinations. To validate the theoretical and simulation models, the WPT system is characterized in various displacement conditions using chicken breast as the media. The measurement results also show a good agreement with the simulation results, thus providing an estimation for the misalignment tolerance range for given specifications. The efficiency performance analysis of the proposed WPT system for various worst-case scenarios also provides a preliminary model for designing a closed-loop wireless power delivery regulation scheme in the future.
Determining the Position and Orientation of In-body Medical Instruments Using Near-Field Magnetic Field Mapping
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The permanent magnet fails due to low power, and static current source requires relatively high power source. The RF field source requires high frequencies to get enough precision, which undergoes high attenuation in the body. At low frequency, when the distance between the source and the receiver array is shorter than the wavelength, the far field assumption fails for localization methods. Therefore, we propose a novel method of mapping the magnetic field vector in the near field region, with which wavelength independent localization is done. We did extensive MATLAB and CST Microwave simulations followed by practical experiments. The proposed method has achieved localization accuracy of less than 1 cm in Y-Z plane, 2 cm in depth (in X-axis) and the maximum orientation error remained 10° in 3-D.
Impact of Electrode Structure on RF-induced Heating for an AIMD Implanted Lead in a 1.5-Tesla MRI System
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It is shown that increasing the size of lead electrode reduces the SAR distribution and temperature rise near the electrode. Our results indicate that a larger electrode size will reduce the magnitudes of the lead transfer function, and subsequently reduces the heating effect near the electrode. Both numerical simulations and experimental measurements were performed to verify the effectiveness of a large electrode in mitigating the RF-induced heating.
Feasibility Study of Hydration Monitoring using Microwaves Part 2: Measurements of Athletes
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Extremity microwave measurement is a promising method for ongoing hydration monitoring, owing to the inherent differences in dielectric properties with varying tissue water content. This paper reports on a feasibility study of textit{in vivo} hydration assessment using microwave measurements in athletes undergoing acute water loss during exercise. We developed and then tested a system for performing reliable microwave property estimation at the forearm. This system was used to measure hydration status in varsity wrestlers before and after a training session. A relationship between estimated permittivity and body weight change due to water loss was found, showing promise for the use of microwaves to assess hydration status. No significant relationship with attenuation was found. A novel method of assessing changes in hydration status is described, which may be of practical use for athletes in guiding fluid replacement during and after exercise.
