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Chen X.-L.,Foundation for Research on Information Technologies in Society ITIS | Benkler S.,Schmid & Partner Engineering AG | Chavannes N.,Schmid & Partner Engineering AG | De Santis V.,Foundation for Research on Information Technologies in Society ITIS | And 5 more authors.
Bioelectromagnetics | Year: 2013

Compliance with the established exposure limits for the electric field (E-field) induced in the human brain due to low-frequency magnetic field (B-field) induction is demonstrated by numerical dosimetry. The objective of this study is to investigate the dependency of dosimetric compliance assessments on the applied methodology and segmentations. The dependency of the discretization uncertainty (i.e., staircasing and field singularity) on the spatially averaged peak E-field values is first determined using canonical and anatomical models. Because spatial averaging with a grid size of 0.5mm or smaller sufficiently reduces the impact of artifacts regardless of tissue size, it is a superior approach to other proposed methods such as the 99th percentile or smearing of conductivity contrast. Through a canonical model, it is demonstrated that under the same uniform B-field exposure condition, the peak spatially averaged E-fields in a heterogeneous model can be significantly underestimated by a homogeneous model. The frequency scaling technique is found to introduce substantial error if the relative change in tissue conductivity is significant in the investigated frequency range. Lastly, the peak induced E-fields in the brain tissues of five high-resolution anatomically realistic models exposed to a uniform B-field at ICNIRP and IEEE reference levels in the frequency range of 10Hz to 100kHz show that the reference levels are not always compliant with the basic restrictions. Based on the results of this study, a revision is recommended for the guidelines/standards to achieve technically sound exposure limits that can be applied without ambiguity. © 2013 Wiley Periodicals, Inc. Source

Gosselin M.-C.,Foundation for Research on Information Technologies in Society ITIS | Gosselin M.-C.,ETH Zurich | Neufeld E.,Foundation for Research on Information Technologies in Society ITIS | Moser H.,Foundation for Research on Information Technologies in Society ITIS | And 12 more authors.
Physics in Medicine and Biology | Year: 2014

The Virtual Family computational whole-body anatomical human models were originally developed for electromagnetic (EM) exposure evaluations, in particular to study how absorption of radiofrequency radiation from external sources depends on anatomy. However, the models immediately garnered much broader interest and are now applied by over 300 research groups, many from medical applications research fields. In a first step, the Virtual Family was expanded to the Virtual Population to provide considerably broader population coverage with the inclusion of models of both sexes ranging in age from 5 to 84years old. Although these models have proven to be invaluable for EM dosimetry, it became evident that significantly enhanced models are needed for reliable effectiveness and safety evaluations of diagnostic and therapeutic applications, including medical implants safety. This paper describes the research and development performed to obtain anatomical models that meet the requirements necessary for medical implant safety assessment applications. These include implementation of quality control procedures, re-segmentation at higher resolution, more-consistent tissue assignments, enhanced surface processing and numerous anatomical refinements. Several tools were developed to enhance the functionality of the models, including discretization tools, posing tools to expand the posture space covered, and multiple morphing tools, e.g., to develop pathological models or variations of existing ones. A comprehensive tissue properties database was compiled to complement the library of models. The results are a set of anatomically independent, accurate, and detailed models with smooth, yet feature-rich and topologically conforming surfaces. The models are therefore suited for the creation of unstructured meshes, and the possible applications of the models are extended to a wider range of solvers and physics. The impact of these improvements is shown for the MRI exposure of an adult woman with an orthopedic spinal implant. Future developments include the functionalization of the models for specific physical and physiological modeling tasks. © 2014 Institute of Physics and Engineering in Medicine. Source

Murbach M.,ITIS Foundation | Murbach M.,ETH Zurich | Christopoulou M.,ITIS Foundation | Christopoulou M.,National Technical University of Athens | And 4 more authors.
Bioelectromagnetics | Year: 2012

A novel exposure system for double-blind human electromagnetic provocation studies has been developed that satisfies the precision, control of fields and potential artifacts, and provides the flexibility to investigate the response of hypotheses-driven electromagnetic field exposure schemes on brain function, ranging from extremely low frequency (ELF) to radio frequency (RF) fields. The system can provide the same exposure of the lateral cerebral cortex at two different RF frequencies (900 and 2140MHz) but with different exposure levels at subcortical structures, and also allows uniform ELF magnetic field exposure of the brain. The RF modulation and ELF signal are obtained by a freely programmable arbitrary signal generator allowing a wide range of worst-case exposure scenarios to be simulated, including those caused by wireless devices. The maximum achievable RF exposure is larger than 60W/kg peak spatial specific absorption rate averaged over 10g of tissue. The maximum ELF magnetic field exposure of the brain is 800A/m at 50Hz with a deviation from uniformity of 8% (SD). © 2012 Wiley Periodicals, Inc. Source

Li C.-H.,ETH Zurich | Douglas M.,ETH Zurich | Ofli E.,Schmid & Partner Engineering AG | Derat B.,Field Imaging | And 3 more authors.
IEEE Transactions on Antennas and Propagation | Year: 2012

The influence of the user's hand holding a mobile phone to the ear on the peak spatial-average Specific Absorption Rate (psSAR) averaged over any 1 g and 10 g of tissue in the head is investigated. This study is motivated by recent reports that found substantial increases in psSAR by the presence of the hand in some cases. Current measurement standards prescribe the measurement of SAR in a head phantom without a hand present. The mechanisms of interaction between the hand and mobile phone models are studied. Simulations and measurements at 900 and 1800 MHz have been conducted to complement the understanding of the hand grip parameters leading to higher SAR in the head. Numerical simulations were conducted on four mobile phone models, and parameters such as the palm-phone distance and hand position were varied. Measurements of 46 commercial mobile phones were made, and the maximum psSAR with different hand positions and palm-phone distances was recorded. Both simulations and measurements have found increases in the psSAR in the head of at least 2.5 dB due to the presence of the hand. Furthermore, the psSAR is sensitive to the hand grip, i.e., the variations can exceed 3 dB. © 2011 IEEE. Source

Toivanen J.I.,University of Jyvaskyla | Stefanski T.P.,ETH Zurich | Kuster N.,ETH Zurich | Chavannes N.,Schmid & Partner Engineering AG
Progress In Electromagnetics Research M | Year: 2011

Three distinctively different implementations of convolutional perfectly matched layer for the FDTD method on CUDA enabled graphics processing units are presented. All implementations store ad- ditional variables only inside the convolutional perfectly matched lay- ers, and the computational speeds scale according to the thickness of these layers. The merits of the different approaches are discussed, and a comparison of computational performance is made using complex real-life benchmarks. Source

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