Time filter

Source Type

Zürich, Switzerland

Feliziani M.,University of LAquila | Cruciani S.,University of LAquila | de Santis V.,ITIS Foundation | Maradei F.,University of Rome La Sapienza
Progress In Electromagnetics Research B | Year: 2012

This paper deals with the time-domain numerical calculation of electromagnetic (EM) fields in linearly dispersive media described by multipole Debye model. The frequency-dependent finite-difference time-domain (FD 2TD) method is applied to solve Debye equations using convolution integrals or by direct integration. Original formulations of FD 2TD methods are proposed using different approaches. In the first approach based on the solution of convolution equations, the exponential analytical behavior of the convolution integrand permits an efficient recursive FD 2TD solution. In the second approach, derived by circuit theory, the transient equations are directly solved in time domain by the FD 2TD method. A comparative analysis of several FD 2TD methods in terms of stability, dispersion, computational time and memory is carried out. Source

Focke F.,University of Basel | Schuermann D.,University of Basel | Kuster N.,ITIS Foundation | Schar P.,University of Basel
Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis | Year: 2010

Extremely low frequency electromagnetic fields (ELF-EMFs) were reported to affect DNA integrity in human cells with evidence based on the Comet assay. These findings were heavily debated for two main reasons; the lack of reproducibility, and the absence of a plausible scientific rationale for how EMFs could damage DNA. Starting out from a replication of the relevant experiments, we performed this study to clarify the existence and explore origin and nature of ELF-EMF induced DNA effects. Our data confirm that intermittent (but not continuous) exposure of human primary fibroblasts to a 50 Hz EMF at a flux density of 1 mT induces a slight but significant increase of DNA fragmentation in the Comet assay, and we provide first evidence for this to be caused by the magnetic rather than the electric field. Moreover, we show that EMF-induced responses in the Comet assay are dependent on cell proliferation, suggesting that processes of DNA replication rather than the DNA itself may be affected. Consistently, the Comet effects correlated with a reduction of actively replicating cells and a concomitant increase of apoptotic cells in exposed cultures, whereas a combined Fpg-Comet test failed to produce evidence for a notable contribution of oxidative DNA base damage. Hence, ELF-EMF induced effects in the Comet assay are reproducible under specific conditions and can be explained by minor disturbances in S-phase processes and occasional triggering of apoptosis rather than by the generation of DNA damage. © 2009 Elsevier B.V. All rights reserved. Source

Murbach M.,ITIS Foundation | Murbach M.,ETH Zurich | Neufeld E.,ITIS Foundation | Capstick M.,ITIS Foundation | And 6 more authors.
Magnetic Resonance in Medicine | Year: 2014

Purpose This article investigates the safety of radiofrequency induced local thermal hotspots within a 1.5T body coil by assessing the transient local peak temperatures as a function of exposure level and local thermoregulation in four anatomical human models in different Z-positions. Methods To quantize the effective thermal stress of the tissues, the thermal dose model cumulative equivalent minutes at 43°C was employed, allowing the prediction of thermal tissue damage risk and the identification of potentially hazardous MR scan-scenarios. The numerical results were validated by B1 +- and skin temperature measurements. Results At continuous 4 W/kg whole-body exposure, peak tissue temperatures of up to 42.8°C were computed for the thermoregulated model (60°C in nonregulated case). When applying cumulative equivalent minutes at 43°C damage thresholds of 15 min (muscle, skin, fat, and bone) and 2 min (other), possible tissue damage cannot be excluded after 25 min for the thermoregulated model (4 min in nonregulated). Conclusion The results are found to be consistent with the history of safe use in MR scanning, but not with current safety guidelines. For future safety concepts, we suggest to use thermal dose models instead of temperatures or SAR. Special safety concerns for patients with impaired thermoregulation (e.g., the elderly, diabetics) should be addressed. © 2013 Wiley Periodicals, Inc. Source

Murbach M.,ITIS Foundation | Murbach M.,ETH Zurich | Neufeld E.,ITIS Foundation | Kainz W.,U.S. Food and Drug Administration | And 3 more authors.
Magnetic Resonance in Medicine | Year: 2014

Purpose Radiofrequency energy deposition in magnetic resonance imaging must be limited to prevent excessive heating of the patient. Correlations of radiofrequency absorption with large-scale anatomical features (e.g., height) are investigated in this article. Theory and Methods The specific absorption rate (SAR), as the pivotal parameter for quantifying absorbed radiofrequency, increases with the radial dimension of the patient and therefore with the large-scale anatomical properties. The absorbed energy in six human models has been modeled in different Z-positions (head to knees) within a 1.5T bodycoil. Results For a fixed B1+ incident field, the whole-body SAR can be up to 2.5 times higher (local SAR up to seven times) in obese adult models compared to children. If the exposure is normalized to 4 W/kg whole-body SAR, the local SAR can well-exceed the limits for local transmit coils and shows intersubject variations of up to a factor of three. Conclusions The correlations between anatomy and induced local SAR are weak for normalized exposure, but strong for a fixed B1+ field, suggesting that anatomical properties could be used for fast SAR predictions. This study demonstrates that a representative virtual human population is indispensable for the investigation of local SAR levels. © 2013 Wiley Periodicals, Inc. Source

Moilanen P.,University of Jyvaskyla | Luukkainen M.,Nokia Inc. | Jekkonen J.,ITIS Foundation | Kangas V.,University of Jyvaskyla
IEEE International Symposium on Electromagnetic Compatibility | Year: 2010

Electromagnetic interference shielding is an important aspect of modern communication and computer technology. Carbon nanotube cellulose nanocomposite (CNTCNC) provides a novel material as an alternative to traditional metal-based shields for EMI shielding. Stratified structures containing CNTCNC layers combined with existing commercial lossy materials (like ferrite sheets) form effective EMI shields without lowering the signal integrity performance. Significant improvement in shielding effectiveness in stacked CNTCNC layers is noteworthy. CNTCNC is essentially like paper when it comes to flexibility and hence it can be easily conformed to the mechanical structure of the device in need of shielding. ©2010 IEEE. Source

Discover hidden collaborations