ITIS Foundation

Zürich, Switzerland

ITIS Foundation

Zürich, Switzerland
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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.

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.

Corcoles J.,Autonomous University of Madrid | Zastrow E.,ItIs Foundation | Kuster N.,ItIs Foundation | Kuster N.,ETH Zurich
Physics in Medicine and Biology | Year: 2017

The increasing use of multiple radiofrequency (RF) transmit channels in magnetic resonance imaging (MRI) systems makes it necessary to rigorously assess the risk of RF-induced heating. This risk is especially aggravated with inclusions of medical implants within the body. The worst-case RF-heating scenario is achieved when the local tissue deposition in the at-risk region (generally in the vicinity of the implant electrodes) reaches its maximum value while MRI exposure is compliant with predefined general specific absorption rate (SAR) limits or power requirements. This work first reviews the common approach to estimate the worst-case RF-induced heating in multi-channel MRI environment, based on the maximization of the ratio of two Hermitian forms by solving a generalized eigenvalue problem. It is then shown that the common approach is not rigorous and may lead to an underestimation of the worst-case RF-heating scenario when there is a large number of RF transmit channels and there exist multiple SAR or power constraints to be satisfied. Finally, this work derives a rigorous SAR-based formulation to estimate a preferable worst-case scenario, which is solved by casting a semidefinite programming relaxation of this original non-convex problem, whose solution closely approximates the true worst-case including all SAR constraints. Numerical results for 2, 4, 8, 16, and 32 RF channels in a 3T-MRI volume coil for a patient with a deep-brain stimulator under a head imaging exposure are provided as illustrative examples. © 2017 Institute of Physics and Engineering in Medicine.

Van Rhoon G.C.,Erasmus Cancer Center | Samaras T.,Aristotle University of Thessaloniki | Yarmolenko P.S.,Duke University | Yarmolenko P.S.,U.S. National Institutes of Health | And 3 more authors.
European Radiology | Year: 2013

Objective: To define thresholds of safe local temperature increases for MR equipment that exposes patients to radiofrequency fields of high intensities for long duration. These MR systems induce heterogeneous energy absorption patterns inside the body and can create localised hotspots with a risk of overheating. Methods: The MRI + EUREKA research consortium organised a "Thermal Workshop on RF Hotspots". The available literature on thresholds for thermal damage and the validity of the thermal dose (TD) model were discussed. Results/Conclusions: The following global TD threshold guidelines for safe use of MR are proposed: 1. All persons: maximum local temperature of any tissue limited to 39°C 2. Persons with compromised thermoregulation AND (a) Uncontrolled conditions: maximum local temperature limited to 39 °C (b) Controlled conditions: TD < 2 CEM43 °C 3. Persons with uncompromised thermoregulation AND (a) Uncontrolled conditions: TD < 2 CEM43° C (b) Controlled conditions: TD < 9 CEM43 °C The following definitions are applied: Controlled conditions A medical doctor or a dedicated trained person can respond instantly to heat-induced physiological stress Compromised thermoregulation All persons with impaired systemic or reduced local thermoregulation Key Points: • Standard MRI can cause local heating by radiofrequency absorption. • Monitoring thermal dose (in units of CEM43° C) can control risk during MRI. • 9 CEM43° C seems an acceptable thermal dose threshold for most patients. • For skin, muscle, fat and bone,16 CEM43° C is likely acceptable. © 2013 European Society of Radiology.

Moilanen P.,University of Jyväskylä | Luukkainen M.,Nokia Inc. | Jekkonen J.,ITIs Foundation | Kangas V.,University of Jyväskylä
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.

Loughran S.P.,University of Zürich | Benz D.C.,University of Zürich | Schmid M.R.,University of Zürich | Schmid M.R.,ETH Zurich | And 6 more authors.
Clinical Neurophysiology | Year: 2013

Objective: To examine the potential sensitivity of adolescents to radiofrequency electromagnetic field (RF EMF) exposures, such as those emitted by mobile phones. Methods: In a double-blind, randomized, crossover design, 22 adolescents aged 11-13. years (12 males) underwent three experimental sessions in which they were exposed to mobile phone-like RF EMF signals at two different intensities, and a sham session. During exposure cognitive tasks were performed and waking EEG was recorded at three time-points subsequent to exposure (0, 30 and 60. min). Results: No clear significant effects of RF EMF exposure were found on the waking EEG or cognitive performance. Conclusions: Overall, the current study was unable to demonstrate exposure-related effects previously observed on the waking EEG in adults, and also provides further support for a lack of an influence of mobile phone-like exposure on cognitive performance. Significance: Adolescents do not appear to be more sensitive than adults to mobile phone RF EMF emissions. © 2013 International Federation of Clinical Neurophysiology.

Douglas M.G.,ItIs Foundation | Kuster N.,ItIs Foundation
IEEE International Symposium on Electromagnetic Compatibility | Year: 2014

The current standardized SAR evaluation technique is optimized with respect to the requirements of maximal repeatability and minimal measurement uncertainty. The uncertainty satisfies the requirement of being independent of the source and source-phantom coupling mechanism. These requirements are best achieved by the current SAR evaluation technique that is adaptive and based on 3D scanning of the induced field inside a homogeneously-filled phantom with a single miniaturized isotropic probe. However, such an evaluation is time consuming, i.e., greater than 10 minutes per scan. Due to an increased demand for faster evaluation methods, novel techniques have recently been proposed and implemented for reconstructing the 3D SAR pattern based on sensor arrays, intelligent scanning protocols or combinations of both. The evaluation can be reduced to less than 1s for array systems and to less than two minutes for intelligent scanning. We compared the performance of 35 commercial phones for two array-system implementations. We will discuss the advantages and limitations/shortcomings of each of the novel fast SAR methods for the compliance testing of wireless devices. © 2014 The Institute of Electronics, Information and Communication Engineer.

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.

Feliziani M.,University of L'Aquila | Cruciani S.,University of L'Aquila | 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.

Zastrow E.,University of Wisconsin - Madison | Zastrow E.,ItIs Foundation | Hagness S.C.,University of Wisconsin - Madison | Van Veen B.D.,University of Wisconsin - Madison | Medow J.E.,University of Wisconsin - Madison
IEEE Transactions on Biomedical Engineering | Year: 2011

A noninvasive microwave beamforming strategy is proposed for selective localized heating of biological tissue. The proposed technique is based on time multiplexing of multiple beamformers. We investigate the effectiveness of the time-multiplexed beamforming in the context of brain hyperthermia treatment by using a high-fidelity numerical head phantom of an adult female from the Virtual Family (ITIS Foundation) as our testbed. An operating frequency of 1 GHz is considered to balance the improved treatment resolution afforded by higher frequencies against the increased penetration through the brain afforded by lower frequencies. The exact head geometry and dielectric properties of biological tissues in the head are assumed to be available for the creation of patient-specific propagation models used in beamformer design. Electromagnetic and thermal simulations based on the finite-difference time-domain method are used to evaluate the hyperthermia performance of time-multiplexed beamforming and conventional beamforming strategies. The proposed time-multiplexing technique is shown to reduce the unintended heating of healthy tissue without affecting the treatment temperature or volume. The efficacy of the method is demonstrated for target locations in three different regions of the brain. This approach has the potential to improve microwave-induced localized heating for cancer treatment via hyperthermia or heat-activated chemotherapeutic drug release. © 2010 IEEE.

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