The objective of this study was to develop anatomically correct whole body human models of an adult male (34 years old), an adult female (26 years old) and two children (an 11-year-old girl and a six-year-old boy) for the optimized evaluation of electromagnetic exposure. These four models are referred to as the Virtual Family. They are based on high resolution magnetic resonance (MR) images of healthy volunteers. More than 80 different tissue types were distinguished during the segmentation. To improve the accuracy and the effectiveness of the segmentation, a novel semi-automated tool was used to analyze and segment the data. All tissues and organs were reconstructed as three-dimensional (3D) unstructured triangulated surface objects, yielding high precision images of individual features of the body. This greatly enhances the meshing flexibility and the accuracy with respect to thin tissue layers and small organs in comparison with the traditional voxel-based representation of anatomical models. Conformal computational techniques were also applied. The techniques and tools developed in this study can be used to more effectively develop future models and further improve the accuracy of the models for various applications. For research purposes, the four models are provided for free to the scientific community.

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The Virtual Family—development of surface-based anatomical models of two adults and two children for dosimetric simulations

Noninvasive Deep Brain Stimulation via Temporally Interfering Electric Fields

Wireless deep brain stimulation of well-defined neuronal populations could facilitate the study of intact brain circuits and the treatment of neurological disorders. Here, we demonstrate minimally invasive and remote neural excitation through the activation of the heat-sensitive capsaicin receptor TRPV1 by magnetic nanoparticles. When exposed to alternating magnetic fields, the nanoparticles dissipate heat generated by hysteresis, triggering widespread and reversible firing of TRPV1(+) neurons. Wireless magnetothermal stimulation in the ventral tegmental area of mice evoked excitation in subpopulations of neurons in the targeted brain region and in structures receiving excitatory projections. The nanoparticles persisted in the brain for over a month, allowing for chronic stimulation without the need for implants and connectors.

https://science.sciencemag.org/content/sci/347/6229/1477.full.pdf

Wireless Magnetothermal Deep Brain Stimulation

Lead-DBS v2: Towards a comprehensive pipeline for deep brain stimulation imaging.

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 84 years 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.

/pdf/development-of-a-new-generation-of-high-resolution-kfibrg3n7x.pdf

Development of a new generation of high-resolution anatomical models for medical device evaluation: the Virtual Population 3.0

IT’IS Database for Thermal and Electromagnetic Parameters of Biological Tissues

The dielectric parameters of the tissue simulating liquids to assess the exposure from mobile phones were determined in a previous study considering the tissue distribution of the exposed regions of the head using a planar layered model and the transmission-line method. Currently, the standards for the compliance testing of wireless devices are being extended to more general exposure situations. This paper uses the same methods considering different locations of the body and the respective variations of the tissue structures and dimensions. The analysis of tissue compositions shows a significant increase of 2.2-4.7 dB of the peak spatial specific absorption rate (SAR) in comparison to the values assessed with current standard liquids. This increase is due to standing-wave effects in tissues with low water content. For a certain distance between the antenna and the body (approximately /spl lambda//3 for a /spl lambda//2 dipole), these standing-wave effects dominate the coupling mechanism, leading to a higher average SAR in layered tissue. The observations were validated using finite-difference time-domain simulations of an anatomical high-resolution human model. Nevertheless, a sound conservative exposure assessment applying phantoms filled with homogeneous standardized liquids is possible if a distance and frequency-dependent scaling factor is applied.

The dependence of electromagnetic far-field absorption on body tissue composition in the frequency range from 300 MHz to 6 GHz

Currently, standards for the compliance testing of wireless devices are being extended to cover a wider frequency band and different usage patterns of mobile phones as well as of novel body-worn and handheld devices. As a consequence, not only the head but also strongly varying tissue distributions of the body are exposed to electromagnetic radiation. Several authors have reported changes in the SAR absorption of body tissue due to the presence of a low permittivity fat layer. This paper identifies two different effects which can lead to increased SAR in layered tissue in comparison to the SAR assessed using homogeneous tissue simulating liquid: (1) for larger distances between the tissue and the antenna, standing wave effects occur depending on the frequency and fat layer thickness. (2) In the very close near-field (distances approximately λ/40), reactive E-field components lead to high local absorption in the skin. The latter effect occurs at lower frequencies and depends on the antenna type. Modification of the parameters of the homogeneous liquids cannot compensate for these effects. However, a conservative exposure estimate can be obtained by applying a multiplication factor between 1 and 3 to the values assessed using current experimental dosimetric techniques.

http://iopscience.iop.org/article/10.1088/0031-9155/51/19/014/pdf

Characterization of the electromagnetic near-field absorption in layered biological tissue in the frequency range from 30 MHz to 6000 MHz

This paper investigates the temperature rise in a 1-D layered tissue model, which is irradiated with nonionizing radiation. Of the numerous tissue configurations that correspond to realistic body trunk and limb representations, only those are examined which maximize the averaged specific absorption rate (SAR). The results show that the old IEEE standard on safety was more conservative in terms of temperature rise than the Non-Ionizing Radiation Protection guidelines. They also indicate that the removal of heat exchange from the skin surface can induce a significant temperature rise in it, which is, however, mostly due to imposing the adiabatic conditions themselves, rather than the electromagnetic energy absorption

A. Klingenbock

Papers

IT’IS Database for Thermal and Electromagnetic Parameters of Biological Tissues

The dependence of electromagnetic far-field absorption on body tissue composition in the frequency range from 300 MHz to 6 GHz

Characterization of the electromagnetic near-field absorption in layered biological tissue in the frequency range from 30 MHz to 6000 MHz

Worst Case Temperature Rise in a One-Dimensional Tissue Model Exposed to Radiofrequency Radiation

Energy Absorption in Layered Biological Tissue and its Consequences on the Compliance Testing of Body-Mounted Wireless Devices