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(Database last updated on Sep 1, 2019)

ID Number 1551
Study Type Engineering & Physics
Model Dielectrometry, Spectroscopy & Tissue Parameters (catch all).
Details

Dielectrometry, Spectroscopy & Tissue Parameters (catch all). In a series of studies by the Gabriel lab, tissue dielectric properties were measured in animal models as a function of age in the frequency range of 300 kHz to 300 MHz. The goal of the analysis was to 1) determine accurate dielectric properties of living tissue and 2) gain insight into the systematic dielectric property variation and age related changes in the composition and structure of the tissue. Such is essential for an understanding of the interaction between electromagnetic radiation and the human body (i.e., correct assessment of human exposure). Most available information on dielectric properties of tissue has been derived from measurements on fully-grown animals. A few studies report systematic changes in the mouse and rabbit brain as a function of age (Thurai et al 1984 and Thurai et al 1985). Peyman et al (2001) carried out dielectric analysis of tissue from newborn to fully grown rats in the frequency range 130MHz-10GHz (including mobile phone frequencies) and confirmed Thurai's findings of an age-related variation in dielectric properties of tissues, suggesting that in humans there may also be an age-related factor relevant to the true assessment of exposure of children (IEGMP, 2000). The effect was most apparent for brain, skull and skin tissues and less noticeable for abdominal tissues. The authors suggest the change with age is due to changes in water content and organic composition. Subsequent papers also report permittivity and conductivity values lower in older tissues, but that such variations affect whole body SAR by less than 5%. In a paper on measurement uncertainty (based upon either numerical or experimental assessments), the authors conclude the major sources of uncertainty involve random error, instrumentation and methodology, calibration drift, and movement of the test cable. They also suggest the SD is a good measure of the uncertainty in measuring dielectric properties of most tissues. A similar study reported on calculating the permittivity of NaCl solutions of different concentrations and temperature. Additional studies ongoing to confirm previously published permittivity and conductivity values as well as to look at differences due to age and age-related factors. Authors' abstract #4968): Haines et al. 2010: The spatial distribution of electromagnetic fields within the human body can be tailored using external dielectric materials. Here, we introduce a new material with high dielectric constant, and also low background MRI signal. The material is based upon metal titanates, which can be made into a geometrically-formable suspension in de-ionized water. The material properties of the suspension are characterized from 100 to 400 MHz. Results obtained at 7 T show a significant increase in image intensity in areas such as the temporal lobe and base of the brain with the new material placed around the head, and improved performance compared to purely water-based gels. AUTHORS' ABSTRACT: Sasaki et al. 2014 (IEEE #5700): Numerous studies have reported the measurements of the dielectric properties of the skin. Clarifying the manner in which the human body interacts with electromagnetic waves is essential for medical research and development, as well as for the safety assessment of electromagnetic wave exposure. The skin comprises several layers: the epidermis, the dermis, and the subcutaneous fat. Each of these skin layers has a different constitution; however, the previous measurements of their dielectric properties were typically conducted on tissue which included all three layers of the skin. This study presents novel dielectric property data for the epidermis and dermis with in vitro measurement at frequencies ranging from 0.5 GHz to 110 GHz. Measured data was compared with literature values; in particular, the findings were compared with Gabriel's widely used data on skin dielectric properties. The experimental results agreed with the data reported by Gabriel for the dermis of up to 20 GHz, which is the upper limit of the range of frequencies at which Gabriel reported measurements. For frequencies of 20-100 GHz, the experimental results indicated larger values than those extrapolated from Gabriel's data using parametric expansion. For frequencies over 20 GHz, the dielectric properties provided by the parametric model tend toward the experimental results for the epidermis with increasing frequency. AUTHOR'S ABSTRACT: Peyman 2011 (IEEE #6034): This paper reviews and summarises the state of knowledge on dielectric properties of tissues; in particular those obtained as a function of age. It also examines the impact of variation in dielectric data on the outcome of recent dosimetric studies assessing the exposure of children to electromagnetic fields. AUTHORS' ABSTRACT: Mohammed et al. 2016 (IEEE #6499): Dielectric properties of dead Greyhound female dogs' brain tissues at different ages were measured at room temperature across the frequency range of 0.3-3 GHz. Measurements were made on excised tissues, in vitro in the laboratory, to carry out dielectric tests on sample tissues. Each dataset for a brain tissue was parametrized using the Cole-Cole expression, and the relevant Cole-Cole parameters for four tissue types are provided. A comparison was made with the database available in literature for other animals and human brain tissue. Results of two types of tissues (white matter and skull) showed systematic variation in dielectric properties as a function of animal age, whereas no significant change related to age was noticed for other tissues. Results provide critical information regarding dielectric properties of animal tissues for a realistic animal head model that can be used to verify the validity and reliability of a microwave head scanner for animals prior to testing on live animals. AUTHORS' ABSTRACT: Mohammed et al. 2017 (IEEE #6866): Developing microwave systems for biomedical applications requires accurate dielectric properties of biological tissues for reliable modeling before prototyping and subject testing. Dielectric properties of tissues decrease with age due to the change in their water content, but there are no detailed age-dependent data, especially for young tissue-like newborns, in the literature. In this article, an age-dependent formula to predict the dielectric properties of biological tissues was derived. In the proposed method, the variation of water concentration in each type of tissue as a function of age was used to calculate its relative permittivity and conductivity. The derived formula shows that the concentration of water in each tissue type can be modeled as a negative exponential function of age. The dielectric properties of each tissue type can then be calculated as a function of the dielectric properties of water and dielectric properties of the organ forming the tissue and its water concentration. The derived formula was used to generate the dielectric properties of several types of human tissues at different ages using the dielectric properties of a human adult. Moreover, the formula was validated on pig tissues of different ages. A close agreement was achieved between the calculated and measured data with a maximum difference of only 2%. AUTHORS' ABSTRACT: Peyman and Gabriel 2010 (IEEE #6867): We have applied the Cole-Cole expression to the dielectric properties of tissues in the frequency range 0.4-10 GHz. The data underpinning the model relate to pig tissue as a function of age. Altogether, we provide the Cole-Cole parameters for 14 tissue types at three developmental stages.

Findings
Status Completed With Publication
Principal Investigator
Funding Agency DOH, UK, MMF, MTHR (NRPB), UK
Country UNITED STATES
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