Document Type

Article

Publication Date

3-22-2016

Comments

This article has been peer reviewed. It is the authors' final version prior to publication in Biomedical Physics & Engineering Express

Volume 2, Issue 2, March 2016, Pages 1-8.

The published version is available at DOI: 10.1088/2057-1976/2/2/025005. Copyright © IPO Publishing

Abstract

Brown adipose tissue (BAT) plays an important role in whole body metabolism and with appropriate stimulus could potentially mediate weight gain and insulin sensitivity. Although imaging techniques are available to detect subsurface BAT, there are currently no viable methods for continuous acquisition of BAT energy expenditure. Microwave (MW) radiometry is an emerging technology that allows the quantification of tissue temperature variations at depths of several centimeters. Such temperature differentials may be correlated with variations in metabolic rate, thus providing a quantitative approach to monitor BAT metabolism. In order to optimize MW radiometry, numerical and experimental phantoms with accurate dielectric properties are required to develop and calibrate radiometric sensors. Thus, we present for the first time, the characterization of relative permittivity and electrical conductivity of brown (BAT) and white (WAT) adipose tissues in rats across the MW range 0.5-10GHz. Measurements were carried out in situ and post mortem in six female rats of approximately 200g. A Cole-Cole model was used to fit the experimental data into a parametric model that describes the variation of dielectric properties as a function of frequency. Measurements confirm that the dielectric properties of BAT (εr = 14.0-19.4, σ = 0.3-3.3S/m) are significantly higher than those of WAT (εr = 9.1-11.9, σ = 0.1-1.9S/m), in accordance with the higher water content of BAT.

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