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The aim of this study was to characterize the hydration fractions of biological tissues and to model these accurately from mixture equations. Hydration fractions, better known as volume fractions, are based on quantification of tissue hydration and accurate knowledge about the physiological composition of tissue fluids. Data on weight loss percentages for excised muscle and adipose tissue from a previous study were utilized for this purpose. The Bruggeman and Maxwell Garnett equations were then used to characterize the dielectric properties of the tissues in terms of mixtures of dry biological constituents and physiological saline solutions. It is shown that these models are accurate in modelling in vivo and ex vivo tissue in different states of hydration. This is based on precise knowledge of the physiological composition of biological fluids and their corresponding percentage contents. RECEIVED

In this paper, the effects of coagulation and temperature on the dielectric properties of human blood are investigated over the frequency range of 400 MHz -20 GHz using freshly extracted blood samples. The dielectric properties are measured using blood in four different sample collection tubes (bottles): one containing pure whole blood, two containing different anticoagulant agents, and one containing clot activator and serum separator. The collected data indicates that additive agents can have a significant impact on the measured dielectric properties of blood, both immediately after the sample is taken, and over longer time periods. This is an important finding as it suggests that measurements of blood properties conducted on sample repositories, or tissue banks, may not be representative of natural blood properties. Further, the results demonstrate that the dielectric properties of normal blood vary over time due to coagulation. Different clotting rates lead to dielectric properties of female and male blood samples that vary distinctly over time. The results also show that the relative permittivity of the anti-coagulated blood decreases with increasing temperature, up to the cross-over point around 10 GHz where the trend reverses.

Dielectric properties of biological tissue are important in view of emerging medical applications. We report on dielectric properties of ex vivo porcine fat and muscle and the effect of 10% formalin and Thiel Embalming solution (TES) as preservatives on the dielectric properties. This study is important as understanding the effect of such preservative solutions would allow for measurements to be done even days after excision. In this study, dielectric measurements were conducted on fat and muscle samples before and after preservation. Measurements were conducted between 0.5 and 20 GHz. All results obtained were fitted to a Debye model and uncertainty limits analyzed carefully. We also present the percentage difference in dielectric properties of fresh tissue and preserved tissue. The results show that changes in the dielectric properties due to tissue preservation depend on the type of tissue studied, the technique used and the test frequency. In fact, an increase in the real part of permittivity ϵ′ of fat was observed compared with a decrease in that measured for muscle, when both preserved in TES. Moreover, the imaginary part of permittivity ϵ″ of muscle preserved in TES increases at low frequency but then decreases at frequencies higher than 10.8 GHz. The changes in the dielectric properties of fat and muscle when preserved in 10% formalin reach a constant value above 5 GHz.

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