Dielectric Properties of Fluid-Saturated Bone - The Effect of Variation in Conductivity of Immersion Fluid

The dielectric permittivity and electrical conductivity of fluid-saturated rat femoral bone were determined as a function of the conductivity of the immersion fluid over a frequency range of 10-100 Hz to 8 MHz. The specimens were equilibrated in various solutions of Hank's balanced salt solution modified to contain various sodium chloride concentrations, with conductivities ranging from 0.13 to 3.55 s/m. The results of these measurements show that the dc conductivity of the tissue is about 1 percent of the conductivity of the immersion solution. Similar conductivity values were predicted from a simple model of the tissue, in which it is assumed that the only significant contribution to the conductivity arises from the capillaries that pass through the tissue. The permittivity of the tissue exhibits a dispersion whose mean relaxation frequency is proportional to the conductivity of the immersion fluid. The permittivity ranges from about 1000 at low frequencies to 10-20 in the high frequency limit. The dielectric data could be fitted to a Cole-Cole function having a distribution parameter of about 0.5-0.6, which suggests the presence of a diffusion-controlled ionic polarization mechanism, although other relaxation processes could also be present.