The dielectric properties of tissues

The dielectric properties of tumor tissue (VX2 carcinoma) and rat femurs from 1 kHz to 13 MHz and bovine cortical bone from 100 Hz to 1 MHz are reported. This was the first study of the dielectric properties of the VX2 carcinoma, an implanted tumor used in research. It was also the first study of the anisotropy of the dielectric properties of cortical bone that was not first frozen or dried. The dielectric properties of bone are also reported as a function of bathing solution and time after the animal\u27s death. The dielectric properties were measured using a computer-controlled impedance analyzer. Lumped-parameter models were used to correct the data. The dielectric data are in good agreement with those from previous studies. The low-frequency conductivity of tumor tissue (VX2 carcinoma) is higher than that of normal liver tissue and the low-frequency permittivity of tumor tissue is lower than that of normal liver tissue. This was probably due to increases in the necrotic volume and extracellular conductivity. The conductivity and permittivity of VX2 carcinoma above 1 MHz were larger than those of the normal liver tissue. This reflects the higher water content of the VX2 carcinoma vs. normal liver tissue (81 vs. 68%). The dielectric properties of bone are anisotropic. The anisotropy in the low frequency conductivity arises largely from the geometry of the larger channels through bone. The effective path length for current through bone is several times the thickness of the sample (4-6x for radial samples and 3x for longitudinal samples). This is suggested by both electrical conductivity and ionic diffusion measurements. The power law dependence of the dielectric properties of bone are consistent with diffusion processes that may occur along the interfaces of bone. Primary and secondary Haversian bone do not exhibit greatly different dielectric relaxations. A study of the accuracy of the impedance analyzer (Hewlett Packard 4192A) used for these measurements indicates that the accuracy of the instrument in the average measurement mode is better than that expected from the manufacturer\u27s specifications