The UHF and microwave dielectric properties of normal and tumour tissues: variation in dielectric properties with tissue water content.

Dielectric measurements have been made on various soft tumour and normal tissues between 0.01 and 17 GHz at body temperature. At microwave frequencies above 1-5 GHz, the tissue dielectric properties can be fitted to Debye equations with the same relaxation frequency (25 GHz) as found for pure water at 37 degrees C. The tissue dielectric properties correlate well with their water contents. The conductivity of the tissue at 0.1 GHz (which is close to that of the cytoplasm itself) increases with the volume fraction of water in the tissue, in a manner consistent with that previously observed in proteins suspended in electrolyte solution. The contribution of the tissue water to the tissue dielectric permittivity at frequencies below 1 GHz is fitted by a function of water content different to that describing the conductivity data. Empirical equations that may be used to predict the dielectric properties of other soft tissues within this wide frequency range are suggested.