THE MEASUREMENT AND ANALYSIS OF THE DIELECTRIC PROPERTIES OF NORMAL AND TUMOR TISSUES AT UHF AND MICROWAVE FREQUENCIES
Accurate knowledge of the dielectric permittivity and conductivity of biological tissue provides direct information about the physical mechanisms of interaction between tissue and electromagnetic fields. This study was undertaken to (1) develop instrumentation for accurate and convenient measurement of the dielectric properties of biological materials up to 18 GHz, and (2) to measure and interpret the dielectric properties to determine the underlying relaxation mechanisms.^ At frequencies between 10 and 100 MHz, dielectric measurements were made using established bridge techniques. At microwave frequencies, a network analyzer system was developed, whereby impedance measurements were made on a sample-filled coaxial line terminated by a short circuit. The theoretical limits of the transmission line technique and the experimental accuracy of the network analyzer system were carefully assessed. This analysis, confirmed by measurements on standard liquids, showed the expected error in the dielectric measurements was about 2 to 3%.^ Measurements were performed on canine normal and tumor tissues, barnacle muscle fibers, and protein solutions. The data were analyzed to obtain information about (1) the dielectric properties of tissue water at microwave frequencies, (2) the variation in the tissue dielectric properties with water content, and (3) dielectric relaxation processes occurring at UHF frequencies.^ Tissue dielectric properties above 1 GHz should closely resemble those of an electrolyte solution, which are well described by the Debye equation. By fitting data to the Debye equation, the relaxation frequency of water was found to be close, if not identical to that of pure water.^ A strong relationship between the measured dielectric properties and the tissue water content was found to exist, although the correlation deviated significantly from that predicted by dielectric mixture theory. This difference could be resolved by considering the water of hydration "bound" to proteins. Hydration values determined from the microwave conductivity data were similar to those determined by studies on protein solutions at lower frequencies.^ The dielectric data vary slowly with frequency around 1 GHz, indicating additional relaxation phenomena. Several possible mechanisms were considered, the most likely being the relaxation of water bound to proteins. An analysis of the dielectric properties of this bound water fraction was performed, based on the microwave conductivity data from protein solutions and tissues. ^
JONATHAN LLOYD SCHEPPS,
"THE MEASUREMENT AND ANALYSIS OF THE DIELECTRIC PROPERTIES OF NORMAL AND TUMOR TISSUES AT UHF AND MICROWAVE FREQUENCIES"
(January 1, 1981).
Dissertations available from ProQuest.