Intracorporal Heat Load Evoked by Electromagnetic Fields

For a realistic assessment of the thermal effects of electromagnetic fields applied accidentally or intentionally in the course of diagnostic or therapeutic procedures it is necessary to take into account the external conditions influencing heat loss, the nonhomogeneities of the body, and the regnlatory processes such as sweat production and blood flow distribution and redistribution, which have an essential impact on the temperature gradient between core and shell of the body and the envirOlUllent and thereby on the formation of intracorporal temperature fields. An intricate problem is the determination of heat transfer between the blood vessels and the tissue. Fonner approaches avoided the explicit representation of the three-dimensional vascular architecture and tried to compute the heat transfer between tissue and bloml using substitutional processes, so called "non-vascular models", either in the form of distributed heat sources and sinks ("bio-heat" approach, Pennes, [1]) or by using an enhanced thermal conductivity index (K.a-approach, Weinbaum & Jiji, [2]). A one-dimensional model which comprised the local temperature in the arteries, in the veins and in the tissue in the direction of blood flow using three separate heat balance equations was proposed by Wissler [3]. The necessary heat transfer coefficients were computed by Baish et al. [4] in the case of closely coupled countercurrent vessels. Both approaches taken together represent the first approach based on tluee separate energy balances for the local temperatures of tissue, arteries and veins. Charny and Levin [5] presented a similar and complete one-dimensional "three equation model", which later on was also used to evaluate the K....approach.