Dielectric Behaviour of Water in Biological Material with Particular Reference to Brain Tissue,
KING'S COLL LONDON (ENGLAND) DEPT OF PHYSICS
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The absorption of microwave energy by biological material at frequencies in excess of 1 GHz is due mainly to the water content. Knowledge of the dielectric properties of water in biological material is therefore a necessary prerequisite for the calculation of energy deposition. However, the water of hydration immediately adjacent to biological macromolecules is subject to chemical forces different from those in bulk water and must in consequence exhibit different dielectric properties. The nature and proportion of this water vary considerably fro one tissue to another and therefore need to be evaluated for each specific case. For adult-rabbit brain material, dielectric measurements show that the water of hydration constitutes about 20 of the total while the remainder has dielectric properties similar to those of pure water. With brain tissue from recently born rabbits, the proportion of water of hydration is indistinguishable from zero.