Dielectric properties of mammalian brain tissue between 1 and 18 GHz

A newly developed frequency domain technique was used to measure the dielectric properties of white matter, grey matter and macerated rabbit brain at 20 and 37 degrees C. An analysis of the data showed that between 1 and 4 GHz there were substantial contributions from processes other than the gamma dispersion. However, above 7.5 GHz it appeared that mainly free water was relaxing although evidence of a small spread of relaxation times was found for the bulk water in the white matter. Mouse and rat brain were also measured but no significant differences were found between the species. The quantity of bound water was estimated but there was no evidence of a difference in the amount between either the tissues or the temperatures.