Frequency dependence of phase shift in edema: a theoretical study with magnetic induction.

A spectroscopic distribution of induction phase shift as a function of relative volume of edema in the brain, lung and muscle was produced from available tissue data and a simple mathematical model of electromagnetic induction in tissue. The results show that the phase shift is sensitive to the relative volume of edema at frequencies higher than approximately 10 MHz. The behaviors of brain, lung and muscle tissues are substantially different from each other. Increasing the volume of tissue has the effect of lowering the frequency at which the phase shift becomes sensitive to the volume of edema. The results indicate that induction measurement of the phase shift has the potential for becoming a robust means for non-contact detection of edema in brain, lung and muscle tissues.