A novel method of studying total body water content using a resonant cavity: experiments and numerical simulation

A novel electromagnetic method of obtaining total body water is proposed, in which the water content is obtained from the dielectric properties as measured by a resonant perturbation technique. A screened room acts as a radio-frequency cavity, in our case resonating at 59 MHz, a frequency at which both real and imaginary parts of the complex permittivity of tissues are correlated to their moisture content. The presence of a human subject in the room leads to both a negative shift in the room's resonant frequency and a reduction in its Q-factor. We simulated the room and the body using the transmission line matrix (TLM) method, a computational electromagnetic code which models the problem in the time domain. Experiment and numerical model showed good agreement for two orientations of the subject. The sensitivity of the technique was investigated by measuring the response before and after the subject drank a small quantity of water, less than 2% of body mass. The resulting change in the resonant frequency was significant, and was also predicted by the numerical model. The proposed technique for studying body composition is simple, non-invasive and employs non-ionizing radio waves at low power.