Measurement of canine cerebral oedema using time domain reflectometry

The complex dielectric constant of canine cerebral white matter correlates with its water content. Time domain reflectometry was used to measure the real dielectric constant and loss factor of 27 oedematous brain samples at frequencies of 100, 250, 500, 750, and 1,000 MHz. The real dielectric constant increased with water content at each frequency. Correlation was least for 100 MHz (R = 0.76) and between 0.87 and 0.89 for the other frequencies. The loss factor decreased with frequency with a correlation coefficient from 0.81-0.84. The in vitro results indicate that use of time domain reflectometry can predict oedema at a sensitivity of approximately 1-2% change of tissue water content.