The present invention describes a system and methods to monitor hydrocephalus and cerebral edema in noninvasive or minimum invasive ways. The system monitors the changes of electromagnetic wave propagations in brain tissues changed by the tissue pathological statues. One of the tissue properties monitored is the tissue permittivity that determines the wave propagation velocity. By avoiding the tissue conductivity that has variations due to many different reasons including non-pathological factors, this approach has advantages of acquiring reliable pathological information of brain tissue and being independent to electrode properties and skin conditions. Several parameters are defined to quantitatively measure and assess hydrocephalus and cerebral edema: relative phase shift (RPS), travel-time difference (TTD), and change of relative wave velocity. The parameters are defined and normalized in distance and time for measuring relative changes for the monitoring applications. The method includes non-invasive and minimum invasive approaches. Amplitude modulated wave and coded waves are used to reduce interference and effectively detect small changes of tissue properties in preferred frequency ranges.
