Abstract: The present invention relates to a method and apparatus for non-invasive monitoring of brain density variations. At least two ultrasonic pulses having different frequencies are provided into the brain for transmission therethrough. The reflected ultrasonic pulses are then sensed and the sensed signal data are then processed for determining at least two phase differences between the phases of the at least two reflected ultrasonic pulses and the phases of the at least two provided ultrasonic pulses. A phase of at least a beat frequency is determined in dependence upon the at least two phase differences. Data indicative of a brain density variation are determined based on the at least two phase differences and the at least a beat frequency.