Microwave Sensing of Brain Water – a Simulation and Experimental Study Using Human Brain Models

This paper introduces a microwave-based approach that aims to non-invasively measure water, particularly cerebrospinal fluid (CSF) dynamics, in the human brain. The microwave measurement technique is well-known in industrial applications. More recently microwave techniques have awakened interest also in biomedical applications. This is the first time it is suggested to be utilized in measurements of brain water, particularly of CSF. Two different head phantoms were built in order to validate the sensitivity of the technique to sense dynamic variations of CSF and water volume inside a human skull. These were comprised of multilayered head phantom, including a real human skull, mimicking the electromagnetic properties of a human head. In addition, the variation of the CSF is evaluated with electromagnetic simulations using a planar layer model and a hemispherical layer model. Moreover, propagation and power flow inside the head model is evaluated using 2D power flow presentations. Reflection sensor principle was selected due to its simplicity and ability to measure relatively thick samples. Importantly, reflection sensor requires only one-port measurement making it very feasible for in vivo brain monitoring. In addition, the measurement setup does not require attachment of the sensor to the head, thus the measurement can be realized also without touching the head. Our experimental study as well as simulation results demonstrated the possibility to non-invasively sense, by microwaves, small dynamic variations in CSF volume in the brain, in particularly in the subarachnoid space.