Passive focused monitoring and non-invasive irradiation of head tissue phantoms at microwave frequencies

In this work, a novel hybrid system able to provide focused microwave radiometric temperature and/or conductivity measurements and hyperthermia treatment via microwave irradiation is experimentally tested. The main module of the system is an ellipsoidal cavity, which provides the appropriate focusing of the electromagnetic energy on the area of interest. The system has been used the past few years in experiments with different configuration setups including phantom, animal and human volunteer measurements yielding promising outcome. New aspects of our research are presented in this paper regarding both radiometry and hyperthermia modules. On one hand, it is examined whether the system is capable of sensing real time progressive local variations of temperature and/or conductivity in customized phantom setups; on the other, the focusing attributes of the system are explored for different positions and types of phantoms used for hyperthermia. The results show that the system is able to detect local concentrated gradual temperature and conductivity variations expressed as an increase of the output radiometric voltage. When contactless focused hyperthermia is performed, the results show significant temperature increase at specific phantom areas. In this case, the effect of a dielectric matching layer placed around the phantoms has been also tested resulting in the enhancement of the energy penetration depth.