Abstract-A technique based on the Green's function theory is used in the present research in order to study theoretically the focusing properties of a constructed 3D non-invasive microwave imaging system, consisting of an ellipsoidal conductive cavity and a radiometric receiver. A double layered spherical human head model is placed on one focal point of the elliptical reflector, while the receiving antenna is placed on the other focus. Making use of the reciprocity theorem, the equivalent problem of the coupling between an elementary dipole and the double layered lossy dielectric human spherical model is solved. Numerical results concerning the electric field distribution inside the head model and in the rest of the cavity, at two operating frequencies (1.5 GHz and 3.5 GHz), are presented and compared to the results of an electromagnetic simulator. Finally, phantom experimental results validate the proof of concept and determine the temperature and spatial attributes of the system.

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We have designed and developed an automatic switching mechanism that deactivates and activates a reception coil during the MR experiment according to the phase it is at. The mechanism uses a feedback loop in which a comparator defines whether the current reception signal derives from the RF excitation pulses or the MR signal and then triggers an analog switch at the back-end of the coil accordingly. We applied the mechanism on a custom-made four channel phased array probe and tested its functionality by transmitting RF pulses to the probe of similar length and power to those used in actual MRI systems. The results presented in this paper demonstrate the robustness of the design and its switching accuracy.