Enhancement of the Focusing Properties of a Passive Radiometry Imaging System: A Theoretical Electromagnetic Study
ABSTRACT A non-invasive imaging system, consisting of an ellipsoidal conductive cavity and radiometric receivers, designed and constructed in our laboratory the past few years is restudied. A means for further improvement of the ellipsoidal reflector's focusing properties thus its performance is herein investigated. The main differentiating factor of our new approach is that the receiving antenna is more realistically modelled and also covered by two layers of different dielectric properties. The present paper provides details on the electromagnetic theoretical analysis of the problem and presents numerical results for the electric field distribution inside the head model, using two main operating frequencies, namely 0.5GHz and 1.5GHz for four distinct cases. The focusing optimization of the system in terms of spatial accuracy and penetration depth is assessed while the method and results are also separately validated.
- [show abstract] [hide abstract]
ABSTRACT: Focused microwave radiometry, aiming mainly in clinical applications at measuring temperature distributions inside the human body, may provide the capability of detecting electrical conductivity variations at microwave frequencies of excitable cell clusters, such as in the case of brain tissues. A novel microwave radiometric system, including an ellipsoidal conductive wall cavity, which provides the required beamforming and focusing, is developed for the imaging of biological tissues via contactless measurements. The measurement is realized by placing the human head in the region of the first focus and collecting the radiation converged at the second by an almost isotropic dipole antenna connected to a sensitive radiometer operating at 3.5 GHz. In order to compute the focusing properties of the ellipsoidal reflector, an accurate electromagnetic numerical analysis is developed using a semianalytical method. The experimental part of this study focuses on measurements of activation of the primary somatosensory (SI) brain area, elicited during the application of the cold pressor test, a standard experimental condition inducing pain. Analysis of the measured data from 16 healthy subjects suggests that this methodology may be able to pick up activation of the SI during the pain conditions as compared with the nonpainful control conditions. Future research is needed in order to elucidate all the interacting factors involved in the interpretation of the presented results. Finally, potential limitations to the generalization of our results and strategies to improve the system's response are discussed.IEEE Transactions on Microwave Theory and Techniques 09/2004; · 2.23 Impact Factor