The inverse problem of a passive multiband microwave intracranial imaging method.

A novel Microwave Radiometry Imaging System (MiRaIS) has been developed and experimentally tested for feasible brain activation "remote" imaging via contactless measurements. The technique implemented, is focused microwave radiometry with the use of an ellipsoidal conductive wall cavity for focusing and a sensitive radiometric receiver for the detection of the brain conductivity and temperature variation. All system attributes in terms of spatial resolution and detection depth have been theoretically calculated. Phantom experimentation as well as human tests using single frequency receivers, have shown promising outcome concerning the potential clinical value of the proposed system, which seems to be able to pick-up brain activation, possibly caused by cortex conductivity changes. Following this research, a four-frequency radiometric receiver with a broadband antenna operating within the range 1.3-3.1GHz has been recently developed. In the present paper, a method for retrieving the conductivity variation profile detected in the above mentioned frequencies is discussed. The inverse problem solution is in detail addressed and indicative measurements are used for the validation of the solution in question. The latter represents the estimation of the conductivity variation of cortical areas, corresponding to the detection depth and spatial resolution predicted by the forward problem solution.