AN ACTIVE MICROWAVE IMAGING-SYSTEM FOR RECONSTRUCTION OF 2-D ELECTRICAL PROPERTY DISTRIBUTIONS

The goal of this work is to develop a microwave-based imaging system f or hyperthermia treatment monitoring and assessment, Toward this end, a four transmit channel and four receive channel hardware device and c oncomitant image reconstruction algorithm have been realized, The hard ware is designed to measure electric fields (i,e,, amplitude and phase ) at various locations in a phantom tank with and without the presence of various heterogeneities using standard heterodyning principles, Pa rticular attention has been paid to designing a receiver with better t han 115 dB of linear dynamic range which is necessary for imaging biol ogical tissue which often has very high conductivity, especially for t issues with high water content, A calibration procedure has been devel oped to compensate for signal loss due to three-dimensional radiation in the measured data, since the reconstruction process is only two-dim ensional at the present time, Results are shown which demonstrate the stability and accuracy of the measurement system, the extent to which the forward computational model agrees with the measured field distrib ution when the electrical properties are known, and image reconstructi ons of electrically unknown targets of varying diameter, In the latter case, images of both the reactive and resistive component of the elec trical property distribution have been recoverable, Quantitative infor mation on object location, size, and electrical properties results whe n the target is approximately one-half wavelength in size, Images of s maller objects lack the same level of quantitative information, but re main qualitatively correct.