Nonactive antenna compensation for fixed-array microwave imaging: Part II - Imaging results

Model-based imaging techniques utilizing microwave signal illumination rely heavily on the ability to accurately represent the wave propagation with a suitable numerical model. To date, the highest quality images from our pro totype system have been achieved utilizing a single transmitter/single rece iver measurement system where both antennas are manually repositioned to fa cilitate multiple illuminations of the imaging region, thus requiring long data acquisition times. In an effort to develop a system that can acquire d ata in a real time manner, a 32-channel network has been fabricated with al l ports capable of being electronically selected for either transmit or rec eive mode. The presence of a complete array of antenna elements at data col lection time perturbs the field distributions being measured, which can sub sequently degrade the image reconstruction due to increased data-model mism atch. Incorporating the nonactive antenna-compensation model from Part I of this paper into our hybrid element near field image reconstruction algorit hm is shown to restore image quality when fixed antenna-array data acquisit ion is used. Improvements are most dramatic for inclusions located in near proximity to the antenna array itself, although cases of improvement in the recovery of centered heterogeneities are also illustrated. Increases in th e frequency of illumination are found to warrant an increased need for nona ctive antenna compensation. Quantitative measures of recovered inclusion sh ape and position reveal a systematic improvement in image reconstruction qu ality when the nonactive antenna-compensation model is employed. Improvemen ts in electrical property value recovery of localized heterogeneities are a lso observed. Image reconstructions in freshly excised breast tissue illust rate the applicability of the approach when used with our two-dimensional m icrowave imaging system.