Spectral imaging for complex clinical breast structures

We have imaged several breast cancer patients at multiple intervals during her neoadjuvant chemotherapy to assess the capability of microwave tomography as a therapy monitoring device. For the patient discussed here, we illustrate the spectral behavior of our tomographic approach in the context of a complex imaging situation with a large scattering tumor along with less frequently encountered structures such as thickened skin in the tumor vicinity. These results demonstrate that the microwave technology is sensitive to dielectric property perturbations associated with treatment-induced physiological changes. In addition, it also confirms previously hypothesized notions that the lower frequency images provide lower resolution but useful counterparts to the enhanced resolution, higher frequency images. This spectral data can be instructive for both UWB radar approaches and multi-frequency or time-domain tomographic approaches. The chemotherapy patients are unique with respect to breast cancer imaging cases in that they usually involve electrically large tumors along with other non-standard features such as extra-thick skin (easily as thick as 1 cm). These large, high contrast features are quite challenging for all types of microwave imaging (radar and tomography-based) and form an important benchmark for testing imaging techniques. For our efforts, we have developed a log transformation as part of the image reconstruction process which we have shown to have superior convergence behavior (i.e. no local minima) while retaining phase wrapping information that is generally lost when only considering more classical minimization criteria. As we will show, this technique requires broadband scattering data which we provide from measurements using our ultrawideband monopole antennas.