Advances in Quantitative Microwave Holography

Abstract

Microwave imaging has been used to observe optically obscured targets for over 40 years. Recently, there has been a push towards developing a microwave imaging technology for use in medical diagnostics. Microwave imaging technology has several advantages over current imaging modalities, including use of nonionizing radiation, and compact inexpensive electronics. However, no microwave diagnostic technology exists yet for clinical use. This is due to complications in estimating the complex near-field scattering of the microwave radiation. Recently, advancements in a direct inversion algorithm known as microwave holography have adapted it to operate on near-field measurements. This method, with simulations, has demonstrated the ability to estimate the relative permittivity of the imaged structures. The purpose of this work is to develop quantitative microwave holography for use in tissue imaging. In addition to the previous version of quantitative microwave holography using the Born approximation, a new version of the method using Rytov's approximation is derived, expanding the versatility of the algorithm. Filtering strategies are also developed to enhance the image-reconstruction quality. However, nonphysical permittivity values are still generated. One possible solution is a constrained optimization strategy, which is derived and implemented. Finally, experimental studies demonstrate the ability of quantitative microwave holography to produce reconstructions of several tissue phantoms.