Quantitative microwave holography is a recent imaging methodology that shows promise in medical diagnostics. It is a real-time direct inversion algorithm that reconstructs the complex permittivity from S-parameter measurements on an acquisition surface outside of the imaged object. It is recognized that this imaging method suffers from limitations in tissue imaging due to a forward model which linearizes a highly nonlinear scattering problem. It is therefore important to study its limitations when reconstruction is aided by certain pre-and post-processing filters which are known to improve the image quality. The impact of filtering on the quantitative result is particularly important. In this work, the reconstruction equations of quantitative microwave holography are derived from first principles. The implementation of two linearizations strategies, Born's approximation and Rytov's approximation, is explained in detail in the case of a scattering model formulated in terms of S-parameters. Furthermore, real-space and Fourier-space filters are developed to achieve the best performance for the given linearized model of scattering. Simulated and experimental results demonstrate the limitations of the method and the necessity of filtering. The two approximations are also compared in experimental tissue reconstructions.

Two real-time reconstruction algorithms, i.e., quantitative microwave holography and scattered-power mapping, have been shown to be successful in the imaging of compressed tissue of relatively small thicknesses such as 1 and 2 cm. In both cases, planar data acquisition of frequency-swept transmission coefficients has been employed. Despite the fact that these algorithms are based on a linear forward model of scattering, they have been capable of providing quantitative estimates of the tissue permittivity due to the experimentally derived kernel of the scattering integral. Here, we demonstrate similar performance with a thicker (approximately 5 cm) compressed-breast phantom. This thickness is greater than or comparable to the median thickness employed in mammography, depending on the view (craniocaudal or mediolateral oblique). The two methods are described in a common mathematical framework for the first time. The importance of the system calibration and the choice of a host medium are discussed through experiments. A new method for focusing onto suspect regions is demonstrated. The limitations of real-time imaging are highlighted, along with an outlook to improve the image resolution and suppressing artifacts without sacrificing the reconstruction speed. Future work aims at validation with high complexity, realistic compressed-breast phantoms.

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A picosecond pulse generator is designed to generate a stable differentiated Gaussian (monocycle) waveform. The design approach to increasing the center frequency, bandwidth and peak-to-peak voltage, as compared to previously reported ultra-wideband (UWB) generators, is described. The 280 ps wide pulse achieves a 1:10 fractional bandwidth (FBW) ratio extending from 500 MHz to beyond 5 GHz at the −10 dB level. A measurement procedure is proposed for evaluating the jitter and noise performance of UWB pulse generators, and it is applied to the fabricated prototype. The procedure exploits jitter and noise definitions from high-speed digital electronics, which are adapted here for the jitter and noise evaluation of UWB pulse generators at microwave frequencies. The problems in obtaining the absolute and relative jitter of a UWB generator are discussed along with proposed solutions. The impact of the input trigger on the pulse stability is demonstrated through the dramatic improvement achieved by the integration of a jitter cleaner in the generator's circuit.