A noise-robust and accuracy-enhanced microwave imaging algorithm is presented for microwave ablation monitoring of cancer treatment. The ablation impact of dielectric change can be assessed by microwave inverse scattering analysis, where the dimension and dielectric drop of the ablation zone enable safe ablation monitoring. We focus on the distorted Born iterative method (DBIM), which is applicable to highly heterogeneous and contrasted dielectric profiles. As the reconstruction accuracy and convergence speed of DBIM depend largely on the initial estimate of the dielectric profile or noise level, this study exploits a prior estimate of the DBIM for the pre-ablation state to accelerate the convergence speed and introduces the matched-filter-based noise reduction scheme in the DBIM framework. The two-dimensional finite-difference time-domain numerical test with realistic breast phantoms shows that our method significantly enhances the reconstruction accuracy with a lower computational cost.

Near range microwave imaging systems have broad application prospects in the field of concealed weapon detection, biomedical imaging, nondestructive testing, etc. In this paper, the technique of optimized sparse antenna array is applied to near range microwave imaging, which can greatly reduce the complexity of imaging systems. In detail, the paper establishes three-dimensional sparse array imaging geometry and corresponding echo model, where the imaging geometry is formed by arranging optimized sparse antenna array in elevation, scanning in azimuth and transmitting broadband signals in range direction; and by analyzing the characteristics of near range imaging, that is, the maximum interval of transmitting and receiving elements is limited by the range from imaging system to targets, we propose the idea of piecewise sparse line array; secondly, by analyzing the convolution principle, we develop a method of arranging piecewise sparse array which can generate the same distribution of equivalent phase centers as filled antenna array; then, the paper deduces corresponding imaging algorithm; finally, the imaging geometry and corresponding algorithm proposed in this paper are investigated and verified via numerical simulations and near range imaging experiments.

A microwave mammography setup for clinical testing was developed and used to successfully carry out an initial clinical test. The equipment is based on multistatic ultra wideband (UWB) radar, which features a multistatic microwave imaging via space time (MS-MIST) algorithm for high resolution and a conformal array with an aspirator for fixing the breast in place. In this paper, an outline of the equipment, a numerical simulation, and clinical test results are presented.

An experimental study concerning Ultra Wideband (UWB) Microwave Radar for breast cancer detection is described. A simple phantom, consisting of a cylindrical plastic container with a low dielectric constant material imitating fatty tissues and a high dielectric constant object emulating tumour, is scanned with a tapered slot antenna operating between 3.1 to 10.6 GHz. A successful detection of a target is accomplished by a visual inspection of a two-dimensional image of the scanned phantom

An electromagnetic (EM) inverse scattering problem that involves the reconstruction of microwave images for dielectric objects is considered in this paper. This ill-posed and nonlinear problem is treated as a global optimization problem, and is solved by the application of micro-genetic algorithm (m-GA). The reconstructed results obtained by m-GA have shown that it is an effective technique for microwave imaging and satisfactory performance is achieved when compared with the conventional genetic algorithms.

In this paper, we propose a passive imaging system for noise-source identification using time-domain waveform sampling. The fundamental concepts are based on optics theory. A waveform of a diffracted field over an entrance pupil is obtained by a digitizing oscilloscope. The phase distributions over the entrance pupil for each frequency are calculated by using Fourier transform of the acquired waveforms. Thus, an image on the focal plane is reconstructed by using inverse Fresnel transform. The most significant advantage of the proposed method is that an image for each frequency can be obtained separately. We confirmed that the proposed method can be used for practical noise-source identification, by experimentally obtaining images for an emission from personal computers.

A Fourier-optics based imaging system for electromagnetic interference (EMI) sources is presented. It is necessary to decrease undesired emissions in order to meet EMI requirements. To investigate this problem, a visualization of electromagnetic (EM) emitting fields is very useful. In this paper, we propose a passive imaging system of EM emitting fields based on Fourier optics. Amplitude and phase values of diffracted fields on an entrance pupil are acquired by using a six-port interferometer. The measured EM fields are then processed on a computer, and an image is retrieved using an inverse Fresnel transform. Experiments are presented, which demonstrate the potential of the proposed method. The proposed system is useful not only in the field of electromagnetic compatibility (EMC), but also for scientific elucidation to discuss the optics and microwave theory of the same viewpoint.

A novel method for image reconstruction of a microwave hologram synthesized from one-dimensional data is proposed. In the data acquisition, an emitting antenna is shifted along a line. At every position of the emitting antenna, the amplitude and phase of diffraction fields are measured with a detecting antenna along a line perpendicular to the shifted direction. An equivalent two-dimensional diffraction field is synthesized from the one-dimensional data sets. The conventional reconstruction method applied to the one-dimensional configuration was the Fresnel approximation method. In this paper, an equivalent diffraction is introduced in order to obtain better images than the Fresnel approximation. An experiment made at 10 GHz shows the usefulness of the proposed method.

Retrieving the unknown parameters of scattering objects from measured field data is the subject of microwave imaging. This is naturally and usually posed as an optimization problem. In this paper, micro genetic algorithm coupled with deterministic method is applied to the shape reconstruction of perfectly conducting cylinders. The combined approach, with a very small population like the micro genetic algorithm, performs much better than the conventional large population genetic algorithms (GA's) in reaching the optimal region. In addition, we propose a criterion for switching the micro GA to the deterministic optimizer. The micro GA is utilized to effectively locate the vicinity of the global optimum, while the deterministic optimizer is employed to efficiently reach the optimum after inside this region. Therefore, the combined approach converges to the optimum much faster than the micro GA. The proposed approach is first tested by a function optimization problem, then applied to reconstruct perfectly conducting cylinders from both synthetic data and real data. Impressive and satisfactory results are obtained for both cases, which demonstrate the validity and effectiveness of the proposed approach.

This paper deals with two different quantitative inversion algorithms for reconstructing the complex permittivity profile of bounded inhomogeneous objects from measured scattered field data. The first algorithm involves an imaging method with single frequency excitation and multiincidence illumination and the second algorithm involves a method with synthetic pulse (multifrequency mode) excitation for objects surrounded by freespace or buried in stratified half-space media. Transmission or reflection imaging protocols are considered depending on aimed applications: microwave imaging in free-space from far-field data for target identification, microwave imaging from near-field data for nondestructive testing (NDT), microwave tomography of buried objects for mine detection and localization, civil engineering and geophysical applications. And Edge-Preserving regularization scheme leading to a significant enhancement in the image reconstructions is also proposed. The methods are illustrated with synthetic and experimental data.

This paper describes the imaging method for a human forearm in the microwave transmission CT at 3GHz. To improve the spatial resolution, the correction method of the diffraction effects is adopted and the high directivity antennas are used. A cross-sectional image of the human forearm is obtained in vivo.