Nadine Joachimowicz

Diffraction tomography: contribution to the analysis of some applications in microwaves and ultrasonics

After a brief presentation of the principles of diffraction tomography, the authors focus on the applications they have investigated in the biomedical and non-destructive testing domains. Typical numerical and experimental results are presented and in their comments they state what they think are the current limitations of this approach and the possible opportunities for future work with this imaging technique.

Convergence and stability assessment of Newton-Kantorovich reconstruction algorithms for microwave tomography

For newly developed iterative Newton-Kantorovitch reconstruction techniques, the quality of the final image depends on both experimental and model noise. Experimental noise is inherent to any experimental acquisition scheme, while model noise refers to the accuracy of the numerical model, used in the reconstruction process, to reproduce the experimental setup. This paper provides a systematic assessment of the major sources of experimental and model noise on the quality of the final image. This assessment is conducted from experimental data obtained with a microwave circular scanner operating at 2.33 GHz. Targets to be imaged include realistic biological structures, such as a human forearm, as well as calibrated samples for the sake of accuracy evaluation. The results provide a quantitative estimation of the effect of experimental factors, such as temperature of the immersion medium, frequency, signal-to-noise ratio, and various numerical parameters.

Quantitative Microwave Imaging for Breast Cancer Detection Using a Planar 2.45 GHz System

Microwave imaging is recognized as a potential candidate for biomedical applications, such as breast tumor detection. In this context, the capability of a planar microwave camera to produce quantitative imaging of high-contrast inhomogeneous objects is investigated. The image reconstruction is achieved by means of an iterative Newton-Kantorovich algorithm. Promising numerical simulation results indicate that the planar geometry is suitable for quantitative imaging, as long as the signal-to-noise ratio is higher than 40 dB. Such a requirement is satisfied with the camera due to appropriate data averaging. Furthermore, different calibration techniques are discussed, aiming to reduce the model error, which results from the limitations of the numerical model involved in the reconstruction to accurately reproduce the experimental setup. The experimental work also includes the development of a phantom using a new fluid tissue equivalent mixture based on Triton X-100. As a final result, this paper shows the first reconstructed quantitative images of a high-contrast inhomogeneous 2-D object obtained by using experimental data from the camera.

Planar and cylindrical active microwave temperature imaging: numerical simulations

A comparative study at 2.45 GHz concerning both measurement and reconstruction parameters for planar and cylindrical configurations is presented. For the sake of comparison, a numerical model consisting of two nonconcentric cylinders is considered and reconstructed using both geometries from simulated experimental data. The scattered fields and reconstructed images permit extraction of very useful information about dynamic range, sensitivity, resolution, and quantitative image accuracy for the choice of the configuration in a particular application. Both geometries can measure forward and backward scattered fields. The backscattering measurement improves the image resolution and reconstruction in lossy mediums, but, on the other hand, has several dynamic range difficulties. This tradeoff between forward only and forward-backward field measurement is analyzed. As differential temperature imaging is a weakly scattering problem, Born approximation algorithms can be used. The simplicity of Born reconstruction algorithms and the use of FFT make them very attractive for real-time biomedical imaging systems.

Breast Phantoms for Microwave Imaging

Herein, we study the dielectric properties of various mixtures susceptible to be used in manufacturing of reference inhomogeneous breast phantoms dedicated to the experimental validation of microwave breast imaging systems in the 0.5-6-GHz frequency range. Particularly, we investigate the stability over time and temperature of these properties and their reproducibility for a given mixture, as well as the ability of some mixtures to mimic the various breast tissues, i.e., to show dielectric properties close to that given by one-pole Debye models that describe the mean relative dielectric permittivity of various tissue types.

SICS: a sensor interaction compensation scheme for microwave imaging

A new formulation is proposed to take into account the sensors used to measure the scattered field in microwave tomography setups. This formulation provides a way to fully compensate the perturbations resulting from the presence of an array of sensors around the target under test. A simple example is given to illustrate how this compensation can be implemented on an iterative Newton-Kantorovich reconstruction algorithm and to demonstrate its efficiency.

Comparison of three integral formulations for the 2-D TE scattering problem

The source of scattering problems found when computing the internal field distribution in the transverse electric (TE) polarization case for 2-D objects is analyzed. It is shown that a modification introduced in a previous study is not required if an appropriate integral formulation is used. Such a formulation is proposed using generalized functions, and it is compared numerically to several other formulations for inhomogeneous dissipative cylinders whose electromagnetic parameters are close to those of biological tissues. The solution associated with this integral formulation appears to behave better than the others, in comparison with the exact analytical solutions. >

Microwave imaging techniques for biomedical applications

Microwaves have been considered for medical applications involving the detection of organ movements and changes in tissue water content. More particularly cardiopulmonary interrogation via microwaves has resulted in various sensors monitoring ventricular volume change or movement, arterial wall motion, respiratory movements, pulmonary oedema, etc. In all these applications, microwave sensors perform local measurements and need to be displaced for obtaining an image reproducing the spatial variations of a given quantity. Recently, advances in the area of inverse scattering theory and microwave technology have made possible the development of microwave imaging and tomographic instruments. This paper provides a review of such equipment developed at Suplec and UPC Barcelona, within the frame of successive French-Spanish PICASSO cooperation programs. It reports the most significant results and gives some perspectives for future developments. Firstly, a brief historical survey is given. Then, both technological and numerical aspects are considered. The results of preliminary pre-clinical assessments and in-lab experiments allow to illustrate the capabilities of the existing equipment, as well as its difficulty in dealing with clinical situations. Finally, some remarks on the expected development of microwave imaging techniques for biomedical applications are given.

Towards a planar Microwave Tomography system for early stage breast cancer detection

In this paper, the advantages of planar Microwave Tomography (MT) applied to early stage breast cancer detection are presented. In the proposed planar configuration, the breast is compressed between two dielectric plates in a configuration similar to that of X-ray mammography. This approach would allow the future implementation of a dual modality imaging system where the advantages of both techniques can be exploited. The research efforts made both at DRÉ/L2S (Supelec) and Poly-grames (École Polytechnique de Montréal), for the development of a planar MT system are described, as well as, the key features of the latter. A numerical validation is used to show how the breast compression can lead to an enhancement of the reconstructed images.

Database of "In Vivo" Measurements for Quantitative Microwave Imaging and Reconstruction Algorithms

Reconstruction algorithms and equipment have been developed for microwave imaging, with emphasis on noninvasive control of deep hyperthermia treatments. Tomographic reconstruction algorithms have also been developed for qualitative spectral and quantitative spatial iterations. The data can be accessed from the e-mail address ftp voltor.upc.es.