Microwave radar and microwave-induced thermoacoustics, recently proposed as promising breast cancer detection techniques, each have shortcomings that reduce detection performance. Making the assumption that the measurement noises experienced when applying these two techniques are independent, we propose a methodology to process the input signals jointly based on a hypothesis testing framework. We present two test statistics and derive their distributions to set the thresholds. The methodology is evaluated on numerically simulated signals acquired from 2-D numerical breast models using finite-difference time-domain method. Our results show that the proposed dual-modality approach can give a significant improvement in detection performance.
Abstract-Microwave radar and microwave-induced thermoacoustic technique exploit the contrast in the permittivity and conductivity between malignant and healthy tissue.They have emerged as promising techniques for detecting breast cancers. This paper compares the imaging capability of these techniques in the presence of homogeneous and heterogeneous breast tissue. Relying on the data from the finite-difference time-domain simulations, the study shows that both techniques are capable of imaging homogeneous objects. In the presence of electromagnetic dispersion and heterogeneity, radar signals suffer from strong dispersion and multiple scattering, which decorrelate the signals with the scatterers. The microwaveinduced thermoacoustic technique takes the advantage of breast being acoustically homogeneous and is capable of generating high-quality images.
Precursor field theory has been developed to describe the dynamics of electromagnetic field evolution in causally attenuative and dispersive media. In Debye dielectrics, the so-called Brillouin precursor exhibits an algebraic attenuation rate that makes it an ideal pulse waveform for communication, sensing, and imaging applications. Inspired by these studies in the electromagnetic domain, the present paper explores the propagation of acoustic precursors in dispersive media, with emphasis on biological media. To this end, a recently proposed causal dispersive model is employed, based on its interpretation as the acoustic counterpart of the Cole¿Cole model for dielectrics. The model stems from the fractional stress¿strain relation, which is consistent with the empirically known frequency power-law attenuation in viscoelastic media. It is shown that viscoelastic media described by this model, including human blood, support the formation and propagation of Brillouin precursors. The amplitude of these precursors exhibits a sub-exponential attenuation rate as a function of distance, actually being proportional to z(-p), where z is the distance traveled within the medium and 0.5
Dielectric media that exhibit dipole relaxation under an externally applied electromagnetic field are commonly described by the causal Debye model. Such media support the formation and propagation of the Brillouin precursor, which propagates with the phase velocity at dc and has an algebraic attenuation rate of its peak amplitude. This interesting property points to several applications of Brillouin precursors for communications and imaging through lossy dispersive media. This paper explores the possibility of pursuing such applications with acoustic pulses. To that end, a recently proposed causal model for viscoacoustic media, which can be interpreted as an extension of the Debye model, is employed to illuminate the analogies and discrepancies between acoustic and electromagnetic precursor fields.
The problem of designing a microwave pulse to minimize its attenuation in dispersive media is solved by formulating an optimization problem at a given point. The solution that maximizes the total energy of the pulse is the impulse response of the medium and its time-reverse. This method is applied to a good conductor, a medium described by the Rocard-Powles-Debye model, and a two-layer medium. This method of solving the pulse design problem using optimization theory can be extended to include other optimization criteria and applied to design pulses for propagation in arbitrary dispersive media.
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