Phase-shifting microwave holography utilizes the antennas to record the hologram. In this technique, the antenna has to perform two-dimensional (2-D) scanning over the test area corresponding to each phase shift in the reference wave. A numerical three-step phase-shifting is proposed for recording the microwave holograms in which only a single 2-D scan over an area is recorded experimentally whereas two remaining phase shifts are introduced numerically. This method is applied for imaging of metallic objects to inspect the feasibility of the proposed method. The qualitative results exhibit its effectiveness while reconstructing the amplitude and phase of an object at a microwave frequency of 8.5 GHz (or λ = 35.29 mm).
KEYWORDS: Tissues, Breast, Dielectrics, Magnetic resonance imaging, 3D modeling, Image segmentation, Data modeling, Microwave imaging, 3D image processing, Image processing
An effective method to develop anatomically real numerical breast phantoms for T1-weighted MR images of different tissue densities is presented. The dielectric properties for breast tissues are calculated and analyzed using different dispersion models (i.e., one- and two-pole cole–cole and Debye models). The method presented in this paper propounds significant improvements in comparison with existing MRI-based numerical phantoms in terms of denoising of images, tissue segmentation, nonlinear mapping of dielectric properties with realistic shapes using all the dispersion models and densitywise classification of phantoms. This method is a multistep approach in which each MRI voxel is mapped with the appropriate dielectric properties according to different dispersion models. The MRI data was collected and interpolated according to the size of the uniform grid for finite difference time domain computations followed by the preprocessing of MR images to enhance them. Thereafter, the voxel intensities were segregated into two groups as adipose and fibro glandular tissues. These tissue intensities were assigned the corresponding dielectric properties. Three-dimensional (3-D) numerical phantoms were created according to all the dispersion models. After the comparison among the models, it has been found that, along with frequency, the dielectric properties vary according to the variation of the dispersion model parameters. It was also observed that the dielectric properties calculated from one-pole cole–cole and two-pole Debye models are more close to the real properties of breast tissues than other models. A generalized method has been defined for developing the 3-D phantoms for all classes of breast according to the inhomogeneity of fibroglandular tissues using the dispersion models. The frequency-dependent and dispersion model parameters-dependent dielectric properties have been assigned to the phantoms. These real-like phantoms after 3-D printing would help researchers working in the field of breast cancer detection studies.
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