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Microwave imaging is of increasing interest for monitoring breast health and treatment. In these applications, the consistency of results over time is important to characterize so that relevant changes can be distinguished from no...
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Microwave imaging is of increasing interest for monitoring breast health and treatment. In these applications, the consistency of results over time is important to characterize so that relevant changes can be distinguished from normal measurement and tissue variation. In this paper, we analyze the consistency of microwave imaging when scanning frequently over several weeks, similar to the treatment monitoring timeframe. A custom microwave transmission system was used to acquire 15 scans from a breast phantom and 14-15 scans from each of 5 volunteers. As expected, the breast phantom showed high similarity when comparing signals, property estimates, and images at different time points. Scans of each volunteer also generally demonstrated consistency over time, as well as between right and left breasts. The characterization of consistency from scanning healthy women provides a baseline from which significant changes due to disease or treatment can be identified.
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This work describes how indirect holography which has previously been applied to the determination of antenna radiation patterns can be adapted for the imaging of passive objects. It provides details of how complex scattered field...
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This work describes how indirect holography which has previously been applied to the determination of antenna radiation patterns can be adapted for the imaging of passive objects. It provides details of how complex scattered field values can be obtained in a simple and inexpensive manner from sampled scalar intensity measurements taken over a single scanning aperture. This work uses indirect holographic techniques to image a number of simple objects including a rectangular metallic plate, a small metal plate covered by a dielectric sheet and a small metallic circular annulus. This work demonstrates that good quality images can be reconstructed from simple scalar intensity patterns. It demonstrates that clear outlines can be obtained in particular from reconstructed phase patterns and that good images can be obtained from objects with dimensions of the order of a half wavelength.
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For the first time, we present a near-field transmission-type microwave imaging (NTMI) system to break the bottleneck of the resolution of microwave imaging (~cm). The theoretical analysis and experimental validation showed that t...
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For the first time, we present a near-field transmission-type microwave imaging (NTMI) system to break the bottleneck of the resolution of microwave imaging (~cm). The theoretical analysis and experimental validation showed that the resolution of the NTMI system was up to 1.55 mm. In view of the advantages of high contrast and nonionizing radiation, the NTMI is suitable for noninvasive mass screening in early breast cancer detection.A near-field transmission-type microwave imaging (NTMI) system was developed to break the bottleneck of the resolution of microwave imaging due to diffraction limitation. The NTMI used a microwave pinhole to control the size of microwave radiation in the near-field region and a high-resolution and highly sensitive detector based on electromagnetic-elastic resonance effect to acquire the transmitted microwave signal. The theoretical analysis and experimental validation showed that the resolution of the NTMI system was up to 1.55 mm, higher than the current resolution (~cm) of microwave imaging. And the contrast of microwave transmittance based on the different electromagnetic characteristics among various tissues was theoretically deduced and experimentally examined. Moreover, a breast phantom was imaged to estimate the imaging capability of the NTMI system with high contrast (3.7:1-16.7:1) and good tissue penetration (>10 cm). Finally, the excised breast of an ewe embedded with an ex vivo human breast tumor was imaged clearly with a contrast of about 1:2.8, which is in good agreement with the X-ray image. Therefore, the NTMI system is suitable for noninvasive mass screening and has a great potential for applications in early breast cancer detection.
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This work describes how indirect holographic techniques, previously applied to the determination of antenna radiation patterns, can be adapted for the imaging of passive objects. It provides details of how complex scattered field ...
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This work describes how indirect holographic techniques, previously applied to the determination of antenna radiation patterns, can be adapted for the imaging of passive objects. It provides details of how complex scattered field values can be obtained in a simple and inexpensive manner from sampled scalar intensity measurements taken over a single scanning aperture. This work provides a brief outline of the basic theory of indirect microwave holography, and how the transformation of the holographic intensity pattern into the Fourier domain enables the isolation of the terms required for complex field reconstruction to be isolated from the remaining terms. The work is supported by a range of experimental results, illustrating the reconstructed complex fields for a number of simple test objects. Back-propagation techniques have also been included to reconstruct complex fields at the position of the scattering objects.
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Optical endoscopy, as one of the common clinical diagnostic modalities, provides irreplaceable advantages in the diagnosis and treatment of internal organs. However, the approach is limited to the characterization of superficial t...
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Optical endoscopy, as one of the common clinical diagnostic modalities, provides irreplaceable advantages in the diagnosis and treatment of internal organs. However, the approach is limited to the characterization of superficial tissues due to the strong optical scattering properties of tissue. In this work, a microwave-induced thermoacoustic (TA) endoscope (MTAE) was developed and evaluated. The MTAE system integrated a homemade monopole sleeve antenna (diameter = 7 mm) for providing homogenized pulsed microwave irradiation to induce a TA signal in the colorectal cavity and a side-viewing focus ultrasonic transducer (diameter = 3 mm) for detecting the TA signal in the ultrasonic spectrum to construct the image. Our MTAE, system combined microwave excitation and acoustic detection; produced images with dielectric contrast and high spatial resolution at several centimeters deep in soft tissues, overcome the current limitations of the imaging depth of optical endoscopy and mechanical wave–based imaging contrast of ultrasound endoscopy, and had the ability to extract complete features for deep location tumors that could be infiltrating and invading adjacent structures. The practical feasibility of the MTAE system was evaluated i n vivo with rabbits having colorectal tumors. The results demonstrated that colorectal tumor progression could be visualized from the changes in electromagnetic parameters of the tissue via MTAE, showing its potential clinical application.
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Current diagnostic techniques for visualizing bones rely on X-rays, which pose potential harm to both patients and surgical staff. Consequently, the demand for a portable imaging system offering high-resolution, radiation-free, an...
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Current diagnostic techniques for visualizing bones rely on X-rays, which pose potential harm to both patients and surgical staff. Consequently, the demand for a portable imaging system offering high-resolution, radiation-free, and three-dimensional (3D) imaging capabilities has emerged. This paper introduces a 3D quantitative microwave imaging technique for visualizing musculoskeletal tissue, commonly employed in diagnostic medical imaging. The proposed imaging method is grounded in a set of contrast source (CS) electromagnetic (EM) modeling equations. Through Landweber inverse processing, the solution for the unknown object's electric susceptibility distribution in the modeling equations is derived. The reconstruction process efficiently and effectively generates a 3D image, composed of the object's electric susceptibility distribution. The efficacy of the proposed imaging technique and microwave imaging system is validated through numerical models with both homogeneous and inhomogeneous properties. Moreover, practical validation is performed using a complex multi-layer inhomogeneous phantom within an anechoic chamber. Finally, considering the medical significance of imaging the spine, particularly in cases of car accidents, the proposed Landweber inverse source imaging method and microwave imaging system are practically tested on the human back area, effectively demonstrating their capabilities in imaging musculoskeletal tissue.
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This paper describes structure of imaging system, imaging mechanism of microwave radiometer, and the microwave radiation image features and recognition. Results of image experiments show: on microwave radiation image, the features...
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This paper describes structure of imaging system, imaging mechanism of microwave radiometer, and the microwave radiation image features and recognition. Results of image experiments show: on microwave radiation image, the features of metal target, water surface and road among trees, grassland and jungle become extremely obvious.
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Based on a reconfigurable spatial dispersive radiation antenna, a microwave compressive sensing imaging method is proposed in this article. According to theoretical analysis, it cannot improve lateral resolution without reducing r...
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Based on a reconfigurable spatial dispersive radiation antenna, a microwave compressive sensing imaging method is proposed in this article. According to theoretical analysis, it cannot improve lateral resolution without reducing range resolution in a traditional dispersion-based microwave imaging system. In this work, the issue is addressed by the proposed tunable traveling wave antenna (T-TWA) and variable spatial dispersion compressed sensing (CS) imaging. The T-TWA realizes mechanical, spatial dispersion radiation reconfiguration within the 6.5–10.5 GHz frequency band while maintaining the radiation surface position fixed. Then, the CS algorithm is applied to implement 2-D imaging and positioning on a 5 mm side length target. Simulation and experiment demonstrate that the proposed system attains a lateral resolution of 2 mm (about 1/20 central wavelength) and a range resolution of 7 mm (about 1/5 central wavelength), exhibiting a tenfold and a fivefold enhancement compared to theoretical, respectively. Compared with the imaging system based on a nonadjustable dispersion antenna, the imaging resolution is improved by more than twice in the lateral direction. The proposed imaging system and the tunable dispersive antenna are applicable in fields like vehicle radar, indoor electromagnetic positioning, etc.
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Calibration measurements play a crucial role in improving the accuracy of both qualitative and quantitative microwave imaging. Ideally, in 3-D near-field imaging, a calibration measurement should be performed at each desired range...
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Calibration measurements play a crucial role in improving the accuracy of both qualitative and quantitative microwave imaging. Ideally, in 3-D near-field imaging, a calibration measurement should be performed at each desired range (or depth) position, which can be very time-consuming. An analytical prediction of the range behavior of the resolvent kernel of scattering can reduce the calibration effort to a single measurement at a reference range position. Range-translation (or range-migration) analytical expressions are already widely used in far-zone radar and acoustic imaging; however, their accuracy deteriorates significantly in near-field scenarios. Here, we propose a range-migration technique for near-field microwave imaging with monostatic and bistatic measurement configurations. From a single measurement of the system point-spread function (PSF), the PSF magnitude and phase are accurately predicted at any desired range position. The proposed migration is performed in real space; however, it can also be applied with Fourier-domain (or
$k$
-space) inversion methods. Here, it is applied with quantitative microwave holography in simulation-based and experimental examples, which validate its performance and illustrate its limitations.
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The standard integral-based microwave tomography suffers from computational limitations associated with Green's function. Those limitations prevent the image reconstruction process from being fast, which is an important requiremen...
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The standard integral-based microwave tomography suffers from computational limitations associated with Green's function. Those limitations prevent the image reconstruction process from being fast, which is an important requirement for urgent medical applications such as stroke detection. To cope with these limitations, significant approximations are usually implemented within the integral equations. Those approximations include considering the imaging antennas as point sources, assuming homogeneity along one of the domain's coordinate axes, and necessitating a background matching medium. These approximations result in some undesirable effects in practice such as reconstructing merely 2-D images with limited accuracy, and manufacturing problems associated with selecting a suitable background matching medium with reasonable dielectric properties. To alleviate some of the above limitations and challenges, this paper introduces a partial differential equation framework for microwave tomography established on the wave and the third Maxwell equations. The proposed method is independent of Green's function and its corresponding limitations. Thus, it can reconstruct 3-D images in a faster manner, particularly in emergency scenarios such as stroke detection where time is life. To validate the proposed method, realistic biomedical head imaging problems are successfully solved, analyzed, and compared to the standard integral-based microwave tomography in terms of computational time and accuracy.
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