Advanced ultrawideband imaging algorithms for breast cancer detection

Ultrawideband (UWB) technology has received considerable attention in recent years as it is regarded to be able to revolutionise a wide range of applications. UWB imaging for breast cancer detection is particularly promising due to its appealing capabilities and advantages over existing techniques, which can serve as an early-stage screening tool, thereby saving millions of lives. Although a lot of progress has been made, several challenges still need to be overcome before it can be applied in practice. These challenges include accurate signal propagation modelling and breast phantom construction, artefact resistant imaging algorithms in realistic breast models, and low-complexity implementations. Under this context, novel solutions are proposed in this thesis to address these key bottlenecks. The thesis first proposes a versatile electromagnetic computational engine (VECE) for simulating the interaction between UWB signals and breast tissues. VECE provides the first implementation of its kind combining auxiliary differential equations (ADE) and convolutional perfectly matched layer (CPML) for describing Debye dispersive medium, and truncating computational domain, respectively. High accuracy and improved computational and memory storage efficiency are offered by VECE, which are validated via extensive analysis and simulations. VECE integrates the state-of-the-art realistic breast phantoms, enabling the modelling of signal propagation and evaluation of imaging algorithms. To mitigate the severe interference of artefacts in UWB breast cancer imaging, a robust and artefact resistant (RAR) algorithm based on neighbourhood pairwise correlation is proposed. RAR is fully investigated and evaluated in a variety of scenarios, and compared with four well-known algorithms. It has been shown to achieve improved tumour detection and robust artefact resistance over its counterparts in most cases, while maintaining high computational efficiency. Simulated tumours in both homogeneous and heterogeneous breast phantoms with mild to moderate densities, combined with an entropy-based artefact removal algorithm, are successfully identified and localised. To further improve the performance of algorithms, diverse and dynamic correlation weighting factors are investigated. Two new algorithms, local coherence exploration (LCE) and dynamic neighbourhood pairwise correlation (DNPC), are presented, which offer improved clutter suppression and image resolution. Moreover, a multiple spatial diversity (MSD) algorithm, which explores and exploits the richness of signals among different transmitter and receiver pairs, is proposed. It is shown to achieve enhanced tumour detection even in severely dense breasts. Finally, two accelerated image reconstruction mechanisms referred to as redundancy elimination (RE) and annulus predication (AP) are proposed. RE removes a huge number of repetitive operations, whereas AP employs a novel annulus prediction to calculate millions of time delays in a highly efficient batch mode. Their efficacy is demonstrated by extensive analysis and simulations. Compared with the non-accelerated method, RE increases the computation speed by two-fold without any performance loss, whereas AP can be 45 times faster with negligible performance degradation

THE APPLICATION OF DISCONTINUOUS GALKERIN FINITE ELEMENT TIME-DOMAIN METHOD IN THE DESIGN, SIMULATION AND ANALYSIS OF MODERN RADIO FREQUENCY SYSTEMS

The discontinuous Galerkin finite element time-domain (DGFETD) method has been successfully applied to the solution of the coupled curl Maxwell’s equations. In this dissertation, important extensions to the DGFETD method are provided, including the ability to model lumped circuit elements and the ability to model thin-wire structures within a discrete DGFETD solution. To this end, a hybrid DGFETD/SPICE formulation is proposed for high-frequency circuit simulation, and a hybrid DGFETD/Thin-wire formulation is proposed for modeling thin-wire structures within a three-dimensional problem space. To aid in the efficient modeling of open-region structures, a Complex Frequency Shifted-Perfectly Matched Layer (CFS-PML) absorbing medium is applied to the DGFETD method for the first time. An efficient CFS-PML method that reduces the computational complexity and improves accuracy as compared to previous PML formulations is proposed. The methods have been successfully implemented, and a number of test cases are provided that validate the proposed methods. The proposed hybrid formulations and the new CFS-PML formulation dramatically enhances the ability of the DGFETD method to be efficiently applied to simulate complex, state of the art radio frequency systems

Implementation of the Finite Difference Time Domain algorithm for the analysis of terahertz waves

The aim of this report is to present results related to the application of the Finite Difference Time Domain (FDTD) method for the study of various devices at terahertz frequencies. The FDTD method has emerged as one of the most widely used numerical analysis methods used for electromagnetic simulations. The FDTD method can be used to solve numerous types of problems ranging from modelling the behaviour of microwave circuits, waveguides, and photonics to simulating terahertz devices and plasmas. In this study the FDTD approach is derived from first principles (finite differences) and explicit equations are shown based on Maxwell's equations. Furthermore, absorbing boundary conditions (ABCs) are discussed for the FDTD method. The algorithm is tested against a range of problems to ensure its validity and accuracy. The FDTD method is then applied for the numerical analysis of a range of devices at terahertz frequencies. The numerical results obtained from the application of the FDTD method to examine a microstrip circuit with filter loading and a Multi-mode Interference (MMI) coupler at terahertz frequencies are discussed in detail. Moreover, the results of the application of the FDTD method for the calculation of the dispersion characteristics of plasmonic waveguides are also presented. Finally, a summary of the work carried out is presented and an outline is given for future research which can be carried out by using the FDTD method for the study of terahertz frequency devices

Physical Knowledge Based Scalable Phased Array Antenna Modeling for Radar Systems

The development of a large-scale phased array radar system such as the future MPAR will need a cost-effective tool for predicting electromagnetic characteristics of antennas. Simulating and optimizing of large finite phased array antennas using commercially available solvers are time-consuming and memory-extensive even though they are highly capable of solving general electromagnetic problems with acceptable accuracy. In this work, a full-wave electromagnetic solver based on finite-difference time-domain (FDTD) method has been developed for simulating phased array antennas. The planar array or array element can be simulated, optimized, or analyzed using FDTD theory based on an orthogonal, regular Cartesian lattice. The FDTD updating equation for diagonally anisotropic material was obtained for periodic structure based on the cylindrical coordinate system. This FDTD algorithm can be used to simulate active element patterns of conformally cylindrical array antennas. The simulation of active element patterns in an infinite faceted-cylindrical array was accomplished with a nonorthogonal and unstructured grid. The derivation of FDTD theory and periodic boundary condition for a structure based on the nonorthogonal and unstructured grid is presented. In this work, two simulation schemes, which are based on computed near-field current density information and the physical knowledge of finite array antennas, were presented for predicting broadside array radiation characteristics with the consumption of relatively low computational resources. The validation of the simulation program and schemes was fulfilled by comparing simulation results with measurements taken by near-field and far-field techniques

Simulation and Design of an UWB Imaging System for Breast Cancer Detection

Breast cancer is the most frequently diagnosed cancer among women. In recent years, the mortality rate due to this disease is greatly decreased thanks to both enormous progress in cancer research, and screening campaigns which have allowed the increase in the number of early diagnoses of the disease. In fact, if the tumor is identied in its early stage, e.g. when it has a diameter of less than one centimeter, the possibility of a cure can reach 93%. However, statistics show that more young aged women are suered breast cancer. The goal of screening exams for early breast cancer detection is to nd cancers before they start to cause symptoms. Regular mass screening of all women at risk is a good option to achieve that. Instead of meeting very high diagnostic standards, it is expected to yield an early warning, not a denitive diagnosis. In the last decades, X-ray mammography is the most ecient screening technique. However, it uses ionizing radiation and, therefore, should not be used for frequent check-ups. Besides, it requires signicant breast compression, which is often painful. In this scenario many alternative technologies were developed to overcome the limitations of mammography. Among these possibilities, Magnetic Resonance Imaging (MRI) is too expensive and time-consuming, Ultrasound is considered to be too operatordependent and low specicity, which are not suitable for mass screening. Microwave imaging techniques, especially Ultra WideBand (UWB) radar imaging, is the most interesting one. The reason of this interest relies on the fact that microwaves are non-ionizing thus permitting frequent examinations. Moreover, it is potentially lowcost and more ecient for young women. Since it has been demonstrated in the literatures that the dielectric constants between cancerous and healthy tissues are quite dierent, the technique consists in illuminating these biological tissues with microwave radiations by one or more antennas and analyzing the re ected signals. An UWB imaging system consists of transmitters, receivers and antennas for the RF part, the transmission channel and of a digital backend imaging unit for processing the received signals. When an UWB pulse strikes the breast, the pulse is re ected due to the dielectric discontinuity in tissues, the bigger the dierence, the bigger the backscatter. The re ected signals are acquired and processed to create the energy maps. This thesis aims to develop an UWB system at high resolution for the detection of carcinoma breast already in its initial phase. To favor the adoption of this method in screening campaigns, it is necessary to replace the expensive and bulky RF instrumentation used so far with ad-hoc designed circuits and systems. In order to realize that, at the very beginning, the overall system environment must be built and veried, which mainly consists of the transmission channel{the breast model and the imaging unit. The used transmission channel data come from MRI of the prone patient. In order to correctly use this numerical model, a simulator was built, which was implemented in Matlab, according to the Finite-Dierence-Time- Domain (FDTD) method. FDTD algorithm solves the electric and magnetic eld both in time and in space, thus, simulates the propagation of electromagnetic waves in the breast model. To better understand the eect of the system non-idealities, two 2D breast models are investigated, one is homogeneous, the other is heterogeneous. Moreover, the modeling takes into account all critical aspects, including stability and medium dispersion. Given the types of tissues under examination, the frequency dependence of tissue dielectric properties is incorporated into wideband FDTD simulations using Debye dispersion parameters. A performed further study is in the implementation of the boundary conditions. The Convolution Perfectly Matched Layer (CPML) is used to implement the absorbing boundaries. The objective of the imaging unit is to obtain an energy map representing the amount of energy re ected from each point of the breast, by recombining the sampled backscattered signals. For this purpose, the study has been carried out on various beamforming in the literature. The basic idea is called as "delay and sum", which is to align the received signals in such a way as to focus a given point in space and then add up all the contributions, so as to obtain a constructive interference at that point if this is a diseased tissue. In this work, Microwave Imaging via Space Time (MIST) Beamforming algorithm is applied, which is based on the above principle and add more elaborations of the signals in order to make the algorithm less sensitive to propagation phenomena in the medium and to the non-idealities of the system. It is divided into two distinct steps: the rst step, called SKin Artifact Removal (SKAR), takes care of removing the contributions from the signal caused by the direct path between the transmitter and receiver, the re ection of skin, as they are orders of magnitude higher compared to the re ections caused by cancers; the second step, which is BEAmForming (BEAF), performs the algorithm of reconstruction by forming a weighted combination of time delayed version of the calibrated re ected signals. As discussed above, more attention must be paid on the implementation of the ad-hoc integration circuits. In this scenario, due to the strict requirements on the RF receiver component, two dierent approaches of the implementation of the RF front-end, Direct Conversion (DC) receiver and Coherent Equivalent Time Sampling (CETS) receiver are compared. They are modeled behaviorally and the eects of various impairments, such as thermal, jitter, and phase noise, as well as phase inaccuracies, non-linearity, ADC quantization noise and distortion, on energy maps and on quantitative metrics such as SCR and SMR are evaluated. Dierential Gaussian pulse is chosen as the exciting source. Results show that DC receiver performs higher sensitivity to phase inaccuracies, which makes it less robust than the CETS receiver. Another advantage of the CETS receiver is that it can work in time domain with UWB pulses, other than in frequency domain with stepped frequency continuous waves like the DC one, which reduces the acquisition time without impacting the performance. Based on the results of the behavioral simulations, low noise amplier (LNA) and Track and Hold Amplier (THA) can be regarded as the most critical parts for the proposed CETS receiver, as well as the UWB antenna. This work therefore focuses on their hardware implementations. The LNA, which shows critical performance limitation at bandwidth and noise gure of receiver, has been developed based on common-gate conguration. And the THA based on Switched Source Follower (SSF) scheme has been presented and improved to obtain high input bandwidth, high sampling rate, high linearity and low power consumption. LNA and THA are implemented in CMOS 130nm technology and the circuit performance evaluation has been taken place separately and together. The small size UWB wide-slot antenna is designed and simulated in HFSS. Finally, in order to evaluate the eect of the implemented transistor level components on system performance, a multi-resolution top-down system methodology is applied. Therfore, the entire ow is analyzed for dierent levels of the RF frontend. Initially the system components are described behaviorally as ideal elements. The main activity consists in the analysis and development of the entire frontend system, observing and complementing each other blocks in a single ow simulation, clear and well-dened in its various interfaces. To achieve that the receiver is modeled and analyzed using VHDL-AMS language block by block, moreover, the impact of quantization, noise, jitter, and non-linearity is also evaluated. At last, the behavioral description of antenna, LNA and THA is replaced with a circuit-level one without changing the rest of the system, which permits a system-level assessment of low-level issues

Advanced Formulations and Applications of Finite Difference Time Domain Analysis

This dissertation deals with advanced formulations and applications of finite difference time domain (FDTD) method. This is composed of four themes. The first deals with the development of a plane wave excitation formulation in FV24, a finite-volume based higher-order FDTD variant. With its excellent phase error performance even for coarse grid, FV24 can be applied to electrically large problems. The plane wave excitation method based on Total field/Scattered field formulation and Discrete planewave technique is demonstrated and validated for FV24. In the latter part of this work different near to farfield transformation approaches possible in FDTD are compared for accuracy.The second part of the research deals with application of FDTD to glass weave-induced skew (GWS) problem. The GWS on a differential pair can cause increased bit error rates affecting the robustness of the digital system, and increased radiated emissions causing compliance failures. The frequency dependence of glass and resin materials properties are modeled using auxiliary differential equation formulation for FDTD, to estimate GWS on a differential pair. The skew numbers are benchmarked with the available commercial solvers. Also, the use of graphical processing units (GPUs) to accelerate the skew simulations is demonstrated.The third part of the research deals with the derivation of numerical dispersion relation (NDR) for spherical FDTD, and the sensitivity study of the associated numerical wave number. Elementary functions native to spherical coordinates are used in the derivation of the numerical dispersion. Given the non-uniform nature of the spherical FDTD grid, the NDR and the corresponding numerical wave number are shown to be position dependent. The latter part of this research includes a study to derive the stability criterion for spherical FDTD and challenges involved therein. The final part of the research studies the effectiveness of different absorbing boundary condition formulations for spherical FDTD in absorbing the waves. It is shown that the split-field formulation of perfectly matched layer (PML) is not as effective as stretched-coordinate formulation. This work includes derivation of continuous-space PML reflection coefficient, update equations for implementation of stretched-coordinate PML in spherical FDTD and analysis of reflection error for different PML parameters

Probing ultra-subwavelength inhomogeneities embedded within dielectric targets using photonic nanojets

The use of optics to detect ultra-subwavelength features embedded within structures is a hot topic for a broad diversity of applications like spectroscopy, nanotechnology, microscopy, and optical data storage discs. Conventional objective lens based optical systems have a fundamental limit on the best possible resolution of about 200 \u03b7m due to the diffraction of light as it propagates into the far-field. There already exist several near-field techniques with the capability to overcome this limitation, but each of these systems has certain drawbacks related to the complexity of the system or to limitations imposed by the system. A photonic nanojet is a very particular beam of light that can provide a practical way to overcome the diffraction limit inherent to far-field techniques. A nanojet is an electromagnetic field envelope formed on the shadow-side surface of a plane-wave-illuminated dielectric microsphere of diameter larger than the wavelength and with refractive index contrast relative to the background medium of less than 2:1. It can maintain a subwavelength transversal beamwidth for distances greater than 2 wavelengths away from the surface of the generating microsphere. This Dissertation provides a computational test of the hypothesis that the backscattered spectrum resulting from photonic nanojet illumination of a three-dimensional (3-D) dielectric structure can reveal the presence and location of ultra-subwavelength, nanoscale-thin weakly contrasting dielectric inhomogeneities within dielectric targets. The effect of surface roughness on the illuminated side of the target is analyzed, and targets ranging from simple dielectric slabs to complex biological cells are studied. The present work is performed through computational electrodynamics modeling based upon the rigorous, large-scale solution of Maxwells equations. Specifically, the 3-D finite-difference time-domain (FDTD) method is employed to test the above hypothesis.\u2