UWB tomography for breast tumor detection

Recent studies show that one in 13 women will suffer from breast cancer throughout his life. In spite of the increase of breast cancer incidence, the mortality is decreasing signi cantly, up to a point that nowadays 90% of localized breast tumors are curable. Nevertheless a tumor only can be cured when is detected in his early stage. In this sense, periodic scanning recommendations in woman over 50 are of vital importance. Currently, X-ray mammography is recognized as the preferred method, however it entails uncomfortable breast compression and exposure to low levels of ionization radiation, which can put some inconvenience for the woman to respect the recommendations. Microwave tomographic imaging techniques appeared as a solution to overcome this drawbacks while o ering a good trade-o between resolution and penetration depth. Moreover healthy and malignant breast tissue present at these frequencies high contrast in dielectric properties which is the magnitude to be imaged. In this Master Thesis a contribution to active microwave imaging for breast tumor detection is presented. Microwave imaging is a nonlinear inverse scattering problem, where complex permittivity of an object is reconstructed from the measured scattered eld produced by this object. To solve that problem, it can be either linearized with some approximation or solved with an iterative algorithm. By using an iterative algorithm, a cost function is optimized to obtain the solution, however it requires to introduce a priori information by assuming any property of the imaged tissue as known, which can pre-condition the solution. In this work, a novel UWB Hybrid Focusing algorithm is proposed, which uses Born approximation to linearize the problem and allows to obtain reconstructions of high contrasted large objects with a reasonable error. The idea behind UWB Hybrid focusing is the incoherent multifrequency combination of coherent multiview focused images. To do that, a number of microwave sensors (transmitters and receivers) are distributed on a circular region that may completely surround the object under investigation to measure scattered elds. Each sensor is alternatively activated as a transmitter, and the received signal at the rest of the sensors is captured, thus allowing to use information from all directions in the reconstruction procedure. UWB signals are proposed as illuminating signals since they are able to provide enhanced image resolution and more clutter rejection when compared to monofrequency reconstructions, which is traduced in the image as a more true and fair reconstrucion with less artifacts that could be interpreted as false positive detections. However the UWB extension of this algorithm has to be carefully done in order to avoid destructive interferences between the reconstructions at diferent frequencies by an incoherent combination. To verify the algorithm, reconstructions of progressively more realistic breast numerical phantoms have been made. When applying large and high contrasted realistic breast phantoms to any image reconstruction algorithm, a matching medium is required to minimize the re ected energy out of the breast. This aspect, together with the capability of the algorithm to deal with the inherent inhomogeneity in the breast, will also be inspected. Furthermore, motivated by the importance of detecting tumors at early stage, the ability to detect small inclusions will be tested. Experimental work is the culminative part of this dissertation. It covers the implementation of a two degrees of freedom imaging setup designed to deal with non-symmetric realistic objects in order to demonstrate the whole functionality of the algorithm. Another issue covered in this part, is the realization of breast phantoms progressively more realistic, restly to verify the functionality of the experimental setup and later to test the capability of the algorithm to detect tumors in phantoms emulating the relative contrasts exhibited by real women breasts

Multi-antenna multi-frequency microwave imaging systems for biomedical applications

Medical imaging refers to several different technologies that are used to view the human body in order to diagnose, monitor, or treat medical conditions. Each type of technology gives different information about the area of the body being studied depending on the radiation used to illuminate de body. Nowadays there are still several lesions that cannot be detected with the current methods in a curable stage of the disease. Moreover they present some drawbacks that limit its use, such as health risk, high price, patient discomfort, etc. In the last decades, active microwave imaging systems are being considered for the internal inspection of light-opaque materials thanks to its capacity to penetrate and differentiate their constituents based on the contrast in dielectric properties with a sub-centimeter resolution. Moreover, they are safe, relatively low-cost and portable. Driven by the promising precedents of microwaves in other fields, an active electromagnetic research branch was focused to medical microwave imaging. The potential in breast cancer detection, or even in the more challenging brain stroke detection application, were recently identified. Both applications will be treated in this Thesis. Intensive research in tomographic methods is now devoted to develop quantitative iterative algorithms based on optimizing schemes. These algorithms face a number of problems when dealing with experimental data due to noise, multi-path or modeling inaccuracies. Primarily focused in robustness, the tomographic algorithm developed and assessed in this thesis proposes a non-iterative and non-quantitative implementation based on a modified Born method. Taking as a reference the efficient, real-time and robust 2D circular tomographic method developed in our department in the late 80s, this thesis proposes a novel implementation providing an update to the current state-of-the-art. The two main contributions of this work are the 3D formulation and the multi-frequency extension, leading to the so-called Magnitude Combined (MC) Tomographic algorithm. First of all, 2D algorithms were only applicable to the reconstruction of objects that can be assumed uniform in the third dimension, such as forearms. For the rest of the cases, a 3D algorithm was required. Secondly, multi-frequency information tends to stabilize the reconstruction removing the frequency selective artifacts while maintaining the resolution of the higher frequency of the band. This thesis covers the formulation of the MC tomographic algorithm and its assessment with medically relevant scenarios in the framework of breast cancer and brain stroke detection. In the numerical validation, realistic models from magnetic resonances performed to real patients have been used. These models are currently the most realistic ones available to the scientific community. Special attention is devoted to the experimental validation, which constitutes the main challenge of the microwave imaging systems. For this reason, breast phantoms using mixtures of chemicals to mimic the dielectric properties of real tissues have been manufactured and an acquisition system to measure these phantoms has been created. The results show that the proposed algorithm is able to provide robust images of medically realistic scenarios and detect a malignant breast lesion and a brain hemorrhage, both at an initial stage

Anàlisi i implementació de tècniques de formació d'imatge i localització UWB

En aquest treball s'han desenvolupat els conceptes de formació d'imatge amb microones, més conegut amb el terme anglès Imaging i la Localització. Aquests dos termes fan referència a la utilització de microones (radiació electromagnètica des de 300 MHz fins a 300 GHz) per obtenir alguna informació d'un objecte situat a una distància curta. Imaging i Localització s'han desenvolupat àmpliament utilitzant senyals de banda estreta, però no ha estat fins els últims temps, que s'ha contemplat la possibilitat d'utilitzar senyals multifreqüència o de banda molt ampla, anomenats Ultra-WideBand. Aquesta idea obre un ventall de noves funcionalitats i ofereix la possibilitat de millorar les prestacions que s'obtenien amb una sola freqüència

Anàlisi i implementació de tècniques de formació d'imatge i localització UWB

En aquest treball s'han desenvolupat els conceptes de formació d'imatge amb microones, més conegut amb el terme anglès Imaging i la Localització. Aquests dos termes fan referència a la utilització de microones (radiació electromagnètica des de 300 MHz fins a 300 GHz) per obtenir alguna informació d'un objecte situat a una distància curta. Imaging i Localització s'han desenvolupat àmpliament utilitzant senyals de banda estreta, però no ha estat fins els últims temps, que s'ha contemplat la possibilitat d'utilitzar senyals multifreqüència o de banda molt ampla, anomenats Ultra-WideBand. Aquesta idea obre un ventall de noves funcionalitats i ofereix la possibilitat de millorar les prestacions que s'obtenien amb una sola freqüència

3D UWB tomography for medical imaging applications

In this paper, a novel 3D UWB tomographic algorithm has been presented for brain hemorrhagic stroke detection. While 2D reconstructions are unable to distinguish between features at different heights, 3D reconstructions allow to obtain a complete representation of the brain and thus to differentiate them. A human brain model has been successfully reconstructed and the position of a blood vessel detected.Peer ReviewedPostprint (published version

Preliminary phantom-based dynamic calibration techniques assessment for microwave colonoscopy systems

Early detection and resection of colon polyp is the best way to reduce colorectal cancer (CRC) mortality. The current method for early detection is colonoscopy, which has a limited field of view, and its efficacy is highly dependant on the endoscopist's experience and colon preparation. This work presents a device for combining microwave imaging with optical colonoscopy. The challenges of this new microwave imaging system are presented, such as the unknown distance to the colon mucosa, which leads to undesired scattered fields and, the antenna size limitations. Four dynamic calibration techniques are proposed to remove the effects of the undefined distance from the imaging region to colon mucosa. These calibration methods are based on averaging the colonoscopy trajectory frames and subtracting the calibration set from the current frame. The phantom preliminary results show that these calibration methods completely delete the undesired scatter.A.G. acknowledges the financial support from DIN2019- 010857, M.G., and W.D acknowledge the financial support from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 960251 and from the European Institute of Innovation and Technology (EIT). J.R. acknowledges the financial support from Agencia Estatal Investigacion PID2019-107885GB-C31/AEI/10.13039/.Peer ReviewedPostprint (author's final draft

Realistic colon phantoms for microwave colonoscopy validation

Colon phantoms that replicate a real colon dielectric properties, shape, and texture are required to verify a microwave colonoscopy system. The realism and accuracy of the phantom are quantified in this study using a method based on the antenna bandwidth variation.Peer ReviewedPostprint (author's final draft

3D UWB magnitude-combined tomographic imaging for biomedical applications. Algorithm validation

Biomedical microwave imaging is a topic of continuous research for its potential in different areas especially in breast cancer detection. In this paper, 3D UWB Magnitude-Combined tomographic algorithm is assessed for this recurrent application, but also for a more challenging one such as brain stroke detection. With the UWB Magnitude-Combined concept, the algorithm can take advantage of both the efficiency of Fourier Diffraction Theorem-based tomographic formulation and the robustness and image quality improvement provided by a multi-frequency combination.Peer ReviewedPostprint (published version

UWB High-contrast robust tomographic imaging for medical applications

In this paper a complete UWB Circular Tomographic System robust to high contrast or large objects, applied to Breast Tumor Detection, is presented. The main contribution of this paper is to focus on the implementation of a two degrees of freedom imaging setup in order to deal with non-symmetric objects and to demonstrate its functionality with realistic breast phantoms.Peer ReviewedPostprint (published version

UWB High-contrast robust tomographic imaging for medical applications

In this paper a complete UWB Circular Tomographic System robust to high contrast or large objects, applied to Breast Tumor Detection, is presented. The main contribution of this paper is to focus on the implementation of a two degrees of freedom imaging setup in order to deal with non-symmetric objects and to demonstrate its functionality with realistic breast phantoms.Peer ReviewedPostprint (published version