Dissertations / Theses on the topic 'Phantom material'

Mammographic techniques used for screening programmes need to be of the highest quality; hence, the need of a good phantom to mimic breast response to radiation. The phantom materials must be sensitive to small changes in the mammography system and provide a means of evaluating the absorbed dose to the breast. These materials have to provide the same attenuation properties as the real tissues being simulated, for the radiation modalities being investigated. Cross-linked hydrophilic copolymers have the potential to be good phantom materials for the breast as their elemental compositions are similar to soft tissue. Two types of hydrophilic copolymer materials used in this study were designated as ED1S and ED4C. They were made from a certain proportionate mixture of methyl methacrylate and vinyl pyrrolidone. The physical properties of the materials such as liquid uptake and dimensional changes in hydration and dehydration processes were studied. The equilibrium water content of ED1S and ED4C fully hydrated in water was 55% and 70% respectively. The samples underwent distortion when dehydrated and a volume approximation formula for the dehydrated samples was derived. The linear attenuation coefficient and the mass attenuation coefficient of the hydrophilic copolymer materials at photon energies in the mammographic energy region were determined. Both a single beam transmission method and a photon transmission tomography method were used. The results were compared with XCOM calculated attenuation coefficients of water and average breasts using the elemental composition found in the literature. It was found that the mass attenuation coefficient of dry hydrophilic copolymer samples closely fit the XCOM calculated old-age breast (Breast 3) and samples fully hydrated in water fit the calculated young-age breast (Breast 1). Measurements were also carried out to determine the linear attenuation coefficient of normal and abnormal breast tissues at four photon energies in the mammographic energy region. The values found were in good accord with calculated average breast values. However, more studies need to be done as only three samples were used. The electron density of the hydrophilic copolymer materials was determined by using the Compton scattering technique. The electron density for dry ED1S sample was (3.1 +/- 0.4) x 1023 electrons per cm3 and for dry ED4C was (4.4 +/- 0.4) x 1023 electrons per cm3.

The use of three gamma annihilation as a new PET molecular imaging modality which can predict tumour hypoxia was proposed by Kacperski and Spyrou in 2004. The positronium and its annihilation, could then serve as an oxygen-sensitive marker. The relative magnitude of three photon annihilation is increased in an oxygen deficient environment. The main questions addressed in this thesis are the potential use of the lanthanum bromide LaBr3: Ce (5%) scintillator detector for three-photon positron annihilation measurements. Also, the optimum source-to-detector distance that achieves good efficiency and sensitivity of the measurements. The other question is finding the best method to prepare in vitro three types of hypoxic samples (mineral water, defibrinated horse blood and semm). In addition, the suitability of the hydrophilic material is examined in terms of hydration behaviour, radiation and physical properties, for use as a phantom that represents the hypoxic tumour in the three-photon positron annihilation measurements. The main critical question is which the best method that could be used to measure the three-photon positron annihilation yields. Also, how does the 3y/2y ratio vary with different oxygen concentrations in different hydrophilic materials? Lanthanum bromide LaBr3: Ce (5%) scintillator detectors have good fast timing resolution, good stopping power and large light output. The LaBr3:Ce (5%) has very good scintillator characteristics, combining high effective Z and density, fast decay time, light emission wavelengths matching that of commonly available photon detectors and excellent energy resolution (~3% at 662 keY). However, it is highly hygroscopic in nature, making it difficult to produce, but its commercial availability has been gradually increasing in recent times. LaBr3: Ce (5%) has come to be accepted for the superior energy resolution it offers. Therefore, LaBr3: Ce (5%) detectors can be considered as the scintillators of choice for determining the yield of 2-and3-y positron annihilation. The characterisation of the detector used was can-ied out in terms of energy resolution and efficiency. The effect of amplifier parameters on the energy resolution was also studied. The 'geometrical solid angles subtended by the source-to-detector distances play an important role in the sensitivity and accuracy of the detector efficiency measurements. Therefore, the efficiency measurements were investigated at various distances to optimise the geometrical solid angle for the LaBr3: Ce (5%) detector for the three photon annihilation measurements. The experimental data were compared with the GATE simulated results obtained. The objective to study the factors that affect dissolved oxygen (DO) in three types of samples (mineral water, defibrinated horse blood and semm) was to investigate the 3y/2y ratio in hypoxic, nOlIDoxic and hyperoxic conditions of tissues for future application in oncology in the detection and quantification of tumour hypoxia. This was achieved by measuring the DO, pH and temperature before, during and after treating the samples with nitrogen, carbon dioxide and ascorbic acid (AnaeroGen). Two methods for the preparation of the in vitro hypoxic samples were investigated and evaluated. Carbon dioxide proved to be most effective for the reduction of DO in the samples. Blood tended to resist DO reduction since it decreased at a much slower rate than in water and semm. Together with the fact that the oxygen level in blood remained low after the end of exposure to the gases and ascorbic acid suggests that the solubility of oxygen in blood depends upon the concentration of haemoglobin as well as upon ligands such as CO2 • CO2 combines with haemoglobin affecting oxygen binding and fonns bicarbonate which further decreases the affinity of haemoglobin to oxygen Hydrophilic materials.

Paramagnetic lanthanide ions have been investigated as possible MIR phantom materials and contrast agents. The aim of this study is to determine if it is possible to apply the well known Solomon-Bloembergen equations to solutions of paramagnetic lanthanide ions that have fast electron spin relaxation times, compared to Gadolinium, the most widely used ion for NMR. Studies of the relaxivity, frequency and temperature dependence, show that there is a considerable difference in those properties over the series. Chelation of the ions to EDTA and DTPA resulted in a decrease in the relaxivity which was directly proportional to the decrease in the number of water molecules in the inner co-ordination sphere. The fit of the Solomon-Bloembergen equations to the variable frequency and temperature relaxation times showed that theory is valid for the fast electron spin ions and allowed the calculation of the electron spin relaxation times. This showed that there is a difference of 5 orders of magnitude between Gadolinium, the ion demonstrated to have a slow electron spin relaxation time, and the remaining ions. The addition of EDTA chelated forms of these ions to agarose gels produced NMR phantom materials with relaxation time characteristics that could be chosen to fulfil a desired application. The biodistribution of Gd-DTPA was investigated using ESR and NMR. The concentration of Gd-DTPA in excised rat tissue, 20 minutes after intraperitoneal injection, was determined, by the change in NMR water proton relaxation time from that of a control tissue, and by ESR from direct measurement of the microwave power absorbed by the sample, which is directly proportional to the number of unpaired electron spins in the sample. The results from these two methods of determining contrast agent concentration agree well with each other both in the order of biodistribution and on the absolute concentrations.

Colonoscopy is the current standard for colorectal cancer screening. This procedure requires improvement since it causes patient pain and can even result in injury. Novel colonoscopy devices have to be evaluated to gain information about their performance. At the preclinical stage of the device development the evaluation is typically performed in laboratory experiments. For these experiments an artificial environment is required which can recreate the anatomical and biomechanical features of the colon. A colonoscopy simulator for the evaluation of colonoscopy devices was developed within the ERC funded CoDIR project (Colonic Disease Investigation by Robotic Hydrocolonoscopy). The here developed simulator had to provide a colon phantom with realistic biomechanical properties as well as a sensor setup to measure signals which can be used to quantify the performance of devices which are tested within the simulator. Related literature was reviewed and possible tissue mimicking materials were selected. The suitability of the selected materials was evaluated by testing the frictional and elastic properties of the materials and subsequently comparing the results to those of colon tissue. PVA cryogel was selected as the most suitable material as it exhibits comparable elasticity and coefficients of friction. The tissue mimicking materials were mould casted into phantoms which were designed to represent the anatomical features of the colon. A simulator environment was developed which integrates the phantom as well as force and pressure sensors into a functional system. The sensors measure mesenteric forces and intraluminal pressures which can be related to the performance of tested devices. The simulator allows the arrangement of the sensors and the phantoms in an adjustable, modular approach. The simulator environment was successfully applied in the evaluation of a novel colonoscopy device. The results indicate that PVA cryogels exhibit unique mechanical properties which can be compared to those of colon tissue. The developed colonoscopy simulator provides a promising tool which can aid the development of novel colonoscopy devices.

Thesis (M.A.)--Boston University
The purpose of our study was to determine if it is possible to acquire CTA images of small vessels using lower concentrations of iodinated contrast material without substantially diminishing image quality. A custom designed multi-purpose phantom was used to test multiple concentrations of iodinated contrast material using low x-ray tube voltage experimental CTA protocols. A single scan using 120 kVp and Noise Index at a setting of 23 was compared to scans using 100 kVp and 80 kVp tube voltages and Noise Index settings of 23, 21, and 19. Lower tube voltages did produce increased attenuation in contrast material regions of interest, however, increased image noise caused the CNR and FOM for the currently established imaging protocol to be superior to the experimental protocols tested. Despite minor decreases in image quality, the experimental imaging protocols were able to produce images utilizing significantly decrease levels of radiation dose. Given minor changes in imaging quality, the ability to substantially reduce dose while maintaining a satisfactory level of image quality was positive. Further experimentation with low kVp CTA imaging utilizing additional NI settings is warranted to measure possible further improvements in image quality while still maintaining low radiation dose.

The radiation dose in radiation therapy is mainly measured by ion chamber. The ion chamber measurement will not be accurate if there is not enough phantom material surrounding the ion chamber to provide the electron equilibrium condition. The lack of electron equilibrium will cause a reduction of dose. This may introduce problems in treatment planning. Because some planning algorithms cannot predict the reduction, they over estimate the dose in the region. Electron disequilibrium will happen when the radiation field size is too small or the density of irradiated material is too low to provide sufficient electrons going into the dose volume. The amount of tissue required to provide electron equilibrium in a 6MV photon beam by three methods: direct calculation from Klein-Nisina equation, measurement in low density material phantom and a Monte Carlo simulation is done to compare with the measurement, an indirect method from a planning algorithm which does not provide an accurate result under lateral electron disequilibrium. When the error starts to happen in such planning algorithm, we know that the electron equilibrium conditions does not exist. Only the 6MV photon beam is investigated. This is because in most cases, a 6MV small fields are used for head and neck (larynx cavity) and 6MV fields are commonly used for lung to minimise uncertainity due to lateral electron at higher energies.
Master of Science (Hons)

Brachytherapy is radiation therapy performed by placing a radiation source near or inside a tumor. Difference between the current water-based brachytherapy dose formalism (TG-43) and new model based dose calculation algorithms (MBSCAs) can differ by more than a factor of 10 in the calculated doses. There is a need for voxel-by-voxel cross-section assignment, ideally, both the tissue composition and mass density of every voxel should be known for individual patients. A method for determining tissue composition via three material decomposition (3MD) from dual energy CT scans was developed at Linköping university. The method (named DIRA) is a model based iterative reconstruction algorithm that utilizes two photon energies for image reconstruction and 3MD for quantitative tissue classification of the reconstructed volumetric dataset. This thesis has investigated the accuracy of the 3MD method applied on prostate tissue in an anthropomorphic phantom when using two different approximations of soft tissues in DIRA. Also the distributions of CT-numbers for soft tissues in a contemporary dual energy CT scanner have been determined. An investigation whether these distributions can be used for tissue classification of soft tissues via thresholding has been conducted. It was found that the relative errors of mass energy absorption coefficient (MEAC) and linear attenuation coefficient (LAC) of the approximated mixture as functions of photon energy were less than 6 \% in the energy region from 1 keV to 1 MeV. This showed that DIRA performed well for the selected anthropomorphic phantom and that it was relatively insensitive to choice of base materials for the approximation of soft tissues. The distributions of CT-numbers of liver, muscle and kidney tissues overlapped. For example a voxel containing muscle could be misclassified as liver in 42 cases of 100. This suggests that pure thresholding is insufficient as a method for tissue classification of soft tissues and that more advanced methods should be used.

Um mimetizador de tecido, mais conhecido como phantom, é um objeto que mimetiza tecidos biológicos e são importantes para caracterização e calibração de equipamentos de imagens médicas como ultrassonografia, e no desenvolvimento de novas modalidades de imagens como a fotoacústica. Este trabalho aborda o desenvolvimento de um gel à base de óleo mineral e polímeros para phantom para aplicações em técnicas acústicas e ópticas. Os polímeros utilizados foram o elastômero tribloco tipo estireno-etileno/butileno-estireno (SEBS) e o polietileno de baixa densidade (PEBD). Foram confeccionados três grupos géis poliméricos com porcentagem de SEBS entre 5%-15% de SEBS, 0%-9% de PEBD. Os géis foram caracterizados acusticamente pela velocidade do som e coeficiente de atenuação através de transdutores de imersão com frequências entre 2,25 MHz-10 MHz, e opticamente entre 400-1200 nm pelos coeficientes de absorção, espalhamento e Albedo. Foi observada velocidade do som entre 1458,6 ± 3,1 m/s e 1480,7 ± 1,9 m/s, sendo compatíveis com valores para gordura; coeficiente de atenuação entre 0,6 ± 0,1 dB/cm a 2,25 MHz e 11,3 ± 0,1 dB/cm a 10 MHz, compatíveis para tecidos moles; coeficiente de absorção em 532 nm entre 0,11-2,62 cm-1 e em 1064 nm entre 0,09-1,70 cm-1, e uma banda de absorção em torno de 930 nm com gordura; o coeficiente de espalhamento em 532 nm entre 0,15 -3,96 cm-1 e em 1064 nm entre 0,17- 3,20 cm-1, valores inferiores para tecidos moles. O coeficiente Albedo mostrou que os géis apresentam caráter absorvedor entre 400-1200 nm. Foi desenvolvido um phantom para imagem por fotoacústica com um dos géis estudados (7%SEBS/5%PEBD) e com uma inclusão com pigmento de urucum e foram feitas imagens fotoacústicas em 532 nm e 1024 nm. Foi observado o sinal fotoacústico mais intenso para a imagem em 532 nm. Com este trabalho pode-se obter uma boa caracterização acústica e óptica de géis formados a partir de polímeros do tipo SEBS em conjunto com o PEBD ainda não descritos na literatura. Os materiais desenvolvidos se mostraram bons mimetizadores para tecidos compostos de gordura e com potencial para aplicações em fotoacústica.
Phantoms are structures composed by materials that mimic specific properties of biological tissues and they are commonly used to calibrate and characterize current medical imaging techniques such as ultrasound and optical imaging, and new imaging modalities such as photoacoustics. In this dissertation we developed an oil-based tissue mimicking gel material with mineral oil, triblock copolymer styrene-ethylene/butylene styrene (SEBS) and low-density polyethylene (LDPE). The gel phantoms were prepared mixing SEBS and LDPE in mineral oil at room temperature, varying the SEBS concentration between 5%15%, and low-density polyethylene (LDPE) between 0%-9% and glass microspheres. Acoustic properties such speed of sound and attenuation coefficient were measured using five unfocused ultrasound transducers with frequencies ranging between 2.2510 MHz. Optical properties such albedo, scattering and absorption coefficients ranging from 400-1200 nm were measured. Speed of sound from 1458.6 ± 3.1m/s and 1480.7 ± 1.9 m/s, and attenuation from 0.6 ± 0.1 dB/cm at 2.25 MHz and 11.3 ± 0.1 dB/cm at 10 MHz were observed. Absorption coefficient at 532 nm between 0.11-2.62 cm-1; at 1064 nm between 0.09-1.70 cm-1 were observed. Peak absorption around 930 nm was observed for all gels. Scattering coefficient at 532 nm between 0.15 -3.96 cm-1 and at 1064 nm between 0.17-3.20 cm-1 were found. Albedo coefficient showed that gels are absorptive characteristic for the selected range of wavelength. A phantom made with a 7% SEBS/5% LDPE gel containing an optical-absorber spherical inclusion made with the same material and annatto were developed. Photoacoustic spectroscopic images of the phantom were acquired using a laser operating at 532 nm and 1064 nm. The photoacoustic signal from the inclusion showed the highest intensities at 532 nm with as expected according to the measured absorption spectrum of annatto. With this dissertation we obtained a suitable acoustic and optical characterization of the SEBS/LDPE gels that was not described in the literature. The materials developed seem suitable to mimic fat tissue and have potential for applications in photoacoustics.

Mimetizadores do tecido biológico são objetos capazes de simular as propriedades mecânicas e acústicas do tecido biológico e são comumente chamados de phantoms. São utilizados para avaliar e calibrar equipamentos de ultrassom, auxiliar no desenvolvimento de transdutores, sistemas computacionais ou técnicas de diagnóstico e para treinamento em procedimentos médicos guiados por ultrassom, tais como biópsia de tireóide e mama, anestesia regional, entre outros. O objetivo deste trabalho foi avaliar o efeito da reticulação com glutaraldeído sobre as propriedades das blendas gelatina/poli (álcool vinílico) visando à produção de um material para ser usado como mimetizador do tecido biológico para ultrassonografia (phantoms). Inicialmente blendas de gelatina/PVA com diferentes concentrações dos polímeros na mistura (80/20, 60/40 e 40/60) foram preparadas e caracterizadas. Posteriormente, estas blendas foram reticuladas com 0,5% de glutaraldeído em pH 4 e 5 durante 5, 15, 30 e 60 min, e também com 1,0% de glutaraldeído em pH 5 durante 5min, pois observou-se que este tempo foi suficiente para obter um material com boas propriedades. As blendas foram caracterizadas em função de suas propriedades mecânicas, ângulo de contato, perda de umidade, velocidade de propagação do som e coeficiente de atenuação acústica. A concentração dos polímeros na blenda influenciou nas propriedades mecânicas, higroscópicidade e na perda de umidade dos géis formados. Assim, um aumento na concentração de PVA diminuiu a rigidez e o módulo de Young, e aumentou a velocidade do som das blendas gelatina/PVA. Acima de 60% de PVA houve separação de fases nas blendas com e sem reticulação. A reticulação com glutaraldeído aumentou a rigidez e diminuiu a hidrofilicidade da blenda. A blenda gelatina/PVA 80/20 reticulada com 0,5% de glutaraldeído em pH 5 apresentou as características mais promissoras para o desenvolvimento de materiais mimetizadores do tecido biológico.
Tissue mimicking materials are objects capable of mimic mechanical and acoustic properties of biological tissues and are commonly called phantoms. These objects are used to evaluate and calibrate ultrasound machines, development ultrasound transducer, informatics system or diagnostic techniques and for ultrasound-guided procedures training such as thyroid and breast biopsy, regional anesthesia, and others. The aim of this study was to evaluate the effect of the cross-linked of gelatin/polyvinyl alcohol (PVA) blends utilizing glutaraldehyde, resulting in a material for applications in ultrasound guided training phantoms. Gelatin/PVA blends were prepared with different concentrations of each polymer (80/20, 60/40, and 40/60) and characterized. Also, the same concentrations of the blends were cross-linked using 0.5% glutaraldehyde at pH4 and 5 for 5, 15, 30 and 60 minutes, and 1.0 % of glutaraldehyde at pH 5 for 5 minutes. The resulting blends were characterized by mechanical properties, contact angle, moisture loss, speed of sound and acoustic attenuation. The concentration of the polymers influenced over the mechanical properties, hygroscopicity e moisture loss of the manufactured blends. The increase of the amount of the PVA in the manufactured blends decreased the stiffness and increased the acoustic attenuation, moisture loss, hygroscopicity and speed of sound. Blends with more than 60% of PVA resulting in phase separation of the material. Glutaraldehyde cross-linked gelatin/PVA blend with a proportion of 80/20 with 0.5% of glutaraldehyde at pH 5 presented the most suitable properties for ultrasound-guided training phantoms.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 27-30).
Glial scar tissue forms in the brain as a response to the implant injury and hampers the effectiveness of the implant treatment. Constant relative micromotion between the mechanically mismatched neural implant and brain tissue is thought to play a key role glial scar formation. This study investigated the effects of poly(ethylene glycol) (PEG) hydrogel coatings for glass brain implant devices on strain fields imposed by those devices to brain tissue due to micromotion in the brain. PEG hydrogels were created using macromers of 2000-8000 Mw and 5-20 wt.% in solution. The moduli of the hydrogels were calculated via Hertzian analysis of force-deflection curves produced using an AFM tip as a nanoindenter. The moduli of the samples did not change significantly with change in macromer Mw, but did change with solution concentration. 20% gels had moduli of 120-180 kPa and 5-10% gels had moduli of 0-20 kPa. The strains imposed by the coated devices were found to be lower at the surface by ~30% as compared to uncoated and the strain field dropped off much more quickly.
by Maxwell Ethan Plaut.
S.B.

Many applications of ultrasound test phantoms require that the acoustical properties of the phantom should closely match those of soft tissue. Numerous commercial test phantoms of this type are available for use with clinical ultrasound scanners, which use frequencies up to 20 MHz. However, scanners designed for imaging small animals in preclinical studies, typically operate at much higher frequencies. No commercially available test phantoms exist for use at frequencies above 20 MHz. The aim of this work was to develop a tissue-mimicking-material (TMM) that closely matches the acoustic properties of small animal tissues at high frequencies (HF). Such a material would, therefore, be suitable for ultrasound test phantoms for application with HF ultrasound scanners (20 MHz to 50 MHz). A three-step approach was adopted to address this lack of a suitable HF-TMM. Firstly, verify the acoustic characteristics of the existing IEC agar-based TMM. Secondly, establish the acoustic properties (speed of sound and attenuation coefficient) of small animal tissue at high frequencies. Thirdly, develop a TMM which exhibits, as closely as possible, these small animal tissue acoustic characteristics. A pulse-echo substitution method was used throughout to characterise the materials and the tissue samples. The speed of sound and attenuation coefficient of an IEC agar-based TMM were measured using two different techniques. Initially, a widely used method was tried, where samples are wrapped in film and placed in degassed, deionised water for assessment. The second technique was developed and validated for use in this work. In this method, TMM samples were uncovered (without film) and were both stored and assessed in a TMM preserving fluid. The second method provided up to four times more consistent results. The acoustical properties of the individual components of the IEC agar-based TMM were then measured in order to determine whether the overall attenuation coefficient of the agar TMM was a linear sum of the attenuation coefficients of its component parts. Within experimental uncertainties, this was found to be the case. This is a key observation from which the formulation of an agar TMM, matching the acoustic properties of small animal tissue, can be facilitated. The acoustical properties (speed of sound and attenuation coefficient) of mouse brain, liver, and kidney were measured using a preclinical ultrasound scanner.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Pour contourner la difficulté de maillage des méthodes numériques existantes de l’homogénéisation des composites, une méthode originale, nommée la méthode des éléments finis du domaine fantôme (PFEM), est proposée dans cette thèse. Le PFEM s'appuie sur les calculs d'intégrales avec des maillages distincts basés sur un principe de domaine fictif. En d'autres termes, un maillage structuré est utilisé pour l'ensemble du domaine et les autres maillages indépendants sont utilisés pour les inclusions. Les maillages des inclusions seront liés au maillage du domaine via une matrice de substitution. Le PFEM est non seulement capable de calculer les propriétés effectives avec KUBC, SUBC et les conditions périodiques, mais aussi peut être utilisé dans tous les problèmes qui peuvent être résolus par le FEM classique, comme les problèmes aux limites de Dirichlet ou de Neumann. Des expériences numériques dans les cas 2D et 3D, avec des inclusions de géométrie élémentaire telles que disque, carré, sphère, cube et ellipsoïde, ont été réalisées pour valider le PFEM. Les convergences linéaires d'erreurs relatives par rapport aux solutions de référence telles que le modèle de Mori-Tanaka et la méthode de transformation de Fourier rapide sont présentées pour les propriétés effectives en thermique et en élastique. Nous avons illustrés quelques caractéristiques intéressantes du PFEM, par exemple la flexibilité au niveau du maillage d'inclusion, en montrant un exemple avec une pellicule sphérique très mince
To circumvent the meshing difficulty of the existing numerical methods for composites homogenization, an original finite element method,named Phantom domain Finite Element Method (PFEM), is proposed in this thesis. The PFEM relies on computations of integrals with independent meshes based on a fictitious domain principle. In other words, one structured mesh is used for the entire domain, and independent meshes are used for the inclusions. The inclusion meshes will be related to the structured mesh through a substitution matrix. The PFEM is not only capable of calculating effective properties in homogenization technique with KUBC, SUBC and periodic condition, but also can be used in all the problems which can be solved by the FEM, such as the Dirichlet or Neumann boundary value problems. Numerical experiments in two or three dimensional cases, with inclusions of elementary geometry such as disk, square, sphere,cube and ellipsoid, have been performed to validate the PFEM method. Linear convergences of relative errors with respect to reference solutions such as the Mori-Tanaka model and the Fast Fourier Transform method are shown for thermal and elastic effective properties. We have illustrated some interesting features of the PFEM, such as the total flexibility concerning the inclusions meshes, by showing an example with a very thin pellicle sphere

Conselho Nacional de Desenvolvimento Científico e Tecnológico
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Fundação de Amparo a Pesquisa do Estado de Minas Gerais
Os desenvolvimentos teóricos e experimentais na área de biomateriais têm sido aplicados diretamente a distintos campos da Medicina (odontologia, medicina regenerativa e radioterapia). Esses avanços foram concentrados tanto para diagnosticar doenças como para a quantificação de seus graus de progressão. Na perspectiva desses estudos, biomateriais estão sendo projetados e confeccionados para aplicação em diversas áreas da ciência, proporcionado avanços no radiodiagnóstico, na dosimetria para radioterapia e na calibração de equipamentos radioterápicos. Desenvolver um phantom a partir de um biomaterial se tornou um grande aliado da Medicina no tratamento de pacientes com doenças oncológicas, possibilitando melhor desempenho dos equipamentos, com a finalidade de redução dos danos causados ao tecido sadio devido ao excesso de exposição à radiação. Este trabalho utilizou polímeros: quitosana e gelatina para confecção das estruturas poliméricas e foi possível controlar as diferentes formas de produção e processamento, caracterizar e avaliar o biopolímero por técnicas físicas (ELT,MEV, e DEI) e, por consequência, analisar a aplicabilidade como phantom pulmonar de camundongo. Foi possível avaliar a morfologia dos biomateriais quantitativamente por microscopia eletrônica de varredura associada a técnica de imagem. A relevância deste trabalho se concentra em desenvolver um phantom a partir de biomateriais poliméricos que possa atuar como objeto simulador fornecendo alto contraste de imagem quando submetido a análise. Dessa forma, a escolha da técnica DEI foi satisfatória uma vez que trata-se de uma técnica de imagem de raios X de alta resolução. As imagens obtidas por DEI têm mostrado os detalhes da microestrutura interna dos biomateriais produzidos as quais possuem ≈ 10 μm de dimensão. Os phantoms confeccionados apresentaram densidade variando de 0,08 a 0,13 g/cm3.
The theoretical and experimental developments in the biomaterials area have been directly applied to different fields of Medicine (odontology, regenerative medicine and radiotherapy). These advances have focused both for diagnosing diseases such as for quantifying degrees of progression. From the perspective of these studies, biomaterials are being designed and manufactured for application in various areas of science, provided advances in diagnostic radiology, radiotherapy dosimetry and calibration of radiotherapy equipment. Develop a phantom from a biomaterial has become a great ally of medicine in the treat patients with oncological diseases, allowing better performance of the equipment in order to reduce damage to healthy tissue due to excessive exposure to radiation. This work used polymers: chitosan and gelatin, for making the polymeric structures and controlled for different types of production and processing, characterizing and evaluating the biopolymer by physical techniques (STL, SEM and DEI) and therefore analyze applicability as phantom mouse lung. It was possible to evaluate the morphology of biomaterials quantitatively by scanning electron microscopy associated with imaging technique. The relevance of this work focuses on developing a phantom from polymeric biomaterials that can act as phantom providing high image contrast when subjected to analysis. Thus, the choice of DEI technique is satisfactory since it is an imaging technique of X-ray high resolution. The images obtained by DEI have shown the details of the internal microstructure of the biomaterial produced which have ≈ 10 μm dimension. The phantoms had made density ranging from 0.08 a 0.13 g/cm3.
Tese (Doutorado)

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O aumento na longevidade humana fez surgir uma série de doenças com a idade; em contrapartida o avanço da medicina possibilitou o diagnóstico precoce e o tratamento de várias doenças antes incuráveis. Esse cenário atual estendese também aos animais domésticos (cães e gatos - PETs) que dobraram sua expectativa de vida nas últimas décadas, fato que os humanos demoraram séculos para alcançar. Do mesmo modo que os humanos, esse aumento na longevidade dos animais veio acompanhado de doenças relacionadas com a idade, entre elas o câncer. Uma das terapias utilizadas atualmente no tratamento do câncer é a radioterapia, técnica que utiliza a radiação ionizante para destruir as células tumorais (volume-alvo) com mínimo prejuízo aos tecidos circunvizinhos sadios (órgãos de risco). Essa técnica exige a realização periódica de testes de controle de qualidade, incluindo a dosimetria com a utilização de objetos simuladores equivalentes ao tecido, de modo a verificar a dose de radiação recebida pelo paciente em tratamento e compará-la posteriormente com a dose de radiação calculada pelo sistema de planejamento. A rápida expansão do mercado de impressoras 3D abriu caminho para uma revolução na área da saúde. Atualmente os objetos simuladores por impressão 3D estão sendo usados em planejamentos de Radioterapia para a localização espacial e mapeamento das curvas de isodose, realizando, assim, um planejamento mais personalizado para cada campo de radiação, além da confecção de implantes dentais, customização de próteses e confecção de bólus. Diante do exposto esse trabalho projetou e desenvolveu um objeto simulador chamado de \"Canis Morphic\" utilizando uma impressora 3D e materiais tecido-equivalentes para a realização dos testes de controle de qualidade e otimização das doses na área de Radioterapia em animais (cães). Os resultados obtidos demonstraram-se promissores na área de criação de simuladores por impressão 3D, com materiais de baixo custo, para aplicação no controle de qualidade em Radioterapia veterinária.
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
Mammography is a diagnostic imaging method in which interpretation depends on knowledge of radiological aspects as well as the clinical exam and pathophysiology of breast diseases. In this work a mammography phantom was developed to be used for training in the operation of mammographic x-ray equipment, image quality evaluation, self-examination and clinical examination of palpation. Polyurethane was used for the production of the phantoms for its physical and chemical properties and because it is one of the components normally used in prostheses. According to the range of flexibility of the polyurethane, it was possible to simulate breasts with higher or lower amount of adipose tissue. Pathologies such as areolar necrosis and tissue rejection due to surgery reconstruction after partial mastectomy were also simulated. Calcifications and nodules were simulated using the following materials: polyethylene, poly (methyl methacrylate), polyamide, polyurethane and poly (dimethyl silicone). Among these, polyethylene was able to simulate characteristics of calcification as well as breast nodules. The results from mammographic techniques used in this paper for the evaluation of the phantoms are in agreement with data found in the literature. The image analyses of four phantoms indicated significant similarities with the human skin texture and the female breast parenchyma. It was possible to detect in the radiographic images produced regions of high and low radiographic optical density, which are characteristic of breasts with regions of different amount of adipose tissue. The stiffnesses of breast phantoms were adjusted according to the formulation of the polyurethane which enabled the production of phantoms with distinct radiographic features and texture similar to human female breast parenchyma. Clinical palpation exam of the phantoms developed in this work indicated characteristics similar to human breast in skin texture, areolar region and parenchyma
A mamografia ? um m?todo de diagn?stico por imagem, cuja interpreta??o depende do conhecimento dos aspectos radiol?gicos assim como da cl?nica e da fisiopatologia das doen?as mam?rias. A metodologia deste trabalho permitiu o desenvolvimento de um simulador (phantom) mam?rio com aplica??o voltada para o uso did?tico em equipamento mamogr?fico, avalia??o de qualidade da imagem dos equipamentos mamogr?ficos, autoexame e treinamento did?tico para o exame cl?nico de palpa??o. O material usado para a produ??o do simulador foi ? base de poliuretano sendo consideradas suas propriedades f?sicas, qu?micas e por ser este um dos componentes de pr?teses utilizadas em seres humanos. Variando a faixa de flexibilidade do poliuretano foi poss?vel simular mamas com maior e menor quantidade de tecido adiposo, resultados verificados nas imagens dos exames mamogr?ficos. Patologias de necrose da ar?ola da mama e degenerativas ocasionadas por rejei??o de tecido devido ? cirurgia de reconstitui??o ap?s mastectomia parcial, tamb?m foram simuladas. Calcifica??es e n?dulos foram simulados utilizando os seguintes materiais: polietileno, poli(metacrilato de metila), poliamida, poliuretano e o poli(silicone de dimetila). Destaca-se entre estes materiais o polietileno que apresentou caracter?sticas tanto de calcifica??o quanto n?dulo. Os resultados das t?cnicas mamogr?ficas utilizadas neste trabalho para os exames mamogr?ficos dos phantoms est?o de acordo com a faixa de valores encontrados na literatura. A an?lise das imagens realizadas para quatro phantoms indicaram semelhan?as significativas com a textura da pele e do par?nquima da mama humana feminina. Foi poss?vel detectar nas imagens radiogr?ficas geradas regi?es de baixa e alta densidade ?ptica radiogr?fica, caracter?stica de mamas com regi?es de menor e maior quantidade de tecido adiposo. Devido ? formula??o do poliuretano formado ocorreu varia??o da rigidez do simulador mam?rio, o que possibilitou a produ??o de mamas com caracter?sticas radiogr?ficas distintas al?m de textura similar ao par?nquima da mama humana feminina. Foram observadas as caracter?sticas similares da textura da pele, regi?o areolar e par?nquima no exame cl?nico palpat?rio dos simuladores desenvolvidos neste trabalho

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O propósito de um objeto simulador é representar a alteração do campo de radiação provocada pela absorção e espalhamento em um dado tecido ou órgão de interesse. Suas características geométricas e de composição devem estar próximos o máximo possível aos valores associados ao seu análogo natural. Estruturas anatômicas podem ser transformadas em objetos virtuais 3D por técnicas de imageamento médico (p. ex. Tomografia Computadorizada) e impressas por prototipagem rápida utilizando materiais como, por exemplo, o ácido poliláctico. Sua produção para pacientes específicos requer o preenchimento de requisitos como a acurácia geométrica com a anatomia do individuo e a equivalência ao tecido, de modo que se possa realizar medidas utilizáveis, e ser insensível aos efeitos da radiação. O objetivo desse trabalho foi avaliar o comportamento de materiais impressos 3D quando expostos a feixes de fótons diversos, com ênfase para a qualidade de radiotherapia (6 MV), visando a sua aplicação na dosimetria clínica. Para isso foram usados 30 dosímetros termoluminescentes de LiF:Mg,Ti. Foi analisada também a equivalência entre o PMMA e o PLA impresso para a resposta termoluminescente de 30 dosímetros de CaSO4:Dy. As irradiações com feixes de fótons com qualidade de radioterapia foram simuladas com o uso do sistema de planejamento Eclipse™, com o Anisotropic Analytical Algorithm e o Acuros® XB Advanced Dose Calculation algorithm. Além do uso do Eclipse™ e dos testes dosimétricos, foram realizadas simulações computacionais utilizando o código MCNP5. As simulações com o código MCNP5 foram realizadas para calcular o coeficiente de atenuação de placas impressas expostas a diversas qualidades de raios X de radiodiagnóstico e para desenvolver um modelo computacional de placas impressas 3D.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Peripheral vascular grafts are used for the treatment of peripheral arterial disease and arteriovenous grafts for vascular access in end stage renal disease. The development of neo-intimal hyperplasia and thrombosis in the distal anastomosis remains the main reason for occlusion in that region. The local haemodynamics produced by a graft in the host vessel is believed to significantly affect endothelial function. Single spiral flow is a normal feature in medium and large sized vessels and it is induced by the anatomical structure and physiological function of the cardiovascular system. Grafts designed to generate a single spiral flow in the distal anastomosis have been introduced in clinical practice and are known as spiral grafts. In this work, spiral peripheral vascular and arteriovenous grafts were compared with conventional grafts using ultrasound and computational methods to identify their haemodynamic differences. Vascular-graft flow phantoms were developed to house the grafts in different surgical configurations. Mimicking components, with appropriate acoustic properties, were chosen to minimise ultrasound beam refraction and distortion. A dual-beam two-dimensional vector Doppler technique was developed to visualise and quantify vortical structures downstream of each graft outflow in the cross-flow direction. Vorticity mapping and measurements of circulation were acquired based on the vector Doppler data. The flow within the vascular-graft models was simulated with computed tomography based image-guided modelling for further understanding of secondary flow motions and comparison with the experimental results. The computational assessments provided a three-dimensional velocity field in the lumen of the models allowing a range of fluid dynamic parameters to be predicted. Single- or double-spiral flow patterns consisting of a dominant and a smaller vortex were detected in the outflow of the spiral grafts. A double- triple- or tetra-spiral flow pattern was found in the outflow of the conventional graft, depending on model configuration and Reynolds number. These multiple-spiral patterns were associated with increased flow stagnation, separation and instability, which are known to be detrimental for endothelial behaviour. Increased in-plane mixing and wall shear stress, which are considered atheroprotective in normal vessels, were found in the outflow of the spiral devices. The results from the experimental approach were in agreement with those from the computational approach. This study applied ultrasound and computational methods to vascular-graft phantoms in order to characterise the flow field induced by spiral and conventional peripheral vascular and arteriovenous grafts. The results suggest that spiral grafts are associated with advanced local haemodynamics that may protect endothelial function and thereby may prevent their outflow anastomosis from neo-intimal hyperplasia and thrombosis. Consequently this work supports the hypothesis that spiral grafts may decrease outflow stenosis and hence improve patency rates in patients.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1988.
Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 84-88).

The radiation dose in radiation therapy is mainly measured by ion chamber. The ion chamber measurement will not be accurate if there is not enough phantom material surrounding the ion chamber to provide the electron equilibrium condition. The lack of electron equilibrium will cause a reduction of dose. This may introduce problems in treatment planning. Because some planning algorithms cannot predict the reduction, they over estimate the dose in the region. Electron disequilibrium will happen when the radiation field size is too small or the density of irradiated material is too low to provide sufficient electrons going into the dose volume. The amount of tissue required to provide electron equilibrium in a 6MV photon beam by three methods: direct calculation from Klein-Nisina equation, measurement in low density material phantom and a Monte Carlo simulation is done to compare with the measurement, an indirect method from a planning algorithm which does not provide an accurate result under lateral electron disequilibrium. When the error starts to happen in such planning algorithm, we know that the electron equilibrium conditions does not exist. Only the 6MV photon beam is investigated. This is because in most cases, a 6MV small fields are used for head and neck (larynx cavity) and 6MV fields are commonly used for lung to minimise uncertainity due to lateral electron at higher energies.

碩士
國立屏東科技大學
材料工程研究所
104
We use the hiding gelatin, oil, organic-inorganic composite materials etc., to form the biomimetic materials. These biomimetic materials are similar in many different parts of the body of biological tissue. By varying the ratio of oil, it can be selected to mimic the human body in different parts of biological tissue, and can be measured in the microwave frequency range between 500 MHz to 20 GHz to find the trend of characteristics of dielectric constant and conductivity. Effect of dopants on the dielectric characteristics, long-term stability, and conductivity also be discussed in this study. Without doping, the dielectric constant was equal to 23±2 approximately. Results showed with doping of carbon based materials that the dielectric constant and conductivity both increased about 5% to 20%, and the increment was dependent on the doping amount. By properselection of doping amount of the carbon based materials, the prepared material could map the required dielectric properties of special tissues. The proposed materials were suitable for the phantom used in the microwave medical imaging system.

碩士
國立陽明大學
放射醫學科學研究所
94
Abstract Brachytherapy is a method of treatment in which sealed radioactive sources are used to deliver radiation at a short distance by interstitial, intracavitary. The treatment planning system (TPS) based on the dosimetry around brachytherapy source 192Ir in water. Most of previous studies bases on the dosimetry around brachytherapy source 192Ir in water. The purpose of this study is to analysis the dose distribution near the interface of different phantom materials around brachytherapy source 192Ir. In this study, a Monte Carlo (MC) simulation has been used to calculate the dose distribution in water, bone, lung ,and interface regions, respectively. MD55 Gafchromic film, glass dosimeter (GD), solid water phantom, bone phantom, and lung tissue phantom are used in this work. GD and film measurement are also performed to verify the results of MC simulation, respectively. The MC simulation results of radial dose function and anisotropy function in water are in agreement with published data. The dose distribution in bone shows more attenuation and scatter than in water. In contrast, the dose distribution in lung shows more less attenuation and scatter than in water. The MC simulation results and measurement data are in agree within 5% to each other while the radial distance is larger than 0.5cm. The interface dose difference between tissue lung-bone, water-lung, and water-bone are ranging from 6.18 to 13.84%, 1.59 to 12.05%, 0.29 to 1.39%, respectively. The TPS must be adjustment according to the density of tissue to improve the dose output value and medical quality. Keyword : Monte Carlo, Gafchromic film, glass dosimeter

This work describes the development of an optical probe for measuring movement of tissue particles deep inside which are loaded by an ultrasound remote palpation device. The principle of the method is that ultrasound force which can be applied inside the tissue makes the tissue particles vibrate and this vibration phase-modulates the light intercepting the insoniified region which results in a modulated speckle intensity on detection outside the object. This speckle intensity modulation detected through the measured intensity autocorrelation is a measure of the vibration amplitude. Since the vibration amplitude is related to the local elastic properties of the medium, the measured modulation depth in intensity autocorrelation can be used to map the elastic property in the insonified region. In this work, first the ultrasound induced force is calculated for both plane and focused ultrasound beams, and converted to amplitude of vibration and refractive index modulation, solving the forward elastography equation. Light propagation inside an insonified object is modelled using Monte Carlo simulation and the amplitude and intensity correlations are computed. The modulation depth on the autocorrelation is estimated and shown that it is inversely correlated to the local elastic modulus and optical absorption coefficient. It is further shown that whereas the variation in modulation depth is linear with respect to absorption coefficient, the same variation with elastic property is nonlinear. These results are verified experimentally in a tissue mimicking phantom. The phantom was constructed out of poly vinyl alcohol(PVA) whose optical, mechanical and acoustic properties are independently controlled. It is also shown that for loading with focused ultrasound beam the displacement is almost along the ultrasound transducer axis and therefore the contribution from refractive index modulation alone can be ascertained by probing the insonified perpendicular to the transducer axis. This helps one to find the contribution to the modulation depth from the ultrasound-induced vibration, which can be used to compute a quantitative estimate of the elastic modulus from the modulation depth.

[ES] La constante evolución de la tecnología y la búsqueda de nuevas aplicaciones que mejoren la vida de las personas ha llevado a la incorporación de estas tecnologías en el organismo. Las redes inalámbricas de área corporal (WBAN) son un buen ejemplo de esto, que consisten en redes de comunicaciones ubicadas en el propio cuerpo, tanto en la superficie como implantadas en su interior mediante el uso de dispositivos inalámbricos. Estas redes utilizan el cuerpo humano como medio de transmisión, por lo que debe evaluarse la influencia del mismo sobre la propagación. Además, las nuevas generaciones de comunicaciones móviles se están moviendo hacia el uso de frecuencias cada vez más altas, como las ondas milimétricas, que son más sensibles a la presencia de cualquier objeto en el entorno, incluidos los humanos. La investigación y el diseño de antenas y dispositivos que tengan en cuenta el cuerpo humano requiere pruebas en el entorno donde se supone que deben usarse. Los fantomas se convierten en una herramienta para evaluar la transmisión de señales electromagnéticas en un medio equivalente al cuerpo para evitar la experimentación en humanos o animales. Además de eso, se puede estudiar la influencia de estas ondas electromagnéticas sobre los propios tejidos en cuanto a la tasa de absorción específica (SAR).
[CAT] L'evolució constant de la tecnologia i la recerca de noves aplicacions que milloren la vida de les persones ha portat a la incorporació d'aquestes tecnologies en l'organisme. Les xarxes sense fils d'àrea corporal (WBAN) són un bon exemple d'açò, que consisteixen en xarxes de comunicacions ubicades al propi cos, tant en la superfície com implantades en el seu interior mitjançant l'ús de dispositius sense fils. Aquestes xarxes empren el cos humà com a medi de transmissió, per la qual cosa se n'ha d'avaluar la influència sobre la propagació. A més, les noves generacions de comunicacions mòbils s'estan movent cap a l'ús de freqüències cada vegada més altes, com les ones mil·limètriques, que són més sensibles a la presència de qualsevol objecte en l'entorn, incloent-hi els humans. La investigació i el disseny d'antenes i dispositius que tinguen en compte el cos humà requereix proves en l'entorn on se suposa que han d'usar-se. Els fantomes esdevenen una eina per a avaluar la transmissió de senyals electromagnètics en un medi equivalent al cos per tal d'evitar l'experimentació en humans o animals. A més d'això, es pot estudiar la influència d'aquestes ones electromagnètiques sobre els teixits mateixos en relació amb la taxa d'absorció específica (SAR).
[EN] The constant evolution of technology and the search for new applications that improve people's lives has led to the arrival of the incorporation of these technologies in the organism. Wireless body area networks (WBANs) are a good example of this, consisting of communications networks located in the body itself, both on the surface and implanted inside it through the use of wireless devices. These networks use the human body as the transmitting medium, so its influence over the propagation has to be assessed. Besides, new generations of mobile communications are moving towards the use of higher frequencies, as the millimetre waves, which are more sensitive to the presence of any object in the environment, including humans. The research and design of antennas and devices that take into account the human body requires testing in the environment where these are supposed to be used. Phantoms become a tool for evaluating the transmission of electromagnetic signals in a body-equivalent medium in order to avoid experimentation on humans or animals. In addition to that, the influence of these electromagnetic waves over the tissues themselves can be studied with regard to the specific absorption rate (SAR).
This thesis has been possible thanks to the funding contribution of the Universitat Polit`ecnica de Val`encia through the PAID-01-16 programme. This work was also supported by the UPV-IIS La Fe programme (STUDER, 2016 and EMOTE, 2017). The research stay was supported by the European Union’s Erasmus+ funding programme under a traineeship grant.
Castelló Palacios, S. (2019). Wideband Electromagnetic Body Phantoms for the Evaluation of Wireless Communications in the Microwave Spectrum [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/132182
TESIS

Η υπερθερμία αποτελεί μια επικουρική μέθοδο θεραπείας του καρκίνου και η βιοϊατρική έρευνα τις τελευταίες δεκαετίες, με σκοπό την εκμετάλλευση και την ανάδειξη των ιδιοτήτων της μεθόδου, στοχεύει στην εφαρμογή της στην κλινική πράξη. Μία προσπάθεια με παρόμοιο σκοπό γίνεται τα τελευταία χρόνια στο Εργαστήριο Μικροκυμάτων και Οπτικών Ινών (ΕΜΟΙ) της σχολής Ηλεκτρολόγων Μηχανικών και Μηχανικών Υπολογιστών (ΗΜΜΥ) του Εθνικού Μετσόβιου Πολυτεχνείου, όπου έχει σχεδιαστεί και κατασκευαστεί ένα σύστημα υπερθερμίας. Το προτεινόμενο σύστημα ενσωματώθηκε σε ένα τρισδιάστατο σύστημα παθητικής μικροκυματικής ραδιομετρικής απεικόνισης (ΜiRaIS) για διαγνωστικές εφαρμογές εγκεφάλου, το οποίο μελετήθηκε και κατασκευάστηκε στα πλαίσια διδακτορικής διατριβής στο ίδιο εργαστήριο της σχολής ΗΜΜΥ. Στην παρούσα διπλωματική εργασία γίνεται η θεωρητική και πειραματική μελέτη του προτεινόμενου συστήματος της υπερθερμίας. Η αρχή λειτουργίας του είναι όμοια με αυτή του MiRaIS και βασίζεται στη χρήση μια ελλειψοειδούς αγώγιμης κοιλότητας για εστίαση της ακτινοβολίας επιλεκτικά στους ιστούς που χρήζουν θεραπείας. Ο ανακλαστήρας για εστίαση, που κατασκευάστηκε και χρησιμοποιήθηκε στην πειραματική διαδικασία, βελτιώνει την εργονομία του συστήματος, διατηρώντας παράλληλα της ιδιότητες εστίασης του πρωτότυπου ελλειψοειδούς. Στα πλαίσια της παρούσας διπλωματικής εργασίας πραγματοποιήθηκε θεωρητική μελέτη και μοντελοποίηση της διάταξης με σκοπό τη βελτίωση των ιδιοτήτων εστίασής της, καθώς και πειραματικές μετρήσεις του συνολικού συστήματος υπερθερμίας-μικροκυματικής ραδιομετρίας. Στη θεωρητική μελέτη, με χρήση του λογισμικού xFDTD που βασίζεται στη μέθοδο των πεπερασμένων διαφορών στο πεδίο του χρόνου, ερευνώνται δυο μέθοδοι για τη βελτίωση των ιδιοτήτων εστίασης του συστήματος (βάθος διείσδυσης της ακτινοβολίας, χωρική διακριτική ικανότητα) με τη χρήση διηλεκτρικών υλικών. Τα υλικά αυτά τοποθετούνται στο εσωτερικό του ελλειψοειδούς καθώς και γύρω από το μοντέλο κεφαλιού ως στρώματα προσαρμογής για την επίτευξη βηματικής αλλαγής της διηλεκτρικής σταθεράς στη διεπιφάνεια αέρα-μοντέλο ανθρώπινου κεφαλιού. Στην πρώτη προσέγγιση, το εσωτερικό του ελλειψοειδούς ανακλαστήρα γεμίζει με διηλεκτρικό υλικό χαμηλών απωλειών, με τα αποτελέσματα να δείχνουν σημαντική βελτίωση της χωρικής διακριτικής ικανότητας του συστήματος. Στη δεύτερη προσέγγιση του προβλήματος, χρησιμοποιείται ένα ημισφαίριο από διηλεκτρικό γύρω από το μοντέλο κεφαλιού, με τα αποτελέσματα να δείχνουν την αντίστοιχη βελτίωση της χωρικής διακριτικής ικανότητας και παράλληλα σημαντική μείωση των ανεπιθύμητων περιοχών εστίασης της ενέργειας. Η πειραματική διάταξη τοποθετήθηκε σε ανηχοϊκό θάλαμο, όπου και πραγματοποιήθηκαν όλες οι μετρήσεις. Παράλληλα με τα πειράματα υπερθερμίας, μελετήθηκε η δυνατότητα εφαρμογής της μεθόδου της μικροκυματικής ραδιομετρίας με τη γεωμετρία του προτεινόμενου συστήματος. Η μέθοδος της μικροκυματικής ραδιομετρίας θα μπορούσε να παρέχει τον έλεγχο της θερμοκρασίας της ακτινοβολούμενης περιοχής κατά τη διάρκεια των συνεδριών της υπερθερμίας. Στις πειραματικές διαδικασίες που ακολουθήθηκαν, χρησιμοποιήθηκαν ομοιώματα νερού, τα οποία στη φάση της υπερθερμίας υπέδειξαν τις περιοχές εστίασης της ενέργειας για τη συχνότητα ακτινοβολίας, ενώ στη φάση της μικροκυματικής ραδιομετρίας βοήθησαν στη μελέτη της θερμοκρασιακής διακριτικής ικανότητας του συστήματος. Επίσης, διενεργήθηκαν μετρήσεις με στρώματα προσαρμογής από διηλεκτρικά υλικά, τα οποία τοποθετούνταν γύρω από το αντικείμενο ενδιαφέροντος, για την πληρέστερη κατανόηση της επίδρασης των υλικών αυτών στις ιδιότητες εστίασης του συστήματος και για την επιβεβαίωση των αντίστοιχων θεωρητικών αποτελεσμάτων.
The application of hyperthermia process has been widely used in clinical research and efforts are being made for its implementation in clinical practice, as many researchers have used this method as an adjunct treatment procedure for cancer. During the past two decades, a great deal of research has been carried out, with the aim of developing effective techniques for hyperthermia treatment, primarily using RF, microwave, and ultrasound energy. A similar effort is carried out in the Laboratory of Microwaves and Fiber Optics (MFOL), School of Electrical and Computer Engineering, National Technical University of Athens (NTUA), where a proposed hyperthermia system has been designed and constructed. A system for deep brain hyperthermia treatment, designed to also provide passive measurements of temperature and/or conductivity variations inside the human body, is presented in this paper. The proposed system comprises both therapeutic and diagnostic modules, operating in a totally contactless way, based on the use of an ellipsoidal beamformer to achieve focusing on the areas under treatment and monitoring. The radiometry monitoring module, the Three Dimensional Passive Microwave Radiometry Imaging System (MiRaIS), has been studied, designed and constructed in the framework of a PhD thesis in the same laboratory of MFOL. In the present thesis, the proposed system is theoretically and experimentally studied. The operation principal is based on the use of an ellipsoidal conductive wall cavity for focusing the emitted radiation on the tissues that should accept treatment. The ellipsoidal cavity, which was constructed and used in the experimentation procedure, is newly developed and improves the system’s ergonomy retaining at the same time the focusing properties of the prototype system. In the framework of the present study, theoretical modelling and experimentation of the proposed system was carried out in order to examine and improve its focusing attributes. In the theoretical study, two methods for the improvement of the system’s focusing properties (e.g. penetration depth of the electromagnetic field, spatial sensitivity) using dielectric materials are tested with the use of a commercially available software tool, xFDTD (x-Finite Difference Time Domain). The materials are placed inside the ellipsoidal or used as matching layers around the head model for the achievement of a stepped change of the refraction index on the air-human head model interface. In the first approach, the ellipsoidal volume is filled with a low loss dielectric material in order to improve the system’s spatial sensitivity. In the second approach, a hemi-sphere also filled with a dielectric material is placed around the human head model and the results revealed the improvement of the system’s spatial sensitivity and the reduction of the undesirable auxiliary energy-absorbing areas. The experiments were performed inside an anechoic chamber providing maximum accuracy by avoiding any external interference. Along with the hyperthermia experiments, the implementation of the microwave radiometry process was also tested with the proposed system. Microwave radiometry could provide the temperature monitoring of the radiated area during the hyperthermia sessions. In the experimental procedures water phantoms were used, which during hyperthermia indicated the energy-absorbing areas at the irradiation frequency, and during microwave radiometry revealed the system’s temperature sensitivity. Also, measurements were conducted using dielectric matching layers, placed around the medium of interest, in order to fully understand the effect of those materials on the system’s focusing properties as well as to confirm the respective theoretical results. Taking into consideration the present study and the advantage of the non invasive character of the proposed brain hyperthermia system, it is concluded that further research is required in order to explore its potentials at becoming a part of the standard treatment protocol of brain malignancy in the future.

Η υπερθερμία αποτελεί μια επικουρική μέθοδο θεραπείας του καρκίνου και η βιοϊατρική έρευνα τις τελευταίες δεκαετίες, με σκοπό την εκμετάλλευση και την ανάδειξη των ιδιοτήτων της μεθόδου, στοχεύει στην εφαρμογή της στην κλινική πράξη. Μια προσπάθεια με παρόμοιο σκοπό γίνεται τα τελευταία χρόνια στο Εργαστήριο Μικροκυμάτων και Οπτικών Ινών (ΕΜΟΙ) της σχολής Ηλεκτρολόγων Μηχανικών και Μηχανικών Υπολογιστών (ΗΜΜΥ) του Εθνικού Μετσόβιου Πολυτεχνείου, όπου έχει σχεδιαστεί και κατασκευαστεί ένα μικροκυματικό σύστημα υπερθερμίας. Το προτεινόμενο σύστημα ενσωματώθηκε σε ένα τρισδιάστατο σύστημα παθητικής μικροκυματικής ραδιομετρικής απεικόνισης (ΜiRaIS), το οποίο παρέχει τη δυνατότητα παρακολούθησης των μεταβολών της θερμοκρασίας και της αγωγιμότητας της υπό εξέταση περιοχής σε πραγματικό χρόνο και μελετήθηκε και κατασκευάστηκε στα πλαίσια παλαιότερης διδακτορικής διατριβής στο ίδιο εργαστήριο της σχολής ΗΜΜΥ. Στην παρούσα διδακτορική διατριβή γίνεται η θεωρητική και πειραματική μελέτη του προτεινόμενου συστήματος υπερθερμίας. Η αρχή λειτουργίας του συστήματος είναι όμοια με εκείνη του MiRaIS και βασίζεται στη χρήση μιας ελλειψοειδούς αγώγιμης κοιλότητας για εστίαση της ακτινοβολίας επιλεκτικά στους ιστούς που χρήζουν θεραπείας. Ο ανακλαστήρας για εστίαση που κατασκευάστηκε και χρησιμοποιήθηκε στην πειραματική διαδικασία, βελτιώνει την εργονομία του συστήματος, διατηρώντας παράλληλα της ιδιότητες εστίασης του πρωτότυπου ελλειψοειδούς. Στα πλαίσια της παρούσας διατριβής πραγματοποιήθηκε αρχικά η θεωρητική μελέτη και μοντελοποίηση της διάταξης με σκοπό την εξακρίβωση των ιδιοτήτων εστίασης του συστήματος και στη συνέχεια επιχειρήθηκε η βελτίωση των ιδιοτήτων αυτών με χρήση διατάξεων διηελκτρικών υλικών, καθώς και πειραματικές μετρήσεις του συνολικού συστήματος υπερθερμίας-μικροκυματικής ραδιομετρίας. Η θεωρητική ηλεκτρομαγνητική μελέτη του συστήματος έγινε με τη χρήση ενός εμπορικά διαθέσιμου υπολογιστικού πακέτου προσομοίωσης (XFdtd, Remcom Inc.), το οποίο χρησιμοποιεί τη μέθοδο των πεπερασμένων διαφορών στο πεδίο του χρόνου για την επίλυση ηλεκτρομαγνητικών προβλημάτων. Ερευνώνται τρεις διατάξεις διηλεκτρικών υλικών με σκοπό τη βελτίωση των ιδιοτήτων εστίασης του συστήματος, οι οποίες επικεντρώνονται στη μελέτη του βάθους διείσδυσης της ακτινοβολίας και της χωρικής διακριτικής ικανότητας. Τα υλικά τοποθετούνται είτε στο εσωτερικό του ελλειψοειδούς είτε γύρω από το μοντέλο κεφαλιού ως στρώματα προσαρμογής, με σκοπό την επίτευξη βηματικής αλλαγής της διηλεκτρικής σταθεράς στη διεπιφάνεια αέρα-μοντέλο ανθρώπινου κεφαλιού. Τα αποτελέσματα καταδεικνύουν τα πλεονεκτήματα από τη χρήση των διηλεκτρικών υλικών, καθώς παρουσιάζεται βελτίωση και στις δυο παραμέτρους των ιδιοτήτων εστίασης, ανάλογα με τη διάταξη που χρησιμοποιείται, τη θέση του μοντέλου κεφαλιού στο εσωτερικό του συστήματος και τη συχνότητα λειτουργίας. Για τη διενέργεια των πειραμάτων, η πειραματική διάταξη τοποθετήθηκε σε ανηχοϊκό θάλαμο, ο οποίος εξασφαλίζει την απομόνωσή της από τον περιβάλλοντα χώρο. Στις πειραματικές διαδικασίες που ακολουθήθηκαν, χρησιμοποιήθηκαν ομοιώματα, τα οποία στη φάση της υπερθερμίας υπέδειξαν τις περιοχές εστίασης της ενέργειας για την εκάστοτε συχνότητα ακτινοβολίας, ενώ στη φάση της μικροκυματικής ραδιομετρίας βοήθησαν στη μελέτη της θερμοκρασιακής διακριτικής ικανότητας του συστήματος. Η μέθοδος της μικροκυματικής ραδιομετρίας χρησιμοποιήθηκε για την παρακολούθηση των μεταβολών της θερμοκρασίας της ακτινοβολούμενης περιοχής κατά τη διάρκεια των συνεδριών της υπερθερμίας. Επίσης, κατά τη διάρκεια των πειραμάτων πραγματοποιήθηκαν μετρήσεις με στρώματα προσαρμογής από διηλεκτρικά υλικά, τα οποία τοποθετήθηκαν γύρω από το αντικείμενο ενδιαφέροντος και βοήθησαν στην πληρέστερη κατανόηση της επίδρασης της παρουσίας τους στις ιδιότητες εστίασης του συστήματος και στην επιβεβαίωση των αντίστοιχων θεωρητικών αποτελεσμάτων.
The application of hyperthermia process has been widely used in clinical research and efforts are being made for its implementation in clinical practice, as many researchers have used this method as an adjunct treatment procedure for cancer. During the past two decades, a great deal of research has been carried out, with the aim of developing effective techniques for hyperthermia treatment, primarily using RF, microwave and ultrasound energy. A similar effort is carried out in the Laboratory of Microwaves and Fiber Optics (MFOL), School of Electrical and Computer Engineering, National Technical University of Athens (NTUA), where a proposed hyperthermia system has been designed and constructed. A system for deep brain hyperthermia treatment, designed to also provide passive measurements of temperature and/or conductivity variations inside the human body, is presented in the present PhD thesis. The proposed system comprises both therapeutic and diagnostic modules, operating in a totally contactless way, based on the use of an ellipsoidal beamformer to achieve focusing on the areas under treatment and monitoring. The radiometry monitoring module, the Three Dimensional Passive Microwave Radiometry Imaging System (MiRaIS), has been studied, designed and constructed in the framework of a previous PhD thesis in the same laboratory of MFOL. In the present thesis, the proposed system is theoretically and experimentally studied. The operation principal is based on the use of an ellipsoidal conductive wall cavity for focusing the emitted radiation on the tissues that should accept treatment. The ellipsoidal cavity, which was constructed and used in the experimentation procedure, is newly developed and improves the system’s ergonomics retaining at the same time the focusing properties of the prototype system. In the framework of the present work, theoretical modeling and experimentation of the proposed system is carried out in order to examine and improve its focusing attributes. In the theoretical study, three setups are investigated for the improvement of the system’s focusing properties (e.g. penetration depth of the electromagnetic field, spatial sensitivity) using dielectric materials. The research is carried out with the use of a commercially available software tool, XFdtd (Remcom Inc.). The materials are placed inside the ellipsoidal or used as matching layers around the head model for the achievement of a stepped change of the refraction index on the air-human head model interface. The results revealed the possible advantages of using matching dielectric materials, as improvement on the focusing properties of the system is clearly observed, depending on the setup used, the position of the head model inside the system and the operating frequency. The experiments were performed inside an anechoic chamber providing maximum accuracy by avoiding all possible EMC/EMI issues. Along with the hyperthermia experiments, the implementation of the microwave radiometry process was also tested with the proposed system. Microwave radiometry could provide the temperature monitoring of the radiated area during the hyperthermia sessions. In the experimental procedures water phantoms were used, which during hyperthermia indicated the energy absorbing areas at the irradiation frequency, while during microwave radiometry revealed the system’s temperature sensitivity. Also, measurements were conducted using dielectric matching layers, placed around the medium of interest, in order to fully understand the effect of those materials on the system’s focusing properties as well as to confirm the respective theoretical results. Taking into consideration the present study and the advantage of the non invasive character of the proposed brain hyperthermia system, it is concluded that further research is required in order to explore its potentials at becoming a part of the standard treatment protocol of brain malignancy in the future.