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Tesi sul tema "Medical physics"
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1
Lazarine, Alexis D. "Medical physics calculations with MCNP: a primer". Texas A&M University, 2006. http://hdl.handle.net/1969.1/4297.
Testo completoAbstract (sommario):
The rising desire for individualized medical physics models has sparked a
transition from the use of tangible phantoms toward the employment of computational
software for medical physics applications. One such computational software for
radiation transport modeling is the Monte Carlo N-Particle (MCNP) radiation transport
code. However, no comprehensive document has been written to introduce the use of
the MCNP code for simulating medical physics applications. This document, a primer,
addresses this need by leading the medical physics user through the basic use of MCNP
and its particular application to the medical physics field.
This primer is designed to teach by example, with the aim that each example will
illustrate a practical use of particular features in MCNP that are useful in medical
physics applications. These examples along with the instructions for reproducing them
are the results of this thesis research. These results include simulations of: dose from
Tc-99m diagnostic therapy, calculation of Medical Internal Radiation Dose (MIRD)
specific absorbed fraction (SAF) values using the ORNL MIRD phantom, x-ray
phototherapy effectiveness, prostate brachytherapy lifetime dose calculations, and a
radiograph of the head using the Zubal head phantom. Also included are a set of appendices that include useful reference data, code syntax, and a database of input decks
including the examples in the primer. The sections in conjunction with the appendices
should provide a foundation of knowledge regarding the MCNP commands and their
uses as well as enable users to utilize the MCNP manual effectively for situations not
specifically addressed by the primer.
2
Rolland, Jannick Paule Yvette. "Factors influencing lesion detection in medical imaging". Diss., The University of Arizona, 1990. http://hdl.handle.net/10150/185096.
Testo completoAbstract (sommario):
An important goal in medical imaging is the assessment of image quality in a way that relates to clinical efficacy. An objective approach is to evaluate the performance of diagnosis for specific tasks, using ROC analysis. We shall concentrate here on classification tasks. While many factors may confine the performance achieved for these tasks, we shall investigate two main limiting factors: image blurring and object variability. Psychophysical studies followed by ROC analysis are widely used for system assessment, but it is of great practical interest to be able to predict the outcome of psychophysical studies, especially for system design and optimization. The ideal observer is often chosen as a standard of comparison for the human observer since, at least for simple tasks, its performance can be readily calculated using statistical decision theory. We already know, however, of cases reported in the literature where the human observer performs far below ideal, and one of the purposes of this dissertation is to determine whether there are other practical circumstances where human and ideal performances diverge. Moreover, when the complexity of the task increases, the ideal observer becomes quickly intractable, and other observers such as the Hotelling and the nonprewhitening (npw) ideal observers may be considered instead. A practical problem where our intuition tells us that the ideal observer may fail to predict human performance occurs with imaging devices that are characterized by a PSF having long spatial tails. The investigation of the impact of long-tailed PSFs on detection is of great interest since they are commonly encountered in medical imaging and even more generally in image science. We shall show that the ideal observer is a poor predictor of human performance for a simple two-hypothesis detection task and that linear filtering of the images does indeed help the human observer. Another practical problem of considerable interest is the effect of background nonuniformity on detectability since, it is one more step towards assessing image quality for real clinical images. When the background is known exactly (BKE), the Hotelling and the npw ideal observers predict that detection is optimal for an infinite aperture; a spatially varying background (SVB) results in an optimum aperture size. Moreover, given a fixed aperture size and a BKE, an increase in exposure time is highly beneficial for both observers. For SVB, on the other hand, the Hotelling observer benefits from an increases in exposure time, while the npw ideal observer quickly saturates. In terms of human performance, results show a good agreement with the Hotelling-observer predictions, while the performance disagrees strongly with the npw ideal observer.
3
Gharama, Huda. "A Planar Lightguide Power Combiner for Medical Applications". University of Toledo / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1508173552760426.
Testo completo
4
Redd, Randall Alex. "Radiation dosimetry and medical physics calculations using MCNP 5". Texas A&M University, 2004. http://hdl.handle.net/1969.1/467.
Testo completoAbstract (sommario):
Six radiation dosimetry and medical physics problems were analyzed using a beta version of MCNP 5 as part of an international intercomparison of radiation dosimetry computer codes, sponsored by the European Commission committee on the quality assurance of computational tools in radiation dosimetry. Results have been submitted to the committee, which will perform the inter-code comparison and publish the results independently. A comparison of the beta version of MCNP 5 with MCNP 4C2 is made, as well as a comparison of the new Doppler broadening feature. Comparisons are also made between the *F8 and F6 tallies, neutron tally results with and without the use of the S(a,b) cross sections, and analytically derived peak positions with pulse height distributions of a Ge detector obtained using the beta version of MCNP 5.
The following problems from the study were examined:
Problem 1 was modeled to determine the near-field angular anisotropy and dose distribution from a high dose rate 192Ir brachytherapy source in a surrounding spherical water phantom.
Problem 2 was modeled to find radial and axial dose in an artery wall from an intravascular brachytherapy 32P source.
Problem 4 was modeled to investigate the response of a four-element TLD-albedo personal dosimeter from neutrons and/or photons. Significant differences in neutron response with S(a,b) cross sections compared to results without these cross sections were found.
Problem 5 was modeled to obtain air kerma backscatter profiles for 150 and 200 kVp X-rays upon a water phantom. Air kerma backscatter profiles were determined along the apothem and diagonal of the front face of the phantom. A comparison of experimental results is also made.
Problem 6 was modeled to determine indirect spectral and energy fluences upon two neutron detectors within a calibration bunker. The largest indirect contribution was found to come from low energy neutrons with an average angle of 47o where 0o is a plane parallel to the floor.
Problem 7 was modeled to obtain pulse height distributions for a germanium detector. Comparison of analytically derived peaks with peak positions in the spectra are made. An examination of the Doppler broadening feature is also included.
5
Wang, Yi Zhen 1965. "Photoneutrons and induced activity from medical linear accelerators". Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81453.
Testo completoAbstract (sommario):
This study involves the measurement of the neutron equivalent dose ( NED) and the induced activity produced from medical linear accelerators. For the NED, various parameters such as the profile, field effects and energy responses were studied. The NED in a Solid Water(TM) phantom was measured and a new quantity, the neutron equivalent dose tissue-air ratio (NTAR), was defined and determined. Neutron production for electron beams was also measured. For the induced activity, comparisons were carried out between different linacs, fields and dose rates. The half life and activation saturation were also studied. A mathematical model of induced activity was developed to explain the experimental results. Room surveys of NED and induced activity were performed in and around a high energy linear accelerator room. Unwanted doses from photoneutrons and induced activity to the high energy linear accelerator radiotherapy staff and patient were estimated.
6
Förster, Fabian Alexander. "Novel CMOS Devices for High Energy Physics and Medical Applications". Doctoral thesis, Universitat Autònoma de Barcelona, 2020. http://hdl.handle.net/10803/670504.
Testo completoAbstract (sommario):
Els experiments d’alta energia de física (HEP) a col·lisions de partícules demostren la nostra comprensió de l’estructura i la dinàmica de la matèria. Per avançar en el camp, els sistemes d’acceleradors s’actualitzen periòdicament a energies i lluminositats més elevades. Els experiments han de mantenir-se al punt millorant la seva instrumentació de detecció. Els detectors de píxels de silici tenen un paper crític en els experiments HEP. Gràcies a la seva excel·lent resolució de posició, compacitat, velocitat i duresa de la radiació, permeten la reconstrucció de la pista de partícules en entorns d’alta radiació com els col·lisionadors de hadrons. Al seu torn, el seu rendiment permet una excel·lent resolució de paràmetres d’impacte de pista, un ingredient clau per a la identificació de vèrtexs secundaris i l’etiquetatge b del jet. Actualment, el detector estàndard de píxels consisteix en un sensor segmentat, en el qual cada píxel està connectat a un canal de lectura d’un circuit integrat d’aplicacions específiques per a aplicacions (ASIC) mitjançant una tècnica complicada i cara, anomenada enllaç de cop. Un mètode alternatiu per als dispositius de píxels híbrids són els detectors monolítics, que combinen la detecció de partícules i les tasques de processament de senyal al mateix substrat. Aquests tipus de detectors desenvolupats en el procés CMOS han estat utilitzats en el passat, però només recentment es basen en dispositius de radiació durs. sobre aquesta tecnologia s’han proposat. En aquesta tesi s’investiga un primer prototip a mida completa d’un detector monolític desenvolupat en la tecnologia CMOS d’Alta Voltatge (HV-CMOS) com a dispositiu de píxel per a les capes exteriors del futur rastrejador ATLAS actualitzat, que es troba al Gran Col·lisionador d’Hadrons ( LHC) al CERN. A més de l’aplicació d’aquesta tecnologia en experiments HEP, la detecció de fotons de raigs X suaus també s’investiga en una matriu en un dels detectors de píxels HV-CMOS. Per últim, s’explora l’ús de dispositius CMOS per a la detecció de fotons de gairebé infraroig (NIR) amb fotodiode d’Avalanche (APD).Los experimentos de física de alta energía (HEP) en colisionadores de partículas sondean nuestra comprensión de la estructura y la dinámica de la materia. Para avanzar en el campo, los sistemas de aceleración se actualizan periódicamente a mayores energías y luminosidades. Los experimentos tienen que mantenerse al día, mejorando la instrumentación de su detector. Los detectores de píxeles de silicio desempeñan un papel fundamental en los experimentos con HEP. Gracias a su excelente resolución de posición, compacidad, velocidad y dureza de radiación, permiten la reconstrucción de pistas de partículas en entornos de alta radiación como colisionadores de hadrones. A su vez, su rendimiento permite una excelente resolución de parámetros de impacto en la pista, un ingrediente clave para la identificación secundaria de vértices y el etiquetado de chorro b. Actualmente, el detector de píxeles estándar consta de un sensor segmentado, en el que cada píxel está conectado a un canal de lectura de un circuito integrado de aplicación específica (ASIC) a través de una técnica complicada y costosa llamada unión por golpes. Un enfoque alternativo a los dispositivos de píxeles híbridos son los detectores monolíticos, que combinan la detección de partículas y las tareas de procesamiento de señales en el mismo sustrato. Estos tipos de detectores desarrollados en el proceso CMOS se han utilizado en el pasado, pero solo relativamente recientemente basados en dispositivos de radiación dura sobre esta tecnología se han propuesto. En esta tesis, se investiga un primer prototipo de tamaño completo de un detector monolítico desarrollado en la tecnología CMOS de alto voltaje (HV-CMOS) como un dispositivo de píxeles para las capas externas del rastreador ATLAS de actualización futura, que se encuentra en el Gran Colisionador de Hadrones ( LHC) en el CERN. Además de la aplicación de esta tecnología en experimentos HEP, la detección de fotones de rayos X blandos también se investiga en una matriz en uno de los detectores de píxeles HV-CMOS. Por último, se explora el uso de dispositivos CMOS para la detección de fotones de infrarrojo cercano (NIR) con Avalanche Photodiode (APD).
High Energy Physics (HEP) experiments at particle colliders probe our understanding of the structure and dynamics of matter. In order to advance the field, the accelerator systems are periodically upgraded to higher energies and luminosities. Experiments have to keep up, by improving their detector instrumentation. Silicon pixel detectors play a critical role in HEP experiments. Thanks to their excellent position resolution, compactness, speed and radiation hardness, they enable particle track reconstruction in high radiation environments like hadron colliders. In turn, their performance allows excellent track impact parameter resolution, a key ingredient for secondary vertex identification and jet b-tagging. Currently the standard pixel detector consists of a segmented sensor, in which each pixel is connected to a readout channel of an Application-Specific Integrated Circuit (ASIC) through a complicated, and expensive, technique called bump bonding. An alternative approach to hybrid pixel devices are monolithic detectors, which combine the particle sensing and the signal processing tasks in the same substrate.These kinds of detectors developed in the CMOS process have been used in the past, but only relatively recently radiation hard devices based on this technology have been proposed. In this thesis a first full size prototype of a monolithic detector developed in the High Voltage CMOS (HV-CMOS) technology is investigated as a pixel device for the outer layers of the future upgrade ATLAS tracker, which is located in the Large Hadron Collider (LHC) at CERN. Besides the application of this technology in HEP experiments, the detection of soft X-ray photons is also investigated in one matrix in one of the HV-CMOS pixel detectors. Lastly, the usage of CMOS devices for the detection of Near-Infrared (NIR) photons with Avalanche Photodiode (APD) is explored.
7
Andrews, Brian. "Computational Solutions for Medical Issues in Ophthalmology". Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case15275972120621.
Testo completo
8
Scannavini, Maria Giulia. "Medical Compton cameras based on semiconductor detectors". Thesis, University College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251785.
Testo completo
9
Ratcliffe, Naomi. "Potential of a compact low energy proton accelertor for medical applications". Thesis, University of Huddersfield, 2014. http://eprints.hud.ac.uk/id/eprint/23711/.
Testo completoAbstract (sommario):
This thesis explores the potential of a compact low energy (<10MeV) proton accelerator for medical applications such as the production of neutrons for cancer neutron therapy and the production of SPECT (Single Photon Emission Computed Tomography) and PET (Positron Emission Tomography) radioisotopes. During the course of this study the simulation code GEANT4 was used to study yields of these neutrons and isotopes from the typically low threshold high cross-‐section (p,n) reactions. Due to the limits of the current models within GEANT4 some development of a new data-‐driven model for low energy proton interactions was undertaken and has been tested here. This model was found to be suitably reliable for continued study into the low energy production of positron emitting, PET, isotopes of copper and gallium as replacements for the main SPECT isotope technetium-‐99m. While 99mTc is currently the most popular radioisotope being used in over 90% of the worlds nuclear medicine diagnostic procedures supply is under threat by the impending shut down of the current reactor based sources. Simulations of both thin and thick targets were carried out to study the potential of low energy production of these isotopes. The final activity of the radioisotopes after irradiation of these targets produced by the simulations has been shown here to be sufficient for multiple doses. The useable activity is dependent on the efficiency of the extraction process and the time between irradiation and administration.
10
Lazarus, Graeme Lawrence. "Validation of Monte Carlo-based calculations for small irregularly shaped intra-operative radiotherapy electron beams". Doctoral thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/16680.
Testo completo
11
Hough, Jan K. "Assessment of and improvements to a stereophotogrammetric patient positioning system for proton therapy". Master's thesis, University of Cape Town, 1999. http://hdl.handle.net/11427/26784.
Testo completoAbstract (sommario):
Summary in English.Bibliography: pages 125-129.
This thesis describes the construction and use of the facemask at the National Accelerator Centre (NAC) as used to both immobilise and position patients for precision proton radiotherapy. The precision achieved using the stereophotogrammetric (SPG) positioning system is measured, and the shortcomings and errors in using the facemask by the SPG system are measured and analysed. The implementation of improvements made to the SPG system is reported upon, and alternative means of both supporting the fiducial markers and immobilising the patient are investigated and evaluated. The accuracy of positioning a facemask using the SPG system is 1.4 mm and of positioning a newly designed frame is 1.6 mm. These measurements were made without using a patient. It is estimated that the total uncertainty of positioning a patient's tumour at the isocentre is 1.6 (1SD) mm using the facemask and it is estimated that the precision using the frame will be less than this value. The largest component of this error (1.39 mm) is due to the error in obtaining the CT scanner co-ordinates. These results are comparable to those obtained by other investigators. The movement of patient bony landmarks within the facemask was measured to be 1.0 ± 0.8 mm. Three main recommendations are that the CT scanner co-ordinating procedure be improved, the SPG computer program be rewritten in parts to achieve greater speed and accuracy, and that the new frame be used. The frame is easier to manufacture than the facemask and allows real time monitoring of the position of the patient's head by the SPG system thus allowing faster throughput of patients and better positioning quality control.
12
Bhengu, Khumbulani John. "The use of thermoluminescent dosimeters for In-vivo dosimetry in a fast neutron therapy beam". Master's thesis, University of Cape Town, 2000. http://hdl.handle.net/11427/2799.
Testo completoAbstract (sommario):
Bibliography: leaves 72-77.Thermoluminescent detectors (TLD-700) have been investigated for absorbed dose measurements in a p(66)/Be neutron therapy beam at the National Accelerator Centre. Chips were selected based on their reproducibility and chip individual neutron calibration factors were derived. The dose non-linearity was determined in peak 5 and peak 6 and dose non-linearity corrections were performed. The sensitivity of TLD-700 chips with depth and off-axis distance was determined. In-vivo dose measurements were performed on seven patients (9 fields). In the entrance in-vivo dose measurements, a maximal deviation of 3.2 % was detected and a systematic difference of 1.7 % was observed. On the exit side, a maximal deviation of -7.3 % was detected and a systematic difference of -5.1 % was observed. The glow curve peak 6/5 ratio was investigated and found to correlate with the qualitative variations of the average LET in the neutron beam.
13
Engel-Hills, Penelope Claire. "Investigation of the barium enema x-ray examination as a significant contributor to the genetically-significant dose from diagnostic radiology". Master's thesis, University of Cape Town, 1997. http://hdl.handle.net/11427/27128.
Testo completoAbstract (sommario):
The results of a study conducted by Maree (1995) indicated that the genetically-significant dose (GSD) for the white, female population in South Africa was considerably higher than the GSD for females in Great Britain, France and the United States of America. Further to this finding, Maree's study demonstrated that the barium enema x-ray examination was the major contributor to the GSD for this population group. A study of barium enema examinations was embarked on in order to explain the findings of Maree. The study was designed to include dose-area product measurements on patients having the barium enema procedure. In addition patient data and technique factors were recorded. The x-ray equipment used for the investigation was one digital and two non-digital fluoroscopic systems in the Western Cape. The digital unit utilised an overhead tube as did one of the conventional units. The other unit had an undercouch fluoroscopic tube and an overhead tube used for the standard radiography views. Comparison of the dose-area product measurements demonstrated that the unit having an undercouch tube had a mean dose-area product of 99.69 Gy cm² which culminates in a higher dose to the patient than the equipment utilising an overhead tube. The mean dose-area product of the two units with an overhead tube was 56.57 Gy cm² and 51.94 Gy cm² respectively. Free Air Exposure tables based on "RADCOMP Entrance Skin Exposure Software Program" (Nuclear Associates and Zamenhof, 1990) were used together with average technique factors to calculate skin entrance doses. These skin entrance doses were used to calculate gonad doses with the aid of a computer program from the Food and Drug Administration in the USA (Peterson and Rosenstein, 1989). The results were compared with the results of the barium enema component of the research conducted by Maree. The comparison indicated an average gonad dose for males of 242 μGy x 10⁻¹ (present study) compared to 485 μGy x 10⁻¹ (Maree) and an average gonad dose for females of 11185 μGy x 10⁻¹ (present study) compared to 16111 μGy x 10⁻¹ (Maree). Air-kerma at skin entrance was calculated using dose-area product measurements, recorded during the present study, for individual exposures and screening. These values were used to calculate the gonad dose. A discrepancy was demonstrated between the calculation of gonad dose from calculated as opposed measured skin entrance dose. The average gonad dose calculated by Maree is 16111 μGy x 10⁻¹ and the average gonad dose calculated for the present study using the measured skin entrance dose is 4236 μGy x 10⁻¹. This seems to explain the larger GSD estimated by Maree for the white female patients. A national protocol for measuring patient doses from x-ray examinations is proposed for South Africa.
14
Rae, William Ian Duncombe. "Measured dose distributions of iodine-125 sources and the computerised optimisation of their positions in brachytherapy planning". Master's thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/12732.
Testo completoAbstract (sommario):
Includes bibliographies.The use of 1-125 seeds in brachytherapy is widespread and becoming increasingly varied. The spatial dose distributions around two types of 1-125 seeds in general use, were measured using a Geiger-Muller chamber. Seeds with the 1-125 adsorbed onto resin spheres had a 10% less anisotropic dose distribution than seeds containing a silver wire with the 1-125 adsorbed onto it. An interpolative method was developed for fast dose calculations taking this anisotropy into account.
15
Hayward, Robert M. "A Coarse Mesh Transport Method with general source treatment for medical physics". Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31696.
Testo completoAbstract (sommario):
Thesis (M. S.)--Nuclear and Radiological Engineering and Medical Physics, Georgia Institute of Technology, 2010.Committee Chair: Rahnema, Farzad; Committee Member: Wang, Chris; Committee Member: Zhang, Dingkang. Part of the SMARTech Electronic Thesis and Dissertation Collection.
16
Pellegrini, Giulio. "Technology development of 3D detectors for high energy physics and medical imaging". Thesis, University of Glasgow, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269510.
Testo completo
17
Barker, Jolene. "APPLICATIONS OF THE BIVARIATE GAMMA DISTRIBUTION IN NUTRITIONAL EPIDEMIOLOGY AND MEDICAL PHYSICS". VCU Scholars Compass, 2008. http://scholarscompass.vcu.edu/etd/1623.
Testo completoAbstract (sommario):
In this thesis the utility of a bivariate gamma distribution is explored. In the field of nutritional epidemiology a nutrition density transformation is used to reduce collinearity. This phenomenon will be shown to result due to the independent variables following a bivariate gamma model. In the field of radiation oncology paired comparison of variances is often performed. The bivariate gamma model is also appropriate for fitting correlated variances. A method for simulating bivariate gamma random variables is presented. This method is used to generate data from several bivariate gamma models and the asymptotic properties of a test statistic, suggested for the radiation oncology application, is studied.
18
Badawi, Ramsey Derek. "Aspects of optimisation and qualification in 3D positron emission tomography". Thesis, King's College London (University of London), 1998. https://kclpure.kcl.ac.uk/portal/en/theses/aspects-of-optimisation-and-qualification-in-3d-positron-emission-tomography(47a88023-9d6c-453f-aa8d-fcc5b83ae168).html.
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19
Spencer, Richard Glenn Stevens. "31P nuclear magnetic resonance spectroscopy studies of cardiac energetics and function in the perfused rat heart". Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/17227.
Testo completo
20
Blackburn, Megan Satterfield. "Numerical benchmarking of a coarse-mesh transport (COMET) method for medical physics applications". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29763.
Testo completoAbstract (sommario):
Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010.Committee Chair: Farzad Rahnema; Committee Co-Chair: Eric Elder; Committee Member: C.-K. Chris Wang; Committee Member: Rebecca Howell; Committee Member: Sang Cho. Part of the SMARTech Electronic Thesis and Dissertation Collection.
21
Scacca, Caroline C. "Nanotechnology and its Medical Applications: Focused on Biosensors and Neuro-regeneration". Miami University Honors Theses / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=muhonors1240451880.
Testo completo
22
Tiwary, Ashok. "Approximations to the theory of radiative transfer in dense media appropriate to medical applications". Thesis, University of Essex, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336925.
Testo completo
23
Robson, Kevin John. "Film viewing conditions in x-ray mammography and their effect on observer performance". Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247824.
Testo completo
24
Marques, Jefferson Luiz Brum. "High-resolution electrocardiogram analysis". Thesis, University of Sheffield, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263558.
Testo completo
25
Jones, Elizabeth Anne. "The production and use of proton-induced ultrasoft X-rays". Thesis, Queen Mary, University of London, 1988. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1487.
Testo completoAbstract (sommario):
A 700 keV Van de Graaff accelerator was used to accelerate protons onto solid targets of different light elements to produce ultrasoft, characteristic X-rays (< 5 keV). The proton energies were calibrated using the (p, y) resonances at 633 keV in Aluminium and at 340 and 483 keV in Fluorine. The X-ray emission characteristics of Aluminium, Carbon, Gold, Silicon/Carbon, Silicon/Nitrogen and Titanium/Boron were studied as a function of incident proton energy, angle of inclination of the target (30° - 60° to the proton beam) and angle of detection of the X-rays (40° - 130° to the beam). Detection of the X-rays was achieved using a gas-flow proportional counter directly coupled to a low-noise pre-amplifier. The resulting spectra, recorded on a multichannel analyser, were well fitted by linear combinations of single Gaussian curves to give peak position (X-ray energy), width and area (X-ray intensity). Carbon contamination of the target surface was studied in detail for the Aluminium target. A number of low beam currents onto the target (10 - 70 nA) were used for total irradiation times of up to 17 hours in order to establish the degree of overall X-ray energy mixing. The information gained from the study of both the Carbon contamination and the X-ray emission characteristics was used to propose practical optimum conditions for the production of ultrasoft X-rays by proton bombardment in their application to biological and biochemical irradiations. A computer code, capable of following the electron track histories resulting from ultrasoft X-ray interactions has been used to compare the details of such energy deposition with the results of mammalian cell irradiations made at the M. R. C. Radiobiology Unit for a number, of different ultrasoft X-ray energies. Such a-comparison has been used to try to identify the mechanisms of radiation action. Included in this work is the application of the computer code to a variety of. characteristic X-ray photon energies, thus extending the available, calculated data.
26
Marinos, Nikolas L. "Monte Carlo calculations and measurement of photon beams shaped by multileaf collimators in radiation therapy". Thesis, Queen Mary, University of London, 1999. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1747.
Testo completoAbstract (sommario):
A model based on Monte Carlo techniques is developed to transport ionising radiation through the radiation head of a 6MV linear accelerator fitted with multileaf collimators Major emphasis is given to the detailed geometrical descriptiqn of the multileaf collimator. The model produces dose distributions in water from photon beams defined by the jaws and the multileaf collimator. The model accounts for contaminant electrons in the photon beam, off-axis x-ray radiation originating at the collimator and the transmission and penumbra effects of the side planes and front face of the leaves in the multileaf collimator Dose distributions in water calculated by the model are compared with experiment using lonisation chambers, diodes and film and found to be within 1 5% The transmission and the penumbra of the multileaf collimator leaves calculated by the Monte Carlo model are compared with experiment and found to be in good agreement
27
Yao, Zhen. "OPTIMIZING RF AND GRADIENT COILS IN MRI". Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1402058570.
Testo completo
28
Alarady, Mamdooh R. "Characterization of Image Quality between Multi-Slice Computed Tomography and Cone Beam Computed Tomography for Clinical Used Protocols in Radiation Therapy Treatment Planning". University of Toledo Health Science Campus / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=mco151080400269082.
Testo completo
29
Qureshi, Touseef Ahmad. "Extraction of arterial and venous trees from disconnected vessel segments in fundus images". Thesis, University of Lincoln, 2016. http://eprints.lincoln.ac.uk/23687/.
Testo completoAbstract (sommario):
The accurate automated extraction of arterial and venous (AV) trees in fundus images subserves investigation into the correlation of global features of the retinal vasculature with retinal abnormalities. The accurate extraction of AV trees also provides the opportunity to analyse the physiology and hemodynamic of blood flow in retinal vessel trees. A number of common diseases, including Diabetic Retinopathy, Cardiovascular and Cerebrovascular diseases, directly affect the morphology of the retinal vasculature. Early detection of these pathologies may prevent vision loss and reduce the risk of other life-threatening diseases. Automated extraction of AV trees requires complete segmentation and accurate classification of retinal vessels. Unfortunately, the available segmentation techniques are susceptible to a number of complications including vessel contrast, fuzzy edges, variable image quality, media opacities, and vessel overlaps. Due to these sources of errors, the available segmentation techniques produce partially segmented vascular networks. Thus, extracting AV trees by accurately connecting and classifying the disconnected segments is extremely complex. This thesis provides a novel graph-based technique for accurate extraction of AV trees from a network of disconnected and unclassified vessel segments in fundus viii images. The proposed technique performs three major tasks: junction identification, local configuration, and global configuration. A probabilistic approach is adopted that rigorously identifies junctions by examining the mutual associations of segment ends. These associations are determined by dynamically specifying regions at both ends of all segments. A supervised Naïve Bayes inference model is developed that estimates the probability of each possible configuration at a junction. The system enumerates all possible configurations and estimates posterior probability of each configuration. The likelihood function estimates the conditional probability of the configuration using the statistical parameters of distribution of colour and geometrical features of joints. The parameters of feature distributions and priors of configuration are obtained through supervised learning phases. A second Naïve Bayes classifier estimates class probabilities of each vessel segment utilizing colour and spatial properties of segments. The global configuration works by translating the segment network into an STgraph (a specialized form of dependency graph) representing the segments and their possible connective associations. The unary and pairwise potentials for ST-graph are estimated using the class and configuration probabilities obtained earlier. This translates the classification and configuration problems into a general binary labelling graph problem. The ST-graph is interpreted as a flow network for energy minimization a minimum ST-graph cut is obtained using the Ford-Fulkerson algorithm, from which the estimated AV trees are extracted. The performance is evaluated by implementing the system on test images of DRIVE dataset and comparing the obtained results with the ground truth data. The ground truth data is obtained by establishing a new dataset for DRIVE images with manually classified vessels. The system outperformed benchmark methods and produced excellent results.
30
Li, Rong Ding 1967. "Dynamic electron arc therapy with the Clinac-21EX linac". Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101603.
Testo completoAbstract (sommario):
Electron arc therapy is the treatment modality for superficial tumors involving large curved surfaces. At the McGill University Health Centre, the characteristic angle beta concept was developed for the dosimetry and treatment planning of electron arc therapy. In this work, this concept was verified in dynamic mode with the new generation linac of Varian(TM), the Clinac-21 EX.Radial PDDs were measured for beta angles varying from 60º--120º of electron arc beams with energies of 6 MeV, 9 MeV, and 12 MeV and 2-D isodose distributions of electron arc beams were studied as well. Dose penumbral regions exist at the beam start area and stop area, and the size of these regions is a function of the beam energy and the field width. When shielded with a tertiary collimator, the size of the penumbral regions and the dose levels in the penumbral regions were reduced significantly, and it is sufficient for the shielding to cover exactly the start field and the stop field of the arc beam in a clinical setting.
The dose rate of the electron arc beam was investigated. It was found that the dose rate at the depth of dose maximum linearly increased with the arc beam field width and was independent of the arc angle.
31
Sperling, Nicholas Niven. "A Novel Algorithm for the Reconstruction of an Entrance Beam Fluence from Treatment Exit Patient Portal Dosimetry Images". University of Toledo / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1384521982.
Testo completo
32
Satterfield, Megan E. "Application of a heterogeneous coarse-mesh transport method (COMET) to radiation therapy problems". Thesis, Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-11192006-213749/.
Testo completo
33
Kalita, Spartak A. "Transfer of students' learning about x-rays and computer-assisted tomography from physics to medical imaging". Diss., Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/1052.
Testo completo
34
Cetnar, Ashley. "Valued Discourse in Oral Examinations for Medical Physicists". The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1606920639129938.
Testo completo
35
Greer, Peter Brian. "A dual assembly multileaf collimator for radiotherapy". Title page, table of contents and abstract only, 2000. http://web4.library.adelaide.edu.au/theses/09PH/09phg81659.pdf.
Testo completoAbstract (sommario):
Bibliography: leaves 241-250. A multileaf collimator for radiation therapy has been designed that splits each leaf bank into two vertically displaced assemblies or levels with each level consisting of alternate leaves and leaf spaces. The radiation profiles transmitted for image formation through the collimator design were investigated to examine their dependence on the collimator design features.
36
Ecabert, Olivier [Verfasser]. "Segmentation and Physics-Based Modeling of Medical Images for Brain Shift Compensation / Olivier Ecabert". Aachen : Shaker, 2004. http://d-nb.info/117054584X/34.
Testo completo
37
Yavuzkanat, Nuray. "Development of novel scintillation detection techniques for use in nuclear physics and medical applications". Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/12651/.
Testo completoAbstract (sommario):
This thesis describes the practical application of scintillation detector techniques and focuses on how to enhance their potential for use in the new concept spectroscopy method called HELIOS, combination of the magnetic resonance image (MRI) and positron emission tomography (PET) called PET-MRI system, and other medical applications. Optically coupled LaBr3(Ce) with Hamamatsu avalanche photomultiplier first tested inside a (nearly) 1T magnetic field, resulting in the field does not have an adverse impact on the performance of the detector. A magnetic resonance image was also successfully obtained when a scintillation detector system interfaced with a homogeneous magnetic field inside the brain phantom, but detector current influenced on the MR image. In Chapter 2, there are the further investigations into various scintillation detector systems such as Phoswich-PMT, CsI and LYSO coupled with SensL position sensitive SiPM. SensL new-generation blue sensitive B and C series SiPMs have an innovative silicon photomultiplier structure resulting in an additional readout signal for fast timing application. SensL SiPMs with the large photosensitive area studied regarding their characteristics and coincidence time measurement. According to the measurement result, the dependencies of bias voltage, temperature, gain and dark current were consistent with the literature. Coincidence time resolution was gradually improved from 512 ps to 276 ps for 6 mm C-SiPM by changing set-up and adding transformer in the circuit. A novel antimatter detector system developed for medical applications. GEANT4 based GATE 7.0 simulation was used for optimum scintillator thickness investigation to measure the activity directly from positrons rather than gamma radiation without any interference between scintillator and radiopharmacy. Various detector designs successfully tested for microfluidic chip and blood counter applications (measured volume from 94μ to 0.11μ ). The half-life of 68 Ga was experimentally calculated to be 62.11±8 minutes resulting in agreement with the literature if they overlap within their uncertainties. The new detector is cost-effective, based on very simple working principle, user-friendly, easy to modify into another system, and achievable nanoscale volume. Therefore, the objective of this research is to aid significantly in deciding a final design for the detector system before serial manufacturing and before applying for the patent.
38
Bugno, Jacob R. "Development and Implementation of a GafChromic EBT In-Vivo Personal Dosimetry System". University of Toledo Health Science Campus / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=mco1222876677.
Testo completo
39
Williams, Eric. "Dose Modification Factor Analysis of Multi-Lumen Brachytherapy Applicator with Monte Carlo Simulation". University of Toledo Health Science Campus / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=mco1352570600.
Testo completo
40
Stambaugh, Cassandra. "The Evaluation and Study of Modern Radiation Dosimetry Methods as Applied to Advanced Radiation Therapy Treatments Using Intensity Modulated Megavoltage Photon Beams". Scholar Commons, 2015. https://scholarcommons.usf.edu/etd/5587.
Testo completoAbstract (sommario):
The purpose of this work is to evaluate quasi-3D arrays for use with intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) and to determine their clinical relevance. This is achieved using a Delta4 from Scandidos and ArcCheck from Sun Nuclear and the associated software. While certain aspects of these devices and software have been previously evaluated, the main goal of this work is to evaluate the new aspects, such as reconstructing dose on a patient CT set, and extending the capabilities. This includes the capability to reconstruct the dose based on a helical delivery as well as studying the dose to a moving target using measurement-guided motion simulations.
It was found that Sun Nuclear's ArcCheck/3DVH system exhibited excellent agreement for dose reconstruction for IMRT/VMAT using a traditional C-arm linear accelerator and stringent 2%/2mm comparison constraints. It also is a powerful tool for measurement-guided dose estimates for moving targets, allowing for many simulations to be performed based on one measurement and the target motion data. For dose reconstruction for a helical delivery, the agreement was not as good for the stringent comparison but was reasonable for the clinically acceptable 3%/3mm comparison. Scandidos' Delta4 shows good agreement with stringent 2%/2mm constraints for its dose reconstruction on the phantom. However, the dose reconstruction on the patient CT set was poor and needs more work.
Overall, it was found that quasi-3D arrays are powerful tools for dose reconstruction and treatment plan comparisons. The ability to reconstruct the dose allows for a dose resolution comparable to the treatment plan, which negates the previous issues with inadequate sampling and resolution issues found when just comparing the diodes. The ability to quickly and accurately compare many plans and target motions with minimum setup makes the quasi-3D array an attractive tool for both commissioning and patient specific quality assurance.
41
Hegi-Johnson, Fiona. "Let there be light: Harnessing the power of new imaging technologies to improve outcomes for lung cancer radiotherapy patients". Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/20169.
Testo completoAbstract (sommario):
This thesis is an attempt to develop a formal evaluation framework to bridge the gap between the traditional clinical trial approach for evaluating new radiotherapy technologies and an implementation driven model in which new technologies are implemented in clinical practice with little planned evaluation. The opening chapter describes the requirements for state-of-the-art lung cancer radiotherapy, and is followed by a chapter reviewing the evidence for and evaluating stereotactic ablative body radiotherapy in a phase II trial. Two novel imaging technologies are described and evaluated: CT ventilation and independent kilovoltage intra-fraction monitoring. Computed Tomography Ventilation Imaging (CTVI) is an experimental imaging modality that derives regional lung function information from non-contrast respiratory-correlated CT datasets. Here, we evaluate the CTVI clinical validation literature and present a validation study comparing CTVI derived regional ventilation imaging with Ventilation Perfusion (V/Q) SPECT-CT. The final chapter of this thesis presents our initial work on kilovoltage intrafraction monitoring (KIM) in lung cancer patients. KIM uses on-board kV imaging, to monitor the intrafraction motion of tumours during the radiotherapy treatment. KIM’s significance lies in making real-time imaging accessible, as this has required expensive, specialised systems up till now. We present here our clinical trial protocol and initial results in our first 3 patients, as well as our validation work comparing KIM to a commercially available system. This is one of the first studies to explicitly address the complexity of trial design in the early phase evaluation in medical imaging technologies, which often require iterative modification during the process of evaluation, as well as providing a rigorous pathway to evaluate toxicity and efficacy. At a broader level, this work provides a foundation for a new framework for the evaluation of radiotherapy technologies. The development of evidence for the benefit of radiotherapy technologies has largely focused on the assessment of dosimetric surrogates for clinical effectiveness. The benefits of new technologies are often perceived to be self-evident by the radiation oncology community, but this failure to rigorously demonstrate the clinical benefit of expensive technologies diminishes our ability to advocate for large scale investment. By bridging this gap we intend to strike a balance between the need for high quality evidence and the economic reality faced by developers of medical imaging technologies, providing a framework for the safe and rapid implementation of new technologies for lung cancer radiotherapy.
42
Brown, Oliver. "Novel dissymmetric copper bis(thiosemicarbazone) complexes for medical diagnostic imaging by positron emission tomography". Thesis, University of Kent, 2015. https://kar.kent.ac.uk/53590/.
Testo completoAbstract (sommario):
Bis(thiosemicarbazone) ligand derivatives and their metal complexes have long been of interest as they have applications as anticonvulsants, super-oxide dismutase-like radical scavengers, in the investigation of Alzheimer’s disease and diagnostic imaging. Copper (II) bis(thiosemicarbazone) derivatives have been used extensively in the imaging of oxygen deficient (hypoxic) cells for the detection and imaging of cancerous tissues and heart disease via Positron Emission Tomography (PET). It is possible to fine tune the bis(thiosemicarbazone) complexes redox potentials and lipophilicity by altering the substituents on the Q1 and Q2 position and the R1, R2, R3 and R4 locations respectively. To date only symmetric bis(thiosemicarbazone) ligands (R1=R3, R2=R4) have been evaluated for hypoxia imaging. This thesis reports the synthesis of dissymmetric ligands (R1≠R3, R2≠R4) in order to gain further control of the properties of the complexes and therefore the locations they will migrate to. A range of ligands has also been synthesised for the monitoring of copper metabolism within the brain for the investigation of Alzheimer’s disease and other neurodegenerative disorders. Ligand synthesis has been achieved by controlling the condensation reactions between dicarbonyl compounds and 4-substituted-3-thiosemicarbazides. Synthesis via an alternative acetal protecting method has also been investigated. Thirty bis(thiosemicarbazone) ligands have been successfully synthesised, of which thirteen are symmetric and seventeen dissymmetric. From this library of ligands, eighteen copper complexes have been synthesised along with twenty zinc complexes. The zinc complexes have the potential to act as convenient precursors for the rapid synthesis of radio-copper complexes via a transmetalation method. All ligands, complexes and intermediates have been fully characterised by a range of techniques including IR spectroscopy, Raman spectroscopy, NMR spectroscopy, UV-vis spectroscopy, elemental analysis and mass spectroscopy. A new cyclic by-product from the ligand synthesis has also been isolated and fully characterised.
43
Liang, Kaidi. "Fibre Optics Approach to Dosimetry". Thesis, University of Canterbury. Physics, 2012. http://hdl.handle.net/10092/8957.
Testo completoAbstract (sommario):
Dosimetry is the methodology of determining the amount of radiation energy imparted in matter and volume. Although several techniques and devices are available for use in both laboratory and clinical settings, most rely on certain conditions, assumptions and approximations to convert the energy into radiation dose. The many uncertainties from current techniques are introduced due to the material differences between the sensitive detector volume and the phantom material, typically water.
The aim of this thesis is to use the water sample itself to detect the amount of radiation energy that has been imparted upon it. Radiation energy absorbed by the sample is ultimately converted into heat, raising the temperature of the sample and changing the refractive index property. The refractive index change results in a shortening of the optical path length and as a result, light passing through the sample experiences a phase change. Phase information cannot be directly measured, as it is merely a property of light wave propagation, thus another technique must be used. Digital holographic interferometry was employed to capture snapshots of the sample’s changing state over time, and when compared with a reference, the interference phase information was extracted and used to calculate the refractive index change, which can then be related to radiation absorbed dose.
The aim of this research was to design and build interferometry setups using holographic interferometry to determine the refractive index change induced by radiation and to explore the possibilities of using fibre optics. Experiments were conducted on the setups to determine the validity of the method and the accuracy of the system.
With external heating sources in the forms of an open flame and infrared laser, we could see distinct heating patterns formed in the phase images. The phase allowed the calculation of the temperature and therefore energy from the change in refractive index, but was limited to phase differences within 2π between the images, due to wrapped phases. In the stability tests, we demonstrated the accuracy of the system and found it was heavily influenced by the amount of vibration in the vicinity. In the short term, a standard deviation of 0.015 degrees was recorded but a larger standard deviation of 0.078 degrees was measured in the longer term. We can be confident of the temperature measurements to within 0.1 of a degree, equal to hundreds of Grays in radiation dose, however this is not sufficiently accurate for dosimetry. Future work may include improving accuracy by reducing the vibration in the system.
44
Soltaninejad, Mohammadreza. "Supervised learning-based multimodal MRI brain image analysis". Thesis, University of Lincoln, 2017. http://eprints.lincoln.ac.uk/30883/.
Testo completoAbstract (sommario):
Medical imaging plays an important role in clinical procedures related to cancer, such as diagnosis, treatment selection, and therapy response evaluation. Magnetic resonance imaging (MRI) is one of the most popular acquisition modalities which is widely used in brain tumour analysis and can be acquired with different acquisition protocols, e.g. conventional and advanced. Automated segmentation of brain tumours in MR images is a difficult task due to their high variation in size, shape and appearance. Although many studies have been conducted, it still remains a challenging task and improving accuracy of tumour segmentation is an ongoing field. The aim of this thesis is to develop a fully automated method for detection and segmentation of the abnormal tissue associated with brain tumour (tumour core and oedema) from multimodal MRI images. In this thesis, firstly, the whole brain tumour is segmented from fluid attenuated inversion recovery (FLAIR) MRI, which is commonly acquired in clinics. The segmentation is achieved using region-wise classification, in which regions are derived from superpixels. Several image features including intensity-based, Gabor textons, fractal analysis and curvatures are calculated from each superpixel within the entire brain area in FLAIR MRI to ensure a robust classification. Extremely randomised trees (ERT) classifies each superpixel into tumour and non-tumour. Secondly, the method is extended to 3D supervoxel based learning for segmentation and classification of tumour tissue subtypes in multimodal MRI brain images. Supervoxels are generated using the information across the multimodal MRI data set. This is then followed by a random forests (RF) classifier to classify each supervoxel into tumour core, oedema or healthy brain tissue. The information from the advanced protocols of diffusion tensor imaging (DTI), i.e. isotropic (p) and anisotropic (q) components is also incorporated to the conventional MRI to improve segmentation accuracy. Thirdly, to further improve the segmentation of tumour tissue subtypes, the machine-learned features from fully convolutional neural network (FCN) are investigated and combined with hand-designed texton features to encode global information and local dependencies into feature representation. The score map with pixel-wise predictions is used as a feature map which is learned from multimodal MRI training dataset using the FCN. The machine-learned features, along with hand-designed texton features are then applied to random forests to classify each MRI image voxel into normal brain tissues and different parts of tumour. The methods are evaluated on two datasets: 1) clinical dataset, and 2) publicly available Multimodal Brain Tumour Image Segmentation Benchmark (BRATS) 2013 and 2017 dataset. The experimental results demonstrate the high detection and segmentation performance of the III single modal (FLAIR) method. The average detection sensitivity, balanced error rate (BER) and the Dice overlap measure for the segmented tumour against the ground truth for the clinical data are 89.48%, 6% and 0.91, respectively; whilst, for the BRATS dataset, the corresponding evaluation results are 88.09%, 6% and 0.88, respectively. The corresponding results for the tumour (including tumour core and oedema) in the case of multimodal MRI method are 86%, 7%, 0.84, for the clinical dataset and 96%, 2% and 0.89 for the BRATS 2013 dataset. The results of the FCN based method show that the application of the RF classifier to multimodal MRI images using machine-learned features based on FCN and hand-designed features based on textons provides promising segmentations. The Dice overlap measure for automatic brain tumor segmentation against ground truth for the BRATS 2013 dataset is 0.88, 0.80 and 0.73 for complete tumor, core and enhancing tumor, respectively, which is competitive to the state-of-the-art methods. The corresponding results for BRATS 2017 dataset are 0.86, 0.78 and 0.66 respectively. The methods demonstrate promising results in the segmentation of brain tumours. This provides a close match to expert delineation across all grades of glioma, leading to a faster and more reproducible method of brain tumour detection and delineation to aid patient management. In the experiments, texton has demonstrated its advantages of providing significant information to distinguish various patterns in both 2D and 3D spaces. The segmentation accuracy has also been largely increased by fusing information from multimodal MRI images. Moreover, a unified framework is present which complementarily integrates hand-designed features with machine-learned features to produce more accurate segmentation. The hand-designed features from shallow network (with designable filters) encode the prior-knowledge and context while the machine-learned features from a deep network (with trainable filters) learn the intrinsic features. Both global and local information are combined using these two types of networks that improve the segmentation accuracy.
45
Saunders, Jessica. "Secondary prompt gamma-rays to improve proton range verification". Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55003.
Testo completoAbstract (sommario):
The goal of this research is to evaluate the secondary prompt gamma (PG) yield from proton therapy at high characteristic energies from MC model simulations and experimental data. Recent studies indicate that target composition influences PG characteristic energy and yield, and the quantification of PG may be used to offer real-time dose verification for proton therapy. In this study PG analysis was performed for MC simulations to evaluate the characteristic measurements and total yield of secondary PG emitted from a target in the 0-8 MeV range from a proton therapy beam over a range of four different beam energies (70 MeV, 160 MeV, 200 MeV, 220 MeV). This was repeated in several target materials (carbon, calcium oxide, calcium fluoride, PMMA, and HDPE) in order to evaluate the influence of the incident energy and the target material on the PG yield and energy spectra. PG energy spectra determined from the specified target materials indicated that the 3.74 MeV energy peak shows a linear correlation between PG intensity and calcium mass fraction of the target material. 6.13 MeV and 4.44 MeV energy peak are not unique to the respective, oxygen and combined oxygen and carbon, mass fraction of the target material. This relationship is complicated by the addition of calcium within the target. Experimental data was collected in order to validate the computational model based on comparison of relative characteristic energy peek intensities. The relative peak ratio determined from experimental data is in good agreement with model prediction, the combined peak ratio is within 0.2%.
46
Gill, Sukhdeep Kaur. "A Study of Evaluation of Optimal PTV Margins for Patients Receiving Prostate IGRT based on CBCT Data Dose Calculation". University of Toledo Health Science Campus / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=mco1404732511.
Testo completo
47
Liang, Chen. "Design of miniature microscope objective optics for biomedical imaging". Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/280105.
Testo completoAbstract (sommario):
The topic of this dissertation is on the design and construction of miniature microscope objective optics. The design of miniature microscope objective is both similar and different from conventional microscope objective. The design and construction of two miniature microscope objectives are presented in this dissertation. The first one is a high numerical aperture (NA), water-immersion objective and it is a part of a fiber confocal reflectance microscope (FCRM). The second one is a moderate NA dry objective and it is a part of a miniature microscope array (MMA). The capability, complexity and fabrication method of the two miniature objectives are different but they both share some similar design traits as result of their miniaturization. FCRM's miniature objective has a NA of 1.0 and it is designed to operate at near infrared lambda = 1,064 nm. It is 7 mm in outer diameter and 21 mm in length (measured from object plane to image plane). This kind of dimension is approximately 10 times smaller than a conventional microscope objective of similar caliber. Sub-micrometer resolution has been experimentally demonstrated with this miniature objective. MMA's miniature objective has a NA of 0.4 and it is designed to operate over the visible spectrum. It is 1.2 mm in diameter and 9.4 mm in length. The image quality of MMA's miniature objective is experimentally demonstrated to be comparable to the state-of-art commercial microscope objective.
48
Lee, Junwon. "The development of a miniature imaging system: Design, fabrication and metrology". Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/289892.
Testo completoAbstract (sommario):
The topic of dissertation is on the development of a miniature imaging device named as multi-modal miniature microscope [a.k.a. 4M Device]. Generally speaking, the development of an optical imaging device involves three main processes: optical design, fabrication and metrology. They are interdependent and often comprise a feedback loop. This dissertation will address these three processes sequentially. The 4M device is miniature compound microscope consisting of miniature optics, electronic imaging device, and mechanical device. Every component is integrated on single silicon substrate. The main purpose of 4M device is to provide an imaging capability for the detection of pre-cancer without biopsy. It uses a novel optics called hybrid lens that is fabricated by using a grayscale photomask and photolithographic technique. The hybrid lens is made of sot-gel material and glass substrate. It has 1.2mm of diameter and its surface is conic. Given lens design constraints from the fabrication, the series of lens design for 4M device are implemented and presented. Each design delivers diffraction-limited imaging performance with N.A ranging from 0.4 to 0.7. The 4M device that is currently built has 0.4 of N.A. The imaging quality assessments of 4M device are also implemented in quantitative and qualitative ways. There are two instruments for imaging quality assessment: Multi-modal imaging testbed for entire imaging device and Shack-Hartmann wavefront sensor for individual element. The qualitative assessment includes multi-modal imaging experiments under different illumination modes. The object is a cervical cancer cell prepared by Dr. Kortum's Group at Univ. of Texas at Austin. The qualitative assessment includes the surface characterization and wavefront measurement of individual optics and the MTF measurement of entire device. The results of imaging quality assessment show the potential of 4M device for medical imaging device. They also explain the degradation of imaging quality.
49
Greer, Andrew I. M. "Nanopatterning strategies for titanium based medical implants". Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/5756/.
Testo completoAbstract (sommario):
This thesis documents the work of Andrew I. M. Greer undertaken for the fulfilment of the requirements for the Degree of Doctor of Philosophy. The project, funded by the EPSRC and MRC, is to develop a nanofabrication processing strategy compatible with titanium based orthopaedic implants. Such a development will facilitate the translation from current and historical in vitro analysis of cell-stimulating nanotopographical cues to in vivo studies upon an implant relevant material. The work presented opens by summarising the social motives and consequences before contextualising the project aims with reference to existing approaches in the field. The thesis progresses through a series of different nanofabrication approaches until an effective strategy satisfying the goals of the project is devised. Thereafter the strategy is explored with its results characterised from a material level through to a biological level. Ultimately the primary goal of the project is realised through the development of novel sol-gel chemistry capable of retaining a nanopattern and transforming into titania, the natural composition at the surface of a titanium based implant. Furthermore, nanofeatures previously too stringent to fabricate for a comprehensive biological study are readily achievable using the documented strategy and fundamental studies have been carried out which indicate that the features concerned are highly effective at up-regulating early indicators of bone formation.
50
Badal, Soler Andreu. "Development of advanced geometric models and acceleration techniques for Monte Carlo simulation in Medical Physics". Doctoral thesis, Universitat Politècnica de Catalunya, 2008. http://hdl.handle.net/10803/6615.
Testo completoAbstract (sommario):
Els programes de simulació Monte Carlo de caràcter general s'utilitzen actualment en una gran varietat d'aplicacions.Tot i això, els models geomètrics implementats en la majoria de programes imposen certes limitacions a la forma dels objectes que es poden definir. Aquests models no són adequats per descriure les superfícies arbitràries que es troben en estructures anatòmiques o en certs aparells mèdics i, conseqüentment, algunes aplicacions que requereixen l'ús de models geomètrics molt detallats no poden ser acuradament estudiades amb aquests programes.
L'objectiu d'aquesta tesi doctoral és el desenvolupament de models geomètrics i computacionals que facilitin la descripció dels objectes complexes que es troben en aplicacions de física mèdica. Concretament, dos nous programes de simulació Monte Carlo basats en PENELOPE han sigut desenvolupats. El primer programa, penEasy, utilitza un algoritme de caràcter general estructurat i inclou diversos models de fonts de radiació i detectors que permeten simular fàcilment un gran nombre d'aplicacions. Les noves rutines geomètriques utilitzades per aquest programa, penVox, extenen el model geomètric estàndard de PENELOPE, basat en superfícices quàdriques, per permetre la utilització d'objectes voxelitzats. Aquests objectes poden ser creats utilitzant la informació anatòmica obtinguda amb una tomografia computeritzada i, per tant, aquest model geomètric és útil per simular aplicacions que requereixen l'ús de l'anatomia de pacients reals (per exemple, la planificació radioterapèutica). El segon programa, penMesh, utilitza malles de triangles per definir la forma dels objectes simulats. Aquesta tècnica, que s'utilitza freqüentment en el camp del disseny per ordinador, permet representar superfícies arbitràries i és útil per simulacions que requereixen un gran detall en la descripció de la geometria, com per exemple l'obtenció d'imatges de raig x del cos humà.
Per reduir els inconvenients causats pels llargs temps d'execució, els algoritmes implementats en els nous programes s'han accelerat utilitzant tècniques sofisticades, com per exemple una estructura octree. També s'ha desenvolupat un paquet de programari per a la paral·lelització de simulacions Monte Carlo, anomentat clonEasy, que redueix el temps real de càlcul de forma proporcional al nombre de processadors que s'utilitzen.
Els programes de simulació que es presenten en aquesta tesi són gratuïts i de codi lliures. Aquests programes s'han provat en aplicacions realistes de física mèdica i s'han comparat amb altres programes i amb mesures experimentals.
Per tant, actualment ja estan llestos per la seva distribució pública i per la seva aplicació a problemes reals.
Monte Carlo simulation of radiation transport is currently applied in a large variety of areas. However, the geometric models implemented in most general-purpose codes impose limitations on the shape of the objects that can be defined. These models are not well suited to represent the free-form (i.e., arbitrary) shapes found in anatomic structures or complex medical devices. As a result, some clinical applications that require the use of highly detailed phantoms can not be properly addressed.
This thesis is devoted to the development of advanced geometric models and accelration techniques that facilitate the use of state-of-the-art Monte Carlo simulation in medical physics applications involving detailed anatomical phantoms. To this end, two new codes, based on the PENELOPE package, have been developed. The first code, penEasy, implements a modular, general-purpose main program and provides various source models and tallies that can be readily used to simulate a wide spectrum of problems. Its associated geometry routines, penVox, extend the standard PENELOPE geometry, based on quadric surfaces, to allow the definition of voxelised phantoms. This kind of phantoms can be generated using the information provided by a computed tomography and, therefore, penVox is convenient for simulating problems that require the use of the anatomy of real patients (e.g., radiotherapy treatment planning). The second code, penMesh, utilises closed triangle meshes to define the boundary of each simulated object. This approach, which is frequently used in computer graphics and computer-aided design, makes it possible to represent arbitrary surfaces and it is suitable for simulations requiring a high anatomical detail (e.g., medical imaging).
A set of software tools for the parallelisation of Monte Carlo simulations, clonEasy, has also been developed. These tools can reduce the simulation time by a factor that is roughly proportional to the number of processors available and, therefore, facilitate the study of complex settings that may require unaffordable execution times in a sequential simulation.
The computer codes presented in this thesis have been tested in realistic medical physics applications and compared with other Monte Carlo codes and experimental data. Therefore, these codes are ready to be publicly distributed as free and open software and applied to real-life problems.