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Egbe, Nneoyi Onen. "Measurement of dose in diagnostic radiology and the effect of dose reduction on image quality." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources. Online version available for University members only until March, 23, 2010, 2008. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=25469.
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Adhikari, Shishir Raj. "PLEXAR IMAGING: A STARTUP DETERMINED TO SOLVE THE CT DOSE VARIABILITY PROBLEM." Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1374236161.
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Morén, Björn. "Mathematical Modelling of Dose Planning in High Dose-Rate Brachytherapy." Licentiate thesis, Linköpings universitet, Optimeringslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-154966.
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Cancer is a widespread type of diseases that each year affects millions of people. It is mainly treated by chemotherapy, surgery or radiation therapy, or a combination of them. One modality of radiation therapy is high dose-rate brachytherapy, used in treatment of for example prostate cancer and gynecologic cancer. Brachytherapy is an invasive treatment in which catheters (hollow needles) or applicators are used to place the highly active radiation source close to or within a tumour. The treatment planning problem, which can be modelled as a mathematical optimization problem, is the topic of this thesis. The treatment planning includes decisions on how many catheters to use and where to place them as well as the dwell times for the radiation source. There are multiple aims with the treatment and these are primarily to give the tumour a radiation dose that is sufficiently high and to give the surrounding healthy tissue and organs (organs at risk) a dose that is sufficiently low. Because these aims are in conflict, modelling the treatment planning gives optimization problems which essentially are multiobjective. To evaluate treatment plans, a concept called dosimetric indices is commonly used and they constitute an essential part of the clinical treatment guidelines. For the tumour, the portion of the volume that receives at least a specified dose is of interest while for an organ at risk it is rather the portion of the volume that receives at most a specified dose. The dosimetric indices are derived from the dose-volume histogram, which for each dose level shows the corresponding dosimetric index. Dose-volume histograms are commonly used to visualise the three-dimensional dose distribution. The research focus of this thesis is mathematical modelling of the treatment planning and properties of optimization models explicitly including dosimetric indices, which the clinical treatment guidelines are based on. Modelling dosimetric indices explicitly yields mixedinteger programs which are computationally demanding to solve. The computing time of the treatment planning is of clinical relevance as the planning is typically conducted while the patient is under anaesthesia. Research topics in this thesis include both studying properties of models, extending and improving models, and developing new optimization models to be able to take more aspects into account in the treatment planning. There are several advantages of using mathematical optimization for treatment planning in comparison to manual planning. First, the treatment planning phase can be shortened compared to the time consuming manual planning. Secondly, also the quality of treatment plans can be improved by using optimization models and algorithms, for example by considering more of the clinically relevant aspects. Finally, with the use of optimization algorithms the requirements of experience and skill level for the planners are lower. This thesis summary contains a literature review over optimization models for treatment planning, including the catheter placement problem. How optimization models consider the multiobjective nature of the treatment planning problem is also discussed.
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Mason, Joshua William. "Advanced dose calculations and imaging in prostate brachytherapy treatment planning." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/7623/.
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Brachytherapy using low dose rate (LDR) permanent seed implant or high dose rate (HDR) temporary implant is a well established treatment for prostate cancer. This study investigates the use of advanced dose calculation and imaging techniques to improve clinical prostate brachytherapy treatments. Monte Carlo (MC) simulations are used to assess the impact of source interactions and tissue composition effects that are ignored by the TG-43U1 dose calculation algorithm used in clinical practice. MC simulation results are validated using experimental phantom measurements. The development of prostate cancer may be driven by a dominant intra-prostatic lesion (DIL) but standard brachytherapy treatments prescribe the same dose level to the whole prostate. This study assesses the feasibility of multi-parametric (mp-MRI) guided focal boost treatments that escalate dose to the DIL to improve tumour control and of focal treatments that target the DIL to reduce treatment related side effects. Source interactions and tissue effects are shown to reduce the dose that is delivered to patients in LDR treatments, particularly for patients with calcifications, however the dosimetric impact is small compared to other uncertainties in LDR seed implant brachytherapy. For HDR treatments attenuation by steel catheters has only a small impact on dose distributions. Feasibility of mp-MRI guided focal boost HDR prostate brachytherapy is demonstrated in terms of tumour delineation and the ability to dose escalate the DIL without increased dose to normal tissues. The dosimetric feasibility of LDR and HDR focal therapy treatments is demonstrated. Focal therapy treatments are shown to be more sensitive to source position errors than whole gland treatments. MC simulations of focal therapy treatments show that there are no additional concerns in terms of dosimetric accuracy compared to standard whole gland treatments. Advanced dose calculation and imaging techniques can improve clinical prostate brachytherapy treatments.
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Thompson, Carla M. "The Utility of Patient-Specific CT Dose Estimation Maps." Cleveland State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=csu1440534502.
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Hessdorfer, Holger [Verfasser], Michael [Akademischer Betreuer] Fiederle, and Tilo [Akademischer Betreuer] Baumbach. "A novel 2D in-line Bragg magnifier imaging system for dose-efficient X-ray imaging at synchrotrons." Freiburg : Universität, 2020. http://d-nb.info/1231712007/34.
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Giles, David. "Cone-beam computed tomography: imaging dose during CBCT scan acquisition and accuracy of CBCT based dose calculations." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=95242.
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Cone beam computed tomography (CBCT) is a recent development in radiotherapy for use in image guidance. Image guided radiotherapy using CBCT allows visualization of soft tissue targets and critical structures prior to treatment. Dose escalation is made possible by accurately localizing the target volume while reducing normal tissue toxicity. The kilovoltage x-rays of the cone beam imaging system contribute additional dose to the patient. In this study a 2D reference radiochromic film dosimetry method employing GAFCHROMICTM model XR-QA film is used to measure point skin doses and dose profiles from the Elekta XVI CBCT system integrated onto the Synergy linac. The soft tissue contrast of the daily CBCT images makes adaptive radiotherapy possible in the clinic. In order to track dose to the patient or utilize on-line replanning for adaptive radiotherapy the CBCT images must be used to calculate dose. A Hounsfield unit calibration method for scatter correction is investigated for heterogeneity corrected dose calculation in CBCT images. Three Hounsfield unit to density calibration tables are used for each of four cases including patients and an anthropomorphic phantom, and the calculated dose from each is compared to results from the clinical standard fan beam CT. The dose from the scan acquisition is reported and the effect of scan geometry and total output of the x-ray tube on dose magnitude and distribution is shown. The ability to calculate dose with CBCT is shown to improve with the use of patient specific density tables for scatter correction, and for high beam energies the calculated dose agreement is within 1%.La tomographie par faisceaux conique (CBCT) informatisée a été récemment développée en radiothérapie pour l'utilisation de guidage par imagerie. La radiothérapie guidée par imagerie (IGRT) utilisant le CBCT, permet la visualisation des cibles à tissus mous et des structures critiques avant le traitement. En localisant précisément la cible, une « escalade » de dose est rendue possible et la toxicité des tissus sains est réduite. Les rayons-X à basse énergie (kilovoltage) du system d'imagerie du CBCT, contribue à une dose additionnelle pour le patient. Dans cette étude, une méthode dosimétrique utilisant un film 2D radiochromic (Gafchromic film, model XR-QA) a été employé pour mesurer des points de dose à la peau ainsi que des profiles de dose. Cette étude a été réalisée à l'aide d'un system d'Elekta XVI CBCT installé sur un accélérateur linéaire du Synergy. Le contraste des images quotidiennes du CBCT des tissus mous rend possible au niveau clinique l'utilisation de la radiothérapie adaptive. Dans le but de suivre la dose administrée au patient ou utiliser de la replanification en ligne pour la radiothérapie adaptive, les images CBCT doivent être utilisées pour le calcul de dose. Une calibration des unités de Hounsfield par méthode de correction de dispersion est examinée dans le cas de dose calculée dans des milieux hétérogènes pour les images CBCT. Trois unités de Hounsfield par table de calibration de densité sont utilisées pour chaque des quatre cas incluant des patients et un fantôme anthropomorphique. Le calcul de dose pour chaque cas est comparé avec les résultats cliniques standards de tomographie par faisceaux en éventail. La dose acquise avec le scanner est reportée et l'effet géométrique du scanner ainsi que le débit total du tube a rayon-X sur la magnitude et la distribution de la dose sont montrés. La capacité de calculer la dose avec un CBCT est présentée dans le but d'amélio
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Williams, Michelle Claire. "Computed tomography imaging of the heart." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/25852.
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Computed tomography imaging has revolutionised modern medicine and we can now study the body in greater detail than ever before. Cardiac computed tomography has the potential to provide information not just on coronary anatomy, but also on myocardial function, perfusion and viability. This thesis addresses the optimisation and validation of computed tomography imaging of the heart using a wide volume 320-multidetector scanner. Computed tomography coronary angiography now has diagnostic accuracy comparable to invasive coronary angiography. However, radiation dose remains an important concern. It is therefore important to minimise computed tomography radiation dose while maintaining image quality. I was able to demonstrate that iterative reconstruction and patient tailored imaging techniques led to a 39% reduction in radiation dose in computed tomography coronary angiography, while maintaining subjective and objective assessments of image quality. In addition, I demonstrated that diagnostic images can be obtained in 99% of unselected patients presenting with suspected coronary artery disease when using single heart-beat 320- multidetector computed tomography coronary angiography. Computed tomography myocardial perfusion imaging can provide additional and complementary information as compared to computed tomography coronary angiography that can aid diagnosis and management. I established both quantitative and qualitative assessment of computed tomography myocardial perfusion imaging and validated it against both a clinical “gold-standard”, fractional flow reserve during invasive coronary angiography, and a physiological “gold-standard”, positron emission tomography with oxygen-15 labelled water. Finally, I was able to show that techniques to reduce radiation dose can also be applied to computed tomography myocardial perfusion imaging, leading to a 60% reduction in radiation dose, while maintaining image quality. In my thesis, I have established that comprehensive cardiac angiographic and perfusion imaging can be performed with wide volume computed tomography in a broad generalizable population of patients with relatively low radiation exposure. These techniques provide both structural and functional assessments from a single imaging modality that are valid and readily applicable to the clinic in the assessment and management of patients with suspected coronary artery disease.
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South, Christopher Peter. "The use of functional imaging to design optimal radiotherapy dose distributions." Thesis, Institute of Cancer Research (University Of London), 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538528.
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Milioni, de Carvalho Pablo. "Low-Dose 3D Quantitative Vascular X-ray Imaging of the Breast." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112210/document.
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Contexte : Le cancer du sein est le cancer le plus fréquent et le deuxième cancer le plus mortel chez la femme. Les techniques d'imagerie constituent un élément essentiel pour le dépistage, le diagnostic, la stadification et le traitement du cancer du sein. L'imagerie par résonance magnétique avec injection de produit de contraste (CE-MRI) est actuellement la technique d'imagerie standard pour la détection du développement vasculaire anormal et des prises de contraste des lésions mammaires. CE-MRI est cependant très coûteuse et peu disponible. De plus, sa résolution spatiale pourrait être insuffisante pour la détection de certains types de lésions, et ne permet pas d'imager les amas de microcalcifications. Le développement de l'angiomammographie double-énergie (CESM) a permis l'utilisation des produits de contraste intraveineux en clinique avec des appareils conventionnels de mammographie. Cependant, CESM est une technique de projection 2D et présente, par conséquence, des limites pour décrire la structure 3D interne des lésions et pour fournir une information fonctionnelle 3D précise.La tomosynthèse numérique du sein avec injection de produit de contraste (CE-DBT) et le scanner dédié du sein avec injection de produit de contraste (CE-bCT) sont deux techniques d'imagerie actuellement en investigation par des groupes de recherche académiques et industriels. Il est cependant anticipé que le potentiel quantitatif de la CE-DBT soit limité, en raison de la faible résolution en profondeur due à l'ouverture angulaire limitée de la DBT. CE-bCT, avec sa résolution spatiale quasi-isotrope et son intensité de signal proportionnelle au coefficient d'atténuation linéaire, est supposée offrir une information quantitative plus précise, bien qu'une utilisation à faible dose de radiation reste toujours un défi.Objectifs : L'objectif de cette thèse a été d'étudier la faisabilité de la méthode CE-bCT et sa capacité à détecter et localiser des tumeurs vascularisées, ainsi que d'offrir de l'information morphologique et fonctionnelle précise sur les tumeurs. Pour comprendre la valeur ajoutée de la CE-bCT par rapport à CE-DBT, le potentiel quantitatif des deux méthodes a également été comparé. Nos études ont été réalisées grâce à des simulations par ordinateur, validées par des mesures expérimentales.Méthodes : Dans un premier temps, une plateforme de simulation capable de modéliser différentes techniques d'imagerie du sein par rayons X, et fournissant des images radiographiques de fantômes numériques simples et complexes, a été implémentée et validée. Deuxièmement, une étude d'optimisation pour la technique CE-bCT basée sur une approche double-énergie a été réalisée, dans le but de maximiser la qualité des images équivalentes-iode ainsi que des images morphologiques. Enfin, le potentiel quantitatif des méthodes CE-bCT et CE-DBT a été comparé au travers de l'évaluation de la détectabilité, de la caractérisation, de la localisation et de la mesure de l'étendue 3D des lésions iodées. Dans une étude impliquant des observateurs humains, la détectabilité et la caractérisation des lésions iodées de différentes tailles, formes et concentrations ont été comparées entre CE-bCT et CE-DBT, grâce à l'utilisation d'un fantôme anthropomorphique numérique du sein.Conclusions : Les études de simulation menées pendant cette thèse suggèrent que le scanner dédié du sein avec injection de produit de contraste iodé pourrait être une technique réalisable pour la détection, localisation et caractérisation des tumeurs du sein, pour un niveau de dose comparable à une mammographie standard. Bien que les comparaisons préliminaires avec CE-DBT suggèrent une performance comparable sur la détection et caractérisation, l'information 3D complète combinée avec une haute résolution spatiale font de CE-bCT une évolution intéressante de CESM vers une évaluation quantitative 3D des prises de contraste, et une alternative potentielle à CE-MRI pour certaines indications cliniquesBackground: Worldwide, breast cancer is the most common cancer and second deadliest cancer in women. Diagnostic imaging techniques are a critical part for screening, diagnosis, tumor staging and cancer therapy of the breast. Contrast-Enhanced Magnetic Resonance Imaging (CE-MRI) is the current standard imaging technique allowing detection of abnormal vascular development and lesion contrast uptake. CE-MRI is however very costly and not widely available. Moreover, its spatial resolution might not be sufficient to depict certain types of lesions including microcalcifications. The development of Contrast-Enhanced Spectral Mammography (CESM) has made the clinical use of intravenous contrast enhancement with conventional mammography possible. However, CESM is a 2D projection technique and therefore presents limitations to depict the 3D internal structures of lesions and to provide accurate quantitative 3D functional information.Contrast-Enhanced Digital Breast Tomosynthesis (CE-DBT) and dedicated Contrast-Enhanced Breast CT (CE-bCT) are two breast imaging modalities currently under investigation by academic and industrial research groups. It is however anticipated that the quantitative potential of CE-DBT is limited, due to the inherent low depth-resolution of limited opening angle DBT modality. CE-bCT with quasi-isotropic spatial resolution and voxel signal intensity proportional to the linear attenuation coefficient is believed to offer more accurate quantitative information, though a low-dose operation is still a challenge.Objectives: The purpose of this thesis has been to study the technical feasibility of CE-bCT and its potential to accurately depict and localize tumors, as well as to provide accurate quantitative morphological and functional imaging information about tumors, at low radiation dose levels. To understand the incremental value of CE-bCT over CE-DBT, the quantitative potential of both technologies have been compared. This investigation has been performed through computer simulations.Methods: At first, a simulation platform capable of modeling various X-ray breast imaging techniques and providing radiographic images of simple and complex computational phantoms was developed and validated. Secondly, an optimization study of a CE-bCT technique based on a dual-energy approach was performed, aiming to maximize image quality of iodine-enhanced and morphological images. Finally, the quantitative potential of CE-bCT and CE-DBT was compared through the assessment of iodine-enhanced lesion detectability, characterization, localization and 3D extent measurement. In a human observer study, depiction and characterization of iodine-enhanced lesions of different sizes, shapes and iodine uptakes was compared between CE-bCT and CE-DBT using a mesh-based anthropomorphic breast phantom.Conclusions: The simulation studies in this PhD thesis suggest that dual-energy iodine-injected CE-bCT could be a feasible technique for breast tumor depiction, localization and characterization, with dose levels comparable to standard mammography. While preliminary comparisons with CE-DBT suggests comparable depiction and characterization performance, the fully 3D information combined with high spatial resolution confirms CE-bCT as an interesting low-dose evolution of CESM toward 3D quantitative assessment of contrast uptakes and potential alternative to
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Valente, M. A. "Fricke gel dosimetry for 3D imaging of absorbed dose in radiotherapy." Doctoral thesis, Università degli Studi di Milano, 2007. http://hdl.handle.net/2434/41638.
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The overall aim of this thesis was to develop improvements for 3D dosimetry system, based on Fricke solution, in order to achieve accurate 3D absorbed dose distributions by means of visible light transmittance analysis. Such a system would represent a useful tool for 3D treatment planning verification.
In particular, the main objectives were:
To make a Fricke gel dosimeter selecting proper gelling substance and optimizing gel quantity according to the dosimeter response.
To develop a Fricke gel dosimeter preparation protocol in order to establish an optimal elaboration process.
To evaluate the characteristics of the Fricke gel dosimeter for dose distribution measurements.
To reduce the uncertainties in dose distribution determination using Fricke gel dosimeters.
To study the diffusion properties of the Fricke gel dosimeter, allowing a comparison with alternative non-diffusive polymer gel.
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Panizzi, Laura. "Sviluppo di un sistema per l'ottimizzazione della dose in radioterapia tramite "dose-painting" basato sui voxel." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5964/.
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Il presente lavoro è stato svolto presso la struttura di Fisica Medica dell'Azienda Ospedaliera IRCCS "Arcispedale S. Maria Nuova" di Reggio Emilia e consiste nello sviluppo di un sistema per l'ottimizzazione della dose in Radioterapia tramite dose-painting basato sui voxel. Il dose painting è una tecnica di pianificazione del trattamento di radioterapia che si basa sull'assegnazione o ridistribuzione della dose secondo le informazioni biologiche e metaboliche che i moderni sistemi di imaging sono in grado di fornire.
La realizzazione del modulo di calcolo BioOPT è stata possibile grazie all'utilizzo dei due software open-source Plastimatch e CERR, specifici per l'elaborazione e la registrazione di immagini mediche di diversi tipi e formati e per la gestione, la modifica e il salvataggio di piani di trattamento di radioterapia creati con la maggior parte dei software commerciali ed accademici. Il sistema sviluppato è in grado di registrare le immagini relative ad un paziente, in generale ottenute da diverse tipologie di imaging e acquisite in tempi diversi ed estrarre le informazioni biologiche relative ad una certa struttura. Tali informazioni verranno poi utilizzate per calcolare le distribuzioni di dose "ottimale" che massimizzano il valore delle funzioni radiobiologiche utilizzate per guidare il processo di redistribuzione della dose a livello dei voxel (dose-painting). In questo lavoro il modulo è stato utilizzato principalmente per l'ottimizzazione della dose in pazienti affetti da Glioblastoma, un tumore cerebrale maligno tra i più diffusi e mortali.
L'ottimizzatore voxel-based, infatti, è stato sviluppato per essere utilizzabile all'interno di un progetto di ricerca finanziato dal Ministero della Salute per la valutazione di un programma di terapia che include l'uso di un innovativo acceleratore lineare ad alto rateo di dose per la cura di tumori cerebrali in fase avanzata. Al fine di migliorare il trattamento radiante, inoltre, lo studio include la somministrazione della dose tramite dose-painting con lo scopo di verificarne l'efficacia.
I risultati ottenuti mostrano che tramite il modulo sviluppato è possibile ottenere distribuzioni di dose eterogenee che tengono conto delle caratteristiche biologiche intratumore stimate a partire dalle immagini multimodali. Inoltre il sistema sviluppato, grazie alla sua natura 'open', è altamente personalizzabile a scopi di ricerca e consente di simulare distribuzioni di dose basate sui voxel e di confrontarle con quelle ottenute con i sistemi commerciali ad uso clinico, che non consentono questo tipo di ottimizzazioni.
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Peters, Nazlea Behardien. "Determination of effective dose and entrance skin dose from dose area product values for barium studies in adult patients at a large tertiary hospital in the Western Cape." Thesis, Cape Peninsula University of Technology, 2017. http://hdl.handle.net/20.500.11838/2627.
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Thesis (MSc (Radiography))--Cape Peninsula University of Technology, 2018.Background and objectives The issue of patient doses received during fluoroscopy procedures, raised concerns for the researcher, as there may have been probable past skin injuries or deterministic injuries that may not have been documented. Amongst the radiology staff, there was very little understanding of what the actual dose area product (DAP) value means in real terms of effective dose and entrance skin dose. The aims of the study were to: i) Measure the radiation doses received by the patient and determine a simple means of defining the DAP value to the radiographer in terms of the dose received by the patient. ii) Determine the effective dose, entrance skin dose and the relationship with the DAP value to assist with developing a conversion co-efficient for dose indicators. Method Direct radiation dose measurements can be obtained through DAP meters attached to the diagnostic equipment, but the DAP value is not an direct indication of the effective dose received by the patient. The DAP values captured from the DICOM header information for barium fluoroscopic procedures at a large tertiary was analysed and Diagnostic Reference levels (DRL) were determined for barium swallow, meal and enema procedures. The effective and skin doses were calculated by means of the Monte Carlo program. The results were compared to published values. The relationship between the entrance skin dose and the DAP value was determined and conversion factors were calculated. Results Correlation between the DAP and entrance skin dose and comparative 75th percentile threshold values were determined for barium swallow (BaS), barium meal (BaM) and barium enema (BaE) procedures. Effective to DAP conversation factors for BaS, BaM and BaE are 0.19, 0.26 and 0.60 respectively and 0.15, 0.11 and 0.14 for entrance skin to DAP. Conclusion The the research showed the relationship between the effective dose, entrance skin dose and DAP value and a simple, practical and applicable explanation of the DAP value by means of conversion factors.
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Zhou, Tunhe. "Low-dose phase-contrast X-ray imaging: a comparison of two methods." Thesis, KTH, Fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91744.
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Chan, Gordon Ho-Chi. "Beta and electron dose imaging using a microspectrophotometer system and radiochromic film." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0030/NQ66259.pdf.
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Chan, Gordon H. "Beta and electron dose imaging using a microspectrophotometer system and radiochromic film /." *McMaster only, 1999.
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Kotiaho, A. (Antti). "Radiation dose determination using MOSFET and RPL dosimeters in x-ray imaging." Doctoral thesis, Oulun yliopisto, 2019. http://urn.fi/urn:isbn:9789526222653.
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Abstract Medical x-ray imaging is used to visualise patients’ anatomical structures and in some cases their physiology. X-rays are ionizing radiation, thus their use needs to be optimised, as stochastic effects are assumed to increase linearly with the exposure dose. Imaging protocols need to be optimised to a radiation dose level that follows the as low as reasonably achievable principle without compromising the diagnostic value of the image. Different methods can be used to help in the optimisation process, such as simulations, radiation dose and image quality assessments with dosimeters and phantoms and utilising the latest technology in the most efficient way. The purpose of this doctoral thesis was to investigate the applicability of metal-oxide-semiconductor-field-effect-transistor (MOSFET) dosimeters for dose determinations in conventional x-ray and computed tomography (CT) examinations. Additionally, dose optimising methods were investigated in dental panoramic imaging using radiophotoluminescence (RPL) dosimeters. Anthropomorphic phantoms were used in every study to simulate patients, as their structures enable dosimeters to be positioned at locations that correspond to different organs. The MOSFET’s properties for dose determinations were evaluated against the reference dosimeter in a conventional x-ray set-up. Comparisons of absorbed and effective doses in thorax x-ray imaging were made between RPLs, MOSEFTs and Monte Carlo simulations. The effect of the organ-based tube current modulation and bismuth shields were compared against the reference imaging method in a chest CT with one scanner model. Absorbed doses and quantitative image quality were evaluated using each method. Possible dose reduction from segmented dental panoramic tomography (sDPT) imaging was compared against full DPT. Dose measurements were done using RPL dosimeters in pediatric and adult set-up using phantoms. MOSFETs are accurate enough to be used in conventional x-ray and CT, but they require a careful calibration before use as their reproducibility is limited with low doses. Bismuth shields provided the best dose reduction, but with a negative impact on quantitative image quality, especially when metal artefact removal software was used. The final study showed that the use of sDPT programmes and pediatric protocols enable a notably dose reduction compared to the full DPT adult protocolTiivistelmä Lääketieteellisessä kuvantamisessa käytetään röntgensäteilyä potilaan anatomian ja joissain tapauksissa fysiologian visualisointiin. Röntgensäteily on ionisoivaa ja stokastisten vaikutusten kasvaessa oletettavasti lineaarisesti säteilyn funktiona, tulee säteilyn olla kokonaisvaltaisesti optimoitua. Kuvauksissa käytetyn röntgensäteilyn käytön tulee noudattaa ALARA-periaatetta, minkä vuoksi kuvauksessa tulee käyttää niin vähän säteilyä kuin vain mahdollista, diagnostiikan vaarantumatta. Optimoinnin apuna voidaan käyttää esim. simulointeja, annos- ja kuvanlaatumäärityksiä dosimetreilla ja fantomeilla, tai laitevalmistajien tuomia uusia teknologioita. Tämän väitöskirjan tarkoituksena oli tutkia metallioksidi-puolijohdekanavatransistorien (MOSFET) soveltuvuutta natiiviröntgentutkimuksissa ja tietokonetomografiassa (TT). Lisäksi työssä tutkittiin hammaskuvauksissa käytettyjä annossäästömenetelmiä radiofotoluminesenssidosimetreilla (RPL). Potilasvasteena työssä käytettiin antropomorfisia fantomeita, minkä ansiosta säteilyannoksia voidaan mitata eri elimiä vastaavilta kohdilta. MOSFET annosmittarin ominaisuuksia arvioitiin natiiviröntgenasetelmassa referenssimittariin nähden. Absorboituneiden ja efektiivisten annosten eroa MOSFET:tien, RPL:ien ja simulointien kesken tutkittiin keuhkoröntgentutkimuksessa. Pintakudoksia säästävän putkivirranmodulointimenetelmän ja vismuttisuojien vaikuttavuutta verrattiin TT:ssä referenssimetelmää vasten. Vaikuttavuutta arvioitiin absorboituneiden annosten ja kvantitatiivisen kuvanlaadun avulla. Segmentoidun hammaspanoraamakuvauksen (sDPT) annossäästömahdollisuuksia verrattiin tavalliseen panoraamakuvaukseen. Annosmääritykset tehtiin käyttäen RPL dosimetreja lapsi- ja aikuisfantomeissa. MOSFET dosimetreja voidaan käyttää annosmäärityksiin natiiviröntgenkuvauksissa ja TT:ssä, mutta niiden kalibrointi ja toistettavuus matalilla annoksilla aiheuttaa kuitenkin rajoituksia niiden käytölle. Vismuttisuojat tuottivat parhaan annossäästön, huonontaen kuitenkin kuvanlaatua. Kuvanlaadun huonontuminen oli erityisen huomattavaa, kun metallista aiheutuvien kuvavirheiden poistamiseen suunniteltua ohjelmaa käytettiin. Viimeinen tutkimus osoitti, että sDPT ohjelmat ja lapsille suunnatut protokollat mahdollistavat huomattavan annossäästön verrattuna aikuisten kokopanoraamaan
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Doruyter, Alexander Govert George. "Imaging of renal hyperparathyroidism using SPECT/CT with low-dose localizing CT." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85695.
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Thesis (MMed)--Stellenbosch University, 2013.ENGLISH ABSTRACT: Background: Hybrid imaging using single photon emission computed tomography/low dose (x-ray) computed tomography (SPECT/LDCT) is of benefit in preoperative scintigraphy of primary hyperparathyroidism. The role of SPECT/LDCT in preoperative assessment of renal hyperparathyroidism has not yet been examined. The aim of the study was to determine whether SPECT/LDCT conferred any benefit over SPECT alone in terms of detection and/or localization of hyperfunctioning parathyroid tissue in this patient group. Methods: A retrospective study of patients with renal hyperparathyroidism and positive planar and SPECT scintigraphy was undertaken. All patients underwent planar scintigraphy using 99mTc-pertechnetate immediately followed by 99mTc-sestamibi as well as SPECT/LDCT 60 min after sestamibi injection and a delayed static image to assess for differential washout at 2-3 hours. Planar subtraction images were generated. For each patient, two nuclear physicians reported on planar+ SPECT images followed by planar + SPECT/LDCT images (assisted by a radiologist). Confidence for the presence of hyperfunctioning parathyroid tissue as well as confidence of location was scored on a Likert-type scale. Interpretation of planar + SPECT was compared with interpretation of planar + SPECT/LDCT. The impact of LDCT on equivocal lesions and number of ectopic lesions detected was also assessed. Results: Twenty patients (M:13; F:7) imaged between February 2008 and June 2011 were included [mean age: 40 years (24 – 55)]. Mean creatinine was 687 μmol/l (169-1213), mean corrected calcium: 2.55 mmol/l (1.95-3.33) and median PTH 167 pmol/l (2.4 - >201). Thirty-five lesions were detected on planar and SPECT and this was unchanged after assessment of the LDCT data. Confidence for the presence of parathyroid pathology changed in 5 patients (5 lesions) with the addition of LDCT. LDCT changed the mean confidence of parathyroid pathology from 3.17 to 3.29 (p=0.16). Addition of LDCT reduced the number of equivocal lesions from 18 (14 patients) to 14 (10 patients) (p=0.13). The addition of LDCT changed localization in 4 lesions (3 patients). Confidence in localization of pathology changed in 9 lesions (7 patients) and the mean localization confidence score was improved from 4.2 to 4.46 (p=0.002) with LDCT. The number of lesions classified as ectopic increased from 5 (on planar+SPECT) to 8 (with addition of LDCT) (p=0.25). Conclusion: In renal hyperparathyroidism SPECT/LDCT altered localization of lesions detected on planar and SPECT alone and improved reader confidence of localization accuracy. SPECT/LDCT conferred no additional benefit over SPECT in terms of detection, confidence of parathyroid pathology or ability to distinguish equivocal from non-equivocal parathyroid lesions. The addition of LDCT did not detect significantly more ectopic lesions. Whereas the minor improvement in reader confidence of localization (with addition of LDCT) was of questionable clinical significance, we speculate that the changed and presumably improved localization of lesions on SPECT/LDCT had potential clinical impact in a significant proportion of patients. On this basis we recommend the use of hybrid SPECT/LDCT in imaging of renal hyperparathyroidism when surgery is considered.
AFRIKAANSE OPSOMMING: Agtergrond: Hibriedbeelding met enkelfoton emissie rekenaartomografie / lae dosis rekenaartomografie (EFERT/LDRT) is voordelig in pre-operatiewe beelding van primêre hiperparatiroïedisme. Die rol van EFERT/RT in pre-operatiewe evaluering van renale hiperparatiroïedisme is nog nie ondersoek nie. Die doel van hierdie studie was om in hierdie pasiëntgroep te bepaal of EFERT/RT 'n voordeel bo EFERT alleen verleen. Metode: 'n Retrospektiewe studie van pasiënte met renale hiperparatiroïedisme en positiewe planare en EFERT flikkergrafie is onderneem. Na die toediening van 99mTc-pertegnetaat is planare beelding op alle pasiënte gedoen, onmiddellik gevolg deur 99mTc-sestamibi sowel as EFERT/RT beelding 60 min na sestamibi inspuiting en 'n laat statiese beeld vir differensiële uitwas op 2-3 uur. Planare subtraksiebeelde is verkry. Twee kerngeneeskundiges het die planare + EFERT beelde van elke pasiënt gerapporteer, waarna die planare + EFERT/RT beelde met die hulp van 'n radioloog gerapporteer is. Sekerheid oor die teenwoordigheid van hiperfunksionerende paratiroïedweefsel sowel as die sekerheid oor die lokalisering daarvan, is op 'n Likert-tipe skaal verkry. Interpretasie van planare + EFERT is vergelyk met die interpretasie van planare + EFERT/RT. Die impak van LDRT op twyfelagtige letsels en die aantal ektopiese letsels waargeneem, is ook bepaal. Resultate: Twintig pasiënte (M:13; F:7) met beelding tussen Februarie 2008 en Junie 2011 is ingesluit [gemiddelde ouderdom: 40 jaar (24-55)] . Die gemiddelde kreatinien was 687 μmol/l (169-1213), gemiddelde gekorrigeerde kalsium 2.55 mmol/l (1.95-3.33) en mediaan PTH 167 pmol/l (2.4->201). Vyf en dertig letsels is op planare en EFERT beelde waargeneem en was onveranderd na assessering van die LDRT-data. Sekerheid oor die teenwoordigheid van paratiroïedpatologie het verander in 5 pasiënte (5 letsels) met die toevoeging van LDRT. LDRT het die gemiddelde sekerheid van paratiroïedpatologie van 3.17 tot 3.29 verander (p = 0.16). Toevoeging van LDRT het die aantal twyfelagtige letsels van 18 (14 pasiënte) tot 14 (10 pasiënte) verminder (p = 0.13). Die byvoeging van LDRT het die lokalisering in 4 letsels (3 pasiënte) verander. Sekerheid oor die lokalisering van patologie is in 9 letsels (7 pasiënte) verander en die gemiddelde lokalisering betroubaarheidswaarde is verbeter van 4.2 tot 4.46 (p = 0.002) met LDRT. Met die byvoeging van LDRT het die aantal letsels geklassifiseer as ektopies van 5 tot 8 (p = 0.25) toegeneem. Gevolgtrekking: In renale hiperparatiroïedisme het EFERT/RT die lokalisering van letsels wat op planare + EFERT beelding alleen waargeneem is, verander en die leser se vertroue om akkuraat te lokaliseer verbeter. EFERT/LDRT het geen bykomende voordeel bo EFERT in terme van die opsporing, sekerheid van paratiroïedpatologie of onderskeidingsvermoë tussen twyfelagtige teenoor nie-twyfelagtige paratiroïedletsels verleen nie. Met die byvoeging van LDRT is nie beduidend meer ektopiese letsels gevind nie. Terwyl die geringe verbetering in die sekerheid van lokalisering (met die byvoeging van LDRT) van twyfelagtige kliniese betekenis was, spekuleer ons dat die verandering en vermoedelik verbeterde lokalisering van letsels op EFERT/LDRT ʼn potensiële kliniese impak het in 'n beduidende aantal pasiënte. Die gebruik van EFERT/LDRT in die beelding van renale hiperparatiroïedisme wanneer chirurgie oorweeg word, word dus vir bogenoemde rede aanbeveel.
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Lamba, Michael A. S. "Radiation Dose Mapping Using Magnetic Resonance Imaging in a Superheated Emulsion Chamber." University of Cincinnati / OhioLINK, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=ucin962393412.
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Dalhart, Adam M. "A Verification of Deformable Dose and Treatment Planning Software in the Evaluation of Dose to Targets and Normal Structures in SBRT Patients." University of Toledo Health Science Campus / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=mco1404777373.
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Dashtbani, Moghari Mahdieh. "Motion and radiation dose reduction in quantitative CT perfusion imaging of acute stroke." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/28021.
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Computed tomography perfusion (CTP) imaging provides vital decision-support for physicians in the diagnosis and treatment planning for acute ischaemic stroke. Serial three-dimensional frames collected over 1-2 minutes during the transit of contrast agent enables visualisation of the integrity of the cerebral vasculature and underpins quantitative haemodynamic modelling to characterise stroke lesions.
Notwithstanding the value of CTP imaging for stroke management, there are two areas of fundamental limitation: the increased likelihood of motion-induced corruption of the serial (4D) data compared to conventional 3D neuroimaging CT scans that complete within seconds, and the noise-limiting radiation exposure to patients to ensure that robust haemodynamic modelling can be performed. The overarching aim of this thesis was to develop methods to address these key limitations in CTP imaging, thereby improving the accuracy of image-based stroke analysis and long-term outcomes for patients.
Our starting point was to characterise the prevalence, severity, temporal behaviour and dependencies of head movement during CTP imaging studies, and to quantify its clinical impact. Based on this understanding, a predictive model was established to identify patient-specific risk factors for motion. The model implicated stroke severity quantified by the National Institutes of Health Stroke Scale (NIHSS), patient age and time from stroke onset to imaging as the most important factors, all of which can be used pre-emptively to mitigate motion risk in CTP imaging. The results also showed that the accuracy of image interpretation and treatment decision making can potentially be improved for at least a fifth of CTP studies by developing retrospective intra-frame motion correction methods to augment conventional inter-frame motion correction.
Although motion correction is well-recognised as an important pre-requisite to haemodynamic modelling in CTP image analysis, only inter-frame alignment is used and the impact of intra-frame corruption caused by continuous motion is ignored. We investigated the Intel RealSense D415 depth sensor, a compact, markerless and consumer-grade optical motion tracking device, for potential use in providing rapid and accurate pose estimates for continuous motion in CTP imaging. Suitability of the device was characterised with respect to thermal stability and jitter, static and dynamic six degree-of-freedom pose accuracy, and adaptability to the clinical setting. A conservative pose accuracy estimate for robotically controlled phantom motion was < 2 mm and < 1°, and for volunteer motion inside a clinical CT scanner was < 3 mm and < 1°. The device therefore shows promise for CTP motion correction but would likely need to be used in a multi-Intel D415 sensor configuration, or used to augment data-driven methods.
To simultaneously reduce the radiation dose and the likelihood of motion during a CTP acquisition, we attempted to reduce the scan duration by reducing the number of frames acquired. This was achieved using a novel application of a stochastic adversarial video prediction approach trained to predict late CTP image frames from early frames, thereby avoiding the truncation of the wash-out phase of contrast agent transit. Using this approach to predict the last 18 CTP frames resulted in bolus shape characteristics deviating by < 4 ± 4% compared to the ground-truth. Average volumetric error of the hypo-perfused region was overestimated by 28.36 mL (22%) and the corresponding spatial agreement was 83% (mean dice coefficient). The results showed that predicting the last 18 frames can preserve the majority of clinical content of the images while simultaneously reducing the scan duration and radiation dose by 65% and 54.5%, respectively.
The final strategy developed in this thesis was a radiation dose reduction method based on using a 3D generative adversarial network (GAN) to synthesise normal-dose CTP images from low-dose images. The method incorporated pre-processing aimed at leveraging the full spatio-temporal (4D) information of CTP data within a 3D GAN architecture. The quality of GAN-denoised images was assessed via image quality metrics, expert quality rating, and the preservation of the lesion characteristics. The results showed that prioritising temporal information in adapting 4D CTP data to the 3D GAN model resulted in better restoration of tissue haemodynamic information. The average lesion volumetric error reduced significantly by 18 - 29% and dice coefficient improved significantly by 15 - 22% at 50% and 25% of normal radiation dose using the GAN model.
In summary, this thesis reports novel quantitative methods to improve our patient-specific understanding of the impact and dependencies of head motion during CTP imaging, the potential use of practical consumer-grade motion tracking devices for comprehensive motion-corrected CTP imaging, and two state-of-the-art deep learning-based approaches for radiation dose reduction in CTP imaging. The proposed methods lay the foundation for improved image-based stroke analysis and optimised CTP imaging workup and radiation dose, thereby providing more robust decision-support for physicians to improve patient outcomes.
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Flaccavento, Giselle. "Imaging tools for live cell micro-irradiation survival studies." Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589627.
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Micro-irradiation systems are used to analyse the effect of ionizing radiation at the cellular and tissue level, targeting individual cells within a population with a controlled low dose. Cell survival experiments using micro-irradiation systems are limited by factors including: 1) the radiation attenuation and optical properties of the chosen cell dish substrate, 2) the registration of the cell dish before and after irradiation or between multiple imaging modalities and 3) the analysis of the cell or colony growth after irradiation. In this thesis, a set of tools have been developed to improve micro-irradiation experiments and to increase the accuracy of information provided by the cell survival data. The first contribution, the substrate cell dish evaluation, provides a set of characteristics defining the substrates used for micro-irradiation experiments based on minimal energy loss and optical clarity using unstained cell imaging. The second contribution was the development of a novel and low cost fiducial marking device for micro-irradiation experiments using an 808 nm laser and providing marks suitable for imaging with multiple modalities. The minimum focused spot diameter was calculated as 22.9 urn and the device was used to create fiducial marks with diameters ranging from 20 urn to 130 urn. The third contribution, the development of a cell counting methodology for use with a lens-free imaging device, has been shown to accurately count thousands of cells suitable for immediate analysis. Approximately 1000 cell colonies, containing 17 729 cells on 11 cell dishes were used for testing and training for automatic cell counting. Validation of the cell counting method showed that 76% and 89% of the cell colonies were counted within a ± 20% and ± 30% error of the ground truth, respectively. Further development of the fiducial marking device, by modifying the choice of laser and making it suitable for multiple types of cell dish substrates, would increase the applications of the device. Development of the cell counting methodology for different cells line, and for cells grown on multiple types of substrates, would make the system suitable for analysis of a wide variety of cell survival studies. The cell counting methodology, applied to the CyMap lens-free imaging device, has the potential to be an extremely useful and cost effective tool for cell survival studies.
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Rodriguez, Colmeiro Ramiro German. "Towards Reduced Dose Positron Emission Tomography Imaging Using Sparse Sampling and Machine Learning." Thesis, Troyes, 2021. http://www.theses.fr/2021TROY0015.
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Cette thèse étudie le problème de dose de radiation dans les études de Tomographie par Émission de Positons (PET). Trois aspects du PET-scan sont analysées. La première partie de cette thèse est dédiée à la technologie PET-scan. Deux techniques sont développées pour le PET-scan à faible dose : l’AR-PET. Une première stratégie de sélection et de placement de photomultiplicateurs est proposée, augmentant la résolution énergétique. Une technique de localisation d’impacts des photons gamma dans les cristaux solides de scintillation est développé. Cette technique est basée sur des réseaux de neurones artificiels et sur une acquisition unique de champ. Nous montrons qu’une augmentation de la sensibilité du détecteur est obtenue. Dans la deuxième partie de cette thèse, la reconstruction de l’image PET avec l’aide de maillages est étudiée. Un algorithme de reconstruction qui utilise une série de maillages 2D pour décrire la distribution 3D du radiotraceur est proposé, résultant en une diminution du nombre de points d’échantillonnage et rendant possible l’optimisation et la parallélisation des maillages. Enfin, la génération de l’image d’atténuation au moyen de réseaux de neurones artificiels profonds est explorée. L’apprentissage du réseau de neurones se fait à travers une transformation d’images PET FDG sans correction d’atténuation pour produire une image de tomodensitométrie (CT) synthétique. La conclusion des travaux de cette thèse pose la base pour l’usage de PET-scan à bas coût et a faible dose, via l’usage d’une image d’atténuation artificielleThis thesis explores the reduction of the patient radiation dose in screening Positron Emission Tomography (PET) studies. It analyses three aspects of PET imaging, which can reduce the patient dose: the data acquisition, the image reconstruction and the attenuation map generation. The first part of the thesis is dedicated to the PET scanner technology. Two optimization techniques are developed for a novel low-cost and low-dose scanner, the AR-PET scanner. First a photomultiplier selection and placement strategy is created, improving the energy resolution. The second work focuses on the localization of gamma events on solid scintillation crystals. The method is based on neural networks and a single flood acquisition, resulting in an increased detector’s sensitivity. In the second part, the PET image reconstruction on mesh support is studied. A mesh-based reconstruction algorithm is proposed which uses a series of 2D meshes to describe the 3D radiotracer distribution. It is shown that with this reconstruction strategy the number of sample points can be reduced without loosing accuracy and enabling parallel mesh optimization. Finally the attenuation map generation using deep neural networks is explored. A neural network is trained to learn the mapping from non attenuation corrected FDG PET images to a synthetic Computerized Tomography. With these approaches, this thesis lays a base for a low-cost and low-dose PET screening system, dispensing the need of a computed tomography image in exchange of an artificial attenuation map
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Vazquez, Quino Luis Alberto. "Relation between the patient dose and the image quality for commercial imaging devices." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2008. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Morgan, Ashraf. "Measuring Radiation Dose in Computed Tomography Using Elliptic Phantom and Free-In-Air, and Evaluating Iterative Metal Artifact Reduction Algorithm." Cleveland State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=csu1472078731.
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Hepworth, Stephen J. "Investigations into polymer gel dosimetry using magnetic resonance imaging." Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/978/.
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Kam, Chi-kong. "A survey on doctors' awareness and attitude of radiation dose of imaging examination in Hong Kong." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/b3972413x.
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Edeling, Madita. "Target Volume Delineation In Hypoxia Dose Painting." Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-256312.
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Purpose: Tumour hypoxia is the result of uncontrolled growth of the tumour and its vasculature and is often found in solid tumours. It has been known for some time that tumour hypoxia is associated with increased radio resistance and poorer treatment outcomes. While there are several techniques to image the tumour’s oxygenation, no metric or guideline exists that helps in automatically delineating those hypoxic cells into target volumes. Even though several hypoxic biomarkers have been developed and tested to detect visualise and localise hypoxic areas, most of these delineated areas show volumes that are not immediately suitable for dose planning (i.e. a speckled hypoxia distribution). This work deals with 18 cases of tumour hypoxia in patients with non-small cell lung cancer (NSCLC) and presents a method that gives guidance on how to construct hypoxic target volumes feasible for dose planning. Materials and Methods: PET-CT scans have been taken with the hypoxic biomarker 18F-HX4. Hypoxic volumes have been extracted using a threshold of 10mmHg. A region growing algorithm was used to develop the HTV delineation method. Individually calculated doses based on the pO2-distribution within the hypoxic target volume have been used for the construction of dose plans with 24 fractions. Results: Treatment plans that boost the hypoxic target volume whilst sparing surrounding organs at risk were possible to construct for those tumours lying outside the mediastinum. Tumours which volumes were partially or fully overlapping with the mediastinum showed conflicts with delivering the dose necessary for a tumour control probability (TCP) of at least 95% and not exceeding the dose constraints set for the mediastinum.
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Torres, Ruiz Mauricio Nicolàs. "A fundamental study of organic scintillation for X-ray dosimetry in medical imaging." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE042.
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La scintillation organique correspond au phénomène d’émission de lumière par un matériau moléculaire à la suite de l’excitation de celui-ci par un rayonnement externe d’énergie donnée. Lors de l’interaction, le dépôt d’énergie induit des transitions électroniques peuplant des états dont la plupart se désexcite de manière non radiative, à l’exception d’une, entre le premier état électronique singulet et l’état fondamental de la molécule. Lors de cette relaxation, un photon de fluorescence est émis. Cette émission a deux origines : i) l’excitation directe par le rayonnement primaire et les électrons secondaires ; elle donne lieu à une émission dite rapide ou prompte ; ii) l’ionisation par le rayonnement primaire et les électrons secondaires ; elle donne lieu à une émission dite lente ou différée. Ce travail de recherche fondamentale, à la fois théorique et expérimental, fait l’analyse de toutes les étapes du processus, de l’interaction primaire à l’émission de fluorescence, de manière à relier la dose déposée à la quantité de lumière émise, à des fins d’applications en dosimétrie médicale. Il repose sur la mesure des déclins de fluorescence de deux molécules modèles, l’anthracène et le paraterphényle, excitées par un flux continu de rayons X, et la séparation des contributions rapide et lente de la lumière émise, aux énergies médicales. Une modélisation analytique des processus physiques conduisant à l’émission de lumière, au regard de la dose déposée, a ensuite été effectuée, faisant apparaître de nombreux résultats originaux. Dans un premier temps, un dispositif expérimental original a été développé, basé sur la technique TCSPC (Time-Correlated Single Photon Counting), afin de pouvoir mesurer des déclins temporels de fluorescence en résolution nanoseconde et sous flux d’irradiation continu. Dans un second temps, nous avons développé une nouvelle approche mathématique permettant d’extraire finement les composantes rapides et lentes du signal. L’analyse des résultats a montré, pour la première fois, l’existence d’un rapport R constant et uniquement fonction du matériau, entre les rendements d’excitation et d’ionisation. Le caractère constant de ce rapport ne peut être attribué qu’à un mécanisme d’autoionisation moléculaire au sein d’un matériau se comportant intrinsèquement comme une chambre d’ionisation proportionnelle pour l’ionisation secondaire de basse énergie. Ceci est en accord total avec la linéarité observée entre l’intensité totale de lumière différée (ionisation) et la dose mesurée par une chambre d’ionisation proportionnelle. Une étude plus approfondie des mécanismes d’excitation, au regard du rapport R, a également permis de montrer, pour la première fois, une proportionnalité directe entre l’intensité totale de la lumière prompte et le dépôt d’une dose que nous avons baptisé dose d’excitation. Cette dose a été observée comme étant de 4 à 14 fois supérieure à celle mesurée par une chambre d’ionisation. Ce résultat original majeur devra impérativement conduire à des études futures afin de mieux comprendre les dégâts infligés à la matière organique et biologique par les excitationsOrganic scintillation is the emission of light by an organic scintillator when irradiated by an external source of radiation depositing enough energy to excite the molecule. Electronic states are populated by the electronic transitions generated by the deposited energy. The states de-excite through radiationless transitions, except for one, the transition between the first electronic state and the ground state where a photon of fluorescence is emitted. This light has two different origins: i) direct excitation caused by primary radiation or secondary electrons which leads to an emission knows as prompt; ii) ionization caused by primary radiation or secondary electrons generate what is known as the delayed component. This fundamental research was based on both theoretical and experimental work. We studied all the different processes in organic scintillation, from the interaction between the incident radiation and matter to the emission of light in order to find the relationship between fluorescence and the deposited dose, to the application to medical dosimetry. Two well known organic scintillators, anthracene and p-terphenyl, were excited using an X-ray source set at typical medical imaging parameters. The light emitted was acquired and an analytical model was used to describe the different processes that led to light emission revealing interesting new results.An experimental setup, based on the Time Correlated Single Photon Counting (TCSPC) technique, was developed to acquire fluorescence decay curves with nanosecond resolution using a continuous X-ray source. Afterwards, these curves were analyzed using an innovative mathematical approach in order to determine the prompt and delayed components.Results showed the ratio, defined as R, between the prompt and delayed components of fluorescence was constant and independent of the energy of the incident X-rays and that the response of the delayed component of fluorescence was linear to an ionization chamber. These observations were explained by considering that the only process taking place within the molecule after excitation was autoionization. Hence, the response of organic scintillator was the same as the one of an ionization chamber. Furthermore, due to the constant ration R, the response of prompt component of fluorescence was linear to the ionization chamber as well. This was the first time this behavior was observed and we referred to it as excitation dose. This dose was between 4 and 14 times bigger than the one measured with the ionization chamber. These original results suggested that energy is deposited mainly through excitation processes, suggesting the need for further studies to better understand the damage caused by excitation to the living
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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.
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Hellström, Terese. "Deep-learning based prediction model for dose distributions in lung cancer patients." Thesis, Stockholms universitet, Fysikum, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-196891.
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Background To combat one of the leading causes of death worldwide, lung cancer treatment techniques and modalities are advancing, and the treatment options are becoming increasingly individualized. Modern cancer treatment includes the option for the patient to be treated with proton therapy, which can in some cases spare healthy tissue from excessive dose better than conventional photon radiotherapy. However, to assess the benefit of proton therapy compared to photon therapy, it is necessary to make both treatment plans to get information about the Tumour Control Probability (TCP) and the Normal Tissue Complication Probability (NTCP). This requires excessive treatment planning time and increases the workload for planners. Aim This project aims to investigate the possibility for automated prediction of the treatment dose distribution using a deep learning network for lung cancer patients treated with photon radiotherapy. This is an initial step towards decreasing the overall planning time and would allow for efficient estimation of the NTCP for each treatment plan and lower the workload of treatment planning technicians. The purpose of the current work was also to understand which features of the input data and training specifics were essential for producing accurate predictions. Methods Three different deep learning networks were developed to assess the difference in performance based on the complexity of the input for the network. The deep learning models were applied for predictions of the dose distribution of lung cancer treatment and used data from 95 patient treatments. The networks were trained with a U-net architecture using input data from the planning Computed Tomography (CT) and volume contours to produce an output of the dose distribution of the same image size. The network performance was evaluated based on the error of the predicted mean dose to Organs At Risk (OAR) as well as the shape of the predicted Dose-Volume Histogram (DVH) and individual dose distributions. Results The optimal input combination was the CT scan and lung, mediastinum envelope and Planning Target Volume (PTV) contours. The model predictions showed a homogenous dose distribution over the PTV with a steep fall-off seen in the DVH. However, the dose distributions had a blurred appearance and the predictions of the doses to the OARs were therefore not as accurate as of the doses to the PTV compared to the manual treatment plans. The performance of the network trained with the Houndsfield Unit input of the CT scan had similar performance as the network trained without it. Conclusions As one of the novel attempts to assess the potential for a deep learning-based prediction model for the dose distribution based on minimal input, this study shows promising results. To develop this kind of model further a larger data set would be needed and the training method could be expanded as a generative adversarial network or as a more developed U-net network.
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Trigila, Carlotta. "Development of a portable gamma imaging system for absorbed radiation dose control in molecular radiotherapy." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS285.
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La thérapie interne par radionucléides est encore aujourd’hui un domaine peu exploité parmi les différentes modalités de traitement contre le cancer. Son spectre d’applications est toutefois en pleine évolution grâce notamment à l'apparition de nouveaux radiopharmaceutiques émetteurs beta ou alpha (peptides, alpha-thérapie ²²³ Ra, alpha-immunothérapie ²²¹ As,...) (Ersahin 2011). Dans ce contexte, la grande hétérogénéité des doses délivrées et des effets observés, à la fois en terme de toxicité et de réponse, démontrent qu'une dosimétrie personnalisée est essentielle pour optimiser le traitement (Strigari 2011). En pratique clinique, la dosimétrie de la tumeur et des organes à risque (foie, rein, ...) repose sur l’image de la biodistribution et de la cinétique précise du radiopharmaceutique chez chaque patient. Ces images peuvent être réalisées avec un traceur pré-thérapeutique pour planifier le traitement ou après celui-ci, afin de corréler directement les effets observés aux doses délivrées de manière à optimiser le protocole (activité maximum à injecter, intervalle entre les injections). Les contraintes de détection imposées par les protocoles de traitement sont très différentes de celles associées à un examen diagnostique (Flux 2011, Konijnenberg 2011). Les gamma-caméras conventionnelles ne sont ainsi pas adaptées à la détection de fortes activités de rayonnements gamma d'énergies inférieures à 100 keV (²²³ Ra) ou supérieures à 300 keV (¹³¹I, ⁹⁰Y). D’autre part, les fortes activités des traceurs injectés exigent généralement que le patient reste isolé, ce qui le rend donc plus difficilement accessible par les techniques d’imagerie standard. Enfin, la disponibilité de ces systèmes est incompatible avec un échantillonnage temporel précis de la cinétique du traceur, qui joue un rôle très important dans la quantification des doses absorbées. L'objectif de ma thèse était de proposer de nouvelles approches instrumentales visant à renforcer le contrôle de la dose délivrée aux patients lors d'un traitement de radiothérapie moléculaire. Ceci est réalisé en réduisant les incertitudes associées à la quantification de l'activité (et donc au calcul de la dose absorbée) grâce à l'utilisation d'un système d'imagerie compact et hautement optimisé. Il consistait à mettre au point et à optimiser une gamma-caméra mobile miniaturisée à haute résolution spécialement conçue pour améliorer l'évaluation quantitative individuelle de la distribution hétérogène et de la bio-cinétique du radiotraceur avant et après administration du traitement. L'étude était axée sur le traitement des maladies bénignes et malignes de la thyroïde à l'aide de l'¹³¹ I. Le premier prototype de la caméra, avec un champ de vue de 5x5 cm² , consiste en un collimateur à trous parallèles à haute énergie, réalisé en impression 3D et optimisé par simulations Monte Carlo, couplé à un scintillateur inorganique continu, lu par une technologie récente basée sur des matrices de photomultiplicateurs au silicium (SiPM). Ses propriétés intrinsèques, en termes d'énergie et de réponse spatiale, ont été testées avec des sources ponctuelles de ⁵⁷ Co et ¹³³ Ba. Le premier prototype de la caméra a été calibré avec de l'¹³¹ I. La calibration du système conduit à une résolution spatiale globale de (3.14±0.03) mm et à une sensibilité moyenne de (1.23±0.01) cps/MBq, le deux à 5 cm de distance. Nous avons effectué les premières études précliniques avec l'utilisation de différents fantômes thyroïdiens imprimés en 3D, avec et sans nodules, remplis de ¹³¹ I. Des résultats très prometteurs ont été atteints (valeurs de RC proches de l’unité), qui mettent en évidence ses performances adaptées à une quantification précise dans un contexte clinique assez réalisteTargeted radionuclide therapy is still a developing area among the different treatment modalities against cancer. However, its range of applications is rapidly expanding thanks to the emergence of new radiopharmaceuticals labeled with beta or alpha emitters (peptides, ²²³ Ra alpha-therapy, ²²¹ As alpha- immunotherapy, ...) (Ersahin 2011). In that context, the large heterogeneity of absorbed doses and the range of effects observed, both in terms of toxicity and response, demonstrate that individualized patient dosimetry is essential to optimize this therapy (Strigari 2011). In clinical practice, patient-specific dosimetry of tumors and organs-at-risk (liver, kidney, ...) is image-based and rely on the quantification of radio- pharmaceutical uptake as a function of time. These images can be obtained from either a pre-therapy tracer study or from a previous therapy procedure. The detection constraints imposed by the treatment protocols are very different from those associated with diagnostic imaging. (Flux 2011 Konijnenberg 2011). Thus, conventional gamma cameras are not suited for detecting high activity of gamma emitters with energy below 100 keV (²²³ Ra) or greater than 300 keV (¹³¹ I, ⁹⁰Y ). Moreover, high activities of the injected tracer typically require isolation of the patient, making the use of standard imaging devices difficult. Finally, the availability of these devices is incompatible with an accurate temporal sampling of the kinetics of the tracer, which is a key parameter for the quantification of the absorbed doses. The objective of my thesis was precisely to propose new instrumental and methodological approaches aiming to strengthen the control of the dose released to patients during molecular radiotherapy. This is achieved by reducing the uncertainties associated to activity quantification (and therefore to the absorbed dose calculation) through the use of a compact and highly optimized imaging system. Specifically, the work consisted in the development and optimization of a miniaturized, high-resolution mobile gamma camera specifically designed to improve the individual quantitative assessment of the heterogeneous distribution and biokinetics of the radiotracer before and after treatment administration. The study was focused on the treatment of benign and malign thyroid disease with ¹³¹ I. The first prototype of the mobile camera, with a field of view of 5x5 cm², consists of a high-energy parallel- hole collimator, optimized with Monte Carlo simulation and made with 3D printing, coupled to a 6 mm thick continuous CeBr3 scintillator readout by a recent and well-suited technology based on arrays of Silicon Pho- tomultiplier (SiPMs) detectors. Its intrinsic properties, in term of energy and spatial response, have been tested with collimated point source of ⁵⁷Co and ¹³³Ba. The first feasibility prototype has been then calibrated with a line and five cylindrical sources filled with ¹³¹ I. The system calibration leads to an overall spatial resolution of (3.14±0.03) mm at a distance of 5 cm and a sensitivity that decreases with distance and slightly changes with source size. An average sensitivity of (1.23±0.01) cps/MBq has been found at 5 cm. In order to test the quantification capability of the camera, the first preclinical planar studies involved the use of different 3D-printed thyroid phantoms filled with ¹³¹ I, with and without nodules. Although corresponding to a relatively ideal, but realistic, clinical situation (no superimposition of background activity), the optimized imaging features of the camera leads to very promising results, with activity recovery factors that deviate of around 2% from the unity
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Boiret, Mathieu. "Towards chemometric methodologies on hyperspectral imaging for low dose compound detection : application on Raman microscopy." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS291.
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L’imagerie hyperspectrale est désormais considérée comme un outil analytique à part entière dans l’industrie pharmaceutique, aussi bien au cours du développement pour assurer la qualité d’un produit que pour résoudre des problématiques de production après la mise sur le marché du médicament. Dans ces travaux, la microscopie Raman est utilisée pour étudier la distribution en principes actifs et excipients au sein d’une forme pharmaceutique solide, en se focalisant tout particulièrement sur l’identification d’un composé faiblement dosé. Ce dernier est défini comme étant un produit ayant de faibles contributions spatiale et spectrale, signifiant qu’il est distribué dans quelques pixels de l’image avec une information spectrale peu présente dans un spectre de mélange. Alors que la plupart des algorithmes chimiométriques se basent sur la décomposition de moments statistiques, nécessitant une variation suffisante entre les échantillons (les pixels d’une image), les limites de ces outils pour résoudre ce cas spécifique sont rapidement atteintes.La première partie de la thèse met en évidence les difficultés de détection d’un composé faiblement dosé en utilisant l’analyse en composantes indépendantes et la résolution multivariée de courbes. Des méthodologies de travail sont proposées pour contourner ces limitations. Pour les deux techniques, les étapes de réduction de dimensions apparaissent comme des paramètres critiques de la méthode. La seconde partie de la thèse se focalise sur l’espace des signaux pour déterminer des cartes d’absence/présence de constituants ou pour détecter des constituants dans une formulation inconnue, en se basant sur des espaces spectraux portant une information relative aux constituants de la formulation. Les techniques proposées sont parfaitement adaptées à la détection d’un composé faiblement dosé et ces méthodes pourraient être adaptées à d’autres techniques de mesure ou d’autres domaines d’applicationHyperspectral imaging is now considered as a powerful analytical tool in the pharmaceutical environment, both during development to ensure the drug product quality and to solve production issues on commercialized products.In this thesis, Raman microscopy is used to study the distribution of actives and excipients in a pharmaceutical drug product, by especially focusing on the identification of a low dose compound. This latter product is defined as a compound which has low spatial and spectra contributions, meaning that it is scattered in a few pixels of the image and that its spectral response is mixed with the other compounds of the formulation. While most chemometric tools are based on the decomposition of statistical moments (requiring sufficient variations between samples or image pixels), some limitations have been rapidly reached. The first part of this thesis highlights the difficulty to detect a low dose compound in a product by using independent component analysis or multivariate curve resolution. Different methodologies are proposed to circumvent these limitations. For both techniques, reduction of dimensions and filtering steps appears as critical parameters of the method. The second part of the thesis focusses on the signal space to determine absence/presence compound maps or to detect the compounds in an unknown formulation. The proposed methods are only based on the spectral space of each formulation compound. There are perfectly suitable to a low dose compound and should be well-adapted to other analytical techniques or to other environments
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Ariga, Eiji, Shigeki Ito, Shizuhiko Deji, Takuya Saze, and Kunihide Nishizawa. "Development of dosimetry using detectors of diagnostic digital radiography systems." American Association of Physicists in Medicine, 2007. http://hdl.handle.net/2237/8818.
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Abdullah, Kamarul Amin. "Optimisation of CT protocols for cardiac imaging using three-dimensional printing technology." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/18607.
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Objective: This thesis investigates the application of 3D-printing technology for optimising coronary CT angiography (CCTA) protocols using iterative reconstruction (IR) as a dose optimisation strategy. Methods: In phase one, a novel 3D-printed cardiac insert phantom for the Lungman phantom was developed. The attenuation values of the printed phantom were compared to CCTA patients and Catphan® 500 images. In phase two, the printed phantom was scanned at multiple dose levels, and the datasets were reconstructed using different IR strengths. The image quality characteristics were measured to determine the dose reduction potential. In phase three, the influence of IR strengths with low-tube voltage for dose optimisation studies was investigated. The printed phantom and the Catphan® 500 were scanned at different tube currents and voltages. The results were compared to the patient datasets to measure the agreement between the phantoms and patient datasets. Results: In phase one, the attenuation values were consistent between the printed phantom, patient and Catphan® 500 images. In phase two, the results showed that decreasing dose levels had significantly increased the image noise (p<0.001). The application of various IR strengths had yielded a stepwise improvement of noise image quality with a dose reduction potential of up to 40%. In phase three, the results showed a significant interaction between the effects of low-tube voltage and the IR strengths on image quality (all p<0.001) but not the attenuation values. The mean differences were small between the patient-phantom datasets. The optimised CT protocols allowed up to 57% dose reduction in CCTA protocols while maintaining the image quality. Conclusions: The 3D-printed cardiac insert phantom can be used to evaluate the effect of using IR on dose reduction and image quality. This thesis proposes and validates a new method of developing phantoms for CCTA dose optimisation studies.
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Bravaglieri, Lisa. "ClinQC: quality control of an X-ray imaging system using clinical images." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/12172/.
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The work presented in this thesis is part of a research project of Leiden University Medical Center (LUMC) in The Netherlands. It belongs to the field of Diagnostic Radiology analysed from a Medical Physics point of view. After a short overview of the weekly quality controls of an X-ray imaging device, performed using simple phantoms, the thesis focuses on a novel approach called ClinQC (Clinical images-based Quality Control): it has the purpose to monitor the stability of imaging devices, aiming at the early detection of changes in image quality or radiation dose, by deriving quality parameters from chest images of routine patient examinations. The ClinQC algorithm extracts the noise from clinical images and derives the main dose quantities. The noise study presented in this thesis comprehends a validation of the algorithm, performed in several ways: image deteriorations, simulations, phantom studies and real clinical examples. For dose and homogeneity studies only some preliminary results are presented. The thesis collects also some ideas of improvement that can be considered for the future versions of the algorithm and to extend the ClinQC project to other X-ray anatomies and imaging modalities.
The obtained similar results for the two compared methods prove that ClinQC is able to give immediate feedbacks of the quality of the imaging devices using patient images. It provides reliable, on-the-fly and sensitive parameters of the quality of the X-ray imaging system, that have the same physical meaning and similar relative variation as the quality indicators of the gold standard QClight method. It can be concluded that the ClinQC algorithm could be already applied in clinical practice, with the initial support of the QClight weekly quality control. In this way, a comparison between the two methods in a real test period will be a guide to find the necessary adjustments of the algorithm until the final version is being installed and stably used in clinical practice.
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Jarry, Geneviève. "Study of novel techniques for verification imaging and patient dose reconstruction in external beam radiation therapy." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103025.
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Treatment delivery verification is an essential step of radiotherapy. The purpose of this thesis is to develop new methods to improve the verification of photon and electron beam radiotherapy treatments. This is achieved through developing and testing (1) a way to acquire portal images during electron beam treatments, (2) a method to reconstruct the dose delivered to patients during photon beam treatments and (3) a technique to improve image quality in kilovoltage (kV) cone beam computed tomography (CBCT) by correcting for scattered radiation. The portal images were acquired using the Varian CL21EX linac and the Varian aS500 electronic portal imaging device (EPID). The EGSnrc code was used to model fully the CL21EX, the aS500 and the kV CBCT system.We demonstrate that portal images of electron beam treatments with adequate contrast and resolution can be produced using the bremsstrahlung photons portion of the electron beam. Monte Carlo (MC) calculations were used to characterize the bremsstrahlung photons and to obtain predicted images of various phantoms. The technique was applied on a head and neck patient.
An algorithm to reconstruct the dose given to patients during photon beam radiotherapy was developed and validated. The algorithm uses portal images and MC simulations. The primary fluence at the detector is back-projected through the patient. CT geometry to obtain a reconstructed phase space file. The reconstructed phase space file is used to calculate the reconstructed dose to the patient using MC simulations. The reconstruction method was validated in homogeneous and heterogeneous phantoms for conventional and IMRT fields.
The scattered radiation present in kV CBCT images was evaluated using MC simulations. Simulated predictions of the scatter distribution were subtracted from CBCT projection images prior to the reconstruction to improve the reconstructed image quality. Reducing the scattered radiation was found to improve contrast and reduce shading artifacts.
MC simulations, in combination with experimental techniques, have been shown to be valuable tools in the development of treatment verification methods. The three novel methods presented in this thesis contribute to the improvement of radiotherapy treatment verification. They can potentially improve treatment outcome by ensuring a better target coverage.
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Kam, Chi-kong, and 甘志江. "A survey on doctors' awareness and attitude of radiation dose of imaging examination in Hong Kong." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B3972413X.
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Aydarous, Abdulkadir Sheikh. "Development of imaging techniques for determining dose distributions around discrete radioactive particles found in the environment." Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415424.
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Lança, Luís Jorge Oliveira Carrasco. "Radiological imaging in digital systems: the effect of exposure parameters in diagnostic quality and patient dose." Doctoral thesis, Universidade de Aveiro, 2011. http://hdl.handle.net/10773/3950.
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Doutoramento em Tecnologias da SaúdeEsta tese pretende contribuir para o estudo e análise dos factores relacionados com as técnicas de aquisição de imagens radiológicas digitais, a qualidade diagnóstica e a gestão da dose de radiação em sistema de radiologia digital. A metodologia encontra-se organizada em duas componentes. A componente observacional, baseada num desenho do estudo de natureza retrospectiva e transversal. Os dados recolhidos a partir de sistemas CR e DR permitiram a avaliação dos parâmetros técnicos de exposição utilizados em radiologia digital, a avaliação da dose absorvida e o índice de exposição no detector. No contexto desta classificação metodológica (retrospectiva e transversal), também foi possível desenvolver estudos da qualidade diagnóstica em sistemas digitais: estudos de observadores a partir de imagens arquivadas no sistema PACS. A componente experimental da tese baseou-se na realização de experiências em fantomas para avaliar a relação entre dose e qualidade de imagem. As experiências efectuadas permitiram caracterizar as propriedades físicas dos sistemas de radiologia digital, através da manipulação das variáveis relacionadas com os parâmetros de exposição e a avaliação da influência destas na dose e na qualidade da imagem. Utilizando um fantoma contrastedetalhe, fantomas antropomórficos e um fantoma de osso animal, foi possível objectivar medidas de quantificação da qualidade diagnóstica e medidas de detectabilidade de objectos. Da investigação efectuada, foi possível salientar algumas conclusões. As medidas quantitativas referentes à performance dos detectores são a base do processo de optimização, permitindo a medição e a determinação dos parâmetros físicos dos sistemas de radiologia digital. Os parâmetros de exposição utilizados na prática clínica mostram que a prática não está em conformidade com o referencial Europeu. Verifica-se a necessidade de avaliar, melhorar e implementar um padrão de referência para o processo de optimização, através de novos referenciais de boa prática ajustados aos sistemas digitais. Os parâmetros de exposição influenciam a dose no paciente, mas a percepção da qualidade de imagem digital não parece afectada com a variação da exposição. Os estudos que se realizaram envolvendo tanto imagens de fantomas como imagens de pacientes mostram que a sobreexposição é um risco potencial em radiologia digital. A avaliação da qualidade diagnóstica das imagens mostrou que com a variação da exposição não se observou degradação substancial da qualidade das imagens quando a redução de dose é efectuada. Propõe-se o estudo e a implementação de novos níveis de referência de diagnóstico ajustados aos sistemas de radiologia digital. Como contributo da tese, é proposto um modelo (STDI) para a optimização de sistemas de radiologia digital.
In the present study an attempt has been made to contribute for the analysis of the factors related with the technical acquisition, the quality of the diagnostic image and dose management in digital detector systems for projection radiography. The thesis methodology is organized in two components. The observational component is based on a retrospective and transversal design. The data collected from CR and DR systems allowed the evaluation of exposure parameters from digital images, absorbed dose and exposure index to the detector. Under this classification (retrospective and transversal design) it was also possible to develop diagnostic quality evaluations from digital radiographic images: observer performance studies from digital images stored in the PACS. Under the experimental component of this thesis several experiments using phantoms were performed in order to evaluate the relation between dose and image quality. The experiments allowed the characterization of physical properties of digital image systems and manipulation of variables such as those related to exposure parameters and evaluation of its influence in dose and image quality. Using a contrast-detail phantom, anthropomorphic phantoms and an animal bone phantom it was possible to provide objective measures concerning the quantification of diagnostic quality and measures of object detectability. According to the research undertaken several conclusions could be highlighted. Quantitative measures of DR and CR detectors performance provide a basis for optimization, allowing to measure and determinate the physical properties of digital radiology image systems. Exposure parameters being used in digital radiography shows that current routine radiographic practice does not comply with European guidelines concerning exposure techniques. There is a need to evaluate, improve and establish a baseline reference aiming exposure optimization and provide new guidelines for current digital systems. Exposure parameters influence patient dose in digital radiology but image quality perception seems not to be affected with exposure variation. Studies performed both with phantoms and patients showed that overexposure is a potential risk when working with digital systems. Evaluation of diagnostic quality of digital images when a variation of exposure parameters is provided showed no substantial decrease in image quality when dose reduction is achieved. New dose reference levels should be studied and implemented according to the digital system characteristics and performance. A conceptual framework (STDI) is proposed as an attempt to provide a practical method to optimize digital radiology systems.
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Sramek, Benjamin Koerner. "Scatter correction, intermediate view estimation and dose characterization in megavoltage cone-beam CT imaging a dissertation /." San Antonio : UTHSC, 2008. http://proquest.umi.com.libproxy.uthscsa.edu/pqdweb?did=1588783021&sid=1&Fmt=2&clientId=70986&RQT=309&VName=PQD.
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Kjellsson, Lindblom Emely. "Time, dose and fractionation: accounting for hypoxia in the search for optimal radiotherapy treatment parameters." Doctoral thesis, Stockholms universitet, Fysikum, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-148301.
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The search for the optimal choice of treatment time, dose and fractionation regimen is one of the major challenges in radiation therapy. Several aspects of the radiation response of tumours and normal tissues give different indications of how the parameters defining a fractionation schedule should be altered relative to each other which often results in contradictory conclusions. For example, the increased sensitivity to fractionation in late-reacting as opposed to early-reacting tissues indicates that a large number of fractions is beneficial, while the issue of accelerated repopulation of tumour cells starting at about three weeks into a radiotherapy treatment would suggest as short overall treatment time as possible. Another tumour-to-normal tissue differential relevant to the sensitivity as well as the fractionation and overall treatment time is the issue of tumour hypoxia and reoxygenation. The tumour oxygenation is one of the most influential factors impacting on the outcome of many types of treatment modalities. Hypoxic cells are up to three times as resistant to radiation as well-oxygenated cells, presenting a significant obstacle to overcome in radiotherapy as solid tumours often contain hypoxic areas as a result of their poorly functioning vasculature. Furthermore, the oxygenation is highly dynamic, with changes being observed both from fraction to fraction and over a time period of weeks as a result of fast and slow reoxygenation of acute and chronic hypoxia. With an increasing number of patients treated with hypofractionated stereotactic body radiotherapy (SBRT), the clinical implications of a substantially reduced number of fractions and hence also treatment time thus have to be evaluated with respect to the oxygenation status of the tumour. One of the most promising tools available for the type of study aiming at determining the optimal radiotherapy approach with respect to fractionation is radiobiological modelling. With clinically validated in vitro-derived tissue-specific radiobiological parameters and well-established survival models, in silico modelling offers a wide range of opportunities to test various hypotheses with respect to time, dose, fractionation and details of the tumour microenvironment. Any type of radiobiological modelling study intended to provide a realistic representation of a clinical tumour should therefore take into account details of both the spatial and temporal tumour oxygenation. This thesis presents the results of three-dimensional radiobiological modelling of the response of tumours with heterogeneous oxygenation to various fractionation schemes, and oxygenation levels and dynamics using different survival models. The results of this work indicate that hypoxia and its dynamics play a major role in the outcome of radiotherapy, and that neglecting the oxygenation status of tumours treated with e.g. SBRT may compromise the treatment outcome substantially. Furthermore, the possibilities offered by incorporating modelling into the clinical routine are explored and demonstrated by the development of a new calibration function for converting the uptake of the hypoxia-PET tracer 18F-HX4 to oxygen partial pressure, and applying it for calculations of the doses needed to overcome hypoxia-induced radiation resistance. By hence demonstrating how the clinical impact of hypoxia on dose prescription and the choice of fractionation schedule can be investigated, this project will hopefully advance the evolution towards routinely incorporating functional imaging of hypoxia into treatment planning. This is ultimately expected to result in increased levels of local control with more patients being cured from their cancer.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 6: Manuscript.
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Beshtawi, Khaled Raed. "‘Recommendations for the development of a framework for radiological imaging studies during implant therapy in SA’." University of the Western Cape, 2021. http://hdl.handle.net/11394/7744.
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Philosophiae Doctor - PhDRadiographic examination is an essential facet of dental implant therapy, and the success of this therapy depends on a suitable treatment based on adequate clinical and radiographic information. International organisational bodies have published guidelines on the use of radiographic imaging during implant therapy, but since the cone beam computed tomography modality became available, a need for the development of comprehensive imaging guidelines to limit the misuse of this modality became necessary. There is a lack of stringency regarding the recommendations and guidelines on radiographic imaging modalities used during implant therapy. This is due to variations in practice, experience, and socioeconomic factors. The most recent published global guidelines and recommendations and their relevance to dental implant therapy are described in this chapter.
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Sassi, Salem Ahmed. "Region of interest imaging technique : a novel approach to increase image contrast within the region of interest and reduce patient dose in fluoroscopy." Thesis, St George's, University of London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264975.
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Setlur, Nagesh Swetadri Vasan. "Improved imaging for x-ray guided interventions| A high resolution detector system and patient dose reduction technique." Thesis, State University of New York at Buffalo, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3613101.
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Over the past couple of decades there has been tremendous advancements in the field of medicine and engineering technology. Increases in the level of integration between these two branches of science has led to better understanding of physiology and anatomy of a living organism, thus allowing for better understanding of diseases along with their cures and treatments. The work presented in this dissertation aims at improving the imaging aspects of x-ray image guided interventions with endovascular image guided intervention as the primary area of application.
Minimally invasive treatments for neurovascular conditions such as aneurysms, stenosis, etc involve guidance of catheters to the treatment area, and deployment of treatment devices such as stents, coils, balloons, etc, all under x-ray image guidance. The features in these device are in the order of a few 10 µm's to a few 100 µm's and hence demand higher resolution imaging than the current state of the art flat panel detector. To address this issue three high resolution x-ray cameras were developed. The Micro Angiography Fluoroscope (MAF) based on a Charge Coupled Device (MAF-CCD), the MAF based on Complementary Metal Oxide Semiconductors (MAF-CMOS) and the Solid State X-ray Image Intensifier based on Electron Multiplying CCDs. The construction details along with performance evaluations are presented. The MAF-CCD was successfully used in a few interventions on human patient to treat neurovascular conditions, primarily aneurysm. Images acquired by the MAF-CCD during these procedures are presented.
A software platform CAPIDS was previously developed to facilitate the use of the high resolution MAF-CCD in a clinical environment. In this work the platform was modified to be used with any camera. The upgrades to CAPIDS, along with parallel programming including both the Graphics Processing Unit (GPU) and Central Processing Unit (CPU) are presented.
With increasing use of x-ray guidance for minimally invasive interventions, a major cause of concern is that of prolonged exposure to x-ray radiation that can cause biological damage to the patient. Hence during x-ray guided procedures necessary steps must be taken to minimize the dose to the patient. In this work a novel dose reduction technique, using a combination of Region of Interest (ROI) fluoroscopy to reduce dose along with spatially different temporal filtering to restore image quality is presented.
Finally a novel ROI imaging technique for biplane imaging in interventional suites, combining the use of high resolution detector along with dose reduction technique using ROI fluoroscopy with spatially different temporal filtering is presented.
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Shazeeb, Mohammed S. "MRI Contrast Agent Studies of Compartmental Differentiation, Dose-Dependence, and Tumor Characterization in the Brain: A Dissertation." eScholarship@UMMS, 2011. http://escholarship.umassmed.edu/gsbs_diss/504.
Full textAbstract:
Magnetic resonance imaging (MRI) has increasingly become the preferred imaging modality in modern day research to study disease. MRI presents an imaging technique that is practically non-invasive and without any ionizing radiation. This dissertation presents the use of contrast agents in MRI studies to differentiate compartments, to study dose dependence of relaxation times, and to characterize tumors using signal amplifying enzymes in the brain.
Differentiating compartments in the brain can be useful in diffusion studies to detect stroke at an early stage. Diffusion-weighted NMR techniques have established that the apparent diffusion coefficient (ADC) of cerebral tissue water decreases during ischemia. However, it is unclear whether the ADC change occurs due to changes in the intracellular (IC) space, extracellular (EC) space, or both. To better understand the mechanism of water ADC changes in response to ischemic injury, making IC and EC compartment specific measurements of water diffusion is essential. The first study was done where manganese (Mn2+) was used as an IC contrast agent. Mn2+ uptake by cells causes shortening of the T1 relaxation time of IC water. The relative difference in T1 relaxation times between the IC and EC compartments can be used to discriminate between the MR signals arising from water in the respective compartments.
Mn2+ is also widely used in manganese-enhanced MRI (MEMRI) studies to visualize functional neural tracts and anatomy in the brain in vivo. In animal studies, the goal is to use a dose of Mn2+ that will maximize the contrast while minimizing its toxic effects. The goal of dose study was to investigate the MRI dose response of Mn2+ in rat brain following SC administration of Mn2+. The dose dependence and temporal dynamics of Mn2+ after SC injection can prove useful for longitudinal in vivo studies that require brain enhancement to persist for a long period of time to visualize neuroarchitecture like in neurodegenerative disease studies.
Contrast agents, in addition to their use in compartmental differentiation and dose studies, can be used for imaging tumors. The last study in this dissertation focuses on imaging EGF receptors in brain tumors. We tested a novel pretargeting imaging approach that includes the administration of humanized monoclonal antibody (anti-EGFR mAb, EMD72000) linked to enzymes with complementing activities that use a low-molecular weight paramagnetic molecule (diTyr-GdDTPA) as a reducing substrate administered following the mAb conjugates. We analyzed the differential MR tumor signal decay in vivo using orthotopic models of human glioma. The patterns of MR signal change following substrate administration revealed differences in elimination patterns that allowed distinguishing between non-specific and specific modes of MR signal decay.
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Shazeeb, Mohammed S. "MRI Contrast Agent Studies of Compartmental Differentiation, Dose-Dependence, and Tumor Characterization in the Brain: A Dissertation." eScholarship@UMMS, 2010. https://escholarship.umassmed.edu/gsbs_diss/504.
Full textAbstract:
Magnetic resonance imaging (MRI) has increasingly become the preferred imaging modality in modern day research to study disease. MRI presents an imaging technique that is practically non-invasive and without any ionizing radiation. This dissertation presents the use of contrast agents in MRI studies to differentiate compartments, to study dose dependence of relaxation times, and to characterize tumors using signal amplifying enzymes in the brain.
Differentiating compartments in the brain can be useful in diffusion studies to detect stroke at an early stage. Diffusion-weighted NMR techniques have established that the apparent diffusion coefficient (ADC) of cerebral tissue water decreases during ischemia. However, it is unclear whether the ADC change occurs due to changes in the intracellular (IC) space, extracellular (EC) space, or both. To better understand the mechanism of water ADC changes in response to ischemic injury, making IC and EC compartment specific measurements of water diffusion is essential. The first study was done where manganese (Mn2+) was used as an IC contrast agent. Mn2+ uptake by cells causes shortening of the T1 relaxation time of IC water. The relative difference in T1 relaxation times between the IC and EC compartments can be used to discriminate between the MR signals arising from water in the respective compartments.
Mn2+ is also widely used in manganese-enhanced MRI (MEMRI) studies to visualize functional neural tracts and anatomy in the brain in vivo. In animal studies, the goal is to use a dose of Mn2+ that will maximize the contrast while minimizing its toxic effects. The goal of dose study was to investigate the MRI dose response of Mn2+ in rat brain following SC administration of Mn2+. The dose dependence and temporal dynamics of Mn2+ after SC injection can prove useful for longitudinal in vivo studies that require brain enhancement to persist for a long period of time to visualize neuroarchitecture like in neurodegenerative disease studies.
Contrast agents, in addition to their use in compartmental differentiation and dose studies, can be used for imaging tumors. The last study in this dissertation focuses on imaging EGF receptors in brain tumors. We tested a novel pretargeting imaging approach that includes the administration of humanized monoclonal antibody (anti-EGFR mAb, EMD72000) linked to enzymes with complementing activities that use a low-molecular weight paramagnetic molecule (diTyr-GdDTPA) as a reducing substrate administered following the mAb conjugates. We analyzed the differential MR tumor signal decay in vivo using orthotopic models of human glioma. The patterns of MR signal change following substrate administration revealed differences in elimination patterns that allowed distinguishing between non-specific and specific modes of MR signal decay.
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Asuni, Ganiyu. "Investigation of Advanced Dose Verification Techniques for External Beam Radiation Treatment." Medical Physics, 2012. http://hdl.handle.net/1993/21706.
Full textAbstract:
Intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) have been introduced in radiation therapy to achieve highly conformal dose distributions around the tumour while minimizing dose to surrounding normal tissues. These techniques have increased the need for comprehensive quality assurance tests, to verify that customized patient treatment plans are accurately delivered during treatment. In vivo dose verification, performed during treatment delivery, confirms that the actual dose delivered is the same as the prescribed dose, helping to reduce treatment delivery errors. In vivo measurements may be accomplished using entrance or exit detectors. The objective of this project is to investigate a novel entrance detector designed for in vivo dose verification.
This thesis is separated into three main investigations, focusing on a prototype entrance transmission detector (TRD) developed by IBA Dosimetry, Germany. First contaminant electrons generated by the TRD in a 6 MV photon beam were investigated using Monte Carlo (MC) simulation. This study demonstrates that modification of the contaminant electron model in the treatment planning system is required for accurate patient dose calculation in buildup regions when using the device. Second, the ability of the TRD to accurately measure dose from IMRT and VMAT was investigated by characterising the spatial resolution of the device. This was accomplished by measuring the point spread function with further validation provided by MC simulation. Comparisons of measured and calculated doses show that the spatial resolution of the TRD allows for measurement of clinical IMRT fields within acceptable tolerance. Finally, a new general research tool was developed to perform MC simulations for VMAT and IMRT treatments, simultaneously tracking dose deposition in both the patient CT geometry and an arbitrary planar detector system, generalized to handle either entrance or exit orientations. It was demonstrated that the tool accurately simulates dose to the patient CT and planar detector geometries. The tool has been made freely available to the medical physics research community to help advance the development of in vivo planar detectors.
In conclusion, this thesis presents several investigations that improve the understanding of a novel entrance detector designed for patient in vivo dosimetry.
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Dickmann, Jannis Ivo [Verfasser], and Katia [Akademischer Betreuer] Parodi. "Low-dose imaging for particle therapy with fluence-modulated proton computed tomography / Jannis Ivo Dickmann ; Betreuer: Katia Parodi." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2021. http://d-nb.info/1234912058/34.
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lida, Takao, Naureen Mahbub Rahman, Akihiro Matsui, Hiromi Yamazawa, and Jun Moriizumi. "The Measurement of Size Distribution of Indoor Natural Radioactive Aerosols by Imaging Plate Technique." American Institite of Physics, 2008. http://hdl.handle.net/2237/12043.
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