Scattered x-radiation levels associated with various diagnostic procedures were measured with ionization chamber instruments in the small and large animal radiology facilities at the Ontario Veterinary College of the University of Guelph. The occupational radiation exposures incurred by veterinary radiography personnel were monitored using McMaster University's Panasonic UD-702E TLD system. The stray radiation levels and the dosimetric information are compared and discussed. An optimum protocol for radiological health protection surveillance is described. / Thesis / Master of Science (MSc)

Personal är utsatt för spridd strålning när de måste närvara vid CT trauman. Ögat är känsligt för joniserande strålning och det är bevisat att katarakt och strålning har ett samband. Vid CT-multitrauma används många projektioner och långa exponeringar. Studiens syfte är att undersöka hur mycket spridd strålning som personal utsätts för. Hur många gånger/år kan samma personal stå med innan rekommendationerna från ICRP på 20 mSv/år är uppnådd? Det är en kvantitativ studie som utförts empiriskt på två sjukhus med ett fantom. En Siemens 128 slice och en Toshiba 80 slice har använts vid mätningarna. Ett traumaprotokoll användes och en testmätning gjordes och därefter de riktiga mätningarna med dosimetrar från Landauer, placerade på sju mätpunkter i ögonhöjd på olika avstånd från gantryt. Den spridda strålningen var högst närmast gantryt och avtog med avståndet förutom två punkter som hade lägre mätresultat och kan förklaras på grund av dess vinkel från gantryt. Röntgensjuksköterskans ansvar är att informera om var personal bäst kan stå med vid CT trauman och att informera om vikten att variera personal. / Staff who has to attend CT-trauma examination is exposed to scattered radiation. The eye is sensitive to ionizing radiation and there is evidence that cataract and radiation are correlated. At CT-multitrauma long exposures and many projections is taken. The purpose of this study is to examine how much scattered radiation the staff is exposed to. How many times/year can one person in the staff attend a CT-trauma-examination before the ICRP recommendation dose of 20 mSv/year is reached? It is a quantitative study that has been done empirically at two hospitals with a phantom. A Siemens 128 slice and a Toshiba 80 slice were used in the measurements. A trauma protocol was used. One test measurement was done before the real measurements with dosimeters from Landuer placed at seven measure points at eye level at different distances from the gantry. The scattered radiation was highest close to the gantry and decreased with the distance except from two points that had lower measure results and this can be explained by the angle between the gantry and the dosimeter. It’s the radiographer’s responsibility to inform staff of the best place to stand at CT-trauma-examinations and to inform of the importance of alternating staff.

No Brasil, atualmente só há um laboratório de calibração de monitores de radiação de nêutrons, sendo responsável pela guarda e manutenção do padrão brasileiro da fluência de nêutrons, localizado no Laboratório Nacional de Metrologia das Radiações Ionizantes (LNMRI), Rio de Janeiro, no Instituto de Radioproteção e Dosimetria, Comissão Nacional de Energia Nuclear, Rio de Janeiro, com uma demanda grande de serviços com esse tipo de radiação. Com o intuito de descentralizar a oferta de serviços de calibração, surgiu a necessidade da montagem de um segundo Laboratório de Calibração com Nêutrons (LCN), no IPEN. Nas situações práticas envolvendo a calibração de monitores de radiação de nêutrons, um dos problemas principais está relacionado à radiação espalhada, que pode variar dependendo das dimensões do laboratório usado nos procedimentos de calibração. No processo de caracterização do campo de radiação de nêutrons da fonte de 241AmBe, onde foi realizada a avaliação dos espectros, das energias, das taxas de fluência, das taxas de equivalente de dose ambiente [H*(10)] e do coeficiente de conversão de fluência em dose [h*φ(10)] em diferentes posições do LCN, utilizando o feixe completo. A influência da radiação espalhada foi determinada por meio de três técnicas: Métodos de Monte Carlo, de Ajuste Reduzido e do Cone de Sombra. Dos resultados obtidos por meio de simulação e experimentalmente foi possível obter a fração de espalhamento em diferentes distâncias fonte-detector. / In Brazil, there is currently only one calibration laboratory for neutron radiation monitors. It is responsible for the custody and maintenance of the Brazilian neutron fluence standard, located at the Laboratório Nacional de Metrologia das Radiações Ionizantes-LNMRI, Rio de Janeiro, at the Instituto de Radioproteção e Dosimetria, Comissão Nacional de Energia Nuclear, with a great demand of services with this type of radiation. In order to decentralize the calibration service offer, it was necessary to set up a second Neutron Calibration Laboratory (LCN), at IPEN. In practical situations involving the calibration of neutron radiation monitors, one of the main problems is related to scattered radiation, which may vary depending on the size of the laboratory used for the calibration procedures. In the process of characterization of the neutron radiation field of the 241AmBe source, the spectra, the energies, the fluence rate, the ambient dose equivalent rate and the conversion coefficient of fluence in dose at different positions of the LCN, were evaluated using the complete beam. The influence of the scattered radiation was determined by three techniques: Monte Carlo Method, the Reduced Adjustment Method and the Shade Cone Method. From the results obtained through simulation and experimentally, it was possible to obtain the scattering fraction at different source-detector distances.

No Brasil, atualmente só há um laboratório de calibração de monitores de radiação de nêutrons, sendo responsável pela guarda e manutenção do padrão brasileiro da fluência de nêutrons, localizado no Laboratório Nacional de Metrologia das Radiações Ionizantes (LNMRI), Rio de Janeiro, no Instituto de Radioproteção e Dosimetria, Comissão Nacional de Energia Nuclear, Rio de Janeiro, com uma demanda grande de serviços com esse tipo de radiação. Com o intuito de descentralizar a oferta de serviços de calibração, surgiu a necessidade da montagem de um segundo Laboratório de Calibração com Nêutrons (LCN), no IPEN. Nas situações práticas envolvendo a calibração de monitores de radiação de nêutrons, um dos problemas principais está relacionado à radiação espalhada, que pode variar dependendo das dimensões do laboratório usado nos procedimentos de calibração. No processo de caracterização do campo de radiação de nêutrons da fonte de 241AmBe, onde foi realizada a avaliação dos espectros, das energias, das taxas de fluência, das taxas de equivalente de dose ambiente [H*(10)] e do coeficiente de conversão de fluência em dose [h*φ(10)] em diferentes posições do LCN, utilizando o feixe completo. A influência da radiação espalhada foi determinada por meio de três técnicas: Métodos de Monte Carlo, de Ajuste Reduzido e do Cone de Sombra. Dos resultados obtidos por meio de simulação e experimentalmente foi possível obter a fração de espalhamento em diferentes distâncias fonte-detector. / In Brazil, there is currently only one calibration laboratory for neutron radiation monitors. It is responsible for the custody and maintenance of the Brazilian neutron fluence standard, located at the Laboratório Nacional de Metrologia das Radiações Ionizantes-LNMRI, Rio de Janeiro, at the Instituto de Radioproteção e Dosimetria, Comissão Nacional de Energia Nuclear, with a great demand of services with this type of radiation. In order to decentralize the calibration service offer, it was necessary to set up a second Neutron Calibration Laboratory (LCN), at IPEN. In practical situations involving the calibration of neutron radiation monitors, one of the main problems is related to scattered radiation, which may vary depending on the size of the laboratory used for the calibration procedures. In the process of characterization of the neutron radiation field of the 241AmBe source, the spectra, the energies, the fluence rate, the ambient dose equivalent rate and the conversion coefficient of fluence in dose at different positions of the LCN, were evaluated using the complete beam. The influence of the scattered radiation was determined by three techniques: Monte Carlo Method, the Reduced Adjustment Method and the Shade Cone Method. From the results obtained through simulation and experimentally, it was possible to obtain the scattering fraction at different source-detector distances.

Mammography screening aims to reduce the number of breast cancer deaths by early detection of the disease, which is one of the leading causes of deaths for middle aged women in the western world. The risk from the x-ray radiation in mammography is relatively low but still a factor in the benefit-risk ratio of screening. The characterization and optimization of a digital mammography system is presented in this thesis. The investigated system is shown to be highly dose efficient by employing a photon counting detector in a scanning multislit geometry. A novel automatic exposure control (AEC) is proposed and validated in clinical practise. The AEC uses the leading detector edge to measure the transmission of the breast. The exposure is modulated by altering the scan velocity during the scan. A W-Al anode-filter combination is proposed. The characterization of the photon counting detector is performed using the detective quantum efficiency. The effect of the photon counting detector and the multislit geometry on the measurement method is studied in detail. It is shown that the detector has a zero-frequency DQE of over 70\% and that it is quantum limited even at very low exposures. Efficient rejection of image-degrading secondary radiation is fundamental for a dose efficient system. The efficiency of the scatter rejection techniques currently used are quantified and compared to the multislit geometry. A system performance metric with its foundation in statistical decision theory is discussed. It is argued that a photon counting multislit system can operate at approximately half the dose compared to several other digital mammography techniques. / QC 20100825

During X-ray examinations a large part of the radiation is scattered from the patient, contributing to larger radiation doses to medical staff operating inside the examination room. Ionizing radiation contributes to the risk of developing cancer and hereditary diseases but also to the risk of developing cataract.   The aim of this thesis was to investigate the radiation environment and construct three-dimensional maps of the dose distribution, in a Computed Tomography (CT) room during examinations.    Air kerma was measured with real time dosimeters while irradiating an anthropomorphic phantom, using the X-ray tube voltages 100, 120 and 140 kV. The effective dose received by protected and unprotected medical staff inside the CT room during radiation exposure was estimated by using spectra from scattered X-ray radiation, a simulation of X-ray spectra and the dose evaluation program PCXMC. The equivalent dose to the eye lens was estimated by using spectra from scattered X-ray radiation and tabulated conversion factors from air kerma to the personal dose equivalent at 0.07 mm depth, Hp(0.07). From the estimated values of the effective dose and equivalent eye lens dose received by medical staff inside the room, three-dimensional dose distribution maps were constructed. The shielding effectiveness of a lead apron regularly used in the room was examined using tube voltages of 100, 120 and 140 kV.   The radiation dose distributions have a maximum closest to the irradiated phantom for most heights except at eye level where the maximum is shifted outwards along the patient table due to strong shielding by the gantry at eye level. The strong shielding of the gantry is noticed for all energy levels and at all heights but is exceptionally noticeable at eye level. The shielding of the patient table is strongest for the lower heights but is also noticeable at eye level which may seem surprising since there were no objects between the phantom and that point. The dose distribution along directions with minimal shielding seems to follow the inverse square law well. The lead apron is effective but its efficiency decreases for higher photon energies which is expected.   From information about the frequency and durations of CT-guided procedures, the estimated annual effective dose is 1.6-2.3 mSv for protected and 14.3-19.8 mSv for unprotected personnel at the operator position. The estimated annual equivalent eye lens dose is 4.7-7.8 mSv at the operator position. All annual doses at the operator position are below the annual threshold values of 20 mSv set by the ICRP.

No description available.

Depuis l'avènement des premiers appareils imageurs par rayonnement ionisant initié par les prix Nobel Godfrey Newbold Hounsfield et Allan MacLeod Cormack en 1979, le besoin en de nouvelles techniques d'imagerie non invasives n'a cessé de croître. Ces techniques s'appuient sur les propriétés de pénétration dans la matière des rayonnements X et gamma pour détecter une structure cachée sans avoir à détruire le milieu exposé. Elles sont employées dans de nombreux domaines allant de l'imagerie médicale au contrôle non destructif en passant par le contrôle environnemental. Cependant les techniques utilisées jusqu'à maintenant subissent de fortes dégradations dans la qualité des mesures et des images reconstruites. Généralement approchées par un bruit, ces dégradations exigent d'être compensées ou corrigées par des dispositifs de collimation et de filtrage souvent coûteux. Ces dégradations sont principalement dues aux phénomènes de diffusion qui peuvent constituer jusqu'à 80 % du rayonnement émis en imagerie biomédicale. Dès les années 80 un nouveau concept a vu le jour pourcontourner cette difficulté : la tomographie Compton. Cette nouvelle approche propose de mesurer le rayonnement dit diffusé en se plaçant dans des gammes d'énergie (140−511 keV) où l'effet Compton est le phénomène de diffusion prépondérant. L'exploitation de tels dispositifs d'imagerie nécessite une compréhension profonde des interactions rayonnement/matière afin de proposer un modèle, cohérent avec les données mesurées, indispensable à la reconstruction d'images. Dans les systèmes d'imagerie conventionnels (qui mesurent le rayonnement primaire), la transformée de Radon définie sur les lignes droites est apparue comme le modèle naturel. Mais en tomographie Compton, l'information mesurée est liée à l'énergie de diffusion et ainsi à l'angle de diffusion.Ainsi la géométrie circulaire induite par le phénomène de diffusion rend la transformée de Radon classique inadaptée. Dans ce contexte, il devient nécessaire de proposer des transformées de type Radon sur des variétés géométriques plus larges.L'étude de la transformée de Radon sur de nouvelles diversités de courbes devient alors nécessaire pour répondre aux besoins d'outils analytiques de nouvelles techniques d'imagerie. Cormack, lui-même, fut le premier à étendre les propriétés de la transformée de Radon classique à une famille de courbes du plan. Par la suite plusieurs travaux ont été menés dans le but d'étudier la transformée de Radon définie sur différentes variétés de cercles, des sphères, des lignes brisées pour ne citer qu'eux. En 1994 S.J. Norton proposa la première modalité de tomography Compton modélisable par une transformée de Radon sur lesarcs de cercle, la CART1. En 2010 Nguyen et Truong établirent l'inversion de la transformée de Radon sur les arcs de cercle, CART2, permettant de modéliser la formation d'image dans une nouvelle modalité de tomographie Compton. La géométrie des supports d'intégration impliqués dans de nouvelles modalitésde tomographie Compton les conduirent à démontrer l'invertibilité de la transformée de Radon définie sur une famille de courbes de type Cormack, appelée C_alpha. Ils illustrèrent la procédure d'inversion dans le cadre d'une nouvelle transformée, la CART3 modélisant une nouvelle modalité de tomographie Compton.En nous basant sur les travaux de Cormack et de Truong et Nguyen, nous proposons d'établir plusieurs propriétés de la transformée de Radon définie sur la famille C_alpha et plus particulièrement sur C1. Nous avons ainsi démontré deux formules d'inversion qui reconstruisent l'image d'origine via sa décompositionharmonique circulaire et celle de sa transformée et qui s'apparentent à celles établies par Truong and Nguyen. Nous avons enfin établi la bien connue rétroprojection filtrée ainsi que la décomposition en valeurs singulières dans le cas alpha = 1. L'ensemble des résultats établis dans le cadre de cette étude apporte des réponses concrètes a / Since the advent of the first ionizing radiation imaging devices initiated by Godfrey Newbold Hounsfield and Allan MacLeod Cormack, Nobel Prizes in 1979, the requirement for new non-invasive imaging techniques has grown. These techniques rely upon the properties of penetration in the matter of X and gamma radiation for detecting a hidden structure without destroying the illuminated environment. They are used in many fields ranging from medical imaging to non-destructive testing through. However, the techniques used so far suffer severe degradation in the quality of measurement and reconstructed images. Usually approximated by a noise, these degradations require to be compensated or corrected by collimating devices and often expensive filtering. These degradation is mainly due to scattering phenomena which may constitute up to 80% of the emitted radiation in biological tissue. In the 80's a new concept has emerged to circumvent this difficulty : the Compton scattering tomography (CST).This new approach proposes to measure the scattered radiation considering energy ranges ( 140-511 keV) where the Compton effect is the phenomenon of leading broadcast. The use of such imaging devices requires a deep understanding of the interactions between radiation and matter to propose a modeling, consistent with the measured data, which is essential to image reconstruction. In conventional imaging systems (which measure the primary radiation) the Radon transformdefined on the straight lines emerged as the natural modeling. But in Compton scattering tomography, the measured information is related to the scattering energy and thus the scattering angle. Thus the circular geometry induced by scattering phenomenon makes the classical Radon transform inadequate.In this context, it becomes necessary to provide such Radon transforms on broader geometric manifolds.The study of the Radon transform on new manifolds of curves becomes necessary to provide theoretical needs for new imaging techniques. Cormack, himself, was the first to extend the properties of the conventional Radon transform of a family of curves of the plane. Thereafter several studies have been done in order to study the Radon transform defined on different varieties of circles, spheres, broken lines ... . In 1994 S.J. Norton proposed the first modality in Compton scattering tomography modeled by a Radon transform on circular arcs, the CART1 here. In 2010, Nguyen and Truong established the inversion formula of a Radon transform on circular arcs, CART2, to model the image formation in a new modality in Compton scattering tomography. The geometry involved in the integration support of new modalities in Compton scattering tomography lead them to demonstrate the invertibility of the Radon transform defined on a family of Cormack-type curves, called C_alpha. They illustrated the inversion procedure in the case of a new transform, the CART3, modeling a new modeling of Compton scattering tomography. Based on the work of Cormack and Truong and Nguyen, we propose to establish several properties of the Radon transform on the family C_alpha especially on C1. We have thus demonstrated two inversion formulae that reconstruct the original image via its circular harmonic decomposition and itscorresponding transform. These formulae are similar to those established by Truong and Nguyen. We finally established the well-known filtered back projection and singular value decomposition in the case alpha = 1. All results established in this study provide practical problems of image reconstruction associated with these new transforms. In particular we were able to establish new inversion methods for transforms CART1,2,3 as well as numerical approaches necessary for the implementation of these transforms. All these results enable to solve problems of image formation and reconstruction related to three Compton scattering tomography modalities.In addition we propose to improve models and algorithms es

Σκοπός της εργασίας αυτής είναι η χαρτογράφηση της δευτερογενούς ακτινοβολίας ακτινογραφικής λυχνίας μέσα στην αίθουσα εξέτασης, ενός συμβατικού ακτινολογικού μηχανήματος, συναρτήσει διαφόρων ακτινογραφικών παραμέτρων. Στόχος των μετρήσεων αυτών είναι ο υπολογισμός της σκεδαζόμενης ακτινοβολίας και της διαρρέουσας ακτινοβολίας σε διάφορες γωνίες από 0 μοίρες έως και 360 μοίρες, με βήμα 45 μοιρών, χρησιμοποιώντας έναν κυλινδρικό σκεδαστή νερού διαστάσεων: διάμετρος = 38 cm και ύψος 20 cm, σε διάφορες αποστάσεις από τον σκεδαστή (1.0 m, 1.5 m και 2.0 m), για διαφορετικό πάχος φίλτρου λυχνίας και διαφορετικά στοιχεία ακτινογράφησης. / Secondary radiation in classical radiography units in different angles (0-360 angles)and in different distances (1.0 m, 1.5 m and 2.0 m) around the X-Ray tube. The phnatom we use was cylindrical with water, the dimancional of the phantom was: d = 38 cm and h = 20 cm. Different thickness of tube filter and differnt kV,mA,mAs.

Since the advent of the first ionizing radiation imaging devices initiated by Godfrey Newbold Hounsfield and Allan MacLeod Cormack, Nobel Prizes in 1979, the requirement for new non-invasive imaging techniques has grown. These techniques rely upon the properties of penetration in the matter of X and gamma radiation for detecting a hidden structure without destroying the illuminated environment. They are used in many fields ranging from medical imaging to non-destructive testing through. However, the techniques used so far suffer severe degradation in the quality of measurement and reconstructed images. Usually approximated by a noise, these degradations require to be compensated or corrected by collimating devices and often expensive filtering. These degradation is mainly due to scattering phenomena which may constitute up to 80% of the emitted radiation in biological tissue. In the 80's a new concept has emerged to circumvent this difficulty : the Compton scattering tomography (CST).This new approach proposes to measure the scattered radiation considering energy ranges ( 140-511 keV) where the Compton effect is the phenomenon of leading broadcast. The use of such imaging devices requires a deep understanding of the interactions between radiation and matter to propose a modeling, consistent with the measured data, which is essential to image reconstruction. In conventional imaging systems (which measure the primary radiation) the Radon transformdefined on the straight lines emerged as the natural modeling. But in Compton scattering tomography, the measured information is related to the scattering energy and thus the scattering angle. Thus the circular geometry induced by scattering phenomenon makes the classical Radon transform inadequate.In this context, it becomes necessary to provide such Radon transforms on broader geometric manifolds.The study of the Radon transform on new manifolds of curves becomes necessary to provide theoretical needs for new imaging techniques. Cormack, himself, was the first to extend the properties of the conventional Radon transform of a family of curves of the plane. Thereafter several studies have been done in order to study the Radon transform defined on different varieties of circles, spheres, broken lines ... . In 1994 S.J. Norton proposed the first modality in Compton scattering tomography modeled by a Radon transform on circular arcs, the CART1 here. In 2010, Nguyen and Truong established the inversion formula of a Radon transform on circular arcs, CART2, to model the image formation in a new modality in Compton scattering tomography. The geometry involved in the integration support of new modalities in Compton scattering tomography lead them to demonstrate the invertibility of the Radon transform defined on a family of Cormack-type curves, called C_alpha. They illustrated the inversion procedure in the case of a new transform, the CART3, modeling a new modeling of Compton scattering tomography. Based on the work of Cormack and Truong and Nguyen, we propose to establish several properties of the Radon transform on the family C_alpha especially on C1. We have thus demonstrated two inversion formulae that reconstruct the original image via its circular harmonic decomposition and itscorresponding transform. These formulae are similar to those established by Truong and Nguyen. We finally established the well-known filtered back projection and singular value decomposition in the case alpha = 1. All results established in this study provide practical problems of image reconstruction associated with these new transforms. In particular we were able to establish new inversion methods for transforms CART1,2,3 as well as numerical approaches necessary for the implementation of these transforms. All these results enable to solve problems of image formation and reconstruction related to three Compton scattering tomography modalities.In addition we propose to improve models and algorithms es