24 research outputs found

    Diagnostic Reference Levels for digital mammography in Australia

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    Aims: In 3 phases, this thesis explores: radiation doses delivered to women during mammography, methods to estimate mean glandular dose (MGD), and the use of mammographic breast density (MBD) in MGD calculations. Firstly, it examines Diagnostic reference levels (DRLs) for digital mammography in Australia, with novel focus on the use of compressed breast thickness (CBT) and detector technologies as a guide when determining patient derived DRLs. Secondly, it analyses the agreement between Organ Dose estimated by different digital mammography units and calculated MGD for clinical data. Thirdly, it explores the novel use of MBD in MGD calculations, suggesting a new dose estimation called the actual glandular dose (AGD), and compares MGD to AGD. Methods: DICOM headers were extracted from 52405 anonymised mammograms using 3rd party software. Exposure and QA information were utilised to calculate MGD using 3 methods. LIBRA software was used to estimate MBD for 31097 mammograms. Median, 75th and 95th percentiles were calculated across MGDs obtained for all included data and according to 9 CBT ranges, average population CBT, and for 3 detector technologies. The significance of the differences, correlations, and agreement between MGDs for different CBT ranges, calculation methods, and different density estimation methods were analysed. Conclusions: This thesis have recommended DRLs for mammography in Australia, it shows that MGD is dependent upon CBT and detector technology, hence DRLs were presented as a table for different CBTs and detectors. The work also shows that Organ Doses reported by vendors vary from that calculated using established methodologies. Data produced also show that the use of MGD calculated using standardised glandularities underestimates dose at lower CBTs compared to AGD by up to 10%, hence, underestimating radiation risk. Finally, AGD was proposed; it considers differences in breast composition for individualised radiation-induced risk assessment

    Selection and Evaluation of a Silver Nanoparticle Imaging Agent for Dual-Energy Mammography

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    Over the past decade, contrast-enhanced (CE) dual-energy (DE) x-ray breast imaging has emerged as an exciting, new modality to provide high quality anatomic and functional information of the breast. The combination of these data in a single imaging procedure represents a powerful tool for the detection and diagnosis of breast cancer. The most widely used implementation of CEDE imaging is k-edge imaging, whereby two x-ray spectra are placed on either side of the k-edge of the contrast material. Currently, CEDE imaging is performed with iodinated contrast agents. The lower energies used in clinical DE breast imaging systems compared to imaging systems for other organs suggest that an alternative material may be better suited. We developed an analytical model to compare the contrast of various elements in the periodic table. The model predicts that materials with atomic numbers from 42 to 52 should provide the best contrast in DE breast imaging while still providing high-quality anatomical images. Upon consideration, silver was chosen for more detailed study. Through simulation and experimental validation, we determined that not only does silver perform better than iodine when imaged at their respective optimal conditions, but silver is able to provide higher levels of contrast than iodine when imaged with current protocols that are optimal for iodine. Therefore, a silver agent could be translated to the clinic without modification of existing imaging systems or techniques. A prototype silver agent was designed. The agent consists of (i) a silver core for DE contrast, (ii) a silica shell to prevent the release of toxic silver cations, and (iii) a polyethylene glycol layer to improve the biocompatibility of the entire nanostructure. DE imaging with the particles showed a 9-fold increase in contrast when injected into mice, while displaying no acutely toxic effects. The prototype silica-silver nanoparticles represent a first step in developing a biologically stable contrast agent that is specifically suited for DE breast imaging

    Imaging of the Breast

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    Early detection of breast cancer combined with targeted therapy offers the best outcome for breast cancer patients. This volume deal with a wide range of new technical innovations for improving breast cancer detection, diagnosis and therapy. There is a special focus on improvements in mammographic image quality, image analysis, magnetic resonance imaging of the breast and molecular imaging. A chapter on targeted therapy explores the option of less radical postoperative therapy for women with early, screen-detected breast cancers

    Investigation of physical processes in digital x-ray tomosynthesis imaging of the breast

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    Early detection is one of the most important factors in the survival of patients diagnosed with breast cancer. For this reason the development of improved screening mammography methods is one of primary importance. One problem that is present in standard planar mammography, which is not solved with the introduction of digital mammography, is the possible masking of lesions by normal breast tissue because of the inherent collapse of three-dimensional anatomy into a two-dimensional image. Digital tomosynthesis imaging has the potential to avoid this effect by incorporating into the acquired image information on the vertical position of the features present in the breast. Previous studies have shown that at an approximately equivalent dose, the contrast-detail trends of several tomosynthesis methods are better than those of planar mammography. By optimizing the image acquisition parameters and the tomosynthesis reconstruction algorithm, it is believed that a tomosynthesis imaging system can be developed that provides more information on the presence of lesions while maintaining or reducing the dose to the patient. Before this imaging methodology can be translated to routine clinical use, a series of issues and concerns related to tomosynthesis imaging must be addressed. This work investigates the relevant physical processes to improve our understanding and enable the introduction of this tomographic imaging method to the realm of clinical breast imaging. The processes investigated in this work included the dosimetry involved in tomosynthesis imaging, x-ray scatter in the projection images, imaging system performance, and acquisition geometry. A comprehensive understanding of the glandular dose to the breast during tomosynthesis imaging, as well as the dose distribution to most of the radiosensitive tissues in the body from planar mammography, tomosynthesis and dedicated breast computed tomography was gained. The analysis of the behavior of x-ray scatter in tomosynthesis yielded an in-depth characterization of the variation of this effect in the projection images. Finally, the theoretical modeling of a tomosynthesis imaging system, combined with the other results of this work was used to find the geometrical parameters that maximize the quality of the tomosynthesis reconstruction.Ph.D.Andrew Karellas, John N. Oshinski, Xiaoping P. Hu, Carl J. D’Orsi and Ernest V. Garci

    Simulations and experimental assessment of dosimetric evaluations for breast imaging studies with Synchrotron Radiation

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    openNel migliorare la diagnosi precoce del tumore al seno, a partire dal 2006, è attivo a Trieste uno studio clinico che utilizza la luce di sincrotrone come sorgente di raggi x per eseguire l’esame mammografico (Castelli and et al., 2011). Il sincrotrone Elettra (situato sull’altopiano carsico di Basovizza, Trieste) ospita infatti una facility per l’esecuzione dell’esame mammografico lungo la linea di luce SYRMEP (SYnchrotron Radiation for MEdical Physics). A partire dal 2013 è attivo il progetto SYRMA-CT (finanziato dall’Istituto Nazionale di Fisica Nucleare) che ha come principale obbiettivo quello di attuare il primo studio clinico di Breast Computed Tomography con luce di sincrotone. Il progetto SYRMA-CT (SYnchrotron Radiation for MAmmograpy - Computed Tomography) si inserisce nel trend globale di passaggio dalle immagini 2D a quelle 3D e ingloba al suo interno l’esperienza maturata durante la sperimentazione clinica del programma di Mammografia con la Radiazione di Sincrotrone (MSR). Scopo del presente lavoro di dottorato è quello di estendere la grandezza utilizzata per il calcolo della dose in breast-CT (i.e. Mean Glandular Dose, MGD) alla particolare situazione dell’esame con luce di Sincrotrone. L’esame prevede infatti una situazione di irraggiamento parziale dell’organo (da 3 cm fino ad un massimo di 5 cm) e l’utilizzo di una sorgente monocromatica. Nel corso del lavoro di tesi è stato sviluppato un codice di simulazione Monte Carlo basato sul toolkit GEANT4 che permettesse di calcolare i coefficienti necessari per la stima della dose (DgNct ). Il codice è stato validato confrontandolo sia con la letteratura che con specifiche misure sperimentali alla linea di luce SYRMEP. Due grandezze (che estendono il concetto di MGD) per la stima della dose sono state proposte (Mettivier et al., 2016): MGDt (che tiene conto della dose dovuta alla radiaizone diffusa all’esterno della zona irragiata) e MGDv (che considera solo la dose nella regione irraggiata dell’organo). Il codice sviluppato è inoltre utilizzato per l’ottimizzazione dei parametri energetici che saranno alla base del protocollo d’esame da sottoporre al comitato etico. Sono in fase di studio le distribuzioni di dose che tengono conto delle diverse modalità di ir- raggiamento (quali spiral-CT, irraggiamento di tipi step and go, etc.) nonchè la possibilità di stimare le dosi post-exam attraverso l’ implementazione all’interno del codice delle immagini delle pazienti stesse ottenute durante l’esame.SCUOLA DI DOTTORATO DI RICERCA IN FISICATROMBA GIULIANAembargoed_20170317Fedon, ChristianFedon, Christia

    Numerical efficiency calibration of in vivo measurement systems : Monte Carlo simulations of in vivo measurement scenarios for the detection of incorporated radionuclides, including validation, analysis of efficiency-sensitive parameters and customized anthropomorphic voxel models

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    Monte Carlo radiation transport codes were used with virtual models of in vivo measurement equipment. Software was coded to handle memory intensive anthropomorphic voxel models for simulation of measurement scenarios. Tools, methods and models have been validated. Various parameters have been investigated for their sensitivity. Methods based on image registration techniques have been developed to transform existing human models to match with an individual test person
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