13,460 research outputs found
Internal breast dosimetry in mammography: Experimental methods and Monte Carlo validation with a monoenergetic x-ray beam
No full textPurpose: To investigate the performance, such as energy dependence and sensitivity, of thermoluminescent dosimeters (TLD), metal oxide semiconductor field-effect transistor dosimeters (MOSFET), and GafChromicTM films, and to validate the estimates of local dose deposition of a Monte Carlo (MC) simulation for breast dosimetry applications.
Methods: Experimental measurements were performed using a monoenergetic beam at the ELETTRA synchrotron radiation light source (Trieste, Italy). The three types of dosimeters were irradiated
in a plane transversal to the beam axis and calibrated in terms of air kerma. The sensitivity of MOSFET dosimeters and GafChromicTM films was evaluated in the range of 18–28 keV. Three different
calibration curves for the GafChromicTM films were tested (logarithmic, rational, and exponential functions) to evaluate the best-fit curve in the dose range of 1–20 mGy. Internal phantom dose measurements were performed at 20 keV for four different depths (range 0–3 cm, with 1 cm steps) using a homogeneous 50% glandular breast phantom. A GEANT4 MC simulation was modified to match the experimental setup. Thirty sensitive volumes, on the axial-phantom plane were included at each depth in the simulation to characterize the internal dose variation and compare it to the experimental TLD and MOSFET measurements. Experimental 2D dose maps were obtained with the GafChromic TM films and compared to the simulated 2D dose distributions estimated with the MC simulations.
Results: The sensitivity of the MOSFET dosimeters and GafChromicTM films increased with x-ray energy, by up to 37% and 48%, respectively. Dose–response curves for the GafChromicTM film result in an uncertainty lower than 5% above 6 mGy, when a logarithmic relationship is used in the dose range of 1–10 mGy. All experimental values fall within the experimental uncertainty and a good agreement (within 5%) is found against the MC simulation. The dose decreased with increasing phantom depth, with the reduction being ~80% after 3 cm. The uncertainty of the empirical measurements makes the experimental values compatible with a flat behavior across the phantom slab for all the investigated depths, while the MC points to a dose profile with a maximum toward the center of the phantom.
Conclusions: The calibration procedures and the experimental methodologies proposed lead to good accuracy for internal breast dose estimation. In addition, these procedures can be successfully applied
to validate MC codes for breast dosimetry at the local dose level. The agreement among the experimental and MC results not only shows the correctness of the empirical procedures used but also of the simulation parameters
Development of 3D patient-based super-resolution digital breast phantoms using machine learning
No full textDigital phantoms are important tools for optimization and evaluation of x-ray imaging systems, and should ideally reflect the 3D structure of human anatomy and its potential variability. In addition, they need to include a good level of detail at a high enough spatial resolution to accurately model the continuous nature of the human anatomy. A pipeline to increase the spatial resolution of patient-based digital breast phantoms that can be used for computer simulations of breast imaging is proposed. Given a tomographic breast image of finite resolution, the proposed methods can generate a phantom and increase its resolution at will, not only simply through super-sampling, but also by generating additional random glandular details to account for glandular edges and strands to compensate for those that may have not been detected in the original image due to the limited spatial resolution of the imaging system used. The proposed algorithms use supervised learning to predict the loss in glandularity due to limited resolution, and then to realistically recover this loss by learning the mapping between low and high resolution images. They were trained on high-resolution synchrotron images (detector pixel size 60 μm) reconstructed at seven voxel dimensions (60 μm– 480 μm), and applied to patient images acquired with a clinical breast CT system (detector pixel size 194 μm) to generate super-resolution phantoms (voxel sizes 68 μm). Several evaluations were made to assess the appropriateness of the developed methods, both with the synchrotron (relative prediction error 0.010 ± 0.004, recovering accuracy 0.95 ± 0.04), and with the clinical images (average glandularity error at 194 μm: 0.15% ± 0.12%). Finally, a breast radiologist assessed the realism of the developed phantoms by blindly comparing original and phantom images, resulting in not being able to distinguish the real from the phantom images. In conclusion, the proposed method can generate super-resolution phantoms from tomographic breast patient images that can be used for future computer simulations for optimization of new breast imaging technologies
MABS validation through repeated execution and data mining analysis
No full textAgent Based Modelling is the most interesting and advanced approach for simulating a complex system: in a social context, the single parts and the whole are often very hard to describe in detail. Besides, there are agent based formalisms which allow to study the emergency of social behaviour with the creation and study of models, known as artificial societies. Thanks to the ever increasing computational power, it's been possible to use such models to create software, based on intelligent agents, which aggregate behaviour is complex and difficult to predict, and can be used in open and distributed systems. Data mining is born in the last decades in order to help users in finding useful knowledge from the otherwise overwhelming amount of data available nowadays from the web and the data collected every day by companies. Data Mining techniques can therefore be the keystone to reveal non-trivial knowledge expressed by the initial assumption used to build the micro-level of the model and the structure of the society of agents that emerged from the simulation
Automatic estimation of glandular tissue loss due to limited reconstruction voxel size in tomographic images of the breast
No full textAn accurate measurement of the breast glandular fraction, or glandularity, is important for many research and clinical
applications, such as breast cancer risk assessment. We propose a method to estimate the loss of glandular tissue detail
due to the limited voxel size in tomographic images of the breast. CT images of a breast tissue specimen were acquired
using a CdTe single photon counting detector (nominal pixel size of 60 μm) and using a monochromatic synchrotron
radiation x-ray beam. Images were reconstructed using a filtered backprojection algorithm at seven different voxel sizes
(range 60-420 μm, with a 60 μm step) and twelve groups of Regions of Interest (ROIs) with different percentage and
patterns of glandular tissue were extracted. All ROIs within each group contained the same portion of the image (and
therefore the same glandular fraction) reconstructed at a different voxel size. The glandular tissue was segmented and the
glandularity calculated for all ROIs. A machine learning algorithm was trained on the glandularity values as a function of
reconstruction voxel size. After the training was completed, the algorithm could estimate, given a tomographic breast
image reconstructed at a given voxel size with a certain glandularity, the increase (or decrease) of glandularity if the
same image were reconstructed with a smaller (or larger) voxel dimension. The algorithm was tested on six additional
groups of ROIs, resulting in an average relative standard error between the calculated and estimated glandularity of 0.02
± 0.016
Quantitative analysis of thyroid tumors vascularity: A comparison between 3-D contrast-enhanced ultrasound and 3-D Power Doppler on benign and malignant thyroid nodules
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Marco Avellaneda y la muerte de Heredia
No full textLa posición de muchos revisionistas con respecto a Marco Avellaneda, trata de demostrar la habilidad política de nuestro hombre, al servicio de tortuosos planes; ambición de mando, de incontenibles apetitos, etc. Pero esto no es un obstáculo para que, llegado el caso, como ocurre con el traído episodio del caballo que le prestó al teniente Casas, incurran, por razones de banderías, en incomprensible, ingenua contradicción. Marco Avellaneda presta un caballo —y todos lo saben— para que con él vayan a matar a Heredia. En este capítulo especial de la vida de Marco Avellaneda que se relaciona con la muerte de Heredia, la dilucidación del problema tiene indudable importancia
Facades of the Libreria di San Marco in Venice, The: An Interpretation of the Design Process
No full text"A new work in which I propose an interpretation of the design process Sansovino used to create the magnificent facades of the Libreria di San Marco in Venice, a masterpiece of Renaissance architecture." Sent to Marquand librarian by author Dec. 202
Art without an Author: Vasari’s Lives and Michelangelo’s Death
No full textMonografia sulla rappresentazione di Michelangelo nelle due edizioni delle Vite, sulla storia del libro e la questione della sua paternitàBook dedicated to the representation of Michelangelo in Vasari's Lives of the Artists, to the history of the book, and to the problem of its authorshi
Resistencia del concreto de f´c=210 kg/cm2 sustituyendo al cemento por el 5% y 10% ceniza de cola de caballo
No full textEn el presente proyecto de Investigación se encarga de estudiar el comportamiento a través de la resistencia del concreto que tiene la ceniza de cola de caballo (activado) Por ende, buscamos una solución para uso del concreto, que no afecte nuestro ecosistema, debido al uso masivo del cemento portland tipo I y que además el proyecto sea sostenible por el uso de materia prima propia de zona, agregados y cola de caballo, disminuyendo costos, problemas de transporte y contaminación, Y siendo provechoso para el centro poblado de Cambio Puente - Chimbote y para nuestra sociedad.
Se llegó a determinar la resistencia a la compresión del diseño patrón y experimental, dando como resultado que el 5% de ceniza de cola de caballo obtuvo una resistencia de 210.87 kg/cm2 y utilizando el 10 % ceniza de cola de caballo obtuvimos una resistencia de 200.40 kg/cm2, ambos a los 28 días de curado, para lo cual el experimental con el 5 % de ceniza de cola de caballo obtuvo una resistencia optima a la que se quiso llegar, mientras que el diseño patrón obtuvo una resistencia a la compresión de 215.31 kg/cm2 a los 28 días de curado siendo mayor un 2.12% a nuestro diseño experimental del 5 % ceniza de cola de caballo. El proyecto se realizó con la activación térmica de la cola de caballo a 380 C° convirtiéndose en un material puzolamico que posee las mismas propiedades que el cemento portland tipo I, para lo cual se realizó un análisis de fluorescencia de rayos X el cual nos ayudó a encontrar su composición química que nos arrojó los siguientes resultados: Oxido de calcio (9.852) y Oxido de Silice(55.071) los cuales son los principales componentes del cemento.Tesi
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