Aspectos metodológicos para la evaluación de sistemas de tomografía por emisión de positrones empleando técnicas Montecarlo, protocolos estandarizados y diferentes trazadores

Abstract

This thesis analyzes the factors affecting the performance evaluation in positron emission tomography (PET) imaging, focusing on preclinical scanners. It explores the possibilities of standard protocols of assessment on the following aspects: their use as tools to validate Monte Carlo simulation programs, their usefulness as a method for comparing scanners and their validity in the study of the effect of alternative radioisotopes on image quality.Initially we study the methods of performance evaluation oriented to validate PET simulations. For this we present the GAMOS program as a simulation framework and show the results of its validation based on the standard NEMA NU 4-2008 for preclinical PET scanners. This has been accomplished by comparing simulated results against experimental acquisitions in the ClearPET scanner, describing the methodology for the evaluation and selection of NEMA parameters. This section also mentions the contributions developed in GAMOS for PET applications, such as the inclusion of tools for image reconstruction. Furthermore, the evaluation of the ClearPET scanner is used to compare its performance against another preclinical scanner, specifically the rPET-1 system. This is the first complete NEMA NU 4 based characterization study of both systems. At the same time we analyze how do the significant design differences of these two systems, especially the size of the axial field of view and the detectors configuration affect their performance characteristics. 68 Ga is one of the unconventional radioisotopes in PET imaging the use of which is currently significantly increasing; however, it presents the disadvantage of the long positron range (distance traveled by the emitted positron before annihilating with an electron). Besides the positron range, additional gamma photon emission is another physical property characteristic of PET radioisotopes that can affect the reconstructed image quality, as it happens to the isotope 48 V. In this thesis we assess these effects through studies of spatial resolution and image quality. Finally, we analyze the scope of the NEMA NU 4-2008 to carry out such studies, adapting it and proposing possible modifications.iii AgradecimientosMe gustaría dar las gracias en primer lugar a los dos directores que han posibilitado el desarrollo y conclusión de esta tesis. A Miguel Embid, por haber confiado en mi hace ya seis

Influencia de la normativa INEN e ISO en las empresas del sector comercial de la provincia de Cotopaxi

“…El mercado de valores en el Ecuador se da a través de la participación de intermediarios, cumple un rol muy importante al canalizar los ahorros hacia la inversión, con la utilización de instrumentos como acciones, obligaciones, a largo plazo y aun costo menor, iniciando en el año 1970 en el cual se creó la bolsa de valores de Quito y Guayaquil. (Valdospinos Castro, 2012) En la figura 1 se detalla las fuentes de financiamiento que utilizan las empresas el cual principalmente está compuesto por el sistema financiero y público, además del mercado de valores que no es muy conocido en el cual se puede emitir obligaciones y vender acciones.…”