The use of emission-transmission computed tomography for improved quantification in SPECT

The attenuation of photons within the body has been recognised as the major limiting factor hindering the ability of single photon emission computed tomography (SPECT) as a quantitative technique. This thesis investigates several aspects of an emission-transmission SPECT system using the Monte Carlo method and experimental techniques. The system was based on a rotating gamma camera fitted with a parallel hole collimator. The simulation of a transmission study was performed using a simple non-uniform mathematical phantom with two different external sources, a collimated line source and a flood source. The results showed that the attenuation maps were highly dependent on the geometry and photon energy of the source. The collimated line source produced improved image quality with lower statistical noise than the flood source. The results showed that, when high atomic number elements are present in the tissue composition, the attenuation coefficients at different energies are related through a second order polynomial transformation. If the object under study is formed of soft tissue equivalent materials, a linear transformation holds. The attenuation maps generated in the transmission study were used to correct for non-uniform attenuation compensation of an emission phantom. The results showed that non-uniform attenuation compensation improved image quality and reduced noise when compared to data without attenuation compensation. The presence of scattered photons in the emission data reduced the quality of the images and precluded accurate quantification. Absolute quantification was performed using the percent air sensitivity criterion. The largest difference between the theoretical and the Monte Carlo simulated images was approximately 8%. An emission-transmission myocardial perfusion study was simulated using an anthropomorphic phantom. Two photon energies of clinical interest were used, 75 keV and 140 keV, corresponding to the main photon emission energies of 201Tl and 99mTC. The results showed that 99mTc provided better image quality than 201Tl. Non-uniform attenuation compensation produced a very good agreement between the theoretical prediction and the simulation when scatter-free data were considered. The results presented in this thesis indicate that it is not possible to accomplish accurate attenuation compensation in general situations if scatter correction is not applied

Sistema de liberación controlada de morfina y otros fármacos solubles en agua por complejación con sustancias poliméricas

Sistema de liberación controlada de morfina y otros fármacos solubles en agua por complejación con sustancias poliméricas. Método de obtención de un sistema de liberación controlada de fármacos de elevada solubilidad acuosa por complejación con sustancias poliméricas, consistente en hacer reaccionar químicamente una resina acrílica, p.ej. Eudragit L 30D, con la sal del fármaco en cuestión, p.ej. morfina. Primero se neutraliza parcialmente un volumen determinado de suspensión acuosa de Eudragit L 6D, a la que posteriormente se le añade la solución acuosa de la sal del fármaco a complejar, produciéndose la reacción entre el fármaco y la resina y se obtiene un precipitado que, secado en estufa, da lugar al complejo fármaco Eudragit. Es de aplicación en la Industria Farmacéutica para la fabricación de formas sólidas de administración oral que permitan alcanzar rápidamente concentraciones plasmáticas terapéuticas y mantenerlas, posteriormente, durante un período prolongado hasta la total liberación del principio activo, optimizando así la terapia medicamentosa.Españ

Composición farmacéutica y medicamento de liberación controlada de morfina basado en un complejo de morfina con un polímero acrílico

Composición farmacéutica y medicamento de liberación controlada de morfina basado en un complejo de morfina con un polímero acrílico. La composición farmacéutica comprende un complejo de liberación controlada de morfina que contiene morfina complejada con un polímero acrílico, una sal farmacéuticamente aceptable de morfina libre, y uno o más excipientes inertes respecto a la liberación controlada. Dicha composición es útil para elaborar un comprimido oral de liberación controlada de morfina para el tratamiento del dolor crónico severo sin necesidad de tener que administrar simultáneamente morfina vía parenteral.Españ

4to. Congreso Internacional de Ciencia, Tecnología e Innovación para la Sociedad. Memoria académica

Este volumen acoge la memoria académica de la Cuarta edición del Congreso Internacional de Ciencia, Tecnología e Innovación para la Sociedad, CITIS 2017, desarrollado entre el 29 de noviembre y el 1 de diciembre de 2017 y organizado por la Universidad Politécnica Salesiana (UPS) en su sede de Guayaquil. El Congreso ofreció un espacio para la presentación, difusión e intercambio de importantes investigaciones nacionales e internacionales ante la comunidad universitaria que se dio cita en el encuentro. El uso de herramientas tecnológicas para la gestión de los trabajos de investigación como la plataforma Open Conference Systems y la web de presentación del Congreso http://citis.blog.ups.edu.ec/, hicieron de CITIS 2017 un verdadero referente entre los congresos que se desarrollaron en el país. La preocupación de nuestra Universidad, de presentar espacios que ayuden a generar nuevos y mejores cambios en la dimensión humana y social de nuestro entorno, hace que se persiga en cada edición del evento la presentación de trabajos con calidad creciente en cuanto a su producción científica. Quienes estuvimos al frente de la organización, dejamos plasmado en estas memorias académicas el intenso y prolífico trabajo de los días de realización del Congreso Internacional de Ciencia, Tecnología e Innovación para la Sociedad al alcance de todos y todas

Efficient system modeling for a small animal PET scanner with tapered DOI detectors

A prototype small animal positron emission tomography (PET) scanner for mouse brain imaging has been developed at UC Davis. The new scanner uses tapered detector arrays with depth of interaction (DOI) measurement. In this paper, we present an efficient system model for the tapered PET scanner using matrix factorization and a virtual scanner geometry. The factored system matrix mainly consists of two components: a sinogram blurring matrix and a geometrical matrix. The geometric matrix is based on a virtual scanner geometry. The sinogram blurring matrix is estimated by matrix factorization. We investigate the performance of different virtual scanner geometries. Both simulation study and real data experiments are performed in the fully 3D mode to study the image quality under different system models. The results indicate that the proposed matrix factorization can maintain image quality while substantially reduce the image reconstruction time and system matrix storage cost. The proposed method can be also applied to other PET scanners with DOI measurement

Scatter correction in cone-beam computed tomography using convolutional neural networks

A validated Monte Carlo model of the kV imaging system of the TrueBeam STx Linac based on the egs_cbct code of EGSnrc has been used to determine the scatter contribution in cone-beam computed tomography (CBCT) images. Geometrical and anatomical digital phantoms were used in this MC framework to acquire a data set of CBCT images and its respective scatter components. This data set was used to train a deep learning algorithm, based on Convolutional Neural Networks. Specifically, we analyzed the performance of UNets and Generative Adversarial Networks. UNets demonstrate more efficient and precise results, even when trained with a few hundred images. Scatter corrections in CBCT images can be achieved with a trained deep learning-based model in 3 to 4 orders of magnitude faster than MC-based methods.</p

Energy spectra of coincidence events registered in both crystal configurations.

Around 80% of the events are detected through multiple Compton scattering ending in photoelectric absorption. The histograms in the bottom row show the break-down of events where at least one of the coincidence photons underwent 1, 2 or 3 Compton scatterings (CS1, CS2, CS3).</p

Fig 6 -

Δx residual histograms in semi-logarithmic scale in monolithic and pixelated crystals considering a) both MI-SI and MI-MI coincidences, and b) only MI-MI coincidences.</p

Analysis of the reconstructed images (1.5 and 2.0 mm diameter hot rod pies) using either first hit or energy weighted positions.

Analysis of the reconstructed images (1.5 and 2.0 mm diameter hot rod pies) using either first hit or energy weighted positions.</p

Fig 1 -

GATE geometry model of the dual-panel PEM with monolithic (a) and pixelated (b) crystals. The upper reflective layer in the crystals in b) was assumed transparent in this drawing for ease of visualization. Tomographic images reconstructed parallel to the (x, y) plane are referred to as in-plane.</p