Browsing by Author "Tejos Nunez, Cristian Andres"
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- Item3D non-destructive evaluation techniques for wood analysis(2014) Paulina Fernández, M.; Tejos Nunez, Cristian Andres; Rojas, G.; Lillo, I.; Guesalaga, A.; Irarrázaval, P.
- Item3D Quantification of Wall Shear Stress and Oscillatory Shear Index Using a Finite-Element Method in 3D CINE PC-MRI Data of the Thoracic Aorta(2016) Sotelo Parraguez, Julio Andrés; Urbina, Jesus; Valverde, Israel; Tejos Nunez, Cristian Andres; Irarrázaval Mena, Pablo; Andia Kohnenkampf, Marcelo Edgardo; Uribe Arancibia, Sergio A.; Hurtado Sepúlveda, DanielSeveral 2D methods have been proposed to estimate WSS and OSI from PC-MRI, neglecting the longitudinal velocity gradients that typically arise in cardiovascular flow, particularly on vessel geometries whose cross section and centerline orientation strongly vary in the axial direction. Thus, the contribution of longitudinal velocity gradients remains understudied. In this work, we propose a 3D finite-element method for the quantification of WSS and OSI from 3D-CINE PC-MRI that accounts for both in-plane and longitudinal velocity gradients. We demonstrate the convergence and robustness of the method on cylindrical geometries using a synthetic phantom based on the Poiseuille flow equation. We also show that, in the presence of noise, the method is both stable and accurate. Using computational fluid dynamics simulations, we show that the proposed 3D method results in more accurate WSS estimates than those obtained from a 2D analysis not considering out-of-plane velocity gradients. Further, we conclude that for irregular geometries the accurate prediction of WSS requires the consideration of longitudinal gradients in the velocity field. Additionally, we compute 3D maps of WSS and OSI for 3D-CINE PC-MRI data sets from an aortic phantom and sixteen healthy volunteers and two patients. The OSI values show a greater dispersion than WSS, which is strongly dependent on the PC-MRI resolution. We envision that the proposed 3D method will improve the estimation of WSS and OSI from 3D-CINE PC-MRI images, allowing for more accurate estimates in vessels with pathologies that induce high longitudinal velocity gradients, such as coarctations and aneurisms.
- ItemAbnormal nodal and global network organization in resting state functional MRI from subjects with the 22q11 deletion syndrome(2021) Pelgrim, T.A.D.; Bossong, M.G.; Cuiza, A.; Alliende, L.M.; Mena, C.; Tepper, A.; Ramirez-Mahaluf, J.P.; Iruretagoyena, B.; Ornstein, C.; Fritsch, R.; Cruz, J.P.; Tejos Nunez, Cristian Andres; Repetto, G.; Crossley, N.
- ItemAnálisis cuantitativo de variables hemodinámicas de la aorta obtenidas de 4D flow(2012) Julio Sotelo, P.; Rodrigo Salas, F.; Tejos Nunez, Cristian Andres; Chabert, S.; Sergio Uribe, A.
- ItemDeepSPIO: Super Paramagnetic Iron Oxide Particle Quantification using Deep Learning in Magnetic Resonance Imaging(2020) della Maggiora Valdés, Gabriel Eugenio; Milovic Fabregat, Carlos Andrés; Qiu, Wenqi; Liu, Shuang; Milovic Fabregat, Carlos Andres; Sekino, Masaki; Tejos Nunez, Cristian Andres; Uribe Arancibia, Sergio A.; Irarrazaval Barros, PabloThe susceptibility of Super Paramagnetic Iron Oxide (SPIO) particles makes them a useful contrast agent for different purposes in MRI. These particles are typically quantified with relaxometry or by measuring the inhomogeneities they produced. These methods rely on the phase, which is unreliable for high concentrations. We present in this study a novel Deep Learning method to quantify the SPIO concentration distribution. We acquired the data with a new sequence called View Line in which the field map information is encoded in the geometry of the image. The novelty of our network is that it uses residual blocks as the bottleneck and multiple decoders to improve the gradient flow in the network. Each decoder predicts a different part of the wavelet decomposition of the concentration map. This decomposition improves the estimation of the concentration, and also it accelerates the convergence of the model. We tested our SPIO concentration reconstruction technique with simulated images and data from actual scans from phantoms. The simulations were done using images from the IXI dataset, and the phantoms consisted of plastic cylinders containing agar with SPIO particles at different concentrations. In both experiments, the model was able to quantify the distribution accurately.
- ItemGOFOS, ground optical fog observation system for monitoring the vertical stratocumulus-fog cloud distribution in the coast of the Atacama Desert, Chile(2021) del Río, C.; Lobos, F.; Siegmund, A.; Tejos Nunez, Cristian Andres; Osses, P.; Huaman, Z.; Meneses, J.P.; García, J.-L.
- ItemMedición de presiones relativas en aorta torácica y arteria pulmonar de voluntarios sanos y pacientes con Tetralogía de Fallot reparada utilizando la secuencia 4D Flow de resonancia magnética cardíaca(2012) Jesús Urbina, R.; Julio Sotelo, P.; Tejos Nunez, Cristian Andres; Daniel Hurtado, S.; Marcelo Andía, K.; Pablo Irarrázaval, M.; Sergio Uribe, A.
- ItemNoise estimation for the velocity in MRI phase-contrast(2019) Irarrazaval, P.; Dehghan Firoozabadi, A.; Uribe, S.; Tejos Nunez, Cristian Andres; Sing-Long, C.
- ItemReducción de los tiempos de adquisición de imágenes por resonancia magnética utilizando técnicas de compressed sensing(2009) Carlos Sing-Long, C.; Tejos Nunez, Cristian Andres; Pablo Irarrazaval, M.
- ItemReducción de los tiempos de adquisición de imágenes por resonancia magnética utilizando técnicas de compressed sensing(2009) Carlos Sing-Long, C.; Tejos Nunez, Cristian Andres; Pablo Irarrazaval, M.
- ItemSimplex mesh diffusion snakes: Integrating 2D and 3D deformable models and statistical shape knowledge in a variational framework(2009) Tejos Nunez, Cristian Andres; Irarrazaval, P.; Cárdenas-Blanco, A.
- ItemUtilización de la resonancia magnética con contraste de fase para el diagnóstico del síndrome de congestión pelviana(2009) Luis Meneses, Q.; Tejos Nunez, Cristian Andres; Pablo Irarrazabal, M.
- ItemUtilización de la resonancia magnética con contraste de fase para el diagnóstico del síndrome de congestión pelviana(2009) Luis Meneses, Q.; Tejos Nunez, Cristian Andres; Pablo Irarrazabal, M.
- ItemVisualization tools for understanding a complex code from a real application(2009) Campos, F.; Cortazar, E.; Eterovic, Y.; Ramirez, L.; Tejos Nunez, Cristian Andres; Irarrazaval, P.
- ItemVisualization tools for understanding a complex code from a real application(2009) Campos, F.; Cortazar, E.; Eterovic, Y.; Ramirez, L.; Tejos Nunez, Cristian Andres; Irarrazaval, P.
- ItemWeighted neurofeedback facilitates greater self-regulation of functional connectivity between the primary motor area and cerebellum(2021) Vargas, P.; Sitaram, R.; Sepúlveda, P.; Montalba, C.; Rana, M.; Torres, R.; Tejos Nunez, Cristian Andres; Ruiz, S.