Browsing by Author "Tejos Núñez, Cristián Andrés"

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    3D quantification of hemodynamics parameters of pulmonary artery and aorta using finite-element interpolations in 4D flow MR data
    (2015) Sotelo Parraguez, Julio Andrés; Urbina, Jesus.; Valverde, Israel.; Tejos Núñez, Cristián Andrés; Irarrázaval Mena, Pablo; Hurtado Sepúlveda, Daniel; Uribe Arancibia, Sergio A.
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    3D quantification of wall shear stress using finite-element interpolations from 4D flow MR data in the Thoracic Aorta
    (2014) Sotelo Parraguez, Julio Andrés; Urbina, Jesus.; Tejos Núñez, Cristián Andrés; Valverde, Israel.; Hurtado Sepúlveda, Daniel; Uribe Arancibia, Sergio A.
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    A realistic in silico abdominal phantom for quantitative susceptibility mapping
    (2022) Silva, Javier I.; Tejos Núñez, Cristián Andrés; Uribe Arancibia, Sergio A.; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    La aplicación de mapas cuantitativos de susceptibilidad (QSM) ha cobrado un reciente interés en regiones fuera del cerebro, debido a su potencial como biomarcador de sobrecarga de hierro hepático y enfermedad crónica de riñón. No obstante, a diferencia del cerebro, la aplicación de QSM en el abdomen requiere modificar el proceso de reconstrucción para lidiar con las contribuciones adicionales en la señal de fase, provenientes de los gases y el tejido graso. Los trabajos más recientes abordan el problema de las contribuciones de grasa mediante distintas estrategias, pero no evalúan el desempeño de estas ni cómo los errores propagados desde las etapas de pre-procesamiento afectan a los mapas reconstruidos. En este trabajo presentamos un fantoma abdominal de QSM con texturas realistas, el cual puede ser empleado para evaluar y comparar el desempeño de diferentes estrategias de QSM abdominal. Hemos elaborado este fantoma empleando un modelo flexible, que permite emular distintos escenarios de susceptibilidad y contribuciones a la señal de resonancia magnética. A modo de validar su potencial como ground truth, hemos empleado el fantoma para evaluar cómo la estrategia de adquisiciones en fase y la estrategia basada en separación de agua y grasa por Iterative Graph Cuts (ICG) afectan el desempeño de los algoritmos de QSM. Las simulaciones realizadas muestran que el fantoma efectivamente simula valores de susceptibilidad con texturas de apariencia realista, a la vez que presenta una correcta evolución de la señal de fase. Por otro lado, los experimentos de reconstrucción dejan en evidencia el potencial de nuestro fantoma para identificar las fortalezas y debilidades de las distintas estrategias estudiadas, como la tendencia de IGC a propagar errores residuales en regiones con cambios abruptos de susceptibilidad, o la robustez de los métodos de reconstrucción basados en regularización por variación total (TV).
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    A realistic MR compatible aortic phantom to validate hemodynamic parameters from MRI data: aortic coarctation patients comparison using catheterization
    (2015) Urbina, Jesus; Sotelo Parraguez, Julio Andrés; Tejos Núñez, Cristián Andrés; Irarrázaval Mena, Pablo; Andía Kohnenkampf, Marcelo Edgardo; Razavi, Reza; Valverde, Israel; Uribe Arancibia, Sergio A.
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    A subject-independent pattern-based Brain-Computer Interface
    (2015) Ray, Andreas M.; Sitaram, Ranganatha; Rana, Mohit; Pasqualotto, Emanuele; Buyukturkoglu, Korhan; Guan, Cuntai; Ang, Kai-Keng; Tejos Núñez, Cristián Andrés; Zamorano, Francisco; Ruiz Poblete, Sergio Marcelo; Birbaumer, Niels; Aboitiz, Francisco
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    A Survey on Deep Learning and Explainability for Automatic Report Generation from Medical Images
    (2022) Messina, Pablo; Pino, Pablo; Parra Santander, Denis; Soto Arriaza, Álvaro Marcelo; Besa, Cecilia; Uribe Arancibia, Sergio A.; Andía Kohnenkampf, Marcelo Edgardo; Tejos Núñez, Cristián Andrés; Prieto Vásquez, Claudia; Capurro, Daniel
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    Accelerating the acquisition of the 3D Dual Cardiac Phase technique using RPE trajectories
    (2014) Letelier Farías, Karis del Pilar; Andía Kohnenkampf, Marcelo Edgardo; Tejos Núñez, Cristián Andrés; Irarrázaval Mena, Pablo; Prieto Vásquez, Claudia; Uribe Arancibia, Sergio A.
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    Algebraic Reconstruction of Source and Attenuation in SPECT Using First Scattering Measurements
    (Springer, 2018) Cueva, Evelyn; Osses Alvarado, Axel Esteban; Quintana Fresno, Juan Carlos; Tejos Núñez, Cristián Andrés; Courdurier Bettancourt Matias Alejandro; Irarrazaval Mena, Pablo
    Here we present an Algebraic Reconstruction Technique (ART) for solving the identification problem in Single Photon Emission Computed Tomography (SPECT). Traditional reconstruction for SPECT is done by finding the radiation source, nevertheless the attenuation of the surrounding tissue affects the data. In this context, ballistic and first scattering information are used to recover source and attenuation simultaneously. Both measurements are related with the Attenuated Radon Transform and a Klein-Nishina angular type dependency is considered for the scattering. The proposed ART algorithm allow us to obtain good reconstructions of both objects in a few number of iterations.
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    Assessment of blood flow patterns in the pulmonary artery using 4D flow
    (2011) Bächler, Pablo.; Pinochet, Natalia.; Tejos Núñez, Cristián Andrés; Gerard, Crelier; Irarrázaval Mena, Pablo; Uribe Arancibia, Sergio A.
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    Assessment of normal flow patterns in the pulmonary circulation by using 4D magnetic resonance velocity mapping
    (2013) Bächler, Pablo; Pinochet, Natalia; Sotelo Parraguez, Julio Andrés; Crelier, Gérard; Irarrázaval Mena, Pablo; Tejos Núñez, Cristián Andrés; Uribe Arancibia, Sergio A.
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    Calcium (Ca2+) waves data calibration and analysis using image processing techniques
    (2013) Milovic Fabregat, Carlos Andrés; Oses, Carolina; Villalón, Manuel J.; Uribe Arancibia, Sergio A.; Prieto Vásquez, Claudia; Andía Kohnenkampf, Marcelo Edgardo; Irarrázaval Mena, Pablo; Tejos Núñez, Cristián Andrés; Lizama, Carlos
    Abstract Background Calcium (Ca2+) propagates within tissues serving as an important information carrier. In particular, cilia beat frequency in oviduct cells is partially regulated by Ca2+ changes. Thus, measuring the calcium density and characterizing the traveling wave plays a key role in understanding biological phenomena. However, current methods to measure propagation velocities and other wave characteristics involve several manual or time-consuming procedures. This limits the amount of information that can be extracted, and the statistical quality of the analysis. Results Our work provides a framework based on image processing procedures that enables a fast, automatic and robust characterization of data from two-filter fluorescence Ca2+ experiments. We calculate the mean velocity of the wave-front, and use theoretical models to extract meaningful parameters like wave amplitude, decay rate and time of excitation. Conclusions Measurements done by different operators showed a high degree of reproducibility. This framework is also extended to a single filter fluorescence experiments, allowing higher sampling rates, and thus an increased accuracy in velocity measurements.
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    Cardiovascular magnetic resonance findings in a pediatric population with isolated left ventricular non-compaction
    (2012) Uribe Arancibia, Sergio A.; Cadavid, Lina; Parra Rojas, Rodrigo Orlando; Urcelay Montecinos, Gonzalo; Heusser Risopatron, Felipe; Andía Kohnenkampf, Marcelo Edgardo; Tejos Núñez, Cristián Andrés; Irarrázaval Mena, Pablo; Hussain, Tarique
    Abstract Background Isolated Left Ventricular Non-compaction (LVNC) is an uncommon disorder characterized by the presence of increased trabeculations and deep intertrabecular recesses. In adults, it has been found that Ejection Fraction (EF) decreases significantly as non-compaction severity increases. In children however, there are a few data describing the relation between anatomical characteristics of LVNC and ventricular function. We aimed to find correlations between morphological features and ventricular performance in children and young adolescents with LVNC using Cardiovascular Magnetic Resonance (CMR). Methods 15 children with LVNC (10 males, mean age 9.7 y.o., range 0.6 - 17 y.o.), underwent a CMR scan. Different morphological measures such as the Compacted Myocardial Mass (CMM), Non-Compaction (NC) to the Compaction (C) distance ratio, Compacted Myocardial Area (CMA) and Non-Compacted Myocardial Area (NCMA), distribution of NC, and the assessment of ventricular wall motion abnormalities were performed to investigate correlations with ventricular performance. EF was considered normal over 53%. Results The distribution of non-compaction in children was similar to published adult data with a predilection for apical, mid-inferior and mid-lateral segments. Five patients had systolic dysfunction with decreased EF. The number of affected segments was the strongest predictor of systolic dysfunction, all five patients had greater than 9 affected segments. Basal segments were less commonly affected but they were affected only in these five severe cases. Conclusion The segmental pattern of involvement of non-compaction in children is similar to that seen in adults. Systolic dysfunction in children is closely related to the number of affected segments.
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    Caval Blood Flow Distribution in Patients with Fontan Circulation : Quantification by Using Particle Traces from 4D Flow MR Imaging
    (2013) Bächler, Pablo; Valverde, Israel; Pinochet, Natalia; Nordmeyer, Sarah; Kuehne, Titus; Crelier, Gérard; Tejos Núñez, Cristián Andrés; Irarrázaval Mena, Pablo; Beerbaum, P.; Uribe Arancibia, Sergio A.
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    Comparison of parameter optimization methods for quantitative susceptibility mapping
    (2020) Milovic Fabregat, Carlos Andrés; Prieto Vásquez, Claudia; Bilgic, B.; Uribe Arancibia, Sergio A.; Acosta Cabronero, J.; Irarrázaval Mena, Pablo; Tejos Núñez, Cristián Andrés
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    Comparison of q-Space Reconstruction Methods for Undersampled Diffusion Spectrum Imaging Data
    (2020) Varela Mattatall, Gabriel Enrique; Koch, A.; Stirnberg, R.; Chabert, S.; Uribe Arancibia, Sergio A.; Tejos Núñez, Cristián Andrés; Stöcker, T.; Irarrázaval Mena, Pablo
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    Enhancing the Velocity Data From 4D Flow MR Images by Reducing its Divergence
    (2016) Mura, J.; Pino, A. M.; Sotelo Parraguez, Julio Andrés; Valverde, I.; Tejos Núñez, Cristián Andrés; Andía Kohnenkampf, Marcelo Edgardo; Irarrázaval Mena, Pablo; Uribe Arancibia, Sergio A.
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    Fast nonlinear susceptibility inversion with variational regularization
    (2018) Milovic Fabregat, Carlos Andrés; Bilgic, Berkin; Zhao, Bo; Acosta‐Cabronero, Julio; Tejos Núñez, Cristián Andrés
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    Hemodynamic Assessment in Patients with One-and-a-Half Ventricle Repair Revealed by Four-Dimensional Flow Magnetic Resonance Imaging
    (2013) Uribe Arancibia, Sergio A.; Bächler, Pablo; Valverde, Israel; Crelier, Gérard R.; Beerbaum, Philipp; Tejos Núñez, Cristián Andrés; Irarrázaval Mena, Pablo
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    High prevalence of undiagnosed liver cirrhosis and advanced fibrosis in type 2 diabetic patients
    (2016) Arab Verdugo, Juan Pablo; Barrera Martínez, Francisco José; Gallego C.; Valderas Igor, Juan Patricio; Uribe Arancibia, Sergio A.; Tejos Núñez, Cristián Andrés; Serrano, C.; Huete, Isidro; Liberona, J.; Labbé P.; Quiroga, T.; Benitez, Carlos; Irarrázaval Mena, Pablo; Riquelme, A.; Arrese Jiménez, Marco
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    How feedback, motor imagery and reward influence brain self-regulation using real-time FMRI.
    (2015) Sepúlveda Delgado, Pradyumna; Tejos Núñez, Cristián Andrés; Ruiz Poblete, Sergio Marcelo; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    El uso de Neurofeedback (NF) con resonancia magnética funcional en tiempo real (Real-time fMRI neurofeedback, rtfMRI) permite la auto-regulación de la actividad metabólica del cerebro. El control de la actividad cerebral puede generar cambios conductuales, lo cual abre nuevas oportunidades para potenciales aplicaciones tanto terapéuticas como de investigación en neurociencias. El proceso de aprendizaje involucrado en alcanzar auto-regulación de la actividad hemodinámica del cerebro se cree que está relacionado a factores como el tipo y contingencia del feedback, recompensa, el uso de imaginería mental, la duración del entrenamiento, entre otros. Instruir explícitamente a los participantes a usar imaginería mental es una práctica común en experimentos de rtfMRI-NF, bajo el supuesto de que esta estrategia mejorará y acelerará el proceso de aprendizaje. Del mismo modo, se asume que la entrega de recompensa monetaria según desempeño refuerza y mejora la auto-regulación cerebral. Sin embargo, la estrategia óptima para mejorar el control voluntario de la actividad cerebral aún no está clara.