Browsing by Author "Andia Kohnenkampf, Marcelo Edgardo"

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    3D 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, Daniel
    Several 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.
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    Enhancement of cardiac and respiratory sounds for cellphone reproduction by means of digital sound processing methods
    (2024) Echenique Soto, María Belén; Godoy Sánchez, Eduardo Javier; Cádiz Cádiz, Rodrigo Fernando; Andia Kohnenkampf, Marcelo Edgardo
    Telemedicine’s rising popularity, driven by its convenience and accessibility, faces a challenge in remote physical auscultation, particularly for assessing lung and heart sounds. We propose a smartphone-based tele-auscultation approach for capturing lung and heart sounds, based on pitch-shifting customized for smartphone listening, overcoming the technical obstacle found in the limited accuracy of smartphone speakers for reproducing low-frequency sounds, such as heart sounds. We created a database of heart and lung sounds captured with a smartphone, and then we conducted two evaluations, one with sounds from open-source databases and one with sounds from an in-house database. Pitch-shifting algorithms from PaulStretch and SoundTouch libraries were applied, and validated against original recordings through a web survey, initially using conventional headphones, as a first step towards delivering them through loudspeakers. In the open-source database experiment, 71.6% and 80% of 40 final-year medical students indicated preserved clinical information in respiratory and heart sounds, respectively. In the in-house database experiment, 14 physicians and final-year medical students validated the processed audio samples, revealing that 76.5% and 71% of respiratory and heart sounds, respectively, maintained clinical information. These results suggest the potential use of pitch-shifted sounds in tele-auscultation devices like smartphones. However, further research is essential to understand smartphones’ playback capabilities in a clinical setting.
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    Estancia hospitalaria en pacientes con protesis de rodilla y cadera en Chile
    (2024) Vidal Olate, Catalina Victoria; Poblete Arrué, Fernando Cristian; Rivera González, Sofia Viviana; Besa Vial, Pablo José; Andia Kohnenkampf, Marcelo Edgardo
    Introducción: en el contexto de la implementación de la herramienta de gestión y financiamiento de Grupos Relacionados a Diagnóstico (GRD) en Chile y el aumento de las cirugías por artrosis en Chile; el objetivo de este estudio fue analizar la estancia hospitalaria en pacientes con prótesis de cadera y rodilla en Chile entre el 2019 y 2021 y sus factores asociados. Metodología: se realizó un estudio observacional retrospectivo con datos obtenidos de la base de datos del Grupo Relacionado de Diagnóstico (GRD) de FONASA. Se seleccionaron pacientes con egresos con procedimiento quirúrgico nomenclatura CIE-9 de prótesis y se consideró como criterio de exclusión diagnóstico principal con codificado con nomenclatura CIE-10 relacionada a fracturas. Se recogió información sobre el año de la cirugía, edad, sexo y procedimiento. Se describieron los GRD encontrados y la mediana de estancia para cada uno. Resultados: durante el periodo hubo 7.148 egresos hospitalarios con procedimiento de prótesis de cadera y 4.090 de rodilla. El promedio de edad fue de 66,2 ± 11,9 años y el 62% de las pacientes son de sexo femenino. En pacientes con prótesis de cadera y rodilla se encontró una mediana de estancia hospitalaria de 4 días (0-275) y 3 días (0-101) respectivamente (p<0,001). Se encontró una distribución asimétrica de la estancia dentro de las distintas severidades de un GRD. Conclusión: en el periodo de estudio existió variabilidad en las estancias hospitalarias asociadas a un mismo GRD en pacientes con procedimientos por prótesis de rodilla y cadera.
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    Exact classification of nmr spectra from nmr signals
    (Institute of Electrical and Electronics Engineers Inc., 2024) Lehmann, Pedro Izquierdo; Xavier, Aline; Andia Kohnenkampf, Marcelo Edgardo; Sing Long Collao, Carlos Alberto
    Nuclear magnetic resonance (NMR) spectroscopy is routinely used to study the properties of matter. Therefore, different materials can be classified according to their NMR spectra. However, the NMR spectra cannot be observed directly, and only the NMR signal, which is a sum of complex exponentials, is directly observable in practice. A popular approach to recover the spectrum is to perform harmonic retrieval, i.e., to reconstruct exactly the spectrum from the NMR signal. However, even when this approach fails, the spectrum might still be classified accurately. In this work, we model the spectrum as an atomic measure to study the performance of classifying the spectrum from the NMR signal, and to determine how it degrades in the presence of additive noise and changes in field intensity. Although we focus on NMR signals, our results are broadly applicable to sum-of-exponential signals. We show numerical results illustrating our claims.
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    Gallbladder cancer: incidence and survival in a high-risk area of Chile
    (2010) Bertran, Enriqueta; Heise, Katy; Andia Kohnenkampf, Marcelo Edgardo; Ferreccio Readi, Catterina
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    Liver magnetic resonance spectroscopy as an alternative for evaluating Niemann-Pick C disease progression
    (ROYAL SOC CHEMISTRY, 2025) Carvalho Da Silva, Xavier Aline; Oyarzun Isamitt, Juan Esteban; Zacconi Flavia, Cristina Milagro; Zanlungo Matsuhiro, Silvana; Andia Kohnenkampf, Marcelo Edgardo
    Niemann-Pick disease (NP) is a group of rare genetic disorders that affect normal lipid metabolism and cause an accumulation of lipids in the liver, spleen, brain, and bone marrow. NP patients develop brain alterations and a very fast progression of liver damage. The purpose of this study is to characterize the changes in liver lipid composition during the progression of this disease using ex vivo magnetic resonance spectroscopy (MRS) in mouse models with the aim of identifying potential biomarkers to support a future non-invasive technique to follow-up these patients. NP type C (NPC) and wild-type (WT) mice were fed a chow diet and euthanized at 5 weeks of age (n = 5 per group) and 9 weeks of age (n = 5 per group). We extracted lipids from their livers and analyzed them with Gas Chromatography-Mass Spectrometry (GC-MS) and MRS. With the GC-MS analysis, 7 main fatty acids (FA) and cholesterols were quantified. Using MRS, we identified 5 metabolite peaks that correspond to FA only, 3 peaks that correspond to cholesterol only, and 2 peaks that correspond to FA and cholesterol. Our results show that the increase in liver cholesterol is the key biomarker for liver damage in NPC, which is consistent with a bad liver disease prognosis due to the association of increased cholesterol levels and liver inflammation. Additionally, we identified a difference in the pool of FA stored in the NPC compared to the WT mouse livers. Those different liver spectra could provide potential biomarkers for the non-invasive follow-up of NPC patients.