Browsing by Author "Montalba, Cristian"
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- ItemAn off-resonance insensitive orthogonal CSPAMM sequence (ORI-O-CSPAMM) for the acquisition of CSPAMM and MICSR grids in half scan time(2021) Mella, Hernan; Wang, Hui; Montalba, Cristian; Uribe, SergioPurpose: To develop an Off-Resonance Insensitive Orthogonal CSPAMM sequence (ORI-O-CSPAMM) for the acquisition of CSPAMM and MICSR grids in half of the acquisition time.
- ItemAutomatic quantification of fat infiltration in paraspinal muscles using T2-weighted images: An OsiriX application(ELSEVIER SCI LTD, 2020) Arrieta, Cristobal; Urrutia, Julio; Besa, Pablo; Montalba, Cristian; Lafont, Nelson; Andia, Marcelo E.; Uribe, SergioFat infiltration of paraspinal muscles has been related with low back pain and quantified using T2w MR images and manual segmentation techniques. This methodology is time consuming and has low reproducibility. Moreover, the accuracy of T2w images to quantify fat has not been validated. This paper presents the development and validation of an OsiriX application to semi-automatically segment infiltrated fat on T2w images. This software was also utilized to validate the quantification of muscle fat infiltration with T2w images, considering Dixon fat images assessments as a gold standard.
- ItemComparison of Improved Unidirectional Dual Velocity-Encoding MRI Methods(2023) Franco, Pamela; Ma, Liliana; Schnell, Susanne; Carrillo, Hugo; Montalba, Cristian; Markl, Michael; Bertoglio, Cristobal; Uribe, SergioBackground In phase-contrast (PC) MRI, several dual velocity encoding methods have been proposed to robustly increase velocity-to-noise ratio (VNR), including a standard dual-VENC (SDV), an optimal dual-VENC (ODV), and bi- and triconditional methods. Purpose To develop a correction method for the ODV approach and to perform a comparison between methods. Study Type Case-control study. Population Twenty-six volunteers. Field Strength/Sequence 1.5 T phase-contrast MRI with VENCs of 50, 75, and 150 cm/second. Assessment Since we acquired single-VENC protocols, we used the background phase from high-VENC (VENCH) to reconstruct the low-VENC (VENCL) phase. We implemented and compared the unwrapping methods for different noise levels and also developed a correction of the ODV method. Statistical Tests Shapiro-Wilk's normality test, two-way analysis of variance with homogeneity of variances was performed using Levene's test, and the significance level was adjusted by Tukey's multiple post hoc analysis with Bonferroni (P < 0.05). Results Statistical analysis revealed no extreme outliers, normally distributed residuals, and homogeneous variances. We found statistically significant interaction between noise levels and the unwrapping methods. This implies that the number of non-unwrapped pixels increased with the noise level. We found that for beta = VENCL/VENCH = 1/2, unwrapping methods were more robust to noise. The post hoc test showed a significant difference between the ODV corrected and the other methods, offering the best results regarding the number of unwrapped pixels. Data Conclusions All methods performed similarly without noise, but the ODV corrected method was more robust to noise at the price of a higher computational time. Level of Evidence 4 Technical Efficacy Stage 1
- ItemComprehensive Assessment of Left Intraventricular Hemodynamics Using a Finite Element Method: An Application to Dilated Cardiomyopathy Patients(2021) Franco, Pamela; Sotelo, Julio; Montalba, Cristian; Ruijsink, Bram; Kerfoot, Eric; Nordsletten, David; Mura, Joaquin; Hurtado, Daniel; Uribe, SergioIn this paper, we applied a method for quantifying several left intraventricular hemodynamic parameters from 4D Flow data and its application in a proof-of-concept study in dilated cardiomyopathy (DCM) patients. In total, 12 healthy volunteers and 13 DCM patients under treatment underwent short-axis cine b-SSFP and 4D Flow MRI. Following 3D segmentation of the left ventricular (LV) cavity and registration of both sequences, several hemodynamic parameters were calculated at peak systole, e-wave, and end-diastole using a finite element approach. Sensitivity, inter- and intra-observer reproducibility of hemodynamic parameters were evaluated by analyzing LV segmentation. A local analysis was performed by dividing the LV cavity into 16 regions. We found significant differences between volunteers and patients in velocity, vorticity, viscous dissipation, energy loss, and kinetic energy at peak systole and e-wave. Furthermore, although five patients showed a recovered ejection fraction after treatment, their hemodynamic parameters remained low. We obtained several hemodynamic parameters with high inter- and intra-observer reproducibility. The sensitivity study revealed that hemodynamic parameters showed a higher accuracy when the segmentation underestimates the LV volumes. Our approach was able to identify abnormal flow patterns in DCM patients compared to volunteers and can be applied to any other cardiovascular diseases.
- ItemRealistic aortic phantom to study hemodynamics using MRI and cardiac catheterization in normal and aortic coarctation conditions(2016) Urbina, Jesús; Sotelo Parraguez, Julio Andrés; Springmüller P., Daniel; Montalba, Cristian; Letelier, Karis; Tejos Núñez, Cristián Andrés; Irarrázaval Mena, Pablo; Andía Kohnenkampf, Marcelo Edgardo; Razavi, Reza; Valverde, Israel; Uribe Arancibia, Sergio A.
- ItemScan With Me: A Train-the-Trainer Program to Upskill MRI Personnel in Low- and Middle-Income Countries(2024) Mumuni, Abdul Nashirudeen; Eyre, Katerina; Montalba, Cristian; Harrison, Aduluwa; Maharjan, Surendra; Botwe, Francis; Garcia, Marina Fernandez; Zeraii, Abderrazek; Friedrich, Matthias G.; Fatade, Abiodun; Ntusi, Ntobeko A. B.; Lim, Tchoyoson; Garg, Ria; Umair, Muhammad; Ninalowo, Hammed A.; Adeleke, Sola; Anosike, Chinedum; Dako, Farouk; Anazodo, Udunna C.Purpose: Access to MRI in low- and middle-income countries (LMICs) remains among the poorest in the world. The lack of skilled MRI personnel exacerbates access gaps, reinforcing long-standing health disparities. The Scan With Me (SWiM) program aims to sustainably create a network of highly skilled MRI technologists in LMICs who will facilitate the transfer of MRI knowledge and skills to their peers and contribute to the implementation of highly valuable imaging protocols for effective clinical and research use. Methods: The program introduces a case-based curriculum designed using a novel train-the-trainer approach, integrated with peer- collaborative learning to upskill practicing MRI technologists in LMICs. The 6-week curriculum uses the teach-try-use approach, which combines self-paced didactic lectures covering the basics of MR image acquisition (teach) with hands-on expert-guided scanning experience (try) and the implementation of protocols tailored to provide the best possible images on their infrastructures (use). Each program includes research translation skills training using an established advanced MRI technique relevant to LMICs. A pilot program focused on cardiac MRI (CMR) was conducted to assess the program's ' s curriculum, delivery, and evaluation methods. Results: Forty-three MRI technologists from 16 LMICs participated in the pilot CMR program and, over the course of the training, implemented optimized CMR protocols that reduced acquisition times while improving image quality. The training resources and scanner-specific fi c standardized protocols are published openly for public use in an online repository. In general, at the end of the program, learners reported considerable improvements in CMR knowledge and skills. All respondents to the program evaluation survey agreed to recommend the program to their colleagues, while 87% indicated interest in returning to help train others. Conclusions: The SWiM program is the fi rst master class in MRI acquisition for practicing imaging technologists in LMICs. The program holds the potential to help reduce disparities in MRI expertise and access. The support of the MRI community, imaging societies, and funding agencies will increase its reach and further its impact in democratizing MRI.
- ItemValidation of 4D Flow based relative pressure maps in aortic flows(2021) Nolte, David; Urbina, Jesus; Sotelo, Julio; Sok, Leo; Montalba, Cristian; Valverde, Israel; Osses, Axel; Uribe, Sergio; Bertoglio, CristobalWhile the clinical gold standard for pressure difference measurements is invasive catheterization, 4D Flow MRI is a promising tool for enabling a non-invasive quantification, by linking highly spatially resolved velocity measurements with pressure differences via the incompressible Navier-Stokes equations. In this work we provide a validation and comparison with phantom and clinical patient data of pressure difference maps estimators. We compare the classical Pressure Poisson Estimator (PPE) and the new Stokes Estimator (STE) against catheter pressure measurements under a variety of stenosis severities and flow intensities. Specifically, we use several 4D Flow data sets of realistic aortic phantoms with different anatomic and hemodynamic severities and two patients with aortic coarctation. The phantom data sets are enriched by subsampling to lower resolutions, modification of the segmentation and addition of synthetic noise, in order to study the sensitivity of the pressure difference estimators to these factors. Overall, the STE method yields more accurate results than the PPE method compared to catheterization data. The superiority of the STE becomes more evident at increasing Reynolds numbers with a better capacity of capturing pressure gradients in strongly convective flow regimes. The results indicate an improved robustness of the STE method with respect to variation in lumen segmentation. However, with heuristic removal of the wall-voxels, the PPE can reach a comparable accuracy for lower Reynolds' numbers. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )
- ItemVariability of 4D flow parameters when subjected to changes in MRI acquisition parameters using a realistic thoracic aortic phantom(2018) Montalba, Cristian; Urbina, Jesus; Sotelo Parraguez, Julio Andrés; Andía Kohnenkampf, Marcelo Edgardo; Tejos Núñez, Cristián Andrés; Irarrázaval Mena, Pablo; Hurtado Sepúlveda, Daniel; Valverde, Israel; Uribe Arancibia, Sergio A.