DSpace Angular :: Browsing by Author "Uribe, Sergio"

Browsing by Author "Uribe, Sergio"

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A 3D trajectory for undersampling k-space in MRSI applications
(ELSEVIER SCIENCE INC, 2007) Uribe, Sergio; Guesalaga, Andres; Mir, Roberto; Guarini, Marcelo; Irarrazaval, Pablo
Magnetic resonance spectroscopic imaging (MRSI) is a noninvasive technique for producing spatially localized spectra. MRSI presents the important challenge of reducing the scan time while maintaining the spatial resolution. The preferred approach for this is to use time-varying readout gradients to collect the spatial and chemical-shift information. Fast, three-dimensional (3D) spatial encoded methods also reduce the scan time. Despite the existence of several new and faster 3D encoded methods, or k-space trajectories, for magnetic resonance imaging (MRI), only stack of spirals and echo planar have been studied in 3D MRSI. A novel formulation for designing fast, 3D k-space trajectory applicable to 3D MRSI is presented. This approach is simple and consists of rays expanding from the origin of k-space into a revolving sphere, collecting spectral data of all 3D spatial k-space at different times in the same scan. This article describes this new method and presents some results of its application to 3D MRSI. This technique allows some degree of undersampling; hence, it is possible to reconstruct high-quality undersampled spectroscopic imaging in order to recognize different compounds in short scan times. Additionally, the method is tested in regular 3D MRI. This proposed method can also be used for dynamic undersampled imaging. (c) 2007 Elsevier Inc. All rights reserved.
A comparison of phase unwrapping methods in velocity-encoded MRI for aortic flows
(2023) Locke, Miriam; Labra, Jeremias Esteban Garay; Franco, Pamela; Uribe, Sergio; Bertoglio, Cristobal
PurposeThe phase of a MRI signal is used to encode the velocity of blood flow. Phase unwrapping artifacts may appear when aiming to improve the velocity-to-noise ratio (VNR) of the measured velocity field. This study aims to compare various unwrapping algorithms on ground-truth synthetic data generated using computational fluid dynamics (CFD) simulations. MethodsWe compare four different phase unwrapping algorithms on two different synthetic datasets of four-dimensional flow MRI and 26 datasets of 2D PC-MRI acquisitions including the ascending and descending aorta. The synthetic datasets are constructed using CFD simulations of an aorta with a coarctation, with different levels of spatiotemporal resolutions and noise. The error of the unwrapped images was assessed by comparison against the ground truth velocity field in the synthetic data and dual-VENC reconstructions in the in vivo data. ResultsUsing the unwrapping algorithms, we were able to remove aliased voxels in the data almost entirely, reducing the L2-error compared to the ground truth by 50%-80%. Results indicated that the best choice of algorithm depend on the spatiotemporal resolution and noise level of the dataset. Temporal unwrapping is most successful with a high temporal and low spatial resolution (& delta;t=30$$ \delta t=30 $$ ms, h=2.5$$ h=2.5 $$ mm), reducing the L2-error by 70%-85%, while Laplacian unwrapping performs better with a lower temporal or better spatial resolution (& delta;t=60$$ \delta t=60 $$ ms, h=1.5$$ h=1.5 $$ mm), especially for signal-to-noise ratio (SNR) 12 as opposed to SNR 15, with an error reduction of 55%-85% compared to the 50%-75% achieved by the Temporal method. The differences in performance between the methods are statistically significant. ConclusionsThe temporal method and spatiotemporal Laplacian method provide the best results, with the spatiotemporal Laplacian being more robust. However, single-Venc$$ {V}_{\mathrm{enc}} $$ methods only situationally and not generally reach the performance of dual-Venc$$ {V}_{\mathrm{enc}} $$ unwrapping methods.
A comprehensive comparison between shortest-path HARP refinement, SinMod, and DENSEanalysis processing tools applied to CSPAMM and DENSE images
(2021) Mella, Hernan; Mura, Joaquin; Sotelo, Julio; Uribe, Sergio
We addressed comprehensively the performance of Shortest-Path HARP Refinement (SP-HR), SinMod, and DENSEanalysis using 2D slices of synthetic CSPAMM and DENSE images with realistic contrasts obtained from 3D phantoms. The three motion estimation techniques were interrogated under ideal and no-ideal conditions (with MR induced artifacts, noise, and through-plane motion), considering several resolutions and noise levels. Under noisy conditions, and for isotropic pixel sizes of 1.5 mm and 3.0 mm in CSPAMM and DENSE images respectively, the nRMSE obtained for the circumferential and radial strain components were 10.7 +/- 10.8% and 25.5 +/- 14.8% using SP-HR, 11.9 +/- 2.5% and 29.3 +/- 6.5% using SinMod, and 6.4 +/- 2.0% and 18.2 +/- 4.6% using DENSEanalysis. Overall, the results showed that SP-HR tends to fail for large tissue motions, whereas SinMod and DENSEanalysis gave accurate displacement and strain field estimations, being the last which performed the best.
A Spatial Off-Resonance Correction in Spirals for Magnetic Resonance Fingerprinting
(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2021) Coronado, Ronal; Cruz, Gastao; Castillo Passi, Carlos; Tejos, Cristian; Uribe, Sergio; Prieto, Claudia; Irarrazaval, Pablo
In MR Fingerprinting (MRF), balanced Steady-State Free Precession (bSSFP) has advantages over unbalanced SSFP because it retains the spin history achieving a higher signal-to-noise ratio (SNR) and scan efficiency. However, bSSFP-MRF is not frequently used because it is sensitive to off-resonance, producing artifacts and blurring, and affecting the parametric map quality. Here we propose a novel Spatial Off-resonance Correction (SOC) approach for reducing these artifacts in bSSFP-MRF with spiral trajectories. SOC-MRF uses each pixel's Point Spread Function to create system matrices that encode both off-resonance and gridding effects. We iteratively compute the inverse of these matrices to reduce the artifacts. We evaluated the proposed method using brain simulations and actual MRF acquisitions of a standardized T1/T2 phantom and five healthy subjects. The results show that the off-resonance distortions in T1/T2 maps were considerably reduced using SOC-MRF. For T2, the Normalized Root Mean Square Error (NRMSE) was reduced from 17.3 to 8.3% (simulations) and from 35.1 to 14.9% (phantom). For T1, the NRMS was reduced from 14.7 to 7.7% (simulations) and from 17.7 to 6.7% (phantom). For in-vivo, the mean and standard deviation in different ROI in white and gray matter were significantly improved. For example, SOC-MRF estimated an average T2 for white matter of 77ms (the ground truth was 74ms) versus 50 ms of MRF. For the same example the standard deviation was reduced from 18 ms to 6ms. The corrections achieved with the proposed SOC-MRF may expand the potential applications of bSSFP-MRF, taking advantage of its better SNR property.
Accelerating dual cardiac phase images using phase encoding trajectories
(ELSEVIER SCIENCE INC, 2016) Letelier, Karis; Urbina, Jesus; Andia, Marcelo; Tejos, Cristian; Irarrazaval, Pablo; Prieto, Claudia; Uribe, Sergio
A three-dimensional dual-cardiac-phase (3D-DCP) scan has been proposed to acquire two data sets of the whole heart and great vessels during the end-diastolic and end-systolic cardiac phases in a single free-breathing scan. This method has shown accurate assessment of cardiac anatomy and function but is limited by long acquisition times. This work proposes to accelerate the acquisition and reconstruction of 3D-DCP scans by exploiting redundant information of the outer k-space regions of both cardiac phases. This is achieved using a modified radial-phase-encoding trajectory and gridding reconstruction with uniform coil combination. The end-diastolic acquisition trajectory was angularly shifted with respect to the end-systolic phase. Initially, a fully-sampled 3D-DCP scan was acquired to determine the optimal percentage of the outer k-space data that can be combined between cardiac phases. Thereafter, prospectively undersampled data were reconstructed based on this percentage. As gold standard images, the undersampled data were also reconstructed using iterative SENSE. To validate the method, image quality assessments and a cardiac volume analysis were performed. The proposed method was tested in thirteen healthy volunteers (mean age, 30 years). Prospectively undersampled data (R = 4) reconstructed with 50% combination led high quality images. There were no significant differences in the image quality and in the cardiac volume analysis between our method and iterative SENSE. In addition, the proposed approach reduced the reconstruction time from 40 min to 1 min. In conclusion, the proposed method obtains 3D-DCP scans with an image quality comparable to those reconstructed with iterative SENSE, and within a clinically acceptable reconstruction time. (C) 2016 Elsevier Inc. All rights reserved.
Altered Aortic Hemodynamics and Relative Pressure in Patients with Dilated Cardiomyopathy
(2022) Marlevi, David; Mariscal-Harana, Jorge; Burris, Nicholas S.; Sotelo, Julio; Ruijsink, Bram; Hadjicharalambous, Myrianthi; Asner, Liya; Sammut, Eva; Chabiniok, Radomir; Uribe, Sergio; Winter, Reidar; Lamata, Pablo; Alastruey, Jordi; Nordsletten, David
Ventricular-vascular interaction is central in the adaptation to cardiovascular disease. However, cardiomyopathy patients are predominantly monitored using cardiac biomarkers. The aim of this study is therefore to explore aortic function in dilated cardiomyopathy (DCM). Fourteen idiopathic DCM patients and 16 controls underwent cardiac magnetic resonance imaging, with aortic relative pressure derived using physics-based image processing and a virtual cohort utilized to assess the impact of cardiovascular properties on aortic behaviour. Subjects with reduced left ventricular systolic function had significantly reduced aortic relative pressure, increased aortic stiffness, and significantly delayed time-to-pressure peak duration. From the virtual cohort, aortic stiffness and aortic volumetric size were identified as key determinants of aortic relative pressure. As such, this study shows how advanced flow imaging and aortic hemodynamic evaluation could provide novel insights into the manifestation of DCM, with signs of both altered aortic structure and function derived in DCM using our proposed imaging protocol.
An 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, Sergio
Purpose: 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.
Analysis of the passive biomechanical behavior of a sheep-specific aortic artery in pulsatile flow conditions
(2021) Garcia-Herrera, Claudio M.; Cuevas, Alvaro A.; Celentano, Diego J.; Navarrete, Alvaro; Aranda, Pedro; Herrera, Emilio; Uribe, Sergio
In this work, a novel numerical-experimental procedure is proposed, through the use of the Cardiac Simulation Test (CST), device that allows the exposure of the arterial tissue to in-vitro conditions, mimicking cardiac cycles generated by the heart. The main goal is to describe mechanical response of the arterial wall under physiological conditions, when it is subjected to a variable pressure wave over time, which causes a stress state affecting the biomechanical behavior of the artery wall. In order to get information related to stress and strain states, numerical simulation via finite element method, is performed under a condition of systolic and diastolic pressure. The description of this methodological procedure is performed with a sample corresponding to a sheep aorta without cardiovascular pathologies. There are two major findings: the evaluation of the mechanical properties of the sheep aorta through the above-mentioned tests and, the numerical simulation of the mechanical response under the conditions present in the CST. The results state that differences between numerical and experimental circumferential stretch in diastole and systole to distinct zones studied do not exceed 1%. However, greater discrepancies can be seen in the distensibility and incremental modulus, two main indicators, which are in the order of 30%. In addition, numerical results determine an increase of the principal maximum stress and strain between the case of systolic and diastolic pressure, corresponding to 31.1% and 14.9% for the stress and strain measurement respectively; where maximum values of these variables are located in the zone of the ascending aorta and the aortic arch.
Aortic Stenosis: Haemodynamic Benchmark and Metric Reliability Study
(2023) Gill, Harminder; Fernandes, Joao Filipe; Nio, Amanda; Dockerill, Cameron; Shah, Nili; Ahmed, Naajia; Raymond, Jason; Wang, Shu; Sotelo, Julio; Urbina, Jesus; Uribe, Sergio; Rajani, Ronak; Rhode, Kawal; Lamata, Pablo
Aortic stenosis is a condition which is fatal if left untreated. Novel quantitative imaging techniques which better characterise transvalvular pressure drops are being developed but require refinement and validation. A customisable and cost-effective workbench valve phantom circuit capable of replicating valve mechanics and pathology was created. The reproducibility and relationship of differing haemodynamic metrics were assessed from ground truth pressure data alongside imaging compatibility. The phantom met the requirements to capture ground truth pressure data alongside ultrasound and magnetic resonance image compatibility. The reproducibility was successfully tested. The robustness of three different pressure drop metrics was assessed: whilst the peak and net pressure drops provide a robust assessment of the stenotic burden in our phantom, the peak-to-peak pressure drop is a metric that is confounded by non-valvular factors such as wave reflection. The peak-to-peak pressure drop is a metric that should be reconsidered in clinical practice.
Assessment of 4D flow MRI's quality by verifying its Navier-Stokes compatibility
(2022) Garay, Jeremias; Mella, Hernan; Sotelo, Julio; Carcamo, Cristian; Uribe, Sergio; Bertoglio, Cristobal; Mura, Joaquin
4D Flow Magnetic Resonance Imaging (MRI) is the state-of-the-art technique to comprehensively measure the complex spatio-temporal and multidirectional patterns of blood flow. However, it is subject to artifacts such as noise and aliasing, which due to the 3D and dynamic structure is difficult to detect in clinical practice. In this work, a new mathematical and computational model to determine the quality of 4D Flow MRI is presented. The model is derived by assuming the true velocity satisfies the incompressible Navier-Stokes equations and that can be decomposed by the measurements u -> meas$$ {\overrightarrow{u}}_{meas} $$ plus an extra field w ->$$ \overrightarrow{w} $$. Therefore, a non-linear problem with w ->$$ \overrightarrow{w} $$ as unknown arises, which serves as a measure of data quality. A stabilized finite element formulation tailored to this problem is proposed and analyzed. Then, extensive numerical examples-using synthetic 4D Flow MRI data as well as real measurements on experimental phantom and subjects-illustrate the ability to use w ->$$ \overrightarrow{w} $$ for assessing the quality of 4D Flow MRI measurements over space and time.
Assessment of hepatic fatty acids during non-alcoholic steatohepatitis progression using magnetic resonance spectroscopy
(2021) Xavier, Aline; Zacconi, Flavia C. M.; Santana Romo, Fabián Mauricio; Eykyn, Thomas R.; Lavin, Begona; Phinikaridou, Alkystis; Botnar, Rene; Uribe, Sergio; Esteban Oyarzun, Juan; Cabrera, Daniel; Arrese, Marco; Andia, Marcelo E.
Abstract: Introduction and objectives: Non-alcoholic fatty liver disease (NAFLD) encompasses a spectrum of liver abnormalities including steatosis, steatohepatitis, fibrosis, and cirrhosis. Liver biopsy remains the gold standard method to determine the disease stage in NAFLD but is an invasive and risky procedure. Studies have previously reported that changes in intrahepatic fatty acids (FA) composition are related to the progression of NAFLD, mainly in its early stages. The aim of this study was to characterize the liver FA composition in mice fed a Choline-deficient L-amino-defined (CDAA) diet at different stages of NAFLD using magnetic resonance spectroscopy (MRS). Methods: We used in-vivo MRS to perform a longitudinal characterization of hepatic FA changes in NAFLD mice for 10 weeks. We validated our findings with ex-vivo MRS, gas chromatography-mass spectrometry and histology. Results: In-vivo and ex-vivo results showed that livers from CDAA-fed mice exhibit a significant increase in liver FA content as well as a change in FA composition compared with control mice. After 4 weeks of CDAA diet, a decrease in polyunsaturated and an increase in monounsaturated FA were observed. These changes were associated with the appearance of early stages of steatohepatitis, confirmed by histology (NAFLD Activity Score (NAS) = 4.5). After 10 weeks of CDAA-diet, the liver FA composition remained stable while the NAS increased further to 6 showing a combination of early and late stages of steatohepatitis. Conclusion: Our results suggest that monitoring lipid composition in addition to total water/fat with MRS may yield additional insights that can be translated for non-invasive stratification of high-risk NAFLD patients.
Automatic 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, Sergio
Fat 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.
Chemical species separation with simultaneous estimation of field map and T-2* using a k-space formulation
(WILEY-BLACKWELL, 2012) Luis Honorato, Jose; Parot, Vicente; Tejos, Cristian; Uribe, Sergio; Irarrazaval, Pablo
Chemical species separation techniques in image space are prone to incorporate several distortions. Some of these are signal accentuation in borders and geometrical warping from field inhomogeneity. These errors come from neglecting intraecho time variations. In this work, we present a new approach for chemical species separation in MRI with simultaneous estimation of field map and T?2* decay, formulated entirely in k-space. In this approach, the time map is used to model the phase accrual from off-resonance precession and also the amplitude decay due to T?2*. Our technique fits the signal model directly in k-space with the acquired data minimizing the l2-norm with an interior-point algorithm. Standard two dimensional gradient echo sequences in the thighs and head were used for demonstrating the technique. With this approach, we were able to obtain excellent estimation for the species, the field inhomogeneity, and T?2* decay images. The results do not suffer from geometric distortions derived from the chemical shift or the field inhomogeneity. Importantly, as the T?2* map is well positioned, the species signal in borders is correctly estimated. Considering intraecho time variations in a complete signal model in k-space for separating species yields superior estimation of the variables of interest when compared to existing methods. Magn Reson Med, 2012. (C) 2011 Wiley Periodicals, Inc.
Comparison of Improved Unidirectional Dual Velocity-Encoding MRI Methods
(2023) Franco, Pamela; Ma, Liliana; Schnell, Susanne; Carrillo, Hugo; Montalba, Cristian; Markl, Michael; Bertoglio, Cristobal; Uribe, Sergio
Background 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
Comparison of LED- and LASER-based fNIRS technologies to record the human peri-spinal cord neurovascular response
(2024) Caulier-Cisterna, Raill; Appelgren-Gonzales, Juan -Pablo; Oyarzun, Juan -Esteban; Valenzuela, Felipe; Sitaram, Ranganatha; Eblen-Zajjur, Antonio; Uribe, Sergio
Recently, functional Near-Infrared Spectroscopy (fNIRS) was applied to obtain, non-invasively, the human peri-spinal Neuro-Vascular Response (NVR) under a non-noxious electrical stimulation of a peripheral nerve. This method allowed the measurements of changes in the concentration of oxyhemoglobin (O2Hb) and deoxyhemoglobin (HHb) from the peri-spinal vascular network. However, there is a lack of clarity about the potential differences in perispinal NVR recorded by the different fNIRS technologies currently available. In this work, the two main noninvasive fNIRS technologies were compared, i.e., LED and LASER-based. The recording of the human peri-spinal NVR induced by non-noxious electrical stimulation of a peripheral nerve was recorded simultaneously at C7 and T10 vertebral levels. The amplitude, rise time, and full width at half maximum duration of the perispinal NVRs were characterized in healthy volunteers and compared between both systems. The main difference was that the LED-based system shows about one order of magnitude higher values of amplitude than the LASER-based system. No statistical differences were found for rise time and for duration parameters (at thoracic level). The comparison of point-to-point wave patterns did not show significant differences between both systems. In conclusion, the peri-spinal NRV response obtained by different fNIRS technologies was reproducible, and only the amplitude showed differences, probably due to the power of the system which should be considered when assessing the human peri-spinal vascular network.
Comprehensive 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, Sergio
In 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.
Congenital Heart Disease in Children: Coronary MR Angiography during Systole and Diastole with Dual Cardiac Phase Whole-Heart Imaging
(RADIOLOGICAL SOC NORTH AMERICA, 2011) Uribe, Sergio; Hussain, Tarique; Valverde, Israel; Tejos, Cristian; Irarrazaval, Pablo; Fava, Mario; Beerbaum, Philipp; Botnar, Rene M.; Razavi, Reza; Schaeffter, Tobias; Greil, Gerald F.
Purpose: To assess the optimal timing for coronary magnetic resonance (MR) angiography in children with congenital heart disease by using dual cardiac phase whole-heart MR imaging.
Convergence analysis of pressure reconstruction methods from discrete velocities
(2023) Araya, Rodolfo; Bertoglio, Cristobal; Carcamo, Cristian; Nolte, David; Uribe, Sergio
Magnetic resonance imaging allows the measurement of the three-dimensional velocity field in blood flows. Therefore, several methods have been proposed to reconstruct the pressure field from such measurements using the incompressible Navier-Stokes equations, thereby avoiding the use of invasive technologies. However, those measurements are obtained at limited spatial resolution given by the voxel sizes in the image. In this paper, we propose a strategy for the convergence analysis of state-of-the-art pressure reconstruction methods. The methods analyzed are the so-called Pressure Poisson Estimator (PPE) and Stokes Estimator (STE). In both methods, the right-hand side corresponds to the terms that involving the field velocity in the Navier-Stokes equations, with a piecewise linear interpolation of the exact velocity. In the theoretical error analysis, we show that many terms of different order of convergence appear. These are certainly dominated by the lowest-order term, which in most cases stems from the interpolation of the velocity field. However, the numerical results in academic examples indicate that only the PPE may profit of increasing the polynomial order, and that the STE presents a higher accuracy than the PPE, but the interpolation order of the velocity field always prevails. Furthermore, we compare the pressure estimation methods on real MRI data, assessing the impact of different spatial resolutions and polynomial degrees on each method. Here, the results are consistent with the academic test cases in terms of sensitivity to polynomial order as well as the STE showing to be potentially more accurate when compared to reference pressure measurements.
Fully Three-Dimensional Hemodynamic Characterization of Altered Blood Flow in Bicuspid Aortic Valve Patients With Respect to Aortic Dilatation: A Finite Element Approach
(2022) Sotelo, Julio; Franco, Pamela; Guala, Andrea; Dux-Santoy, Lydia; Ruiz-Munoz, Aroa; Evangelista, Arturo; Mella, Hernan; Mura, Joaquin; Hurtado, Daniel E.; Rodriguez-Palomares, Jose F.; Uribe, Sergio
Background and PurposePrognostic models based on cardiovascular hemodynamic parameters may bring new information for an early assessment of patients with bicuspid aortic valve (BAV), playing a key role in reducing the long-term risk of cardiovascular events. This work quantifies several three-dimensional hemodynamic parameters in different patients with BAV and ranks their relationships with aortic diameter. Materials and MethodsUsing 4D-flow CMR data of 74 patients with BAV (49 right-left and 25 right-non-coronary) and 48 healthy volunteers, aortic 3D maps of seventeen 17 different hemodynamic parameters were quantified along the thoracic aorta. Patients with BAV were divided into two morphotype categories, BAV-Non-AAoD (where we include 18 non-dilated patients and 7 root-dilated patients) and BAV-AAoD (where we include the 49 patients with dilatation of the ascending aorta). Differences between volunteers and patients were evaluated using MANOVA with Pillai's trace statistic, Mann-Whitney U test, ROC curves, and minimum redundancy maximum relevance algorithm. Spearman's correlation was used to correlate the dilation with each hemodynamic parameter. ResultsThe flow eccentricity, backward velocity, velocity angle, regurgitation fraction, circumferential wall shear stress, axial vorticity, and axial circulation allowed to discriminate between volunteers and patients with BAV, even in the absence of dilation. In patients with BAV, the diameter presented a strong correlation (> |+/-0.7|) with the forward velocity and velocity angle, and a good correlation (> |+/-0.5|) with regurgitation fraction, wall shear stress, wall shear stress axial, and vorticity, also for morphotypes and phenotypes, some of them are correlated with the diameter. The velocity angle proved to be an excellent biomarker in the differentiation between volunteers and patients with BAV, BAV morphotypes, and BAV phenotypes, with an area under the curve bigger than 0.90, and higher predictor important scores. ConclusionsThrough the application of a novel 3D quantification method, hemodynamic parameters related to flow direction, such as flow eccentricity, velocity angle, and regurgitation fraction, presented the best relationships with a local diameter and effectively differentiated patients with BAV from healthy volunteers.
Functional cardiac MRI in preterm and term newborns
(B M J PUBLISHING GROUP, 2011) Groves, Alan M.; Chiesa, Gaia; Durighel, Giuliana; Goldring, Stephen T.; Fitzpatrick, Julie A.; Uribe, Sergio; Razavi, Reza; Hajnal, Jo V.; Edwards, A. David
Objective To use cardiac MRI techniques to assess ventricular function and systemic perfusion in preterm and term newborns, to compare techniques to echocardiographic methods, and to obtain initial reference data.

Browsing by Author "Uribe, Sergio"

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