Jesus Urbina

Arterial Thoracic Outlet Syndrome: A 32-year Experience

BACKGROUND Clinical manifestations of thoracic outlet syndrome (TOS) differ depending on the compromised anatomic structure. Arterial TOS is the least common (1-5% of all cases of TOS), yet the most threatening, due to the risk of limb loss. METHODS We conducted a retrospective review of consecutive patients treated for arterial TOS between January 1979 and June 2012. Medical records and diagnostic images were reviewed, and follow-up was obtained. RESULTS Nineteen procedures were performed in 18 patients for symptomatic arterial TOS. The average age was 34 years (range 16-69 years), and 12 patients were female (63.2%). Surgical indications were upper limb critical ischemia in 8 (acute in 5 cases and acute-on-chronic in 3 cases) and claudication in 11. Imaging studies revealed a subclavian aneurysm in 7 patients, stenosis in 4 patients, and 2 patients with subclavian artery occlusion. The 6 remaining cases had symptoms caused by arterial compression in dynamic studies without arterial wall damage at rest. All limbs underwent surgery with outlet decompression; in addition, 13 underwent arterial reconstruction, and 7 were treated for distal embolic complications. There were no deaths, amputations, or early reoperations; 1 patient was readmitted 2 weeks after surgery for chylothorax, which resolved with conservative measures. During a mean follow-up of 155.8±103.1 months, 1 patient underwent successful reintervention at 4 months for bypass occlusion. CONCLUSIONS Arterial TOS is an infrequent but relevant manifestation of TOS. An accurate and early diagnosis allows for timely surgery and adequate results, as shown in this group of patients.

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

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.

Quantification of wall shear stress using a finite-element method in multidimensional phase-contrast MR data of the thoracic aorta

We present a computational method for calculating the distribution of wall shear stress (WSS) in the aorta based on a velocity field obtained from two-dimensional (2D) phase-contrast magnetic resonance imaging (PC-MRI) data and a finite-element method. The WSS vector was obtained from a global least-squares stress-projection method. The method was benchmarked against the Womersley model, and the robustness was assessed by changing resolution, noise, and positioning of the vessel wall. To showcase the applicability of the method, we report the axial, circumferential and magnitude of the WSS using in-vivo data from five volunteers. Our results showed that WSS values obtained with our method were in good agreement with those obtained from the Womersley model. The results for the WSS contour means showed a systematic but decreasing bias when the pixel size was reduced. The proposed method proved to be robust to changes in noise level, and an incorrect position of the vessel wall showed large errors when the pixel size was decreased. In volunteers, the results obtained were in good agreement with those found in the literature. In summary, we have proposed a novel image-based computational method for the estimation of WSS on vessel sections with arbitrary cross-section geometry that is robust in the presence of noise and boundary misplacements.

Realistic aortic phantom to study hemodynamics using MRI and cardiac catheterization in normal and aortic coarctation conditions.

To design and characterize a magnetic resonance imaging (MRI)‐compatible aortic phantom simulating normal and aortic coarctation (AoCo) conditions and to compare its hemodynamics with healthy volunteers and AoCo patients.

3D quantification of hemodynamics parameters of pulmonary artery and aorta using finite-element interpolations in 4D flow MR data

Background Several hemodynamic parameters based from 3D cine PC-MRI have been proposed during the last years, including wall shear stress (WSS), oscillatory index (OSI), vorticity and helicity among others. Most of these parameters are quantified using 2D planes, and only few methods have exploited the advantage of using the 3D data. The disadvantage of using 2D planes is that it does not provide the whole distribution of the hemodynamics parameter in the entire vessel of interest. This process is therefore dependent on the user and may lead to results that have low reproducibility. We have developed a computational framework that integrates advanced image processing strategies and computational techniques based on finite element interpolations to perform a 3D quantification of hemodynamics parameters based on 3D cine PC-MRI.

Three‐dimensional quantification of vorticity and helicity from 3D cine PC‐MRI using finite‐element interpolations

We propose a 3D finite‐element method for the quantification of vorticity and helicity density from 3D cine phase‐contrast (PC) MRI.

Accelerating dual cardiac phase images using undersampled radial phase encoding trajectories

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, 30years). 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 40min to 1min. 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.

A realistic MR compatible aortic phantom to validate hemodynamic parameters from MRI data: aortic coarctation patients comparison using catheterization

Background Recently, 3D printing technologies have emerged as a very innovative technique to produce anatomical replicas. Nevertheless, vessel phantoms built up to now are simplified models, with difficulties to obtain parameters with physiological values. The aim of this work is to show and validate a MR compatible thoracic aorta system, designed to obtain hemodynamic parameters within a range comparable to healthy volunteers and patients with aortic coarctation (AoCo).

3D axial and circumferential wall shear stress from 4D flow MRI data using a finite element method and a laplacian approach

To decompose the 3D wall shear stress (WSS) vector field into its axial (WSSA) and circumferential (WSSC) components using a Laplacian finite element approach.

Variability of 4D flow parameters when subjected to changes in MRI acquisition parameters using a realistic thoracic aortic phantom

To assess the variability of peak flow, mean velocity, stroke volume, and wall shear stress measurements derived from 3D cine phase contrast (4D flow) sequences under different conditions of spatial and temporal resolutions.