Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session G07: Focus Session: Advances in Magnetic Resonance Velocimetry II |
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Chair: Chris Elkins Room: 211 |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G07.00001: Assessment of cardiac output effects on bioprosthetic pulmonary valve behavior using magnetic resonance velocimetry Nicole Schiavone, Christopher Elkins, Doff McElhinney, John K. Eaton, Alison Marsden Tetralogy of Fallot (ToF), a congenital heart defect that affects 1 in every 2500 newborns annually, requires surgical repair of the right ventricular outflow tract (RVOT) and subsequent placement of an artificial pulmonary valve. The longevity of bioprosthetic valves is highly variable and there are no standard clinical guidelines regarding their placement or size selection during surgery. This work analyzes the hemodynamics in an RVOT model representative of ToF anatomy using magnetic resonance velocimetry (MRV) at three different cardiac outputs: 2 L/min, 3.5 L/min, and 5 L/min. The same 25mm surgical St. Jude Medical Epic valve was studied in each of the three cases. Valve leaflet motion and flow features, including location of stagnation and reverse flow regions, shape of the jet through the valve at systole, and asymmetry local to the valve, are significantly different for each cardiac output. For example, the asymmetry of the radial velocity during valve closing is more pronounced at lower cardiac outputs. In addition to MRV, high speed videos were taken to analyze the motion of the valve leaflets at each cardiac output. [Preview Abstract] |
Sunday, November 24, 2019 4:01PM - 4:14PM |
G07.00002: Phase-locking MRV: time-resolved pulsatile flow in carotid arteries phantom Don-Gwan An, Doosang Kim, Sang Hyung Lee, Simon Song MRV has been used not only in medical field but in engineering field last decades. In most engineering studies, mean velocities for a steady turbulent flow have been measured by MRV, but a time-resolved velocity measurements are also possible for a periodic flow by utilizing phase-locking technique. We generated a pulsatile flow in a patient-specific carotid artery phantom and successfully obtained time-resolved 3D 3C velocity vectors. The overall experimental setup was designed to reproduce the patient's blood flow measured by US Doppler probe. The blood mimicking glycerin aqueous solution was used as a working fluid. The carotid phantom was constructed with a 3D printer based on the CT image of patient and the actual pulsatile flow. To synchronize the MRV measurement with the pulsatile flow, a digital pulse was transmitted to the MR scanner as trigger when the velocity waveform started. As a result, a time-resolved 3D 3C pulsatile flow with a high spatiotemporal resolution (350 um iso and 25 ms) was obtained. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G07.00003: Assessment of Reynolds stress using 4D Flow MRI for estimating the irreversible pressure drop across a stenosis. Hojin Ha This study demonstrates novel geometry-independent quantification of the irreversible pressure drop across stenoses by quantifying the amount of turbulence production. Based on 4D Flow MRI-based assessment of turbulence mapping using a six-directional icosahedral (ICOSA6) flow encoding scheme for measuring the complete Reynolds stress tensor, the feasibility of 4D Flow MRI for the quantification of irreversible pressure loss was investigated in a range of voxel sizes and signal-to-noise ratios (SNR) by simulating 4D Flow MRI based on data from computational fluid dynamics (CFD). The geometry-independency of the estimation of turbulence production and corresponding irreversible pressure drop was investigated using several stenoses. Finally, experimental acquisitions using 4D Flow MRI with ICOSA6 flow encoding were used to demonstrate the assessment of the irreversible pressure drop. [Preview Abstract] |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G07.00004: MRI-based flow residence time in intracranial aneurysms Omid Amili, Yinghui Li, Filippo Coletti While the mechanisms behind development of thrombosis in cerebral aneurysms is not fully understood, there has been emerging evidence that blood flow residence time is correlated/associated with the lesion. In addition, there have been clinical observations indicating thrombus formation following aneurysm endovascular treatment perhaps due to altered hemodynamics. Therefore, a characterization of the residence time can play an important role in the development of a biomarker for the risk of rupture in untreated aneurysms and risk of thrombo-embolism in treated aneurysms. In this study, we use in vitro 4D MRI velocimetry for several aneurysms performed in a 3 Tesla magnet at submillimeter resolution to compute the flow residence time using both Lagrangian and Eulerian frameworks. As per our previous study, by integration of the volumetric velocity field, Lagrangian tracks of massless tracers are computed, followed by the residence time calculation using the presence of fluid parcels in a local and global sense. In the Eulerian approach, circulation in a plane normal to the axis of the vortex dominating the aneurysm sac is used to estimate the eddy turnover time. The former approach provides a 3D map of the residence time, while the latter estimates the order of magnitude. [Preview Abstract] |
Sunday, November 24, 2019 4:40PM - 4:53PM |
G07.00005: Lagrangian dispersion in the bronchial tree characterized by Magnetic Resonance Velocimetry. Sahar Jalal, Omid Amili, Filippo Coletti The bronchial tree is a complex network whose transport properties are inherently challenging to model, especially because of its multi-scale nature. Most previous studies in this area have followed an Eulerian perspective, characterizing the velocity and/or scalar field within ventilated airways, or documenting the concentration of inhaled particles upon deposition on the walls. In the present study we investigate the Lagrangian dispersion in the central human airways, performing Magnetic Resonance Velocimetry (MRV) in 3D-printed replicas of idealized and realistic bronchial trees. We obtain three-dimensional, three-component velocity fields during the ventilation cycle, and reconstruct the trajectories of virtually released mass-less and inertial particles. We consider both steady inhalation (relevant to drug delivery) and high-frequency ventilation (a common technique of mechanical ventilatory support). This approach allows us to characterize the transport properties of the airway tree and other biological flow systems, leveraging tools commonly used in turbulent and porous media flows. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G07.00006: Cardiovascular Fluid Dynamic Analysis with MRI Velocimetry and MRI-based Computational Simulation David Rutkowski, Alejandro Roldán-Alzate Magnetic resonance imaging (MRI) velocimetry and computational fluid dynamics (CFD) are both methods that offer advantages when used for cardiovascular fluid dynamic analysis. However, each of these methods has its own set of unique limitations. MRI velocimetry offers patient-specific analysis of real fluid flow. However, MRI has some limitations in quantitative and predictive cardiovascular analysis when used as a stand-alone method due to resolution limits and errors that result from manipulation of magnetic field. Fortunately, computational methods may be used to address some of these limitations. CFD provides high resolution data, and relies on boundary conditions that can be manipulated to match physiological or surgical variations of interest. However, standalone CFD can also be limited due to its high dependence on patient-specific boundary conditions, and its need for appropriate validation with physical blood flow. This work was aimed at utilizing the best of both MRI and CFD for cardiovascular fluid dynamic analysis by leveraging the advantages of one method to fill the inherent gaps of the other. This is shown through a number of examples, such as using 4D flow MRI velocimetry to analyze blood flow dynamics in congenital heart disease patients, simulating hepatic blood flow with image-based computational simulation, and coupling imaging, computational simulation, and machine learning methods to improve patient-specific blood flow quantification. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G07.00007: A Method for Improving Magnetic Resonance Concentration Measurements Using Low Flip-Angle and Multiple Concentrations Ian E. Gunady, Andrew J. Banko, Michael J. Benson, Christopher J. Elkins, John K. Eaton Understanding the dispersion of a scalar contaminant through an urban environment has many applications. Magnetic Resonance Concentration (MRC) can be used to measure the 3D mean concentration field. However, the uncertainty of the previous technique is approximately 5{\%} of the injected concentration, limiting the lowest measurable concentration. In the present study, a scalar contaminant release from a discrete building mounted on the wall in a square duct flow is studied. After injection from windows in the building, the scalar disperses in the turbulent building wake. The concentration field is reconstructed from low flip-angle (30 degrees) MRC data that uses multiple concentrations of contrast agent to capture the near and far fields separately. A region of overlap in the linear range of the signal magnitude and scalar concentration relationship is used to stitch two fields together. This technique lowers the noise floor helping to reduce the uncertainty to less than 1{\%}, allowing for previously unobservable near-zero concentration measurements near the wall. MRC data taken at low flip-angle are validated against data collected in the same flow with the established method which uses a flip-angle of 55 degrees. [Preview Abstract] |
Sunday, November 24, 2019 5:19PM - 5:32PM |
G07.00008: Magnetic Resonance Velocimetry of a projectile spinning at constant rotation with sub-millimeter resolution Noah W. Siegel, Aaron P. Schlenker, Bret P. Van Poppel, Michael J. Benson, Christopher J. Elkins, Gregory P. Rodebaugh Magnetic Resonance Velocimetry (MRV) techniques were extended to obtain high-fidelity, three-dimensional veloc- ity field data sets around a projectile spinning at constant rotation with sub-millimeter resolution. A modified M193 5.56mm projectile was specially designed and built to thicken the hydrodynamic boundary layer for the purpose of investigating dynamic instabilities in spin-stabilized projectiles attributable to transient fluctuations in the Magnus moment as the projectile decelerates into the transonic flight regime. Computational fluid dynamics (CFD) simula- tions struggle to accurately predict the Magnus moment for these types of projectiles. The experimental rig rotated the projectile at uniform spin rates in a constant flow of copper-sulfate solution as part of a test section placed within a research-grade MRI magnet. The velocity fields for several spin rates and projectile angles of attack were analyzed and compared to Reynolds Averaged Navier-Stokes (RANS) CFD simulations to identify proposed causes of the Magnus moment, namely boundary layer asymmetries and attached lee side vortices. The experimental MRV data revealed notable lateral boundary layer asymmetries for some combinations of spin rate and angle of attack, while comparable RANS simulations showed no boundary layer effects due to spin or angle of attack. Experimental uncertainty was assessed and found to be similar to comparable methods for measuring velocity field data. [Preview Abstract] |
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