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Gauthier ARP, Stocek N, Newling B. Diffusion tensor imaging of anisotropic inhomogeneous turbulent flow. Phys Rev E 2022; 106:015108. [PMID: 35974538 DOI: 10.1103/physreve.106.015108] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2021] [Accepted: 07/08/2022] [Indexed: 06/15/2023]
Abstract
Inhomogeneous anisotropic turbulent flow is difficult to measure, and yet it commonly occurs in nature and in many engineering applications. This work aims to introduce a technique based on magnetic resonance imaging which can spatially map the degree of turbulence as well as the degree of anisotropy. Our interpretation relies on the eddy diffusion model of turbulence, and combines this with the technique of diffusion tensor imaging. The result is an eddy diffusion tensor, which is represented by a symmetric three-by-three matrix. This tensor contains a wealth of information about the magnitude and directions of the turbulent fluctuations; however, the correlation time must be considered before interpreting this information. In the constricted pipe flow used in this study, the turbulence is greatest in magnitude in the space surrounding the core of the turbulent jet, and the turbulence is highly anisotropic.
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Affiliation(s)
- Amy-Rae P Gauthier
- UNB MRI Centre, University of New Brunswick, 8 Bailey Drive, Fredericton, New Brunswick E3B 5A3, Canada
| | - Noah Stocek
- UNB MRI Centre, University of New Brunswick, 8 Bailey Drive, Fredericton, New Brunswick E3B 5A3, Canada
| | - Benedict Newling
- UNB MRI Centre, University of New Brunswick, 8 Bailey Drive, Fredericton, New Brunswick E3B 5A3, Canada
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Kim W, Choi H, Kweon J, Yang DH, Kim YH. Effects of pannus formation on the flow around a bileaflet mechanical heart valve. PLoS One 2020; 15:e0234341. [PMID: 32530931 PMCID: PMC7292405 DOI: 10.1371/journal.pone.0234341] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Accepted: 05/23/2020] [Indexed: 11/19/2022] Open
Abstract
Some patients with a bileaflet mechanical heart valve (BMHV) show significant increases in the transvalvular pressure drop and abnormal leaflet motion due to a pannus (an abnormal fibrovascular tissue) formed on the ventricular side, even in the absence of physical contact between the pannus and leaflets. We investigate the effects of the pannus shape (circular or semi-circular ring), implantation location and height on the leaflet motion, flow structure and transvalvular pressure drop using numerical simulations. The valve model considered resembles a 25 mm masters HP valve. The mean systolic pressure drop is significantly increased with increasing pannus height, irrespective of its implantation orientation. Near the peak inflow rate, the flow behind the pannus becomes highly turbulent, and the transvalvular pressure drop is markedly increased by the pannus. At the end of valve opening and the start of valve closing, oscillatory motions of the leaflets occur due to periodic shedding of vortex rings behind the pannus, and their amplitudes become large with increasing pannus height. When the pannus shape is asymmetric (e.g., a semi-circular ring) and its height reaches about 0.1D (D (= 25 mm) is the diameter of an aorta), abnormal leaflet motions occur: two leaflets move asymmetrically, and valve closing is delayed in time or incomplete, which increases the regurgitation volume. The peak energy loss coefficients due to panni are obtained from simulation data and compared with those predicted by a one-dimensional model. The comparison indicates that the one-dimensional model is applicable for the BMHV with and without pannus.
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Affiliation(s)
- Woojin Kim
- Department of Mechanical Engineering, Seoul National University, Seoul, Korea
| | - Haecheon Choi
- Department of Mechanical Engineering, Seoul National University, Seoul, Korea
- Institute of Advanced Machines and Design, Seoul National University, Seoul, Korea
- * E-mail:
| | - Jihoon Kweon
- Department of Cardiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea
| | - Dong Hyun Yang
- Department of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea
| | - Young-Hak Kim
- Department of Cardiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea
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Mastikhin I, Arbabi A, Bade KM. Magnetic Resonance Imaging measurements of a water spray upstream and downstream of a spray nozzle exit orifice. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 266:8-15. [PMID: 26999032 DOI: 10.1016/j.jmr.2016.03.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Revised: 03/09/2016] [Accepted: 03/10/2016] [Indexed: 06/05/2023]
Abstract
Sprays are dynamic collections of droplets dispersed in a gas, with many industrial and agricultural applications. Quantitative characterization is essential for understanding processes of spray formation and dynamics. There exists a wide range of measurement techniques to characterize sprays, from direct imaging to phase Doppler interferometry to X-rays, which provide detailed information on spray characteristics in the "far-nozzle" region (≫10 diameters of the nozzle). However, traditional methods are limited in their ability to characterize the "near-nozzle" region where the fluid may be inside the nozzle, optically dense, or incompletely atomized. Magnetic Resonance Imaging (MRI) presents potential as a non-invasive technique that is capable of measuring optically inaccessible fluid in a quantitative fashion. In this work, MRI measurements of the spray generated by ceramic flat-fan nozzles were performed. A wide range of flow speeds in the system (0.2 to >25m/s) necessitated short encoding times. A 3D Conical SPRITE and motion-sensitized 3D Conical SPRITE were employed. The signal from water inside the nozzle was well-characterized, both via proton density and velocity measurements. The signal outside the nozzle, in the near-nozzle region, was detectable, corresponding to the expected flat-fan spray pattern up to 3mm away. The results demonstrate the potential of MRI for measuring spray characteristics in areas inaccessible by other methods.
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Affiliation(s)
- Igor Mastikhin
- MRI Centre, Department of Physics, UNB, Fredericton, NB, Canada.
| | - Aidin Arbabi
- MRI Centre, Department of Physics, UNB, Fredericton, NB, Canada
| | - Kyle M Bade
- Spraying Systems Co., Spray Analysis and Research Services, Wheaton, IL, USA
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Suchá D, Symersky P, Tanis W, Mali WP, Leiner T, van Herwerden LA, Budde RP. Multimodality Imaging Assessment of Prosthetic Heart Valves. Circ Cardiovasc Imaging 2015; 8:e003703. [DOI: 10.1161/circimaging.115.003703] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Echocardiography and fluoroscopy are the main techniques for prosthetic heart valve (PHV) evaluation, but because of specific limitations they may not identify the morphological substrate or the extent of PHV pathology. Cardiac computed tomography (CT) and magnetic resonance imaging (MRI) have emerged as new potential imaging modalities for valve prostheses. We present an overview of the possibilities and pitfalls of CT and MRI for PHV assessment based on a systematic literature review of all experimental and patient studies. For this, a comprehensive systematic search was performed in PubMed and Embase on March 24, 2015, containing CT/MRI and PHV synonyms. Our final selection yielded 82 articles on surgical valves. CT allowed adequate assessment of most modern PHVs and complemented echocardiography in detecting the obstruction cause (pannus or thrombus), bioprosthesis calcifications, and endocarditis extent (valve dehiscence and pseudoaneurysms). No clear advantage over echocardiography was found for the detection of vegetations or periprosthetic regurgitation. Whereas MRI metal artifacts may preclude direct prosthesis analysis, MRI provided information on PHV-related flow patterns and velocities. MRI demonstrated abnormal asymmetrical flow patterns in PHV obstruction and allowed prosthetic regurgitation assessment. Hence, CT shows great clinical relevance as a complementary imaging tool for the diagnostic work-up of patients with suspected PHV obstruction and endocarditis. MRI shows potential for functional PHV assessment although more studies are required to provide diagnostic reference values to allow discrimination of normal from pathological conditions.
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Affiliation(s)
- Dominika Suchá
- From the Departments of Radiology (D.S., W.P.Th.M.M., T.L., R.P.J.B.) and Cardiothoracic Surgery (L.A.v.H.), University Medical Center Utrecht, Utrecht, The Netherlands; Department of Cardiothoracic Surgery, VU University Medical Center, Amsterdam, The Netherlands (P.S.); Department of Cardiology, HagaZiekenhuis, The Hague, The Netherlands (W.T.); and Department of Radiology, Erasmus Medical Center, Rotterdam, The Netherlands (R.P.J.B.)
| | - Petr Symersky
- From the Departments of Radiology (D.S., W.P.Th.M.M., T.L., R.P.J.B.) and Cardiothoracic Surgery (L.A.v.H.), University Medical Center Utrecht, Utrecht, The Netherlands; Department of Cardiothoracic Surgery, VU University Medical Center, Amsterdam, The Netherlands (P.S.); Department of Cardiology, HagaZiekenhuis, The Hague, The Netherlands (W.T.); and Department of Radiology, Erasmus Medical Center, Rotterdam, The Netherlands (R.P.J.B.)
| | - W. Tanis
- From the Departments of Radiology (D.S., W.P.Th.M.M., T.L., R.P.J.B.) and Cardiothoracic Surgery (L.A.v.H.), University Medical Center Utrecht, Utrecht, The Netherlands; Department of Cardiothoracic Surgery, VU University Medical Center, Amsterdam, The Netherlands (P.S.); Department of Cardiology, HagaZiekenhuis, The Hague, The Netherlands (W.T.); and Department of Radiology, Erasmus Medical Center, Rotterdam, The Netherlands (R.P.J.B.)
| | - Willem P.Th.M. Mali
- From the Departments of Radiology (D.S., W.P.Th.M.M., T.L., R.P.J.B.) and Cardiothoracic Surgery (L.A.v.H.), University Medical Center Utrecht, Utrecht, The Netherlands; Department of Cardiothoracic Surgery, VU University Medical Center, Amsterdam, The Netherlands (P.S.); Department of Cardiology, HagaZiekenhuis, The Hague, The Netherlands (W.T.); and Department of Radiology, Erasmus Medical Center, Rotterdam, The Netherlands (R.P.J.B.)
| | - Tim Leiner
- From the Departments of Radiology (D.S., W.P.Th.M.M., T.L., R.P.J.B.) and Cardiothoracic Surgery (L.A.v.H.), University Medical Center Utrecht, Utrecht, The Netherlands; Department of Cardiothoracic Surgery, VU University Medical Center, Amsterdam, The Netherlands (P.S.); Department of Cardiology, HagaZiekenhuis, The Hague, The Netherlands (W.T.); and Department of Radiology, Erasmus Medical Center, Rotterdam, The Netherlands (R.P.J.B.)
| | - Lex A. van Herwerden
- From the Departments of Radiology (D.S., W.P.Th.M.M., T.L., R.P.J.B.) and Cardiothoracic Surgery (L.A.v.H.), University Medical Center Utrecht, Utrecht, The Netherlands; Department of Cardiothoracic Surgery, VU University Medical Center, Amsterdam, The Netherlands (P.S.); Department of Cardiology, HagaZiekenhuis, The Hague, The Netherlands (W.T.); and Department of Radiology, Erasmus Medical Center, Rotterdam, The Netherlands (R.P.J.B.)
| | - Ricardo P.J. Budde
- From the Departments of Radiology (D.S., W.P.Th.M.M., T.L., R.P.J.B.) and Cardiothoracic Surgery (L.A.v.H.), University Medical Center Utrecht, Utrecht, The Netherlands; Department of Cardiothoracic Surgery, VU University Medical Center, Amsterdam, The Netherlands (P.S.); Department of Cardiology, HagaZiekenhuis, The Hague, The Netherlands (W.T.); and Department of Radiology, Erasmus Medical Center, Rotterdam, The Netherlands (R.P.J.B.)
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