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Extending MRI to the Quantification of Turbulence Intensity
Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medicine and Health Sciences, Clinical Physiology . Linköping University, Faculty of Health Sciences. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics . Linköping University, The Institute of Technology. (Cardiovascular MR (www.liu.se/cmr))
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In cardiovascular medicine, the assessment of blood flow is fundamental to the understanding and detection of disease. Many pharmaceutical, interventional, and surgical treatments impact the flow. The primary purpose of the cardiovascular system is to drive, control and maintain blood flow to all parts of the body. In the normal cardiovascular system, fluid transport is maintained at high efficiency and the blood flow is essentially laminar. Disturbed and turbulent blood flow, on the other hand, appears to be present in many cardiovascular diseases and may contribute to their initiation and progression. Despite strong indications of an important interrelationship between flow and cardiovascular disease, medical imaging has lacked a non-invasive tool for the in vivo assessment of disturbed and turbulent flow. As a result, the extent and role of turbulence in the blood flow of humans have not yet been fully investigated.

Magnetic resonance imaging (MRI) is a versatile tool for the non-invasive assessment of flow and has several important clinical and research applications, but might not yet have reached its full potential. Conventional MRI techniques for the assessment of flow are based on measurements of the mean velocity within an image voxel. The mean velocity corresponds to the first raw moment of the distribution of velocities within a voxel. An MRI framework for the quantification of any moment (mean, standard deviation, skew, etc.) of arbitrary velocity distributions is presented in this thesis.

Disturbed and turbulent flows are characterized by velocity fluctuations that are superimposed on the mean velocity. The intensity of these velocity fluctuations can be quantified by their standard deviation, which is a commonly used measure of turbulence intensity. This thesis focuses on the development of a novel MRI method for the quantification of turbulence intensity. This method is mathematically derived and experimentally validated. Limitations and sources of error are investigated and guidelines for adequate application of MRI measurements of turbulence intensity are outlined. Furthermore, the method is adapted to the quantification of turbulence intensity in the pulsatile blood flow of humans and applied to a wide range of cardiovascular diseases. In these applications, elevated turbulence intensity was consistently detected in regions where highly disturbed flow was anticipated, and the effects of potential sources of errors were small.

Diseased heart valves are often replaced with prosthetic heart valves, which, in spite of improved benefits and durability, continue to fall short of matching native flow patterns. In an in vitro setting, MRI was used to visualize and quantify turbulence intensity in the flow downstream from four common designs of prosthetic heart valves. Marked differences in the extent and degree of turbulence intensity were detected between the different valves.

Mitral valve regurgitation is a common valve lesion associated with progressive left atrial and left ventricular remodelling, which may often require surgical correction to avoid irreversible ventricular dysfunction. The spatiotemporal dynamics of flow disturbances in mitral regurgitation were assessed based on measurements of flow patterns and turbulence intensity in a group of patients with significant regurgitation arising from similar valve lesions. Peak turbulence intensity occurred at the same time in all patients and the total turbulence intensity in the left atrium appeared closely related to the severity of regurgitation.

MRI quantification of turbulence intensity has the potential to become a valuable tool in investigating the extent, timing and role of disturbed blood flow in the human cardiovascular system, as well as in the assessment of the effects of different therapeutic options in patients with vascular or valvular disorders.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2010. , 73 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1297
Keyword [en]
Turbulence intensity, cardiovascular disease, blood flow, hemodynamics, magnetic resonance imaging, generalized phase-contrast MRI, turbulent flow
National Category
Biomedical Laboratory Science/Technology Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:liu:diva-52561ISBN: 978-91-7393-453-4 (print)OAI: oai:DiVA.org:liu-52561DiVA: diva2:287585
Public defence
2010-02-12, Elsa-Brändströmsalen, Universitetssjukhuset, Campus US. Linköpings universitet, Linköping, 09:15 (English)
Opponent
Supervisors
Available from: 2010-01-19 Created: 2010-01-04 Last updated: 2013-09-03Bibliographically approved
List of papers
1. Quantification of intravoxel velocity standard deviation and turbulence intensity by generalizing phase-contrast MRI
Open this publication in new window or tab >>Quantification of intravoxel velocity standard deviation and turbulence intensity by generalizing phase-contrast MRI
2006 (English)In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 56, no 4, 850-858 p.Article in journal (Refereed) Published
Abstract [en]

Turbulent flow, characterized by velocity fluctuations, is a contributing factor to the pathogenesis of several cardiovascular diseases. A clinical noninvasive tool for assessing turbulence is lacking, however. It is well known that the occurrence of multiple spin velocities within a voxel during the influence of a magnetic gradient moment causes signal loss in phase-contrast magnetic resonance imaging (PC-MRI). In this paper a mathematical derivation of an expression for computing the standard deviation (SD) of the blood flow velocity distribution within a voxel is presented. The SD is obtained from the magnitude of PC-MRI signals acquired with different first gradient moments. By exploiting the relation between the SD and turbulence intensity (TI), this method allows for quantitative studies of turbulence. For validation, the TI in an in vitro flow phantom was quantified, and the results compared favorably with previously published laser Doppler anemometry (LDA) results. This method has the potential to become an important tool for the noninvasive assessment of turbulence in the arterial tree.

Keyword
phase-contrast magnetic resonance imaging, turbulent flow, intravoxel velocity distribution, turbulence intensity, atherosclerosis
National Category
Medical and Health Sciences Physiology Fluid Mechanics and Acoustics Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:liu:diva-37249 (URN)10.1002/mrm.21022 (DOI)000240897000017 ()34073 (Local ID)34073 (Archive number)34073 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
2. On MRI turbulence quantification
Open this publication in new window or tab >>On MRI turbulence quantification
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2009 (English)In: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 27, no 7, 913-922 p.Article in journal (Refereed) Published
Abstract [en]

Turbulent flow, characterized by velocity fluctuations, accompanies many forms of cardiovascular disease and may contribute to their progression and hemodynamic consequences. Several studies have investigated the effects of turbulence on the magnetic resonance imaging (MRI) signal. Quantitative MRI turbulence measurements have recently been shown to have great potential for application both in human cardiovascular flow and in engineering flow. In this article, potential pitfalls and sources of error in MRI turbulence measurements are theoretically and numerically investigated. Data acquisition strategies suitable for turbulence quantification are outlined. The results show that the sensitivity of MRI turbulence measurements to intravoxel mean velocity variations is negligible, but that noise may degrade the estimates if the turbulence encoding parameter is set improperly. Different approaches for utilizing a given amount of scan time were shown to influence the dynamic range and the uncertainty in the turbulence estimates due to noise. The findings reported in this work may be valuable for both in vitro and in vivo studies employing MRI methods for turbulence quantification.

Keyword
Turbulence quantification, Turbulent flow, Phase-contrast magnetic resonance imaging, Constriction, Numerical flow phantom
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-20746 (URN)10.1016/j.mri.2009.05.004 (DOI)000269613000004 ()
Note

Original Publication: Petter Dyverfeldt, Roland Gårdhagen, Andreas Sigfridsson, Matts Karlsson and Tino Ebbers, On MRI turbulence quantification, 2009, MAGNETIC RESONANCE IMAGING, (27), 7, 913-922. http://dx.doi.org/10.1016/j.mri.2009.05.004 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/

Available from: 2009-09-18 Created: 2009-09-18 Last updated: 2017-12-13
3. Assessment of fluctuating velocities in disturbed cardiovascular blood flow: in vivo feasibility of generalized phase-contrast MRI
Open this publication in new window or tab >>Assessment of fluctuating velocities in disturbed cardiovascular blood flow: in vivo feasibility of generalized phase-contrast MRI
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2008 (English)In: Journal of Magnetic Resonance Imaging, ISSN 1053-1807, E-ISSN 1522-2586, Vol. 28, no 3, 655-663 p.Article in journal (Refereed) Published
Abstract [en]

Purpose

To evaluate the feasibility of generalized phase-contrast magnetic resonance imaging (PC-MRI) for the noninvasive assessment of fluctuating velocities in cardiovascular blood flow.

Materials and Methods

Multidimensional PC-MRI was used in a generalized manner to map mean flow velocities and intravoxel velocity standard deviation (IVSD) values in one healthy aorta and in three patients with different cardiovascular diseases. The acquired data were used to assess the kinetic energy of both the mean (MKE) and the fluctuating (TKE) velocity field.

Results

In all of the subjects, both mean and fluctuating flow data were successfully acquired. The highest TKE values in the patients were found at sites characterized by abnormal flow conditions. No regional increase in TKE was found in the normal aorta.

Conclusion

PC-MRI IVSD mapping is able to detect flow abnormalities in a variety of human cardiovascular conditions and shows promise for the quantitative assessment of turbulence. This approach may assist in clarifying the role of disturbed hemodynamics in cardiovascular diseases.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-43135 (URN)10.1002/jmri.21475 (DOI)000259106900013 ()71980 (Local ID)71980 (Archive number)71980 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
4. In Vitro Assessment of Flow Patterns and Turbulence Intensity in Prosthetic Heart Valves Using Generalized Phase-Contrast Magnetic Resonance Imaging
Open this publication in new window or tab >>In Vitro Assessment of Flow Patterns and Turbulence Intensity in Prosthetic Heart Valves Using Generalized Phase-Contrast Magnetic Resonance Imaging
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Purpose: To assess in vitro the three-dimensional mean velocity field and the extent and degree of turbulenceintensity in different prosthetic heart valves using a generalization of phase-contrast magnetic resonance imaging(PC-MRI).

Material and Methods: Four 27 mm aortic valves (Björk-Shiley Monostrut tilting-disc, St. Jude MedicalStandard bileaflet, Medtronic Mosaic stented and Freestyle stentless porcine valve) were tested under steadyinflow conditions in a Plexiglas phantom. Three-dimensional PC-MRI data were acquired to measure the meanvelocity field and the turbulent kinetic energy (TKE), a direction-independent measure of turbulence intensity.

Results: Velocity and turbulence intensity estimates could be obtained up and downstream of the valves, exceptwhere metallic structure in the valves caused signal void. Distinct differences in the location, extent and peakvalues of velocity and turbulence intensity were observed between the valves tested. The maximum values ofTKE varied between the different valves: tilting disc, 100 J/m3; bileaflet, 115 J/m3; stented, 200 J/m3; stentless,145 J/m3.

Conclusion: The turbulence intensity downstream from a prosthetic heart valve is dependent on the specificvalve design. Generalized PC-MRI can be used to quantify velocity and turbulence intensity downstream fromprosthetic heart valves, which may allow assessment of these aspects of prosthetic valvular function inpostoperative patients.

Keyword
Turbulence intensity, prosthetic heart valves, phase-contrast magnetic resonance imaging
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-53189 (URN)
Available from: 2010-01-19 Created: 2010-01-19 Last updated: 2013-09-03Bibliographically approved
5. Hemodynamic aspects of mitral regurgitation assessed by generalized phase-contrast MRI
Open this publication in new window or tab >>Hemodynamic aspects of mitral regurgitation assessed by generalized phase-contrast MRI
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2011 (English)In: Journal of Magnetic Resonance Imaging, ISSN 1053-1807, E-ISSN 1522-2586, Vol. 33, no 3, 582-588 p.Article in journal (Refereed) Published
Abstract [en]

Purpose: Mitral regurgitation creates a high velocity jet into the left atrium (LA), contributing both volume andpressure; we hypothesized that the severity of regurgitation would be reflected in the degree of LA flowdistortion.

Material and Methods: Three-dimensional cine PC-MRI was applied to determine LA flow patterns andturbulent kinetic energy (TKE) in seven subjects (five patients with posterior mitral leaflet prolapse, two normalsubjects). In addition, the regurgitant volume and the time-velocity profiles in the pulmonary veins weremeasured.

Results: The LA flow in the mitral regurgitation patients was highly disturbed with elevated values of TKE.Peak TKE occurred consistently at late systole. The total LA TKE was closely related to the regurgitant volume.LA flow patterns were characterized by a pronounced vortex in proximity to the regurgitant jet. In some patients,pronounced discordances were observed between individual pulmonary venous inflows, but these could not berelated to the direction of the flow jet or parameters describing global LA hemodynamics.

Conclusion: PC-MRI permits investigations of atrial and pulmonary vein flow patterns and TKE in significantmitral regurgitation, reflecting the impact of the highly disturbed blood flow that accompanies this importantvalve disease.

Place, publisher, year, edition, pages
John Wiley and Sons, 2011
Keyword
Hemodynamics, mitral valve insufficiency, turbulent flow, phase-contrast magnetic resonance imaging, pulmonary veins, blood flow velocity
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-53190 (URN)10.1002/jmri.22407 (DOI)000287951100009 ()
Available from: 2010-01-19 Created: 2010-01-19 Last updated: 2017-12-12

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