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Quantification of intravoxel velocity standard deviation and turbulence intensity by generalizing phase-contrast MRI
Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical 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.
Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Department of Biomedical Engineering, Medical Informatics. Linköping University, The Institute of Technology.
Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical 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.ORCID iD: 0000-0003-1395-8296
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.

Place, publisher, year, edition, pages
2006. Vol. 56, no 4, 850-858 p.
Keyword [en]
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: urn:nbn:se:liu:diva-37249DOI: 10.1002/mrm.21022ISI: 000240897000017Local ID: 34073OAI: oai:DiVA.org:liu-37249DiVA: diva2:258098
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
In thesis
1. Extending MRI to the Quantification of Turbulence Intensity
Open this publication in new window or tab >>Extending MRI to the Quantification of Turbulence Intensity
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
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:nbn:se:liu:diva-52561 (URN)978-91-7393-453-4 (ISBN)
Public defence
2010-02-12, Elsa-Brändströmsalen, Universitetssjukhuset, Campus US. Linköpings universitet, Linköping, 09:15 (English)
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Available from: 2010-01-19 Created: 2010-01-04 Last updated: 2013-09-03Bibliographically approved

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Dyverfeldt, PetterSigfridsson, AndreasEscobar Kvitting, John-PederEbbers, Tino

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