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Correction for acceleration-induced displacement artifacts in phase contrast imaging
Linköping University, Department of Biomedical Engineering. Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Biomedical Engineering. Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences.
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2000 (English)In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 43, no 5, 734-738 p.Article in journal (Refereed) Published
Abstract [en]

The acceleration-induced displacement artifact impairs the accuracy of MR velocity measurements. This study proposes a post processing method for correction of this artifact. Velocity measurements were performed in a flow phantom containing a constriction. Velocity curves were obtained from streamlines parallel to the frequency, phase, and slice directions, respectively. The acceleration-induced displacement artifact was most prominent when the frequency encoding direction was aligned with the flow direction. After correction, velocity assignment improved and a more accurate description of the flow was obtained. In vivo measurements were performed in the aorta in a patient with a repaired aortic coarctation. The correction method was applied to velocity data along a streamline parallel to the frequency encoding direction. The result after correction was a new location of the peak velocity and improved estimates of the velocity gradients.

Place, publisher, year, edition, pages
2000. Vol. 43, no 5, 734-738 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-26712DOI: 10.1002/(SICI)1522-2594(200005)43:5<734::AID-MRM16>3.0.CO;2-ALocal ID: 11306OAI: oai:DiVA.org:liu-26712DiVA: diva2:247262
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2017-12-13
In thesis
1. Accuracy and reproducibility in phase contrast magnetic resonance imaging
Open this publication in new window or tab >>Accuracy and reproducibility in phase contrast magnetic resonance imaging
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Magnetic resonance imaging (MRI) is an imaging modality which provides good conditions for studies of flow and motion in the cardiovascular system. When using the phase contrast imaging technique, it is possible to perform velocity measurements in moving tissues and in blood. The acquired velocity data can be used for subsequent calculation of different parameters used for the assessment of cardiovascular function. These parameters rely on the accuracy and reproducibility of the velocity measurements.

This thesis includes an introduction to phase contrast imaging and how displacement artifacts may hamper the accuracy of velocity measurements using phase contrast imaging. A method for correction of this artifact was developed using the knowledge of the times at which velocity and spatial encoding are carried out in the pulse sequence. The elaboration of this correction method included modifications of a 3D phase contrast pulse sequence and development of post processing algorithms involving streamline calculations. An alternative approach for correction of displacement artifacts is also presented where a pulse sequence, based on tripolar waveforms, inherently compensates for the artifact and, consequently, do not require any post processing algorithms.

The use of the sensitivity encoding (SENSE) method in MRI implies that the scanning time can be reduced dramatically. The SENSE technique can be combined with phase contrast imaging. An important question to answer is how the use of SENSE influences the accuracy and reproducibility in phase contrast imaging. In this thesis expressions are derived showing how the reproducibility of velocity and flow measurements are influenced when applying SENSE at different reduction factors.

As a consequence of the introduction of parallel imaging techniques, such as SENSE, modem MRI systems have the capability of assessing individual coil sensitivities. This information implies new alternatives in the combination of multiple phase images using phased array coils. Conventionally multiple phase images are combined using the weighted mean method, where the squared magnitude values are used as weights. In order to compare these two combination methods, theoretical and experimental studies were performed.

The results of this thesis show that corrupted velocity measurements caused by displacement artifacts can be alleviated using suggested correction methods or pulse sequences. This is of importance for subsequent flow analysis and visualization of stenotic and oblique flow. Phase contrast imaging in combination with SENSE provides opportunities to obtain large reductions in scanning times while keeping the increase of the reproducibility in the velocity and flow measurements within reasonable limits. In terms of phase reproducibility it is shown that the use of individual coil sensitivities in the combination of multiple phase images is equivalent to the conventional weighted mean method. In the accompanying magnitude images, however, signal variations due to coil sensitivities are compensated for when including estimated coil sensitivities.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2004. 73 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 899
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-29441 (URN)14787 (Local ID)91-85295-41-8 (ISBN)14787 (Archive number)14787 (OAI)
Public defence
2004-12-10, Wilandersalen, Universitetssjukhuset, Örebro, 10:15 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-12-03
2. Correction for displacement artifacts in phase contrast magnetic resonance imaging
Open this publication in new window or tab >>Correction for displacement artifacts in phase contrast magnetic resonance imaging
2001 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Magnetic resonance imaging (MRI) is an imaging modality which provides good conditions for studies of flow and motion in the cardiovascular system. A variety of different imaging pulse sequences enables both anatomical and functional studies. When using the phase contrast imaging technique it is possible to perform velocity measurements in moving tissues and in blood. Acquired velocity data can be used for quantitative flow measurements which is valuable information in the assessment of different cardiovascular dysfunctions. In regions where the flow is accelerating and/or moving obliquely relative to the gradient axis, velocity measurements become displaced in the reconstructed velocity image. These displacement artifacts hamper the accuracy of phase contrast imaging and restrict subsequent flow analysis in regions which are of great clinical interest.

This thesis includes an introduction to phase contrast imaging and how displacement artifacts are manifested in the reconstructed velocity image. A theoretical framework is presented which shows how the measured phase shift can be written as a sum of different phase contributions induced by velocity and higher orders of motion. This framework was then used to find the instant during the acquisition of MR data which can be considered as the instant for velocity encoding. Correction methods were developed using the knowledge of the time points at which velocity and spatial encoding are performed in the pulse sequence. The implementation of these correction methods included modifications of a 3D phase contrast pulse sequence and development of post processing algorithms involving streamline calculations. In vitro and in vivo experiments were performed which demonstrated how the displacement artifacts severely distorted the accuracy of phase contrast imaging in regions of stenotic and oblique flow. After correction, significant improvements were achieved which were demonstrated using velocity profiles and streamline visualization.

The results of this thesis shows that corrupted velocity measurements caused by displacement artifacts can be alleviated using the suggested correction methods. This may be of importance for subsequent flow analysis and visualization of stenotic and/or oblique flow.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2001. 46 and two articles p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 910
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-29500 (URN)LiU-TEK-LIC-2001 :47 (Local ID)91-7373-206-0 (ISBN)LiU-TEK-LIC-2001 :47 (Archive number)LiU-TEK-LIC-2001 :47 (OAI)
Presentation
2001-12-14, föreläsningssal 048, Universitetssjukhuset, Campus US, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2014-02-04Bibliographically approved

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Thunberg, PerWigström, LarsWranne, BengtEngvall, JanKarlsson, Matts

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