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Correction for displacement artifacts in phase contrast magnetic resonance imaging
Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
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: urn:nbn:se:liu:diva-29500Local ID: LiU-TEK-LIC-2001 :47ISBN: 91-7373-206-0 (print)OAI: oai:DiVA.org:liu-29500DiVA: diva2:250315
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
List of papers
1. Correction for acceleration-induced displacement artifacts in phase contrast imaging
Open this publication in new window or tab >>Correction for acceleration-induced displacement artifacts in phase contrast imaging
Show others...
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.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-26712 (URN)10.1002/(SICI)1522-2594(200005)43:5<734::AID-MRM16>3.0.CO;2-A (DOI)11306 (Local ID)11306 (Archive number)11306 (OAI)
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2016-03-14
2. Correction for displacement artifacts in 3D phase contrast imaging
Open this publication in new window or tab >>Correction for displacement artifacts in 3D phase contrast imaging
2002 (English)In: Journal of Magnetic Resonance Imaging, ISSN 1053-1807, E-ISSN 1522-2586, Vol. 16, no 5, 591-597 p.Article in journal (Refereed) Published
Abstract [en]

Purpose

To correct for displacement artifacts in 3D phase contrast imaging.

Materials and Methods

A 3D phase contrast pulse sequence was modified so that displacements of velocity measurements were restricted to one direction. By applying a postprocessing method, displaced measurements could be traced back to their accurate positions. Flow studies were performed using a phantom that generated flow through a stenosis, directed oblique relative to the phase and frequency encoding directions. Velocity profiles and streamline visualization were used to compare displaced and corrected velocity data to a reference.

Results

Velocity profiles obtained from the original measurement showed skewed profiles due to the displacement artifact, both at close proximity to the orifice as well as further downstream. After correction, concordance with the reference improved considerably.

Conclusion

The displacement artifact, which restricts the accuracy of phase contrast measurements, can be corrected for using the proposed method. Correction of the phase contrast velocity data may improve the accuracy of subsequent flow analysis and visualization.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-26708 (URN)10.1002/jmri.10187 (DOI)11301 (Local ID)11301 (Archive number)11301 (OAI)
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2016-03-14

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