Correction for displacement artifacts in phase contrast magnetic resonance imaging
2001 (English)Licentiate thesis, comprehensive summary (Other academic)
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.
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 910
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:liu:diva-29500Local ID: LiU-TEK-LIC-2001 :47ISBN: 91-7373-206-0OAI: oai:DiVA.org:liu-29500DiVA: diva2:250315
2001-12-14, föreläsningssal 048, Universitetssjukhuset, Campus US, Linköpings universitet, Linköping, 10:15 (English)
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