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Two-point dixon method with flexible echo times
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Radiology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Radiology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Radiology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Radiology.
2011 (English)In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 65, no 4, 994-1004 p.Article in journal (Refereed) Published
Abstract [en]

The two-point Dixon method is a proton chemical shift imaging technique that produces separated water-only and fat-only images from a dual-echo acquisition. It is shown how this can be achieved without the usual constraints on the echo times. A signal model considering spectral broadening of the fat peak is proposed for improved water/fat separation. Phase errors, mostly due to static field inhomogeneity, must be removed prior to least-squares estimation of water and fat. To resolve ambiguity of the phase errors, a corresponding global optimization problem is formulated and solved using a message-passing algorithm. It is shown that the noise in the water and fat estimates matches the Cramér-Rao bounds, and feasibility is demonstrated for in vivo abdominal breath-hold imaging. The water-only images were found to offer superior fat suppression compared with conventional spectrally fat suppressed images.

Place, publisher, year, edition, pages
2011. Vol. 65, no 4, 994-1004 p.
Keyword [en]
chemical shift imaging, fat suppression, two-point Dixon, water and fat separation
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-150936DOI: 10.1002/mrm.22679ISI: 000288612000011PubMedID: 21413063OAI: oai:DiVA.org:uu-150936DiVA: diva2:409378
Available from: 2011-04-08 Created: 2011-04-08 Last updated: 2012-03-07Bibliographically approved
In thesis
1. Separation of Water and Fat Signal in Magnetic Resonance Imaging: Advances in Methods Based on Chemical Shift
Open this publication in new window or tab >>Separation of Water and Fat Signal in Magnetic Resonance Imaging: Advances in Methods Based on Chemical Shift
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Magnetic resonance imaging (MRI) is one of the most important diagnostic tools of modern healthcare. The signal in medical MRI predominantly originates from water and fat molecules. Separation of the two components into water-only and fat-only images can improve diagnosis, and is the premier non-invasive method for measuring the amount and distribution of fatty tissue.

Fat-water imaging (FWI) enables fast fat/water separation by model-based estimation from chemical shift encoded data, such as multi-echo acquisitions. Qualitative FWI is sufficient for visual separation of the components, while quantitative FWI also offers reliable estimates of the fat percentage in each pixel. The major problems of current FWI methods are long acquisition times, long reconstruction times, and reconstruction errors that degrade image quality.

In this thesis, existing FWI methods were reviewed, and novel fully automatic methods were developed and evaluated, with a focus on fast 3D image reconstruction. All MRI data was acquired on standard clinical scanners.

A triple-echo qualitative FWI method was developed for the specific application of 3D whole-body imaging. The method was compared with two reference methods, and demonstrated superior image quality when evaluated in 39 volunteers.

The problem of qualitative FWI by dual-echo data with unconstrained echo times was solved, allowing faster and more flexible image acquisition than conventional FWI. Feasibility of the method was demonstrated in three volunteers and the noise performance was evaluated.

Further, a quantitative multi-echo FWI method was developed. The signal separation was based on discrete whole-image optimization. Fast 3D image reconstruction with few reconstruction errors was demonstrated by abdominal imaging of ten volunteers.

Lastly, a method was proposed for quantitative mapping of average fatty acid chain length and degree of saturation. The method was validated by imaging different oils, using gas-liquid chromatography (GLC) as the reference. The degree of saturation agreed well with GLC, and feasibility of the method was demonstrated in the thigh of a volunteer.

The developed methods have applications in clinical settings, and are already being used in several research projects, including studies of obesity, dietary intervention, and the metabolic syndrome.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 85 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 701
Keyword
Magnetic resonance imaging, digital image reconstruction, chemical shift imaging, water and fat separation, Dixon method, fat suppression, quantitative MRI, whole-body MRI, fatty acid composition, fat unsaturation, triglycerides, adipose tissue, liver fat, T2* mapping
National Category
Clinical Science
Research subject
Radiology
Identifiers
urn:nbn:se:uu:diva-158111 (URN)978-91-554-8154-4 (ISBN)
Public defence
2011-10-21, Hedstrandsalen, Entrance 70, Uppsala University Hospital, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2011-09-29 Created: 2011-08-31 Last updated: 2011-11-03Bibliographically approved

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Berglund, JohanAhlström, HåkanJohansson, LarsKullberg, Joel

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