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Influence of the FID and off-resonance effects in dense 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 Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Clinical Physiology.
(Department of Radiology, Mie University, Japan)
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 and Medicine Centre, Department of Clinical Physiology UHL.
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2011 (English)In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 65, no 4, 1104-1112 p.Article in journal (Refereed) Published
Abstract [en]

Accurate functional measurement in cardiovascular diseases is important as inaccuracy may compromise diagnostic decisions. Cardiac function can be assessed using displacement encoding with stimulated echoes, resulting in three signal components. The free induction decay (FID), arising from spins undergoing T1-relaxation, is not displacement encoded and impairs the displacement acquired. Techniques for suppressing the FID exist; however, a residual will remain. The effect of the residual is difficult to distinguish and investigate in vitro and in vivo. In this work, the influence of the FID as well as of off-resonance effects is evaluated by altering the phase of the FID in relation to the stimulated echo. The results show that the FID and off-resonance effects can impair the accuracy of the displacement measurement acquired. The influence of the FID can be avoided by using an encoded reference. We therefore recommend the assessment of this influence of the FID for each displacement encoding with stimulated echoes protocol.

Place, publisher, year, edition, pages
Wiley , 2011. Vol. 65, no 4, 1104-1112 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-60266DOI: 10.1002/mrm.22692ISI: 000288612000023OAI: oai:DiVA.org:liu-60266DiVA: diva2:355899
Available from: 2010-10-08 Created: 2010-10-08 Last updated: 2017-12-12
In thesis
1. Assessment of Myocardial Function using Phase Based Motion Sensitive MRI
Open this publication in new window or tab >>Assessment of Myocardial Function using Phase Based Motion Sensitive MRI
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quantitative assessment of myocardial function is a valuable tool for clinical applications and physiological studies. This assessment can be acquired using phase based motion sensitive magnetic resonance imaging (MRI) techniques. In this thesis, the accuracy of these phase based motion sensitive MRI techniques is investigated, and modifications in acquisition and post-processing are proposed.

The strain rate of the myocardium can be used to evaluate the myocardial function. However, the estimation of strain rate from the velocity data acquired with phase-contrast MRI (PC-MRI) is sensitive to noise. Estimation using normalized convolution showed, however, to reduce this sensitivity to noise and to minimize the influence of non-myocardial tissue which could impair the result.

Strain of the myocardium is another measure to assess myocardial function. Strain can be estimated from the myocardial displacement acquired with displacement encoding with stimulated echo (DENSE). DENSE acquisition can be realized with several different encoding strategies. The choice of encoding scheme may make the acquisition more or less sensitive to different sources of error. Two potential sources of errors in DENSE acquisition are the influence of the FID and of  the off-resonance effects. Their influence on DENSE were investigated to determine suitable encoding strategies to reduce their influence and thereby improve the measurement accuracy acquired.

The quality of the DENSE measurement is not only dependent on the accuracy, but also the precision of the measurement. The precision is affected by the SNR and thereby depends on flip angle strategies, magnetic field strength and spatial variation of the receiver coil sensitivity. A mutual comparison of their influence on SNR in DENSE was therefore performed and could serve as a guideline to optimize parameters for specific applications.

The acquisition time is often an important factor, especially in clinical applications where it affects potential patient discomfort and patient through-put. A multiple-slice DENSE acquisition was therefore presented, which allows the acquisition of strain values according to the 16-segment cardiac model within a single breath-hold, instead of the conventional three breath-holds.

The DENSE technique can also be adapted toward comprehensive evaluation of the heart in the form of full three-dimensional three-directional acquisition of the displacement. To estimate the full strain tensor from these data, a novel post-processing technique using a polynomial was investigated. The method yielded accurate results on an analytical model and \textit{in-vivo} strains obtained agreed with previously reported myocardial strains in normal volunteers.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 53 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1341
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:liu:diva-60027 (URN)978-91-7393-302-5 (ISBN)
Public defence
2010-11-12, Conrad, Universitetssjukhuset, Campus US, Linköpings universitet, Linköping, 09:15 (English)
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Supervisors
Available from: 2010-11-16 Created: 2010-10-04 Last updated: 2016-03-14Bibliographically approved

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Haraldsson, HenrikSigfridsson, AndreasEngvall, JanEbbers, Tino

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Center for Medical Image Science and Visualization, CMIVClinical PhysiologyFaculty of Health SciencesDepartment of Clinical PhysiologyDepartment of Clinical Physiology UHLApplied Thermodynamics and Fluid MechanicsPhysiology
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