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In-vivo SNR in DENSE MRI: temporal and regional effects of field strength, receiver coil sensitivity, and flip angle strategies
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.
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, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences.ORCID iD: 0000-0003-1395-8296
Linköping University, Department of Biomedical Engineering, Medical Informatics. Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Faculty of Health Sciences.ORCID iD: 0000-0002-9091-4724
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2011 (English)In: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 29, no 2, 202-208 p.Article in journal (Refereed) Published
Abstract [en]

Aim: The influences on the SNR of DENSE MRI of field strength, receiver coil sensitivity and choice of flip angle strategy have been previously investigated individually. In this study, all of these parameters have been investigated in the same setting, and a mutual comparison of their impact on SNR is presented.

Materials and methods: Ten healthy volunteers were imaged in a 1.5T and a 3T MRI system, using standard 5 or 6 channel cardiac coils as well as 32 channel coils, with four different excitation patterns. Variation of spatial coil sensitivity was assessed by regional SNR analysis.

Results: SNR ranging from 2.8 to 30.5 was found depending on the combination of excitation patterns, coil sensitivity and field strength. The SNR at 3T was 53 ± 26% higher than at 1.5T (p<0.001), whereas spatial differences of 59 ± 26% were found in the ventricle (p<0.001). 32 channel coils provided 52 ± 29% higher SNR compared to standard 5 or 6 channel coils (p<0.001). A fixed flip angle strategy provided an excess of 50% higher SNR in half of the imaged cardiac cycle compared to a sweeping flip angle strategy, and a single phase acquisition provided a six-fold increase of SNR compared to a cine acquisition.

Conclusion: The effect of field strength and receiver coil sensitivity influences the SNR with the same order of magnitude, whereas flip angle strategy can have a larger effect on SNR. Thus, careful choice of imaging hardware in combination with adaptation of the acquisition protocol is crucial in order to realize sufficient SNR in DENSE MRI.

Place, publisher, year, edition, pages
Elsevier , 2011. Vol. 29, no 2, 202-208 p.
Keyword [en]
DENSE, strain, SNR, flip angle, coil sensitivity
National Category
Medical Laboratory and Measurements Technologies
Identifiers
URN: urn:nbn:se:liu:diva-51975DOI: 10.1016/j.mri.2010.08.016ISI: 000287390500008OAI: oai:DiVA.org:liu-51975DiVA: diva2:278377
Note

Original Publication: Andreas Sigfridsson, Henrik Haraldsson, Tino Ebbers, Hans Knutsson and Hajime Sakuma, In-vivo SNR in DENSE MRI: temporal and regional effects of field strength, receiver coil sensitivity, and flip angle strategies, 2011, Magnetic Resonance Imaging, (29), 2, 202-208. http://dx.doi.org/10.1016/j.mri.2010.08.016 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/

Available from: 2009-11-25 Created: 2009-11-25 Last updated: 2017-12-12
In thesis
1. Multidimensional MRI  of Myocardial Dynamics: Acquisition, Reconstruction and Visualization
Open this publication in new window or tab >>Multidimensional MRI  of Myocardial Dynamics: Acquisition, Reconstruction and Visualization
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Methods for measuring deformation and motion of the human heart in-vivo are crucial in the assessment of cardiac function. Applications ranging from basic physiological research, through early detection of disease to follow-up studies, all rely on the quality of the measurements of heart dynamics. This thesis presents new improved magnetic resonance imaging methods for acquisition, image reconstruction and visualization of cardiac motion and deformation.As the heart moves and changes shape during the acquisition, synchronization to the heart dynamics is necessary. Here, a method to resolve not only the cardiac cycle but also the respiratory cycle is presented. Combined with volumetric imaging, this produces a five-dimensional data set with two cyclic temporal dimensions. This type of data reveals unique physiological information, such as interventricular coupling in the heart in different phases of the respiratory cycle.The acquisition can also be sensitized to motion, measuring not only the magnitude of the magnetization but also a signal proportional to local velocity or displacement. This allows for quantification of the motion which is especially suitable for functional study of the cardiac deformation. In this work, an evaluation of the influence of several factors on the signal-to-noise ratio is presented for in-vivo displacement encoded imaging. Additionally, an extension of the method to acquire multiple displacement encoded slices in a single breath hold is also presented.Magnetic resonance imaging is usually associated with long scan times, and many methods exist to shorten the acquisition time while maintaining acceptable image quality. One class of such methods involves acquiring only a sparse subset of k-space. A special reconstruction is then necessary in order to obtain an artifact-free image. One family of these reconstruction techniques tailored for dynamic imaging is the k-t BLAST approach, which incorporates data-driven prior knowledge to suppress aliasing artifacts that otherwise occur with the sparse sampling. In this work, an extension of the original k-t BLAST method to two temporal dimensions is presented and applied to data acquired with full coverage of the cardio-respiratory cycles. Using this technique, termed k-t2 BLAST, simultaneous reduction of scan time and improved spatial resolution is demonstrated. Further, the loss of temporal fidelity when using the k-t BLAST approach is investigated, and an improved reconstruction is proposed for the application of cardiac function analysis.Visualization is a crucial part of the imaging chain. Scalar data, such as regular anatomical images, are straightforward to display. Myocardial strain and strain-rate, however, are tensor quantities which do not lend themselves to direct visualization. The problem of visualizing the tensor field is approached in this work by combining a local visualization that displays all degrees of freedom for a single tensor with an overview visualization using a scalar field representation of the complete tensor field. The scalar field is obtained by iterated adaptive filtering of a noise field, creating a continuous geometrical representation of the myocardial strain-rate tensor field.The results of the work presented in this thesis provide opportunities for improved imaging of myocardial function, in all areas of the imaging chain; acquisition, reconstruction and visualization.

 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 71 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1287
Keyword
MRI, Cardiac motion, myocardial dynamics, strain, tensor, deformation, DENSE, k-t BLAST
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:liu:diva-51489 (URN)978-91-7393-494-7 (ISBN)
Public defence
2009-12-18, Conrad, Campus US, Linköpings Universitet, Linköping, 09:15 (English)
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Supervisors
Available from: 2009-11-30 Created: 2009-11-04 Last updated: 2013-08-28Bibliographically approved

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Sigfridsson, AndreasHaraldsson, HenrikEbbers, TinoKnutsson, Hans

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