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  Conditions for separation and individual quantification of IMCL and EMCL signals in 1H cardiac MRS

Fillmer, A., Hock, A., Cameron, D., & Henning, A. (2016). Conditions for separation and individual quantification of IMCL and EMCL signals in 1H cardiac MRS. Magnetic Resonance Materials in Physics, Biology and Medicine, 29(Supplement 1), S65-S66.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0000-7C3A-5 Version Permalink: http://hdl.handle.net/21.11116/0000-0000-C824-6
Genre: Meeting Abstract

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Fillmer, A, Author
Hock, A, Author
Cameron, D, Author
Henning, A1, 2, 3, Author              
Affiliations:
1Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497794              
2Research Group MR Spectroscopy and Ultra-High Field Methodology, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_2528692              
3Department High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497796              

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 Abstract: Purpose/Introduction: Cardiac 1H MRS (CMRS) is a promising tool for evaluating myocardial lipid metabolism [1]. However, in order to draw meaningful conclusions about lipid concentrations from CMRS spectra, it is necessary to distinguish between intramyocellular lipids (IMCL) and extramyocellular lipids (EMCL), and thus very high spectral quality is required. Previous work [2] demonstrated that metabolite cycling [3] is feasible of producing high quality CMRS spectra, when combined with ECG triggering and navigator-respiration-tracking [4], excellent B0-shimming [5], and retrospective motion correction by phase and frequency alignment [6]. This work investigates whether, and under what conditions, cardiac IMCL and EMCL signals can be separated and independently quantified in these high quality spectra using a standard analysis tool. Subjects and Methods: CMRS spectra were acquired from the interventricular septum of 10 healthy female volunteers in a 3 T scanner (Achieva, Philips Healthcare, Best, NL) using a 32-channel cardiac receive coil. Metabolite-cycled PRESS was applied with image-based B0-shimming, ECG-triggering and navigator-respiration-tracking. Post-processing was performed in MRecon (Gyrotools, Zurich, CH), as detailed in (2), and the resulting spectra were fit in LCModel [7]. Skeletal muscle studies have shown that EMCL’s chemical shift, DxEMCL, is dependent on the angle, h, muscle fibers take with B08. Assuming consistent voxel positioning relative to myocardial fibers, the fit results for DxEMCL were investigated in terms of the angle, a, the voxel takes with B0. Results: Fig. 1 shows an example spectrum; The resulting DxEMCL values agree well with theory and previous skeletal muscle8 work. However, the two data points with the highest and lowest a are clear outliers. Visual inspection of the spectra in question, as well as fits of simulated spectra, indicate that the frequency shift parameter in LCModel is internally constrained. Hence, the true DxEMCL could not be calculated in these spectra. From the fit of equation (1), it follows that cardiac fibers are approximately parallel to B0 at a = 1.5 rad. Within the interval -0.26 rad\a\0.56 rad or, approximately, -23.5ʰ\23.5, the correlation coefficient of the fit is R2 = 0.89. Hence, within that range IMCL and EMCL are well separable and can be independently analyzed. Discussion/Conclusion: This work proves that IMCL and EMCL signals in CMRS can be separated and independently quantified using the standard tool LCModel, provided two conditions are met: (1) spectral quality is sufficiently high; and (2) the angle of the myocardial fibers with respect to B0 within the examined voxel is B 23.5.

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 Dates: 2016-09-29
 Publication Status: Published in print
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 Identifiers: DOI: 10.1007/s10334-016-0568-x
BibTex Citekey: FillmerHCH2016
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Title: 33rd Annual Scientific Meeting of the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB 2016)
Place of Event: Wien, Austria
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Title: Magnetic Resonance Materials in Physics, Biology and Medicine
Source Genre: Journal
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Pages: - Volume / Issue: 29 (Supplement 1) Sequence Number: - Start / End Page: S65 - S66 Identifier: -