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  Optimizing the B0-Shimming for Single Voxel Spectroscopy in the Myocardium at 3T

Fillmer, A., Cameron, D., Frenneaux, M., Dawson, D., & Henning, A. (2013). Optimizing the B0-Shimming for Single Voxel Spectroscopy in the Myocardium at 3T. Magnetic Resonance Materials in Physics, Biology and Medicine, 26(Supplement 1), 478-479.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0001-5186-C Version Permalink: http://hdl.handle.net/21.11116/0000-0001-5187-B
Genre: Meeting Abstract

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 Creators:
Fillmer, A, Author
Cameron, D, Author
Frenneaux, M, Author
Dawson, D, Author
Henning, A1, 2, Author              
Affiliations:
1Research Group MR Spectroscopy and Ultra-High Field Methodology, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_2528692              
2Max Planck Institute for Biological Cybernetics, Max Planck Society, Spemannstrasse 38, 72076 Tübingen, DE, ou_1497794              

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 Abstract: Purpose/Introduction: MR Spectroscopy is a useful tool for investigating heart disease[1,2], which benefits from increasing spectral resolution and SNR at higher B0-field strengths. The complexity of B0-field inhomogeneities, however, increases as well. By comparing spectral quality of projection-based[3,4] and image-based[5,6] B0-shimmed measurements in the interventricular septum, an optimal approach to B0-shimming of the myocardium for spectroscopy applications was determined. Subjects and Methods: Measurements were performed in eight volunteers(25y–37y) on an Achieva whole-body 3T system equipped with 2nd-order spherical-harmonic shim coils and a six-channel cardiac receive coil (Philips Healthcare,Best,NL). To compensate for cardiac and respiratory motion ECG-triggering and a breathing-belt were employed during calibration, B0-shimming and acquisition. Cine images of the myocardium were acquired to position the spectroscopy voxel and estimate the ECG-trigger delay. A non-shimmed B0-map (10slices,3x3x3mm3,ΔTE=1ms) was acquired for image-based B0-shim calculation. Nine non-water-suppressed, PRESS-localized spectra (8averages,TE/TR=60 ms/2000ms,voxel≈8.5x57x44mm3) were obtained per volunteer; one without B0-shimming and eight with different 1st- and 2nd-order B0-shim settings applied. Two B0-shim sets were determined by a FASTESTMAP-related (FM) projection-based B0-shim algorithm[3] and the remaining six, using different shim geometries(fig.1), by an image-based algorithm[5,6], which assigns different weightings to the region of interest (ROI) and a region of less interest (ROLI) during the B0-shim calculation. An ideal Voigt-line was fitted to the water peak and the FWHM was extracted. To quantify line shape distortions the spectra were normalized to their peak value. The Voigt-line fit was scaled accordingly and subtracted from the data. The area between x-axis and the difference-curve measures the deviation of the actual line shape from an ideal Voigt-line. Results: The influence of different B0-shim settings on line shape and width of the acquired non-water-suppressed spectra is clearly visible(fig.(2)). A comparison of FWHM values(fig.(3)) and deviations from a Voigt-line(fig. (4)) of the differently B0-shimmed spectra over all volunteers shows that best results can usually be achieved, when the ROI and a WH ROLI are considered for image-based B0-shimming. However, the use of a non-anatomically-conforming (rectangular) ROLI may lead to significantly reduced B0-shim quality(fig.(3,4)). Furthermore, B0-inhomogeneity correction limited to linear shim terms often gives better results than a 2nd-order correction probably due to imperfect motion correction within the translationally variable 2nd-order fields[7]. Discussion/Conclusion: By employing respiratory-gated and ECG-triggered image-based B0-shimming, including an anatomically conforming ROLI, the potential for improving the B0-shim quality for SV spectroscopy in the myocardium at 3T is demonstrated.

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 Dates: 2013-10
 Publication Status: Published in print
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 Identifiers: DOI: 10.1007/s10334-013-0385-4
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Title: 30th Annual Scientific Meeting ESMRMB 2013
Place of Event: Toulouse, France
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Title: Magnetic Resonance Materials in Physics, Biology and Medicine
Source Genre: Journal
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Pages: - Volume / Issue: 26 (Supplement 1) Sequence Number: - Start / End Page: 478 - 479 Identifier: -