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  In vivo characterization of downfield peaks at 9.4 T: T 2 relaxation times, quantification, pH estimation, and assignments

Borbath, T., Murali-Manohar, S., Wright, A., & Henning, A. (2020). In vivo characterization of downfield peaks at 9.4 T: T 2 relaxation times, quantification, pH estimation, and assignments. Magnetic Resonance in Medicine, Epub ahead. doi:10.1002/mrm.28442.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0006-D9F2-4 Version Permalink: http://hdl.handle.net/21.11116/0000-0006-D9F3-3
Genre: Journal Article

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Borbath, T1, 2, Author              
Murali-Manohar, S1, 2, Author              
Wright, AM1, 2, 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: Relaxation times are a valuable asset when determining spectral assignments. In this study, apparent T2 relaxation times ( Tapp2 ) of downfield peaks are reported in the human brain at 9.4 T and are used to guide spectral assignments of some downfield metabolite peaks. Methods: Echo time series of downfield metabolite spectra were acquired at 9.4 T using a metabolite-cycled semi-LASER sequence. Metabolite spectral fitting was performed using LCModel V6.3-1L while fitting a pH sweep to estimate the pH of the homocarnosine (hCs) imidazole ring. Tapp2 were calculated by fitting the resulting relative amplitudes of the peaks to a mono-exponential decay across the TE series. Furthermore, estimated tissue concentrations of molecules were calculated using the relaxation times and internal water as a reference. Results: Tapp2 of downfield metabolites are reported within a range from 16 to 32 ms except for homocarnosine with Tapp2 of 50 ms. Correcting Tapp2 for exchange rates ( Tcorr2 ) resulted in relaxation times between 20 and 33 ms. The estimated pH values based on hCs imidazole range from 7.07 to 7.12 between subjects. Furthermore, analyzing the linewidths of the downfield peaks and their Tapp2 contribution led to possible peak assignments. Conclusion: Tapp2 relaxation times were longer for the assigned metabolite peaks compared to the unassigned peaks. Tissue pH estimation in vivo with proton MRS and simultaneous quantification of amide protons at 8.30 ± 0.15 ppm is likely possible. Based on concentration, linewidth, and exchange rates measurements, tentative peak assignments are discussed for adenosine triphosphate (ATP), N-acetylaspartylglutamate (NAAG), and urea.

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 Dates: 2020-08
 Publication Status: Published online
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 Identifiers: DOI: 10.1002/mrm.28442
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Title: Magnetic Resonance in Medicine
Source Genre: Journal
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Publ. Info: New York : Wiley-Liss
Pages: - Volume / Issue: Epub ahead Sequence Number: - Start / End Page: - Identifier: ISSN: 0740-3194
CoNE: https://pure.mpg.de/cone/journals/resource/954925538149