Hidehiro Watanabe: “Highly resolved 1H spectroscopy of human brain with 1H decoupling at high field”
CiNet 1F Conference Room
Affiliation of Hidehiro Watanabe
Biological Imaging and Analysis Section, Center for Environmental Measurement and Analysis, National Institute for Environmental Studies
This seminar will be done in Japanese.
Purpose: Glutamate (Glu) and gamma-amino butyric acid (GABA) are major neurotransmitters in human brain. Glutamine (Gln) is precursor and storage form of Glu. It is known to be predominantly synthesized in astrocytes and that it plays an important role in the Glu-Gln cycle in the brain.
Thus, simultaneous detection of Glu, GABA and Gln in vivo will give useful information on the metabolism of Glu and GABA in neurons as well as that of Gln in astrocytes.
However, these resonances are overlapped in 1D 1H spectra of human brain even at higher B0 because these metabolites have complex spin systems as a result of JHH with small chemical shift differences.
Constant time (CT) 2D methods have a potential of good peak resolution through 1H decoupling along F1 direction. In this work, we will develop two types of localized 2D CT methods in vivo for human brain; localized 2D CT-COSY and 2D CT-PRESS methods.
The CT-COSY method has a feature of detecting cross peaks via JHH coupling. The CT-PRESS method has a feature of higher sensitivity because of spin echo signals although only diagonal peaks can be detected.
We will perform absolute quantitation in JHH coupled spin systems using those methods.
Methods: We measured human brain spectra by developed localized CT-COSY and CT-PRESSmethods. In the 2D CT methods, a constant time delay, Tct, of around 100 ms is required for 1H decoupling.
Then, T2 correction is needed for quantitation. We measured T2 of metabolite peaks by the localized CT-COSY sequence with varied Tct values and corrected T2 decay.
Peak volumes on 2D spectra were calculated by our developed 2D LCModel software.
Absolute quantitation was done by the inner water reference method. We also developed a faster absolute quantitation method on CT-PRESS using 2D FT of shared time domain data.
All the measurements were performed using a 4.7 T whole-body MR system with a quadrature TEM coil.
Results: Three diagonal peaks of Glu, GABA and glutamine were clearly resolved both on the localized CT-COSY and CT-PRESS spectra of human brains.
SNR of Glu C4H was improved by a factor of 1.7 in the CT-PRESS spectrum. While concentrations of Glu and GABA were calculated as 8.7 mM and 0.9 mM respectively from the CT-COSY spectra, that of Glu was as 8.0 mM on CT-PRESS spectra.
These results were in good agreement with reported values.
Conclusion: Localized 2D CT methods in vivo have a feature of good peak resolution even for metabolites having JHH coupled spin systems, such as Glu and GABA.
Absolute quantitation on those methods can be performed after T2 corrections.