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Abstract #2905

The Influence of Bold-fMRI (GRE-EPI) on MEGA-PRESS Measurements of GABA Concentrations

Sofie Tapper 1 , Anders Tisell 1,2 , and Peter Lundberg 1,2

1 Radiation Physics, Department of Medicine and Healths Sciences, Linkping University, Linkping University, Linkping, Sweden, 2 Centre for Medical Image Science and Visualization (CMIV), Linkping University, Linkping, Sweden, Linkping University, Linkping, Sweden

In many recent experiments BOLD-fMRI has been combined with quantitative measurements of GABA-concentrations in order to elucidate the correlation between positive or negative BOLD and GABA and Glutamate concentrations in connection with a range of diseases affecting the CNS. GABA MRS is in many cases performed subsequent to the fMRI data-acquisition. As a consequence, the quality of the GABA-measurements heavily depend on the short term stability of the MR-scanner. Our aim was to determine the possibly deleterious effects a BOLD-fMRI (GRE-EPI) experiment had on the stability of MEGA-PRESS measurements, and we have performed investigations of the drift in synthesizer frequency and phase. All measurements were performed both before and after GRE-EPI. The conclusion was that the large influence of EPI-induced gradient heating on quantitative GABA-concentration measurements needs to be corrected for using a procedure taking both the frequency- and phase-drift in each individual dynamic into account.

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