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
Radiation Physics, Department of Medicine
and Healths Sciences, Linkping University, Linkping
University, Linkping, Sweden,
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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