Acquisition and technique

1. MEGA-PRESS SPECTROSCOPY -
IN-VIVO DETECTION OF GABA
GABA
★ Gamma Aminobutyric Acid (GABA) is a major inhibitory
neurotransmitter in mammalian CNS & is integral to managing
brain excitability. GABA peaks are of many importance in various
Neurological disorders e.g. seizures, attention deficit disorder,
cognitive deficit disorders, schizophrenia etc.
★ Due to spectral overlap of the GABA peak with other metabolites
which are present in much greater concentration proven to be
difficult to reliably measure GABA peaks in-vivo by using standard
MR Spectroscopy (MRS).
★ Regular PRESS is often employed to measure
glutamate/glutamine and other metabolites, whereas
MEGA-PRESS provides GABA measurements along with other
metabolites including Glutamate/ Glutamine. MEGA-PRESS is a
widely used spectral editing technique that allows the in-vivo
quantification of GABA metabolites.
TECHNIQUES FOR ACQUISITION
❖ MEGA-PRESS is a difference edited technique which involves the
collection of two interleaved datasets which differ in their treatment
of GABA spin system. First, an editing pulse is applied to GABA
spins at 1.9ppm in order to selectively refocus the evolution of
J-coupling to the GABA spins at 3 ppm (Referred to as “ON”). In
the second data set, the inversion pulse is applied elsewhere so
that J-coupling evolves freely throughout the echo time (Referred
to as “OFF”) of GABA & spins at 7.46ppm.
❖ So, the GABA concentration can be derived during post
processing by subtraction of the refocused ON spectrum from the
non-refocused OFF spectrum retaining only those peaks that are
affected by editing pulse.
SIGNAL QUANTIFICATION & FITTING
❏ The available tools for fitting & quantification of GABA
concentration from edited spectra are LC Model, TARQUIN &
QUEST in jMRUI.
❏ For data processing we used FID-A (MATLAB based tool) to
obtained difference spectra (as shown here) and for further
quantification we used TARQUIN to obtain the quantitative values.
SPECTRAL PEAK & QUANTIFICATION
CONCLUSION & FUTURE SCOPE
➢ GABA and glutamate can be quantified in vivo with high
reproducibility using frequency-domain spectral fitting methods.
MEGA-MRS may provide a clinically useful method for the
assessment of various neurological and neuropsychiatric disorders
➢ Can provide in vivo imaging biomarker for disease diagnosis
and assess the treatment response.
VOXEL PLACEMENT
METHODOLOGY:- DATA ACQUISITION
GUIDED BY:-
Dr. MANOJ KUMAR(ASSISTANT PROFESSOR)
ABHINAY AKKISHETTY(SENIOR RADIOGRAPHER)
PRESENTED BY :-
MANISHA PRADHAN
SAKSHAM KUMAR
(3RD YEAR B.Sc Radiography)
NIMHANS, BANGALORE