(MRS) of the deep brain st tructures at 7. .0T 1803 Proc. Intl. Soc

Magnetic resonance spectroscopy (MRS) of the deep brain sttructures at 7..0T
2
Ravvi Prakash Reddy Nanga1, David R Roalf
R
, Kejia Cai1, Mark Elliott1, Haari Hariharan1, Jam
mes Loughead2, Haarish Poptani1, Ravvinder Reddy1, andd Ruben C Gur2
1
2
Radioology, University of
o Pennsylvania, Philadelphia,
P
Penn
nsylvania, United States,
S
Psychiatryy, University of Peennsylvania, Philaddelphia, Pennsylvaania, United Statess
Introd
duction. Standarrd proton MRS at
a 3.0T allows fo
or exceptional sensitivity to the neurochemistry of many regions of the brain (N
Nacewicz et al.,).
Howevver, direct quantification of spec
cific neurotransm
mitters such as glutamate
g
(Glu) within deep bra
ain structures (e
e.g. amygdala an
nd hippocampus
s)
remain
ns limited at this field strength. Recent
R
advances
s in MRS, especially the use of u ltra-high field 7.0
0T MRS, offer increased sensitivvity and specificitty
for bra
ain neurochemis
stry in deep brain
n structures. Thu
us, the use of 7.0T MRS to inve
estigate brain me
ntification of brain
etabolites may yyield better quan
neurocchemistry since spectral dispers
sion is enhanced
d at this magnetic field. The go
oal of the curren
nt study was to determine if 7.0
0T MRS provides
apprecciable gain in Glutamate/Glutam
G
mine (Glx) signall to noise (SNR)) as compared tto 3.0T, measurre the concentra
ation of Glx in th
he amygdala and
hippoccampus, and dettermine the repro
oducibility of this measurement.
ods. Standard MRS
M
(Point RES
Solved Spectros
scopy; PRESS) was used for a
acquisition at 3.0
0T Siemens sca
anner using 8-channel head co
oil
Metho
3
(Param
meters: TE: 30 ms; TR: 3000 ms;
m Voxel size: 10X10X10 mm ; 128 averages). A modified MRS
S (PRESS) acquiisition was used at 7.0T Siemens
3
scanner using 32-channel head coil (P
Parameters: TE:: 20 ms; TR: 300
00 ms; Voxel sizze: 10X10X10 m
mm ; 128 averag
ges). MRS was ccollected from six
4 years) at two time points ap
pproximately at 90-day intervalss. Data was co
ollected from the amygdala and
male subjects (aged between 22-64
d right). At 7.0T, Glu
G was measurred in glutamate phantoms prepa
ared using PBS b
buffer at pH 7.0 iin three concentrrations [5 mM, 10
hippoccampus (left and
mM, 1
15 mM]. Spectra
a obtained from 7T MRS were processed
p
by ex
xponential apodizzation (10 Hz) o
of the raw free iinduction decay data followed by
Fourie
er transformation, phase correctio
on and then base
eline correction. Metabolite peakss from the deep brain structures were fitted as Gaussian functions
with n
non-linear leastt squares fitting
g (MATLAB “n
nlinfit”
routine
e) followed by integration and then normalize
ed by
water signal for absolute qua
antification of Glx
concentration.
a showed an appreciable gain over
Resullts. 7.0T spectra
3.0T sspectra in deep
p brain structure
es (Figure A, B;; line
broade
ening of 5Hz was used in
n both spectra
a for
compa
arison). Qualitatively, the Glx peak
p
at 2.35 pp
pm is
clearlyy visible in the spectra acquired at 7.0T.
Macro
omolecular peaks (from 0.7 to 1.8
1 ppm) seen in 7T
spectrrum arises most probably due to the shorter echo
o time
used w
when compared to 3T. Mean Glx
G concentration was
16.99 (2.64) mM; [range (13.31-19
9.85); coefficien
nt of
%)] in the amygd
dala and 13.52 (1.80)
variation (CoV = 15.5%
mM; [range (11.21-16.39); CoV = 13.3%] in the
es are comparab
ble to
hippoccampus (Figure C). These value
a rece
ent study at 3.0T
T (Nacewicz et al.,;
a CoV = 15.42
2% in
amygd
dala). Only three subjects ha
ad suitable data
a for
longitu
udinal comparis
son in the am
mygdala (Figure
e D),
howevver they showed high reliability from
f
time 1 to time 2
(intra cclass correlation coefficient = 0.9
92). Finally, to confirm
the sttability of in vivo
o acquisition, Glu
G was measure
ed in
vitro. T
These data show
w that Glu has th
hree resolvable peaks
p
around
d 2.08ppm, 2.35
5ppm and 3.74p
ppm (Figure E). The
2.35 p
ppm peak is the only
o
one used for Glx quantificatiion in
vivo. Quantified Glu concentration
c
ba
ased on MRS me
ethod
a
Glu conce
entration (Figure F).
showss linearity to the actual
Concllusions. Despitte the challenges
s due to field inhomogeneities in imaging deep b rain structures, w
we demonstrated
d the feasibility o
of measuring high
qualityy MRS from amy
ygdala and hippo
ocampus at 7T. In
n this limited study, we further sh
howed that the 7
7T MRS has about 2.5 times SNR
R advantage ove
er
the co
orresponding 3T MRS and provides high quality
y Glx spectra. Re
epeated measurrements showed
d high degree off precision (intra class correlation
coefficcient = 0.92) at 7T.
7 Since the deep brain structurres are invovlved
d in many importa
ant cognitive fun
nctions like memo
ory, emotion and
d other behaviora
al
domaiins, accurate quantification could
d provide insightt into the well-do
ocumented volum
metric and functtional differencess in a variety off neuropsychiatric
disord
ders including sch
hizophrenia and autism.
owledgements. This work was performed at an
a NCRR supported Biomedical Technology an
nd Research Center (P41 RR02
2305) and in part
Ackno
suppo
orted by R21-DA0
032256, T32 MH
H019112 (D.R.R.))-SCHIZOPHRENIA: A NEUROP
PSYCHIATRIC P
PERSPECTIVE, M
MH060722 and M
MH064045.
ences. Nacewic
cz, B. M. et al., (2011) Reliab
ble non-invasive
e measurement of human neurrochemistry usin
ng proton specttroscopy with an
Refere
anatom
mically defined amygdala-specifi
a
c voxel. NeuroIm
mage (In press).
Proc. Intl. Soc. Mag. Reson. Med. 20 (2012)
1803