An Overview of MRS on mTBI
He (Henry) Zhu
VUIIS
Dept. of Radiology and Radiological
Sciences, Vanderbilt Univ.
Magnetic Resonance Spectroscopy
Glutamate
Choline (Cho): marker of Creatine and
(Glu)&Glutamine membrane turnover;
phosphocreatine (Cr
(Gln): Glu is primarytissue change leads to & PCr): related to
excitatory
increase of Cho after
energy consumption;
neurotransmitter; injury
often used as an
Glu-Gln cycle
internal reference, i.e.
controls γMyo-Inositol (mI):
NAA/Cr or Cho/Cr
Aminobutyric acid marker of astrolyte (in
(GABA)
glial cells); increase
after injury
Water (H20):
source of MRI:
structural, DTI,
SWI, fMRI, etc
N-acetyl aspartate
(NAA): marker of
neuronal health
and axon integrity;
decrease after
brain injury.
Recovery: Cognitive vs. Metabolic
Vagnozzi, Signoretti et al Neurosurgery 62: 1286-1296, 2008
Concussion initiates a period of neuron vulnerability, marked by reduced NAA content.
Metabolic recovery does not coincide with, and usually occurs after functional recovery.
“2nd hit” during this vulnerable period will result in more severe damage.
The mTBI challenge: where do you look?
MRI
Cho
Cr
1
NAA
2
Whole-brain coverage is essential for clinical applications to mTBI.
Volume Selective Spectroscopy
TE/4
TE/2
TE/4
PRESS
90˚
TE/2
TM
180˚
180˚
TE/2
TE
SemiLaser
STEAM
90˚
90˚
90˚
90˚
180˚
180˚
MR Spectroscopy and Spectroscopic Imaging of the Brain,
Magnetic Resonance Neuroimaging, Methods in Molecular Biology 711, Zhu & Barker 2011
Interleaved Slice-selective MRSI
OVS
Dualband+ OVS
Suppression
90˚
180˚
RF
OVS
GX
GY
GZ
TE
Slice 1 Slice 2 Slice 3 Slice 4 Slice 5
Zhu, Ouwerkerk, Barker MRM 63: 1486-1492, 2010
3D PRESS vs. Multi-Slice Spin Echo
TR of PRESS
90˚
180˚
180˚
RF
GX
•
90˚
•
TE of PRESS
•
RF
•
G
•
G
G
•
X
GY
Y
GZ
Z
90˚
180˚
•
•
•
•
•
•
90˚
TE of Spin Echo
RF
RF
GX
GX
GY
GY
GZ
GZ
TR of PRESSROI, easy to plan &
TR ofshim
PRESS
Specific
180˚
180˚
180˚
180˚
More Freedom
with90˚ FOV,
resolutions
In-plane ChemicalRFShift Displacement
More Pulses, Higher
SAR, Longer TE
G
Can not be interleaved,
Shorter TR
G
More T1 & T2 lossG at 7T
X
Y
Z
Multi-slice
w/ whole 90˚
slice180˚
coverageTR of Spin Echo
180˚
Allows Dynamic Shimming
RF
Allows Longer TR, Gless T1 loss
Less Pulses, LowerGSAR, Shorter TE
Restrictions on FOV
and resolution
G
Requires fast imaging technique
X
Y
Z
MR Spectroscopy and Spectroscopic Imaging of the Brain,
Magnetic Resonance Neuroimaging, Methods in Molecular Biology 711, Zhu & Barker 2011
MRI
Cho
Cr
NAA
Whole-brain MRSI
Scan parameters:
•5 slices of 13.2mm w/ 2.2mm gaps.;
•FOV=188×240mm w/ matrix size 25×32;
•Voxel size=0.74cm3 ;
•TE/TR = 144ms/2.5s w/ dualband + OVS
suppression;
•SENSE = 4 (2 in AP and 2 in RL) w/ 32channel phased array head coil;
•Fieldmap based global B0 shimming
•MRSI scantime: 15min 20sec.
Center Slice Spectra of 3T MRSI
Atlas-Based MRSI Reconstruction
Template
MNI #38: Right Cingulate Gyrus
MP-RAGE
Pro and Con of translating to 7T
Zhu, Soher, Ouwerkerk, Schär, Barker MRM (2012 In Press)
a) Slice Location
e) Glx
b) MRI
f) mI
g) Cho
c) H20
h) Cr
d) B1
i) NAA
1 slice, FOV=190×210mm. Matrix size = 32×29 Res.=7mm×7mm. Slice thick.=15mm. Voxel
Size=0.74cm3 TE/TR=29ms/4.5s. SAR=53%. SENSE=2×2. Scan Time = 12.5 min.
Higher field strength allows more compounds to be mapped. However, more
restrictive RF conditions limit spatial coverage to 1 slice.
90⁰
0⁰
Only Slice Spectra of 7T MRSI
MRI
Cho
Cr
Application to
mTBI at 3T
NAA
1
2
NAA
Cr
Cho
1
2
•A retired football player (42
years old, in NFL '93-02);
•Persistent headache and
fatigue;
•Imaging results all normal;
•Not possible with a PRESS
box (dashed).
Juvenile Post Auto Accident
MRI
Cho
Cr
NAA
Conclusions
• MR spectroscopy is a natural modality to
evaluate mTBI.
• NAA mapping(s) post-injury can monitor
metabolic recovery.
• Whole-brain coverage is essential as structural
MRI’s are expected to be normal.
• Multi-slice MRSI is better suited for mTBI than
3D PRESS.
• More improvements are needed such as
dynamic shimming and spectral editing for
GABA etc.
Acknowledgements
• VUIIS:
– Victoria Morgan, Sakait Sengupta, Megan Strother (MD),
John Gore
• Philips:
– Michael Schär, Ryan Robison, Charles Nockowski
• JHU:
– Peter Barker, Ronald Owerkerk, Susumu Mori, Jinyuan
Zhou, Jaishri Blakely(MD), Stacy Suskauer(MD)