Adam Steel1,2, Mark Chiew3, Peter Jezzard4, Natalie Voets4, Puneet Plaha4, M. Albert Thomas5, Charlotte J Stagg4, and Uzay E Emir6
1Nuffield Department of Medicine, University of Oxford, Headington, United Kingdom, 2National Institute of Mental Health, National Institutes of Health, Bethesda, DC, United States, 3Nuffield Department of Clinical Neuroscience, University of Oxford, Headington, United Kingdom, 4Nuffield Department of Clinical Neurosciences, University of Oxford, Headington, United Kingdom, 5Department of Radiology, University of California Los Angelas, Los Angeles, CA, United States, 6School of Health Sciences, Purdue University, West Lafayette, IN, United States
Synopsis
In
this study, we demonstrate that a metabolite-cycled semi-LASER pulse
localization with density-weighted concentric rings trajectory (DW-CRT) enables
high-resolution MRSI to be acquired at 3 Tesla within a clinically feasible
acquisition time. High-resolution (5 x 5
x 10 mm3) DW-CRT feasibility at 3T was assessed in 6 healthy
volunteers. Subsequently, the clinical utility of this approach was
demonstrated by mapping the presence of 2-HG in a patient with a grade III
oligodendroglioma tumor.
Introduction
Magnetic resonance spectroscopic imaging (MRSI) is an
appealing technique in both research and clinical settings. However, the
utility of MRSI has been hampered by long acquisition times, and hardware- and
subject-related artifacts [1].
Advances in MRSI acquisition, like DW-CRT and metabolite cycling [2-4],
and preprocessing [3, 5, 6]
have overcome some of these issues. However, these techniques have not been
combined, nor have they been demonstrated at widely available field-strengths. We sought to combine metabolite-cycled DW-CRT
with semi-LASER pulse localization with advanced preprocessing to achieve
high-quality MRSI within a clinically-feasible timescale and demonstrate the
clinical utility by mapping 2-hydroxyglutarate (2-HG) in a patient with a
high-grade brain tumor [7-9].Methods
Six healthy volunteers and one patient were scanned in this
study. Data were collected using a whole-body
3T Prisma MR system (Siemens, Erlangen) with a 32-channel head coil. GRESHIM was used for B0 shimming [10].
Two asymmetric narrow transition-band adiabatic RF pulses with mirrored
inversion profiles were applied in alternate scans to acquire the upfield and
downfield (relative to water) spectral resonances before the semi-LASER
localization [11, 12].
For metabolite-cycling, an 80 Hz transition bandwidth (-0.95 < Mz/M0
< 0.95) and 820 Hz inversion bandwidth (-1 < Mz/M0
< -0.95), 70 to -750 Hz) downfield/upfield from the carrier frequency
(carrier frequency offset=+60 Hz and -60 Hz for downfield and upfield). The sequence used the following adiabatic
pulse parameters: hyperbolic secant
pulse, HS1/2, with R=10 and 0.9 x Tp, tanh/tan pulse
with R=40 and 0.1 x TP) [2].
DW-CRT was prescribed using a Hanning-window [2]
and the following parameters: points-per-ring=64, temporal samples=512,
resolution=5x5x10 mm3, Rings=24, FOV=240x240x10 mm, TR=1350 ms, TE=32
ms, interleaves=4, timeacquire=13.5 min. For the tumor patient, the TE was changed to
110 ms to be sensitive to 2-HG [7].
Prior to LCModel fitting [13],
combined upfield/downfield FIDs were used to remove residual eddy current
effects [14]
and to combine the phased array coil spectra [15].
Hankel-Lanczos single value decomposition (HLSVD) algorithm filtered any
remaining water peak [6],
and a lipid-basis penalty was used to remove lipid contamination [16].
To evaluate tumor abnormalities, 2-hydroxyglutarate (2-HG), N-acetyl-aspartate (NAA),
and choline (Cho) in affected and unaffected tissue were assessed, and a tumor
mask was constructed for the single patient (female, age=72 years; biopsy
confirmed IDH-mutant oligodendroglioma). Equivalent voxels were sampled on the
unaffected hemisphere.Results
The acquisition and preprocessing enabled construction of
high-resolution metabolite maps (Figure 1, Cramer-Rao Lower Bounds in Figure
2). Across all subjects, the median
voxel-wise SNR was 18 (interquartile range=14-22) and linewidth was 7.26 Hz
(interquartile range=6.16-9.733 Hz; Figure 3, lower). The tumor region from the
patient showed abnormal 2-HG, Cho, and NAA Figure 4. As would be expected, the tumor had decreased
NAA and increased choline compared with the unaffected hemisphere. In addition, 2-HG, a specific tumor marker, was
present within the tumor but was virtually absent on the contralateral side. Conclusions
We demonstrated a DW-CRT semi-LASER sequence with metabolite
cycling enables high-resolution metabolite maps to be produced at 3T in a
clinically viable acquisition time. In addition to its robustness in healthy
volunteers, we demonstrate this technique’s sensitivity to abnormalities in a high-grade
tumor patient. Future work should
integrate outer-volume suppression to reduce lipid contamination during
acquisition.Acknowledgements
No acknowledgement found.References
-
Zhu,
H. and P.B. Barker, MR spectroscopy and
spectroscopic imaging of the brain. Methods Mol Biol, 2011. 711: p. 203-26.
-
Emir,
U.E., et al., Non-water-suppressed
short-echo-time magnetic resonance spectroscopic imaging using a concentric
ring k-space trajectory. NMR Biomed, 2017.
-
Hock,
A., et al., Non-water-suppressed proton
MR spectroscopy improves spectral quality in the human spinal cord. Magn
Reson Med, 2013. 69(5): p. 1253-60.
-
Chiew,
M., et al., Density-weighted concentric
rings k-space trajectory for 1 H magnetic resonance spectroscopic imaging at 7
T. NMR Biomed, 2017.
- Bilgic,
B., et al., Fast image reconstruction
with L2-regularization. J Magn Reson Imaging, 2014. 40(1): p. 181-91.
-
Cabanes,
E., et al., Optimization of residual
water signal removal by HLSVD on simulated short echo time proton MR spectra of
the human brain. J Magn Reson, 2001. 150(2):
p. 116-25.
-
Berrington,
A., et al., Improved localisation for
2-hydroxyglutarate detection at 3T using long-TE semi-LASER. Tomography,
2016. 2(2): p. 94-105.
- Emir,
U.E., et al., Noninvasive Quantification
of 2-Hydroxyglutarate in Human Gliomas with IDH1 and IDH2 Mutations. Cancer
Res, 2016. 76(1): p. 43-9.
- Pope,
W.B., et al., Non-invasive detection of
2-hydroxyglutarate and other metabolites in IDH1 mutant glioma patients using
magnetic resonance spectroscopy. J Neurooncol, 2012. 107(1): p. 197-205.
- Shah,
S., et al., Rapid Fieldmap Estimation for
Cardiac Shimming, in Proceedings 17th
Scientific Meeting, International Society for Magnetic Resonance in Medicine.
2009: Honolulu p. 565.
-
Scheenen,
T.W., et al., Short echo time 1H-MRSI of
the human brain at 3T with minimal chemical shift displacement errors using
adiabatic refocusing pulses. Magn Reson Med, 2008. 59(1): p. 1-6.
- Scheenen,
T.W., A. Heerschap, and D.W. Klomp, Towards
1H-MRSI of the human brain at 7T with slice-selective adiabatic refocusing
pulses. MAGMA, 2008. 21(1-2): p.
95-101.
-
Provencher,
S.W., Automatic quantitation of localized
in vivo 1H spectra with LCModel. NMR Biomed, 2001. 14(4): p. 260-4.
-
Klose,
U., In vivo proton spectroscopy in
presence of eddy currents. Magn Reson Med, 1990. 14(1): p. 26-30.
-
Walsh,
D.O., A.F. Gmitro, and M.W. Marcellin, Adaptive
reconstruction of phased array MR imagery. Magn Reson Med, 2000. 43(5): p. 682-90.
- Lee,
J. and E. Adalsteinsson, Reconstruction
with High-Resolution Spatial Priors for Improved Lipid Suppression, in Proceedings 18th Scientific Meeting,
International Society for Magnetic Resonance in Medicine. 2010: Stockholm
p. 965.