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AJNR - American Journal of Neuroradiology

Published ahead of print on June 12, 2008
doi: 10.3174/ajnr.A1171

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Whole-Brain N-Acetylaspartate MR Spectroscopic Quantification: Performance Comparison of Metabolite versus Lipid Nulling

J.-B. Hövener^a,b, D.J. Rigotti^a, M. Amann^c, S. Liu^a, J.S. Babb^a, P. Bachert^b, A. Gass^c, R.I. Grossman^a and O. Gonen^a

^a Department of Radiology, New York University School of Medicine, New York
^b German Cancer Research Center, Division of Medical Physics in Radiology, Heidelberg, Germany
^c Departments of Neurology and Neuroradiology, University Hospital Basel, Basel, Switzerland

View larger version (12K): [in this window] [in a new window]   Fig 1. Whole-head WET (followed by a 13 [100-µs rectangular pulses with 2-ms interpulse delays at 3T] for a 90° readout) single-acquisition 1H proton spectrum. Note the extreme lipid contamination from the bone marrow and subcutaneous adipose tissue distorting and obscuring the NAA signal intensity and confounding its quantification. Cho indicates choline; Cr, creatine.

View larger version (15K): [in this window] [in a new window]   Fig 2. A, The NAA-nulling sequence comprising a BIR4 adiabatic 180° (every second) acquisition followed by a TI = 940 ms to null the NAA signal intensity. WET and a 13 (100-µs rectangular pulses, 2-ms delays at 3T) for a 90° readout with acquisition commencing immediately. Each even transient is subtracted from every odd. Because the TR is long, 10 seconds, and TE 0, minimal T1 or T2 weighting is incurred by the NAA. B, An alternative approach in which the lipids (not the NAA) are nulled with TI = 155 ms. All other pulses and sequence parameters are shared with A. Note that all pulses in either sequence are non-spatial-selective and that the gradient "blips," Gx, Gy, and Gz (all 5 mT/m), therefore, are just crushers. RF indicates radio-frequency.

View larger version (35K): [in this window] [in a new window]   Fig 3. Left, The real part of the whole-head 1H spectra from a male volunteer labeled i.j.a, where "i" (1..3) is the number of the session in the magnet, "j" (1..3) is the number of the back-to-back acquisitions in that session, and a or b indicates the sequence, Fig 2A, -B. Sessions were separated by at least 10 minutes with the subject outside the magnet. Right, Spectra obtained with the same protocol but with the sequence of Fig 2B. Note that both methods yield a whole-brain spectrum, including metabolites other than the NAA. Only the latter, however, is implicitly localized to the brain. mI indicates myo-Inositol; Cho, choline; Cr, creatine; Glu, glutamate.