Estimation of metabolite T1 relaxation times using tissue specific analysis, signal averaging and bootstrapping from magnetic resonance spectroscopic imaging data.
OBJECTIVE
A novel method of estimating metabolite T1 relaxation times using MR spectroscopic imaging (MRSI) is proposed. As opposed to conventional single-voxel metabolite T1 estimation methods, this method investigates regional and gray matter (GM)/white matter (WM) differences in metabolite T1 by taking advantage of the spatial distribution information provided by MRSI.


METHODS
The method, validated by Monte Carlo studies, involves a voxel averaging to preserve the GM/WM distribution, a non-linear least squares fit of the metabolite T1 and an estimation of its standard error by bootstrapping. It was applied in vivo to estimate the T1 of N-acetyl compounds (NAA), choline, creatine and myo-inositol in eight normal volunteers, at 1.5 T, using a short echo time 2D-MRSI slice located above the ventricles.


RESULTS
WM-T 1,NAA was significantly (P < 0.05) longer in anterior regions compared to posterior regions of the brain. The anterior region showed a trend of a longer WM T1 compared to GM for NAA, creatine and myo-Inositol. Lastly, accounting for the bootstrapped standard error estimate in a group mean T1 calculation yielded a more accurate T1 estimation.


CONCLUSIONS
The method successfully measured in vivo metabolite T1 using MRSI and can now be applied to diseased brain.
Ratiney
H
H
Department of Neurology, University of California, 185 Berry Street, Box 0946, San Francisco, CA 94107, USA.
Noworolski
S M
SM
Sdika
M
M
Srinivasan
R
R
Henry
R G
RG
Nelson
S J
SJ
Pelletier
D
D
D000328:Adult; D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology* / Q000378:metabolism*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008657:Metabolic Clearance Rate; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D012815:Signal Processing, Computer-Assisted; D014018:Tissue Distribution
D009419:Nerve Tissue Proteins