Reproducibility and reliability of short-TE whole-brain MR spectroscopic imaging of human brain at 3T

Abstract

Purpose: A feasibility study of an echo-planar spectroscopic imaging (EPSI) using a short echo time (TE) that trades off sensitivity, compared with other short-TE methods, to achieve whole brain coverage using inversion recovery and spatial oversampling to control lipid bleeding.

Methods: Twenty subjects were scanned to examine intersubject variance. One subject was scanned five times to examine intrasubject reproducibility. Data were analyzed to determine coefficients of variance (COV) and intraclass correlation coefficient (ICC) for N-acetylaspartate (NAA), total creatine (tCr), total choline (tCho), glutamine/glutamate (Glx), and myo-inositol (mI). Regional metabolite concentrations were derived by using multi-voxel analysis based on lobar-level anatomic regions.

Results: For whole-brain mean values, the intrasubject COVs were 14%, 15%, and 20% for NAA, tCr, and tCho, respectively, and 31% for Glx and mI. The intersubject COVs were up to 6% higher. For regional distributions, the intrasubject COVs were ≤ 5% for NAA, tCr, and tCho; ≤ 9% for Glx; and ≤15% for mI, with about 6% higher intersubject COVs. The ICCs of 5 metabolites were ≥ 0.7, indicating the reliability of the measurements.

Conclusion: The present EPSI method enables estimation of the whole-brain metabolite distributions, including Glx and mI with small voxel size, and a reasonable scan time and reproducibility.

Keywords: glutamate; glutamine; myo-inositol; short TE MRSI; short acquisition time; whole-brain MRSI.

Fig. 1

(a) Example metabolite maps of NAA, tCho, tCr, ml, and Glx, with every second axial slice shown at 11 mm spacing and displayed with intensity scales as indicated; (b) Example spectra of single voxels from white matter or gray matter in multiple brain regions as indicated on the T1 images; (c) Examples of averaged spectra from 8 voxels of white matter (top) and gray matter (bottom) respectively from the right parietal lobe.

Fig. 2

(a) Mean-value metabolite maps calculated from five repeated studies in standard space, with voxel exclusion criteria as described in the text, displayed with intensity scales as indicated; (b) The corresponding COV maps, displayed with an intensity scale between 0% to 45%.

Fig. 3

Mean regional metabolite concentrations of the 5 repeated scans (Fig.3 middle) and the 20 volunteers (Fig.3 bottom) obtained with multi-voxel analysis and linewidth threshold of 11 Hz, based on atlas-defined lobar anatomic regions which identified nine anatomical regions (Fig.3 top) defining the left and right cerebral lobes and the cerebellum (25). Note: the first letter R = right; the second letter F = frontal, P = parietal, O = occipital, T = temporal; the third letter L = lobe; Cbl = cerebellum.