Fast Mapping of theT2 Relaxation Time of Cerebral Metabolites Using Proton Echo-Planar Spectroscopic Imaging (PEPST)


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Abstract

MetaboliteT2 is necessary for accurate quantification of the absolute concentration of metabolites using long-echo-time (TE) acquisition schemes. However, lengthy data acquisition times pose a major challenge to mapping metaboliteT2. In this study we used proton echo-planar spectroscopic imaging (PEPSI) at 3T to obtain fastT2 maps of three major cerebral metabolites: N-acetyl-aspartate (NAA), creatine (Cre), and choline (Cho). We showed that PEPSI spectra matchedT2 values obtained using single-voxel spectroscopy (SVS). Data acquisition for 2D metabolite maps with a voxel volume of 0.95 ml (32 × 32 image matrix) can be completed in 25 min using five TEs and eight averages. A sufficient spectral signal-to-noise ratio (SNR) forT2 estimation was validated by high Pearson's correlation coefficients between logarithmic MR signals and TEs (R2 = 0.98, 0.97, and 0.95 for NAA, Cre, and Cho, respectively). In agreement with previous studies, we found that theT2 values of NAA, but not Cre and Cho, were significantly different between gray matter (GM) and white matter (WM;P< 0.001). The difference between theT2 estimates of the PEPSI and SVS scans was less than 9%. Consistent spatial distributions ofT2 were found in six healthy subjects, and disagreement among subjects was less than 10%. In summary, the PEPSI technique is a robust method to obtain fast mapping of metaboliteT2. Magn Reson Med 57:859–865, 2007. © 2007 Wiley-Liss, Inc.

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