Fast mapping of the T2 relaxation time of cerebral metabolites using proton echo-planar spectroscopic imaging (PEPSI)

✍ Scribed by Shang-Yueh Tsai; Stefan Posse; Yi-Ru Lin; Cheng-Wen Ko; Ricardo Otazo; Hsiao-Wen Chung; Fa-Hsuan Lin

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 455 KB
• Volume: 57
• Category: Article
• ISSN: 0740-3194
• DOI: 10.1002/mrm.21225

✦ Synopsis

Abstract

Metabolite T~2~ 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 metabolite T~2~. In this study we used proton echo‐planar spectroscopic imaging (PEPSI) at 3T to obtain fast T~2~ maps of three major cerebral metabolites: N‐acetyl‐aspartate (NAA), creatine (Cre), and choline (Cho). We showed that PEPSI spectra matched T~2~ 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) for T~2~ estimation was validated by high Pearson's correlation coefficients between logarithmic MR signals and TEs (R^2^ = 0.98, 0.97, and 0.95 for NAA, Cre, and Cho, respectively). In agreement with previous studies, we found that the T~2~ 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 the T~2~ estimates of the PEPSI and SVS scans was less than 9%. Consistent spatial distributions of T~2~ 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 metabolite T~2~. Magn Reson Med 57:859–865, 2007. © 2007 Wiley‐Liss, Inc.