Human brain-structure resolved T(2) relaxation times of proton metabolites at 3 Tesla

The transverse relaxation times, T(2), of N-acetylaspartate (NAA), total choline (Cho), and creatine (Cr) obtained at 3T in several human brain regions of eight healthy volunteers are reported. They were obtained simultaneously in 320 voxels with three-dimensional (3D) proton MR spectroscopy ((1)H-MRS) at 1 cm(3) spatial resolution. A two-point protocol, optimized for the least error per given time by adjusting both the echo delay (TE(i)) and number of averages, N(i), at each point, was used. Eight healthy subjects (four males and four females, age = 26 +/- 2 years) underwent the hour-long procedure of four 15-min, 3D acquisitions (TE(1) = 35 ms, N(1) = 1; and TE(2) = 285 ms, N(2) = 3). The results reveal that across all subjects the NAA and Cr T(2)s in gray matter (GM) structures (226 +/- 17 and 137 +/- 12 ms, respectively) were 13-17% shorter than the corresponding T(2)s in white matter (WM; 264 +/- 10 and 155 +/- 7 ms, respectively). The T(2)s of Cho did not differ between GM and WM (207 +/- 17 and 202 +/- 8, respectively). For the purpose of metabolic quantification, these values justify to within +/-10% the previous use of one T(2) per metabolite for 1) the entire brain and 2) all subjects. These T(2) values (which to our knowledge were obtained for the first time at this field, spatial resolution, coverage, and precision) are essential for reliable absolute metabolic quantification.