Numerically optimized experiment design for measurement of grey/white matter metabolite T2 in high-resolution spectroscopic images of brain.

T2 relaxation measurements for choline (Cho), total creatine (Cr = creatine + phosphocreatine), and N-acetylaspartate (NAA) were made separately in eight healthy volunteers using an average of forty 0.5 cc volumes (20 from grey matter and 20 from white matter) in spectroscopic images with a 32 x 32 resolution and a 240 mm field of view. In grey matter, the means and standard deviations of the T2 values were 186 +/- 23, 149 +/- 10, and 232 +/- 15 ms for Cho, Cr, and NAA, respectively, and in white matter, the mean T2 values were 178 +/- 16, 143 +/- 8, and 228 +/- 16 ms, respectively, with no significant differences between grey and white matter. The high-resolution measurements of T2 values were possible because of experimental planning based on the minimization of predicted fitting uncertainties. Explicit expressions were derived to estimate the uncertainties in T2 values, and it was found that two spectroscopic images with echo times of 50 and 250 ms, respectively, would yield sufficient precision for T2 measurements. The derivation of the expressions, a discussion of their behavior, and the experimental planning and verification are presented.