Metabolite proton T 2 mapping in the healthy rhesus macaque brain at 3 T

The structure and metabolism of the rhesus macaque brain, an advanced model for neurologic diseases and their treatment response, is often studied noninvasively with MRI and 1 H‐MR spectroscopy. Due to the shorter transverse relaxation time ( T 2 ) at the higher magnetic fields these studies favor, the echo times used in 1 H‐MR spectroscopy subject the metabolites to unknown T 2 weighting, decreasing the accuracy of quantification which is key for inter‐ and intra‐animal comparisons. To establish the “baseline” (healthy animal) T 2 values, we mapped them for the three main metabolites' T 2 s at 3 T in four healthy rhesus macaques and tested the hypotheses that their mean values are similar (i) among animals; and (ii) to analogs regions in the human brain. This was done with three‐dimensional multivoxel 1 H‐MR spectroscopy at (0.6 × 0.6 × 0.5 cm) 3 = 180 μL spatial resolution over a 4.2 × 3.0 × 2.0 = 25 cm 3 (∼30%) of the macaque brain in a two‐point protocol that optimizes T 2 precision per unit time. The estimated T 2 s in several gray and white matter regions are all within 10% of those reported in the human brain (mean ± standard error of the mean): N ‐acetylaspartate = 316 ± 7, creatine = 177 ± 3, and choline = 264 ± 9 ms, with no statistically significant gray versus white matter differences. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.