Brain metabolites B₁-corrected proton T₁ mapping in the rhesus macaque at 3 T

The accuracy of metabolic quantification in MR spectroscopy is limited by the unknown radiofrequency field and T₁. To address both issues in proton (¹H) MR spectroscopy, we obtained radiofrequency field-corrected T₁ maps of N-acetylaspartate, choline, and creatine in five healthy rhesus macaques at 3 T. For efficient use of the 4 hour experiment, we used a new three-point protocol that optimizes the precision of T₁ in three-dimensional ¹H-MR spectroscopy localization for extensive, ∼30%, brain coverage at 0.6 × 0.6 × 0.5 cm ³ = 180-μL spatial resolution. The resulting mean T₁s in 700 voxels were N-acetylaspartate = 1232 ± 44, creatine = 1238 ± 23 and choline = 1107 ± 56 ms (mean ± standard error of the mean). Their histograms from all 140 voxels in each animal were similar in position and shape, characterized by standard errors of the mean of the full width at half maximum divided by their means of better than 8%. Regional gray matter N- acetylaspartate, choline, and creatine T₁s (1333 ± 43, 1265 ± 52, and 1131 ± 28 ms) were 5-10% longer than white matter: 1188 ± 34, 1201 ± 24, and 1082 ± 50 ms (statistically significant for the N-acetylaspartate only), all within 10% of the corresponding published values in the human brain.