Evaluation of cerebral gray and white matter metabolite differences by spectroscopic imaging at 4.1T

Using a 4.1T whole body system, we have acquired ¹H spectroscopic imaging (SI) data of N-acetyl(NA) compounds, creatine (CR), and choline (CH) with nominal voxel sizes of 0.5 cc (1.15 cc after filtering). We have used the SI data to estimate differences in cerebral metabolites of human gray and white matter. To evaluate the origin of an increased CR/NA and CH/NA ratios in gray matter relative to white matter, we measured the T₁ and T₂ of CR, NA, and CH in gray and white matter using moderate resolution SI imaging. In white matter the T₂s of NA, CR, and CH were 233 ± 27, 141 ± 18, and 167 ± 20 ms, respectively, and 227 ± 27, 140 ± 16, and 189 ± 25 ms in gray matter. The T₁ values for NA, CR, and CH were 1267 ± 141, 1487 ± 146, and 1111 ± 136 ms in gray matter and 1260 ± 154, 1429 ± 233, and 1074 ± 146 ms in white matter. After correcting for T₁ and T₂ losses, creatine content was significantly lower in white matter than gray (P < 0.01, t-test), with a white/gray content ratio of 0.8, in agreement with biopsy and in vivo measurements at 1.5 and 2.0T.