BACKGROUNDIn vivo proton magnetic resonance spectroscopy (MRS) provides a noninvasive method of examining a wide variety of cerebral metabolites in both healthy subjects and patients with various brain diseases. Absolute metabolite concentrations have been determined using external and internal standards with known concentrations. When an external standard is placed beside the head, variations in signal amplitudes due to B1 field inhomogeneity and static field inhomogeneity may occur. Hence an internal standard is preferable. The purpose of this study was to quantitatively analyze the metabolite concentrations in normal adult brains and gliomas by in vivo proton MRS using the fully relaxed water signal as an internal standard.

METHODSBetween January 1998 and October 2001, 28 healthy volunteers and 16 patients with gliomas were examined by in vivo proton MRS. Single-voxel spectra were acquired using the point-resolved spectroscopic pulse sequence with a 1.5 T scanner (TR/TE/Ave = 3000 ms/30 ms/64).

RESULTSThe calculated concentrations of N-acetyl-asparatate (NAA), creatine (Cre), choline (Cho), and water (H2O) in the normal hemispheric white matter were (23.59 +/- 2.62) mmol/L, (13.06 +/- 1.8) mmol/L, (4.28 +/- 0.8) mmol/L, and (47,280.96 +/- 5414.85) mmol/L, respectively. The metabolite concentrations were not necessarily uniform in different parts of the brain. The concentrations of NAA and Cre decreased in all gliomas (P < 0.001). The ratios of NAA/Cho and NAA/H2O showed a significant difference between the normal brain and gliomas, and also between the high and low grades (P < 0.001).

CONCLUSIONSQuantitative analysis of in vivo proton MR spectra using the fully relaxed water signal as an internal standard is useful. The concentrations of NAA and the ratios of NAA/H2O and NAA/Cho conduce to discriminating between the glioma and normal brain, and also between the low-grade glioma and high-grade glioma.