Assessment of absolute metabolite concentrations in human tissue by 31 P MRS in vivo . Part I: Cerebrum, cerebellum, cerebral gray and white matter

Absolute metabolite concentrations were determined in four different brain regions using phosphorus magnetic resonance spectroscopy ( 31 P MRS) on 10 healthy adult volunteers. Localized spectra were collected simultaneously from the cerebellum and the cerebrum and, later, from deep white matter and cortical gray matter by means of a two‐volume lSlS pulse sequence and a Helmholtz‐type RF‐coil. Each brain spectrum was quantified with a calibration spectrum from a head‐shaped simulation phantom. A time‐domain fitting routine was used to process the fully relaxed data. Several metabolite concentrations (mmolAiter) differed significantly between the cerebrum and the cerebellum (PME = 3.2 f 0.3 and 4.0 & 0.6, PC:r = 2.9 & 0.3 and 3.9 f 0.4, NTP = 2.9 f 0.2 and 2.6 & 0.2, respectively) and between cortical gray matter and deep white matter (PME = 3.1 f 0.4 and 4.3 ± 0.8, PDE = 10.1 f 2.5 and 14.2 & 2.6, respectively). The concentration of free magnesium ion was found to be similar in all four brain regions (0.53 ± 0.21 mmol/liter) but the intracellular pH was significantly higher in the cerebellum (7.04 ± 0.03) than in the cerebrum (6.99 ± 0.02).