ASSESSMENT OF ABSOLUTE METABOLITE CONCENTRATIONS IN HUMAN TISSUE BY P-31 MRS IN-VIVO .1. CEREBRUM, CEREBELLUM, CEREBRAL GRAY AND WHITE-MATTER

Absolute metabolite concentrations were determined in four different brain regions using phosphorus magnetic resonance spectroscopy (P-31 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 ISIS 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 (mmol/liter) differed significantly between the cerebrum and the cerebellum (PME = 3.2 +/- 0.3 and 4.0 +/- 0.6, PCr = 2.9 +/- 0.3 and 3.9 +/- 0.4, NTP = 2.9 +/- 0.2 and 2.6 +/- 0.2, respectively) and between cortical gray matter and deep white matter (PME = 3.1 +/- 0.4 and 4.3 +/- 0.8, PDE = 10.1 +/- 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).