Magnesium and pH imaging of the human brain at 3.0 Tesla

Multislice, two-dimensional phosphorus 31 spectroscopic imaging (SI) of human brain was performed in 15 normal volunteers on a 3-Tesla magnetic resonance system. Images of free magnesium concentrations and pH as well as phosphoesters, inorganic phosphate, phosphocreatine, and adenosine triphosphate (ATP), were calculated from the SI data. By using the equations of Golding and Golding (Magn. Reson. Med. 1995;33: 467-474), average [Mg²⁺] for all brain regions studied was 0.42 ± 0.05 mM, whereas average brain pH was found to be 7.07 ± 0.03, with no significant regional variations. Phosphorus metabolite concentrations (relative to ATP, assumed to be 3.0 mM/kg wet weight) were 5.39 ± 1.88, 1.30 ± 0.39, 5.97 ± 3.17, and 4.33 ± 1.45 mM/kg wet weight for phosphomonoesters, inorganic phosphate, phosphodiesters, and phosphocreatine (PCr), respectively. These values are in good general agreement with those reported previously. Typical signal-to- noise ratios of 15:1 were obtained for PCr in spectra from nominal 31.5 cc voxel sizes with a 34-min scan time. Limits on spatial resolution and the likely error of the magnesium and pH values are discussed.