Magnesium and pH imaging of the human brain at 3.0 Tesla

Multislice, two-dimensional phosphorus 31 spectroscopic imaging (SI) of hum an brain was performed in 15 normal volunteers on a 3-Tesla magnetic resona nce system. Images of free magnesium concentrations and pH as well as phosp hoesters, 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 br ain regions studied was 0.42 +/- 0.05 mM, whereas average brain pH was foun d 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 wei ght) 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 wit h a 34-min scan time. Limits on spatial resolution and the likely error of the magnesium and pH values are discussed. (C) 1999 Wiley-Liss, Inc.