ASSESSMENT OF ABSOLUTE METABOLITE CONCENTRATIONS IN HUMAN TISSUE BY P-31 MRS IN-VIVO .2. MUSCLE, LIVER, KIDNEY

Absolute metabolite concentrations were assessed in the muscle, the li ver, and the kidney of healthy human volunteers by P-31 MRS. Fully rel axed in vivo spectra were acquired with a surface coil and were locali zed with an adiabatic ISIS pulse sequence. The spectra were quantified with a subsequent measurement of a calibration phantom and were proce ssed iteratively in the time domain. The following mean metabolite con centrations (mmol/liter) were measured in the resting male calf muscle (n = 9), in the fasting liver (n = 12), and in the orthotopic kidney (n = 5): [PME] = 2.0 +/- 0.6, 3.8 +/- 0.7, and 2.6 +/- 0.9, [Pi] = 2.9 +/- 0.3, 1.8 +/- 0.3, and 1.6 +/- 0.4, [PDE] = 3.8 +/- 0.8, 9.7 +/- 1 .5, and 4.9 +/- 1.1, [PCr] = 22.0 +/- 1.2, 0, and 0, [NTP] = 5.7 +/- 0 .4, 2.9 +/- 0.4, and 2.0 +/- 0.3, respectively. Several interesting fi ndings are to be emphasized: The concentrations of Pi, PCr, and NTP we re 20% lower in the muscle of women than of men. In addition, the pH, was significantly lower in female muscle (6.99 +/- 0.03) than in male muscle (7.05 +/- 0.03). The pH, in the liver (7.12 +/- 0.09) and in th e kidney (7.09 +/- 0.08) were higher than in the muscle of both gender s. The free magnesium concentration (mmol/liter) was higher in the liv er (1.40 +/- 0.64) than in the kidney (0.79 +/- 0.39) and in the muscl e (0.52 +/- 0.10).