Assessment of absolute metabolite concentrations in human tissue by 31P MRS in vivo. Part II: Muscle, liver, kidney

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Abstract
Absolute metabolite concentrations were assessed in the muscle, the liver, and the kidney of healthy human volunteers by 31P MRS. Fully relaxed in vivo spectra were acquired with a surface coil and were localized with an adiabatic lSlS pulse sequence. The spectra were quantified with a subsequent measurement of a calibration phantom and were processed iteratively in the time domain. The following mean metabolite concentrations (mmollliter) were measured in the resting male calf muscle (n = 9), in the fasting liver (n = 12), and in the orthiotopic 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 findings are to be emphasized: The concentrations of Pi, PCr, and NTP were 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 the kidney (7.09 ± 0.08) were higher than in the muscle of both genders. The free magnesium concentration (mmollliter) was higher in the lliver (1.40 ± 0.64) than in the kidney (0.79 ± 0.39) and in the muscle (0.52 ± 0.10).