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The method of constrained reconstruction, previously applied to magnetic resonance imaging (MRI), is extended to magnetic resonance spectroscopy. This method assumes a model for the MR signal. The model parameters are estimated directly from the phase encoded data. This process obviates the need for the fast Fourier transform (FFT) (which often exhibits limited resolution and ringing artifact). The technique is tested on simulated data, phantom data, and data acquired from human liver in vivo. In each case, constrained reconstruction offers spatial resolution superior to that obtained with the FFT.

31P nuclear magnetic resonance spectroscopy was used to study the skeletal muscle of 33 normal males and 32 females. Free intracellular magnesium levels and the ratios of the phosphorus metabolites were determined. Males had significantly lower free magnesium levels (499.8 microM +/- 26.3 microM vs. 530.7 microM +/- 36.0 microM, P = 0.001, d.f. = 63, analysis of variance). The free magnesium level (rs = -0.5431, P = 0.001) and the phosphocreatin/Inorganic phosphate ratio in males (rs = -0.4102, P = 0.018), and the phosphocreatine/Inorganic phosphate ratio in females (rn = -0.4759, P = 0.009) fell with the increasing Minnesota Heart Health Program Questionnaire score.

In vivo and in vitro 31P-NMR spectroscopy was used to study the high energy phosphate metabolism of VX-2 tumors implanted into rabbit liver, kidney, and hind-limb muscle. Tumors, at various stages of growth, were first examined by in vivo 31P-NMR spectroscopy, then they were excised and underwent histologic examination and biochemical analysis; both in vitro 31P-NMR and standard enzymatic techniques were used. There was good correlation among the in vivo NMR spectra, the in vitro NMR data, and the biochemical analyses. Although the tumor spectra showed characteristics similar to those reported in the other tumor models, there was a striking variability in the spectra obtained from tumors implanted in the same site and from different sites. There was poor correlation between the degree of necrosis in the tumor and the tumor pH and between the Pi:ATP ratio and necrosis. This variability has important implications for the potential value of using 31P-NMR spectroscopy to monitor tumor growth and therapy in vivo.