In vivo tissue analysis by NMR spectroscopy.

Abstract

Nuclear magnetic resonance (NMR) spectroscopy can be applied to study metabolism and physiology in living tissues and organisms. It is based upon the ability to identify a number of important metabolites in the NMR spectra. Limiting factors are sensitivity and resolution. Concentrations of small metabolites are 4 orders of magnitude lower than those of tissue water and lipids. The consequent reduction in signal intensity leads to the need of signal averaging, the use of surface coils, and large volumes of interest. High magnetic fields are necessary, both to improve spectral resolution and sensitivity. 31P NMR allows one to measure various phosphate metabolites, such as ATP, phosphocreatine (PCr), and inorganic phosphate (Pi). From the chemical shift of the P1 resonance it is possible to determine the intracellular pH value. 31P NMR is therefore particularly suited to follow energy metabolism. 1H NMR spectroscopy can also be used to measure small metabolites. To do this it is necessary to implement techniques for suppression of the intense water and lipid signals. It has been possible to measure various metabolites, such as lactate, N-acetylaspartate, and amino acids in the brains of laboratory animals. 13C NMR spectroscopy can be used to measure and characterize high-concentration components such as lipids and glycogen. The introduction of 13C-labeled substrates allows one to follow metabolism by the 13C NMR method.