Functional magnetic resonance imaging in medicine and physiology.

Magnetic resonance imaging (MRI) is a well-established diagnostic tool that provides detailed information about macroscopic structure and anatomy. Recent advances in MRI allow the noninvasive spatial evaluation of various biophysical and biochemical processes in living systems. Specifically, the motion of water can be measured in processes such as vascular flow, capillary flow, diffusion, and exchange. In addition, the concentrations of various metabolites can be determined for the assessment of regional regulation of metabolism. Examples are given that demonstrate the use of functional MRI for clinical and research purposes. This development adds a new dimension to the application of magnetic resonance to medicine and physiology.

Nuclear magnetic resonance studies on intracellular sodium in human erythrocytes and frog muscle.

The nuclear magnetic resonance (NMR) spectrum of sodium was determined in muscle and erythrocytes using conventional continuous wave techniques. NMR spectra of fresh intact muscle revealed a single line with a width of about 38 Hz equivalent in intensity to about 53% of the total muscle sodium, in general agreement with previous work. Prolonged washing with sodium-free solutions led to a marked loss of both total and NMR-detectable sodium. The NMR-visible sodium remaining in the muscle was somewhat larger than the fraction calculated to remain extracellular and, presumably, was intracellular. The original sodium signal is thus interpreted as arising from both extracellular sodium and the narrow line portion of the signal from intracellular sodium. NMR spectra of sodium were also obtained for human erythrocytes under conditions preserving the sodium transport system. The intensity of the sodium signal in fresh cells was 98% of that present in the same samples after complete hemolysis of the cells. The NMR sodium present in intact cells was 92% of the sodium recovered by flame photometric determination of sodium from ashed samples. It is concluded that no NMR-"invisible" sodium occurs in human erythrocytes and that the presence of such sodium is not necessary for the normal functioning of the sodium transport system in erythrocytes.

Fourier transform spectroscopy.

The recent introduction of Fourier transform methods is revolutionizing IR and NMR spectroscopy. The application of IR interferometry or of NMR pulse methods, followed by Fourier transformation of the resultant interferogram, permits acquisition of spectral data in a time that is orders of magnitude less than by conventional spectroscopic methods. This reduction in time permits the study of transient species, or by "time-averaging" procedures S/N may be improved without the expenditure of inordinate amounts of time. The FT methods finds especially important application in the study of NMR spectra of nuclei of low sensitivity and low abundance, such as (13)C.