Biomedical implications of the relaxation behaviour of water related to NMR imaging

Over the past few years the applications of Nuclear Magnetic Resonance (NMR) techniques have developed along several lines as illustrated in Fig. 1. Imaging reveals tissue contrast in the whole body, isolated organs and small objects, and localises the abnormal behaviour of many soft tissues in the heterogeneous biological space. Tissue discrimination by high-resolution NMR spectroscopy helps to identify the underlying processes responsible for such abnormalities by correlating NMR relaxation times with various biological phenomena under known and well-defined conditions. The application of topical NMR provides a powerful means of obtaining metabolic details and biological information. Finally, the measurements of blood flow by NMR allow an analysis of the velocity distribution function and irregularities of blood flow in specific regions. Efforts are being made to combine proton density images of solid tissues with blood flow measurements to differentiate simultaneously the static and moving spins of water. In recent years extensive clinical trials of imaging and the rapid progress in instrumentation have revealed a great potential for the medical applications of NMR; at the same time they have unfolded a number of deep-rooted problems concerning the interpretation of results. In order to obtain the maximum coherent information available from imaging data and to understand their real significance, considerable interest has developed in complementing the results of in-vivo imaging with in-vitro tissue discrimination.