Biomedical applications of diffusion-weighted NMR techniques

MRI is a well-established tool in clinical diagnosis, but it lacks the specificity that would allow clear distinctions between many disease conditions. That is mainly because it is a spatial tool that lacks functional information. There are several other NMR techniques that could be used to provide functional information and thus improve the specificity of MR diagnostics. One of these is the use of diffusion-weighted (DW) MRI, which provides information about the diffusion of water in tissue. Preliminary animal and clinical results indicate that changes of the diffusion properties in tumors might provide early prediction of response or nonreponse to therapy. Another useful adjunct to MRI is the application of NMR spectroscopy (or MRS), which provides spectroscopic information mainly on the metabolic components of the tissue. However, notwithstanding many years of research, proton MRS has not so far proved a useful adjunct to MRI for the physician. This is mainly because of (a) the presence of the huge solvent water peak and (b) the mixture of both intra- and extracellular metabolic components in the tissue. A further extension of MRS would be the use of DWMRS, which is the application of the DW technique to the spectroscopic components of tissue other than water. Using DWMRS we are able to observe only the intracellular metabolic components and their changes due to drug treatment. In this article we will explore the potential of these DW methods as applied to (a) perfused cells, (b) brain tumors in mice, and (c) human brain tumors.