Vol. 9, No. 3 71 NMR J IMAGING

NMR imaging was proven in recent years to be a useful noninvasive technique (1). It yives the 3-dimensional structure of tissues in vivo; and exploits the differences in concentration of substances (usually water) and their relaxation times as a means to discriminate between tissues. Methods of chemical shift-imaging were developed recently (2-6) which utilize the differences in substance content (NMR spectra) of different tissues to discriminate between them. However, the magnetic fields produced by normal whole body magnets are generally weak and crude, necessitating costly high field whole body magnets. Even with such fields the spectral resolution is too poor to obtain most of the high resolution information. NMR J imaging (7) offers a new probe for tissue discrimination with low resolution and low field magnets, without the limitations mentioned above. The pulse sequence is shown in Fig. 1.