Abstract
1H NMR images of human or animal tissues reflect the spatial distribution of both water (H2O) and methylene (CH2) proton resonance signals. There are several reasons for a separation of these contributions: (i) the large chemical shift dispersion in high magnetic fields (>or=1.5 T) which leads to an apparent spatial shift in 'composite' images between the superimposed H2O and CH2 images; (ii) the evaluation and interpretation of proton H2O and CH2 relaxation times from NMR images; and (iii) the physiological implications of 'water' and 'fat' distributions for medical diagnosis. The authors describe a chemical shift selective (CHESS) imaging technique which destroys the unwanted signal component by means of a selective 90 degrees excitation pulse and a subsequent magnetic field gradient ('homogeneity spoiling gradient') prior to imaging of the wanted component. The new method allows the creation of either a pure 'water' or 'fat' image.