¹H NMR chemical shift selective (CHESS) imaging

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.