A SINGLE-SCAN IMAGING TECHNIQUE FOR MEASUREMENT OF THE RELATIVE CONCENTRATIONS OF FAT AND WATER PROTONS AND THEIR TRANSVERSE RELAXATION-TIMES

A two-component chemical-shift-imaging technique is described from whi ch fat and water images can be obtained in a single scan and in the pr esence of an inhomogeneous field. In addition, the method provides tra nsverse relaxation rates R(2) and R(2)' separately for each of the spe ctral components. The method is a combination and extension of the GES FIDE [gradient echo sampling of FID and echo, J. Ma and F. W. Wehrli, J. Magn. Reson. B 111, 61 (1996)] and the multipoint Dixon techniques. It is based on sampling the descending and ascending portions of a Ha hn spin echo with a train of gradient echoes which are spaced at one-h alf of the chemical-shift modulation period. Processing of the complex echo data, involving an automated phase unwrapping algorithm, affords relative amplitudes and transverse relaxation rates of the two spectr al components. An additional benefit of the method is its superior sig nal-to-noise ratio resulting from echo summation. Applications targete d and illustrated involve MRI osteodensitometry of trabecular bone in the presence of varying fractions of hematopoietic and fatty bone marr ow. (C) 1997 Academic Press.