NON-T-1-WEIGHTED P-31 CHEMICAL-SHIFT IMAGING OF THE HUMAN LIVER

A P-31 chemical shift imaging (CSI) protocol was developed for human l iver studies. It is shown that at the commonly used repetition time (T R) of 1 s T-1-weighting reduces the integrated intensities of liver ph osphate metabolite signals by 18 +/- 15% (inorganic phosphate, P-i) to 46 +/- 10% (phosphodiester, PDE), that is for an RF pulse angle of 60 0 (weighted average) in liver. The loss in signal-to-noise ratio (S/N) at TR = 20 s, sufficient to eliminate spectral distortions caused by saturation, compared with TR = 1 s (47-65%) can be overcome by using o ne-dimensional (1D)-phase encoding with a small number of phase-encode steps. The liver spectra obtained by 1D-CSI with 4-step phase-encodin g (spatial resolution 10 cm) have the highest S/N and, after multiplic ation of the PDE signal by a factor of 1.4, closely reflect the liver metabolite levels. It is concluded that clinical P-31 MR studies of li ver function can be performed without T-1-weighting and that the curre nt practice to compromise the MRS quantification of lever metabolites with uncertainties caused by (differential changes in) T-1-weighting i s not warranted.