Frame-by-frame PRESS 1H-MRS of the brain at 3 T: the effects of physiological motion

1H-MRS at high field has been increasingly utilized to study brain metabolism in healthy and pathological states. The aim of this work was to determine the effects of physiological motion on the results of this exam in the presence of the increased susceptibility differences at high field. Single voxel spectra of various regions in the human brain were acquired using frame-by-frame PRESS 1H-MRS at a 0.5 Hz sampling rate. The frame-by-frame variations of the FID phase and the frequency and fractional amplitude variations of the residual water-signal were analyzed. In the human brain the standard deviations of these variations were 3.9 +/- 0.5 degrees, 0.83 +/- 0.32 Hz, and 0.028 +/- 0.013 of the mean amplitude (n=15). In a motionless phantom, smaller phase and frequency variations were detected in water-suppressed acquisitions. However, the end effects of physiological motion on PRESS 1H-MRS of the brain at 3 T were negligible.