Reduced spatial side lobes in chemical-shift imaging

Density-weighted k-space sampling with spiral trajectories is used to reduc e spatial side robes in chemical-shift imaging (CSI). In this method, more time is spent collecting data at the center of k space and less time at the edges of k space in order to make the sampling density proportional to a g iven apodization function, subject to constraints imposed by gradient perfo rmance and Nyquist sampling. The efficient k-space coverage of spiral-based trajectories enables good control over the sampling density within practic al in vivo scan times. The density-weighted acquisition is compared to a co nventional, non-weighted spiral sampling without the application of a windo w function. For a fixed voxel size and imaging time, the noise variance is observed to be the same for both cases, while spatial side lobes are greatl y reduced with the variable-density sampling. This method is demonstrated o n a normal volunteer by imaging of brain metabolites at 1.5 T with both sin gle slice CSI and volumetric CSI. Magn Reson Med 42:314-323, 1999. (C) 1999 Wiley-Liss, Inc.