Reduced spatial side lobes in chemical‐shift imaging

Density‐weighted k‐space sampling with spiral trajectories is used to reduce spatial side lobes 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 given apodization function, subject to constraints imposed by gradient performance and Nyquist sampling. The efficient k‐space coverage of spiral‐based trajectories enables good control over the sampling density within practical in vivo scan times. The density‐weighted acquisition is compared to a conventional, nonweighted spiral sampling without the application of a window 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 greatly reduced with the variable‐density sampling. This method is demonstrated on a normal volunteer by imaging of brain metabolites at 1.5 T with both single slice CSI and volumetric CSI. Magn Reson Med 42:314–323, 1999. © 1999 Wiley‐Liss, Inc.