Fully automated shim mapping method for spectroscopic imaging of the mouse brain at 9.4 T.

For spectroscopic imaging studies of the mouse brain, it is critical to obtain optimal B(0) homogeneity over a large region of interest (ROI). In this paper, a fully automated shimming method for mouse brain at 9.4 T, based on B(0) mapping, is described. B(0) maps were obtained using a multislice gradient echo sequence with multiple phase evolution time delays with a novel unwrapping scheme. The unwrapping method allows phase maps with large bandwidths (+/-1 kHz) but with high resolution (0.3 Hz/ degrees ) to be acquired in a single acquisition, thereby minimizing the number of iterations required. The SD of the B(0) over the ROI (8 x 5 x 1 mm) was less than 10 Hz after shimming. Application of this method to the in vivo mouse brain allowed reproducible, high-quality spectroscopic data to be collected with 1-microl voxels.