VOLUMETRIC SPECTROSCOPIC IMAGING WITH SPIRAL-BASED K-SPACE TRAJECTORIES

Spiral-based k-space trajectories were applied in a spectroscopic imag ing sequence with time-varying readout gradients to collect volumetric chemical shift information, In addition to spectroscopic imaging of l ow signal-to-noise ratio (SNR) brain metabolites, the spiral trajector ies were used to rapidly collect reference signals from the high SNR w ater signal to automatically phase the spectra and to aid the reconstr uction of metabolite maps. Spectral-spatial pulses were used for excit ation and water suppression. The pulses were designed to achieve stabl e phase profiles in the presence of up to 20% variation in the radiofr equency field. A gridding algorithm was used to resample the data onto a rectilinear grid before fast Fourier transforms. This method was de monstrated by in vivo imaging of brain metabolites at 1.5 T with 10 sl ices of 18 x 18 pixels each. Nominal voxel size was 1.1 cc, spectral b andwidth was 400 Hz, scan time was 18 min for the metabolite scan and 3 min for the reference scan.