Beyond k-space: Spectral localization using higher order gradients

Chemical shift imaging (CST) often suffers from the inconvenient shape of i ts spatial response function (SRF), which affects both localization and sig nal-to-noise ratio. Replacing the magnetic held gradients for phase encodin g by higher order magnetic fields allows a better adjustment of the SRF to the structures in the sample. We combined this principle with the SLOOP (sp ectral localization with optimal pointspread function) technique to simulta neously obtain spectra from several arbitrarily shaped compartments within a sample. Linear combinations of the fields of the shim coils are used to g enerate the pulsed fields for phase encoding. Their shapes are matched to t he given sample geometry by numerical optimization. Using this method, spec tra from a phantom were obtained that show a higher signal-to-noise ratio a nd a strongly reduced contamination compared to an equivalent CSI experimen t. (C) 1999 Academic Press.