Friday, September 4, 2009

Chemical Shift (Localization) Artefacts (MRS)

If the frequency is shifted by -2.7 ppm from the system frequency of 4.7ppm, the result will be a highly accurate display of VOIs in the graphic slice positioning for the NAA signal at 2.0 ppm. Set an even higher frequency shift for outer volume suppression (OVS) of fat signals.

Note the following regarding the use of hybrid CSI sequences:
  1. Signals located outside the set selection frequency may be attenuated in the voxels near the edges of the VOI.
  2. Shift artefact does not affect completely excited inside voxels. The voxels are localized via phase encoding, which has no shift artifact.

Tags: Graphic slice positioning, outer volume suppression, OVS, chemical shift

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