Friday, September 4, 2009

Lipid Contamination (MRS)

Top left: T1W image with spectral FOV (white grid), a PRESS-selected region (blue box) and a region with lipid-contaminated voxels (purple box).  Top right: Same image with the extendd spectral FOV through the unaliasing algorithm (white grid) and the correctly located lipid region (red box).  Also shown are spectra of the purple box before (a) and after (b) lipid unaliasing, and the lipid spectra unaliased into the red box that is an FOV away (c).

Application of B1- and T1-insensitive VSS sequence to 3D MRSI of the brain in volunteers. a: MR image showing the positions of the PRESS box (white box) and VSS band (black line). b: The inclusion of subcutaneous lipids at the left side of the PRESS box caused spectral distortions throughout the entire spectral array (white grid). c: The VSS band was placed to reduce the lipid contamination. The black line indicated the edge of the VSS band. All voxels within the left two columns showed virtually complete suppression of lipid signals.

Spatial response function (SRF) or point spread function (PSF) in chemical shift imaging (CSI).  The PSF, which depends on the sampling and post processing scheme, shows how much signal is contributed to a pixel in CSI from outside this pixel.  The diagram above illustrates how the low-resolution (24 x 24) SI data exacerbates the problem of signal bleeding.  Substantial signals are observed way outside of the selected voxel.

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