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Eliminate Dispersion

Eliminate Dispersion


ED – Eliminate Dispersion

A routine to reduce residual dispersion lines at the center of a water suppressed spectrum was added at the request of Jerry Dallas and Marc Alder at Berlex per the reference:

Adler M., and Wagner, G. "A New Technique for the Removal of Baseline Distortions Caused 
by Strong Water Signals.
" (1991) J. Magn. Reson. 91, 450.

Often, 2D spectra acquired in H2O using water suppression have a large dispersion component to the residual water peak.  The dispersion line has large "wings" that extend on each side of the peak, and this can create substantial baseline distortions.  This cannot be removed by digital filtering.  By subtracting out the dispersion component, these broad wings are eliminated, giving a much flatter baseline and contour plots with less pronounced "zipper" appearance.

Compare the 2 pairs of plots below (single slice and stacked plots).  The first plot shows the broad wings caused by the dispersion component of the residual water peak.  The second one shows the much flatter baseline obtained after removing the dispersion component.  In the stacked plot, notice also the modulation in the amplitude of the peak at 4.3 ppm caused by the variation in phase of the dispersion component of the water peak, which is eliminated when the dispersion component is removed.


To use this command, zoom in on the residual water peak.  That expanded region will be used to fit a dispersion line:

I(w) = a*(wo-w) / { (1/T2)2 + (wo-w)2 }

using three parameters: 

wo – frequency of the center of the water peak.  The peak must be close to zero frequency (center of the spectrum), as this parameter is adjusted over only a small range.

T2 of the water peak

a – amplitude

This fitted calculated dispersion line is subtracted from the entire spectrum (all real data points).

The fit can be made faster by using default values of T2 and/or wo

When ED is executed in the 2-lettered command mode, or in the non-2-lettered command mode with no arguments specified, NUTS uses the displayed zoom region to do a 1 parameter fit to amplitude using a fixed T2 = 10.0 and wo = 0.0

The command will take arguments when operating in the non-2-lettered command mode. Examples are:

ED 1         // same as default mode above
ED 1 20         // 1 parameter fit to amplitude using T2 = 20.0 and wo= zero. 
ED 2         // 2 parameter fit to amplitude and T2 with wo= zero. 
ED 3         // 3 parameter fit to amplitude, T2 and wo.

This can be used in Arrayed Mode to perform the fit on each slice with the single command.


Last updated: 8/30/01