Overview

This tab allows you to perform removal of a residual water peak. A residual water peak is often still present even if a water suppression sequence is used during acquisition. The spectral components comprising the residual water peak is present throughout the time domain signal, affecting fitting in the time-domain. Thus, it is necessary to remove the residual water signal prior to metabolite fitting.

Load the .dat File

To perform water removal, first load in the spectroscopy data from which you want to remove a residual water peak.

Hit the Browse button, navigate to the *.dat file you wish to process, and select the file. Hit the Confirm button to load the data into the application. Upon hitting Confirm, you will see the data plotted in the right panel. The x-axis of is in units of ppm, centered on the frequency of water (i.e. water = 0 ppm).

Selecting HSVD Parameters

The next step is to specify the Hankel singular value decomposition (HSVD) parameters. APPS uses HSVD to model the residual water signal. The residual water signal is then removed by subtracting this model from the spectroscopy data.

The parameters of the HSVD are as follows:

• Number of Points: The number of initial points along the FID to use in forming the Hankel Matrix
• Hankel Matrix Row/Col Ratio: The ratio of the number of rows to the number of columns of the Hankel Matrix
• Signal Related Singular Values: The number of Lorentzian peaks in the model
• Xmin, Xmax: the range of frequencies to model. For water removal, ensure this range is set narrowly, so as to only include the residual water peak, and not any of the metabolite peaks.

Running the Water Removal

Hit the Run Water Removal button to perform the processing. After hitting this button, several pieces of information will be displayed on the application.

First, the HSVD model is plotted along with the data and the residual. The water removed spectrum is also plotted. With these visualizations, you can qualitatively assess how well you picked your HSVD parameters, and how much of the residual water signal was successfully removed. If you are unhappy with the result, you can change the HSVD parameters, hit Run Water Removal again, and see the new results.

Second, the results of the HSVD are displayed in the lower panel. This gives you information about the HSVD parameters used and lists out all the signal related singular values. For each signal related singular value, the frequency, the amplitude, the damping factor, and the phase values are listed.

Saving the Results

Please note that these results are not saved to file until you hit the Save Water Removal Result button. Once you hit the button, a .dat file with the _wr suffix containing the water removed signal is saved in the same location as the spectroscopy data file you had loaded in.