Shift of the observed frequency of the residual water signal

Dear GABA-community,

first of all I would like to thank the developer of GANNET. The toolkit is of very high quality and very straight forward to use. :slight_smile:

Analyzing my MEGAPRESS data with the GANNET toolbox I observe a shift in the observed frequency of the residual water signal with respect to the nominal water frequency (see attached PDF-files). Apart from this the data seems to be of good quality. It would be very helpful for me if someone could give me some advice on this.

meas_MID00158_FID37598_eja_svs_mpress_ACC_Met_1_vox1_fit.pdf (427.2 KB)
meas_MID00158_FID37598_eja_svs_mpress_ACC_Met_1_vox1_load.pdf (377.7 KB)

Here some details:

Scanner: Siemens Magentom Skyra 3T (VE 11C)
Sequence: CMRR MEGAPRESS, TR 3000 ms, TE 68 ms, 3x3x3cm3 voxel, VAPOR water suppression
Software: Ubuntu, GANNET 3.3.2, Matlab R2023a

I’m happy to provide more details.

Best regards,


Hi @margoett,

When you see something like this, it normally means that your acquisition used very strong water suppression (this is not unusual with VAPOR). But it’s nothing to worry about because the data quality is good, and the magnetic field frequency was stable (as you can see from the Cr frequency plot).


Hi Mark,

thank you very much for your advice. This makes me confident that we can now start our study.

All the best,