Negative GABA values

I’m getting negative GABA values…
This was during a visual task in the visual cortex:


Has anyone else seen something like this?

I think this is likely an error with the water being positive


In commonest errors Examples — Gannet
It shows a similar example
And seems to suggest I can change the MRS_struct to include:
ONOFFfirst = ‘offfirst’ or ‘onfirst’
or
Waterpositive = ‘positive’ or ‘negative’

But changing MRS_struct.p.ON_OFF_first to ‘offfirst’ or ‘onfirst’ doesn’t seem to change anything

and I can’t find any ‘waterpositive’ field

Hi @weberam2,

In the latest version of Gannet, the phase of the data is determined automatically. The examples you linked to are for prior versions of Gannet.

In this case, the automatic phasing has failed. You will need to invert the spectra manually. The simplest way to do this is to add this line of code right after line 400 in GannetLoad.m:

MRS_struct.fids.data = -MRS_struct.fids.data;

Remember to comment this line out for all other datasets.

Mark

This worked! Thank YOU!