Extract PRESS reference data

Data Processing
1

Hi all,

I’m currently analyzing a dataset where two subjects lack PRESS reference (water) data—they only have PRESS active (metabolite) data. I’m wondering if there’s a way to derive or estimate PRESS water reference data for these subjects so that I can analyze them consistently with the rest of the dataset.

Upon reviewing their spectrum in OspreyLoad, I noticed that water suppression was applied, leaving minimal residual water signal. Because of this, I don’t think it’s feasible to extract the water signal directly or estimate it from the residual. I’ve heard suggestions like estimating water concentration based on tissue composition, but I would like to hear your advice for that. Are there alternative methods or best practices for handling such cases?

Thanks!

2

Hi Mingrun,

Unfortunately, there isn’t. You need a separate water-unsuppressed spectrum. This signal is weighted by water relaxation, and tissue composition (GM/WM/CSF) can be used to correct for different relaxation times and water contents within each tissue class, but if you don’t have that signal to begin with, you’re missing the very thing that tissue composition corrects.

You also cannot infer anything from residual water signals - the degree of water suppression is highly variable.

Sorry,
Georg

3

Hi Georg,

Thanks! Good to know.

Best,
Mingrun