Problem with the gradient shimming
 

Problem with the gradient shimming

Dear Friends,

I've recently encountered a problem with gradient shimming that has never happened to me before. I can't clearly determine what caused it but it certainly didn't involve anybody manipulating with the probe. Here's the symptom: when running the gmapz experiment, the Z-profiles (before and after gradient) look like this:

http://img833.imageshack.us/img833/2213/zprofilef.png

As you can see the second profile (after the gradient) is distorted at the left edge (more or less severely, depending on a sample - here it's just a tiny "step"). I assume it has something to do with the transverse shims - but I'm not really sure which of them I am supposed to modify. Maybe some of you have experienced this kind of behaviour?

Here's a shimmap I've made using 10% D2O:

http://img26.imageshack.us/img26/4650/shimmap.png

I wonder if this distortion influences my gradient experiments (which use only axial gradient)? 2D spectra seem to be just fine but I'm afraid of the results from diffusion ordered experiments. I'll appreciate any help! Thank you in advance!

D. Kubicki



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