MEGA-PRESS GE: Half of spectra loaded upside down?

MRS Software Osprey
1

Hi there,

I am trying to analyze some 3T GE MEGA-PRES data with Osprey

In the figures that Osprey produces, I noticed that it seems to be loading some of the spectra inverted? I hope this isn’t a very naive mistake of mine

Photo for clarity:

image
image1181×886 58.6 KB

This is the .json I used:

{
“seqType”: “MEGA”,
“editTarget”: [
“GABA”
],
“dataScenario”: “invivo”,
“MM3coModel”: “3to2MM”,
“FWHMMM3co”: “”,
“SpecReg”: “RobSpecReg”,
“SubSpecAlignment”: “L2Norm”,
“UnstableWater”: “0”,
“saveLCM”: “1”,
“savejMRUI”: “0”,
“saveVendor”: “0”,
“saveNII”: “0”,
“savePDF”: “0”,
“method”: “Osprey”,
“ECCmetab”: “1”,
“ECCmm”: “1”,
“includeMetabs”: [
“default”
],
“style”: “Separate”,
“lolim_range”: “0.5”,
“uplim_range”: “4.0”,
“lolim_rangew”: “2.0”,
“uplim_rangew”: “7.4”,
“bLineKnotSpace”: “0.4”,
“fitMM”: “1”,
“basisSet”: “BasisSets/3TGE_MEGAPRESS_68ms”,
“files”: [
“P22016.7”
],
“files_nii”: [
“anat/sub-Rett01_T1w.nii”
],
“file_stat”: [
“”
],
“outputFolder”: [
“osprey”
]
}

Is there a fix for this?

2

Hi,
the two peaks of choline and creatine look normal, therefore I would say that the spectra are not inverted. It looks more like you have strong spurious echos (e.g. lipids from outside the voi) and you see some effects of phase cycling.

Best, Heiner

1 Like
3

As Heiner says, these look like lipid signals to me that are hit by the editing pulses and phased differently across different phase cycling steps. Try and move the voxel a smidge further away from the scalp or change the slice-selective gradient orientations if that is possible on the GE system. What does the aligned/averaged edit-ON spectrum look like?