Siemens: Where is the non water-suppressed spectra?

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1

Hi,

For Siemens PRESS I’m trying to get the water reference spectra but don’t know where to find it. Is this stored in the same twix (.dat) or dicom file as the metabolite spectra?

In the exam card I don’t any option to save the reference.

also: Is a non water-suppressed spectra also acquired for csi, from the whole slab region? If so, is this used for referencing, or does the signal vary too much spatially?

Thank you,
Paul

2

It will depend on the sequence origin (product or research package) as well as the software version. Can you give more information on those? If you have a protocol PDF, we can look at that, too.

3

Hi,
We’re using VE11c. I dont have the protocol pdf at the moment, but I can get it next time I’m at the scanner. I was just using the default PRESS sequence: svs_se I think it’s called.

4

I am pretty certain that the Siemens product sequences do not, by default, acquire/store a water reference signal. I believe there is a setting “ref. scan mode” on the Sequence - Common card that needs to be activated, but again, that option may or may not be there depending on the software version.

5

I’m not aware of there being any sort of integrated water reference scan on VE11c or earlier svs_se implementations. I certainly don’t think its on by default. I’ll fire up the simulator tomorrow to check. Typically people acquire one or more water references as a separate acquisition by disabling the water suppression module, and setting the Tx offset to 0 ppm.

Will

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6

Hi Georg, William,

Thank you for your response, and looking into this. If it’s not part of the exam card options I’ll try with a seperate scan.

averages=1,
Tx:0 ppm,
water suppression: none.
Copy location/slice and adjustment volume of metabolite spectro scan.

Paul
(I guess I assumed there would be a non-suppressed spectro scan as part of the acquisition, because it must be finding the f0 somehow, but this could be a fid or for the whole shim volume I guess. I also thought the Siemens sequence would have this as a standard option to correct for eddy currents. )

7

I would set ‘water suppression’ to ‘RF off’. ‘RF off’ only deactivates the WS pulses, but keeps the WS gradients, so the scan can be used for eddy-current correction.

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8

Just a short update on this. We tried PRESS TE=30 with water suppression. But when we switched to “RF off” it forced the parameter change TE=30 ms to TE=40 ms.

Really strange, but maybe others have had this too.

9

Hi @Paul ,

That doesn’t make much sense. Was it only that change you made? Was any other parameter else right up against a limit?

11

hi, @Paul
I’m not sure if this is what you are looking for, but I got the following reply in the Magnetom forum.
The save all option for Ref. scan mode may give you the water reference.

https://www.magnetom.net/t/does-the-data-acquired-using-the-product-press-svs-se-sequence-comes-with-water-reference-scan/7374

Off – No reference scan

Inline correction – A reference scan is performed. The spectra are corrected (ECC) based on the reference scan. Only the corrected spectra are saved.

No inline correction – A reference scan is performed. The data of reference scan and the uncorrected spectra are saved.

Save all-- A reference scan is performed. The spectra are corrected based on the reference scan. The reference scan, the uncorrected spectra and the corrected spectra are saved.

12

The forced change of TE for Siemens PRESS is not that unusual (sadly), although I’ve usually seen it go from 30m to 33ms. It’s bizarre.