[Intl_DxMedPhys] Recent Tx Gain Variation on Siemens Sola 1.5T MRI

[Steven Shea]

Hi list friends,

I am reaching out regarding recent findings in the ACR Weekly QA on a
Siemens Magnetom Sola 1.5T MRI system at our institution. The recorded Tx
Gain (found as reference amplitude on the Siemens system) started varying
by +/- 30 V since ~July. Previously, it had been rather stable within a
~+/- 5 range (may be a little higher). The graph below demonstrates:
[image: image.png]
I did annual testing in late August and did not identify any other issues
with standard ACR phantom tests, homogeneity tests, or the head coil tests.
I look for any service events that would explain this but could not find
any. I decided not to flag it in my report and I waited a month or more to
see if the variation would continue, which it has. I then went through the
DICOM headers to see if any protocol parameters were changing. They were
not; coil elements selected were also quite consistent (a potential issue
on Siemens systems). I even managed to fish out the Reference Amplitude
values from the Private Tag [0021, 1019]. They confirmed the same
measurements that the technologist had been recording. I could even see
that the reported Reference Amplitude was quite consistent between
different sequences, which means that even if the tech recorded from
different series, it would not have caused above:
[image: image.png]

I should also state that the phantom setup procedure is quite repeatable
due to the Siemens provided holder and one technologist is running the 90%
of the QA. This is a long way of saying I have come to the conclusion that
this is real. (And, yes, I likely over-analyzed the issue.)

My main issue is concern on how I deal with Siemens service on this. If I
send them above, I expect they will come out and run standard tests and
tell me the system is fine. Have any of you ever run into this and know of
causes? Or specific things to test/target? Anything else I or the tech
could do? I would appreciate any insights.

Thanks, Steve

Steven Shea, PhD
Associate Professor, MR Scientist
Department of Radiology & Medical Imaging. Loyola Medicine

PS: I should mention that the system has a known, slow helium leak which is
captured on the center frequency measurements. However, that predates this
issue and has been present for more than +1 year. (It is scheduled to
finally be addressed in the next month -- needless to say that has me at
odds with local service.) I do not feel as though this is the source.
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