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| Result: Searchterm 'SNR'
found in 11 messages |
| Result Pages: [1] 2 3 |
More Results:  Database (46) News Service (3) |
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Michael Cunningham
Fri. 20 Jan.17,
21:18
[Start of:
'Why reset relative SNR value on GE Optima?'
0 Reply]
 Category:
Sequences and Imaging Parameters
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| Why reset relative SNR value on GE Optima? |
Hello, if anyone works on a GE Optima, or any other MRI that has a relative SNR reset button during scan, please explain to me the purpose of this button. I see that it brings the relative SNR back up to 100 percent, but it can't actually be improving the image quality, can it? I just don't understand what the button is actually doing. The manual states that pressing the button brings the value to 100. Clearly. But what is actually happening other than making me feel better about my scan. Thanks.
mjcunningham RT (R) (MR)
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Paul Tesla
Fri. 9 Nov.07,
15:31
[Start of:
'How do you measure SNR?'
0 Reply]
Category:
Basics and Physics
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| How do you measure SNR? |
I know this is a basic question but how do you measure SNR?
This page:
http://dnl.ucsf.edu/users/dweber/dweber_docs/mri_quality.html
tells me to measure an as small as possible ROI for the signal mean and as large as possible ROI for the standard deviation.
But I have a book called "MRI from picture to proton": This says that the standard deviation of the noise (Sn) can be measured using the mean or standard deviation (sd) of a background region. Then you can use the relationship:
Mean = 1.25 Sn
sd = 0.66 Sn
to find Sn. But where do the values 1.25 and 0.66 come from?
It also says that the measured mean of the signal ROI is related to the MR signal instensity (S) using:
Mean = sqrt(S^2 + Sn^2)
But why do they add up quadratically?
Thankyou for your help. Please leave a message or email me,
Paul
-------------
mri.tesla@gmail.com
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Kimberly Wilridge
Wed. 27 Sep.23,
19:37
[Reply (1 of 2) to:
'GE Signa - 17,18,19 Phantoms Found looking for 1'
started by: 'Kimberly Wilridge'
on Fri. 26 Jul.13]
Category:
Coils
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| GE Signa - 17,18,19 Phantoms Found looking for 1 |
I submitted this question years ago. Answer to this question and anyone else with an issue in SNR testing is: it was the phantom. GE coils as with all coils have SET phantoms that should be used due to the system programming. It looks for the gaps/spaces between the phantom balls, blocks, etc. At that time of question above the FE doing the testing was using USAI phantoms (which are large blocks) and GE CTL phantoms are small/mid size balls contained in an acrylic piece. After complete rebuild of 25 CTL's figured I got bench testing these things down to a science, with T1/T2 values higher than OEM. I can thank that FE, because it made me improve my reverse engineering skills, which I've applied to so much since then.
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Renate Semrau
Mon. 28 Aug.23,
07:23
[Reply (1 of 2) to:
'Improving MEDIC/MERGE/M-ffe and GRE/FFE image quality'
started by: 'Dan Lopez'
on Sun. 27 Aug.23]
Category:
Sequences and Imaging Parameters
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| Improving MEDIC/MERGE/M-ffe and GRE/FFE image quality |
Hi,
Sequences with multiple echoes are unfortunately sensitive to motion and flow artifacts, with the mFFE the echoes are still cumulated afterwards. The use of the head-neck coil provides better SNR. Important are good flow compensation, rest slab, try out foldover direction l/r vs. a/p. Shimming may help, synergy is sometimes better as clear, don't take too many slices, but maybe the signal loss is also a technical problem. Problems in the lung region are common. In short, we use 2D T2 TSE with continuous flow comp.
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Reader Mail
Fri. 26 Jul.13,
16:51
[Reply (1 of 2) to:
'STIR and l-spine'
started by: 'shruti soni'
on Wed. 27 Feb.13]
Category:
Sequences and Imaging Parameters
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| STIR and l-spine |
I know from working on various coils and testing the images will vary with synthetic (phantoms) vs actual patient. Main item in coil repair is it scans correct w/a human. And if when you test the coil per Philips given guidelines and set parameters for testing SNR, etc. the coil may be just fine. 2nd the synthetic phantom your using is not compatible with that coil or in the system - found this out with 1.5T phantoms don't work on 0.2T coils.
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