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| Result: Searchterm 'homogeneity'
found in 5 messages |
| Result Pages: [1] |
More Results:  Database (48) News Service (1) |
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Steven Ford
Thu. 3 Mar.11,
20:28
[Reply (1 of 8) to:
'6-1.5T MAGNETS, DIFFERING GRADIENTS'
started by: 'Elise Gough'
on Wed. 23 Feb.11]
 Category:
Applications and Examinations
|
| 6-1.5T MAGNETS, DIFFERING GRADIENTS |
I assume that you mean a t2 fat suppressed sequence. Differing gradient strengths have only an indirect effect on these images. The fat saturation sequences require additional pulses which take time to execute; stronger gradient systems can execute these pulses faster.
If you see different results, it can be caused by a number of factors; if you can describe the differences, that would be helpful. Generally speaking, the quality of the magnet homogeneity makes a big difference. If the small FOV scans (wrist) look different from magnet to magnet, that's probably not the cause.
You should ask your MRI applications specialist about this, and pay attention to the TE and bandwidth. Are the FOV and number of steps the same?
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Donna Nusser
Tue. 18 Aug.09,
19:17
[Start of:
'MRI registry equations'
20 Replies]
Category:
Basics and Physics
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| MRI registry equations |
I'm studying for the registry with the help of the MIC registry review program. I think my mind has turned to mush. I can not figure out the answer to this question or find an equation to help me. Is there anyone out there who can help?!!
"In an ideal 1.0T magnet with perfect homogeneity, if a proton experiences a magnetic field of 1.006T and is positioned 0.5 meter along the positive z-direction and centered along the x and y directions, the z-gradient amplitude is________mT/m."
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peter hobden
Wed. 14 Feb.07,
15:35
[Reply (1 of 3) to:
'Geometric distortion'
started by: 'ergun ahunbay'
on Tue. 2 Jan.07]
Category:
Artifacts
|
| Geometric distortion |
Dear Listers,
I have some questions about the image distortions in MRI:
1) Are the magnetic field inhomogeneities the only cause of image distortions? Does RF-inhomogeneities cause distortions or just signal inaccuracies?
There are other factors that can affect the /amount/ of distortion. Run an EPI sequence and change the bandwidth and see the image change shape.
There are other causes of image distortion which are not necessarily directly related to field homogeneity.
It is a complicated question you are asking here!
2) Is it accurate to say that a spiral sequence would not have distortion due to magnetic field inhomogeneity(, but it would have blurring). Would there be image geometric distortions with a spiral imaging?
I guess you are talking about spiral filling of k-space?? The sampling time reduction will help to reduce distortion to some extent.
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ergun ahunbay
Tue. 2 Jan.07,
19:20
[Start of:
'Geometric distortion'
2 Replies]
Category:
Artifacts
|
| Geometric distortion |
Dear Listers,
I have some questions about the image distortions in MRI:
1) Are the magnetic field inhomogeneities the only cause of image distortions? Does RF-inhomogeneities cause distortions or just signal inaccuracies?
2) Is it accurate to say that a spiral sequence would not have distortion due to magnetic field inhomogeneity(, but it would have blurring). Would there be image geometric distortions with a spiral imaging?
thank you very much in advance
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William Flemming
Tue. 29 Mar.05,
02:49
[Reply (1 of 2) to:
'MR image of an eye'
started by: 'Reader Mail '
on Tue. 14 Dec.04]
Category:
Applications and Examinations
|
| MR image of an eye |
Depending on the sequence and the field strength there can be artifacts that look like eye movement and are difficult to separate. To avoid eye movement should the patient not only close the eyes or fix a point, but also with closed eyes think about not to move the eyes.
Other artifacts (e.g. ghosting) can be reduced with fat suppression, reduction of the water fat shift, T1 with a long TE (to reduce the brightness of fat), and/or a higher matrix.
Also the perfect positioning of the coil and a homogeneity correction will improve the image quality. I do not know a post processing program that removes those artifacts.
Regards
Bill
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