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| Result: Searchterm 'Distortion'
found in 4 messages |
| Result Pages: [1] |
More Results:  Database (12) |
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proton spin
Fri. 26 Mar.10,
09:00
[Start of:
'Distortion in large FOV'
1 Reply]
 Category:
Artifacts
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| Distortion in large FOV |
I'm interested in evaluating the distortion of MRI in large fields of view (25 x 25 x 25 cm), in a context of radiotherapy. Unfortunately phantoms available on the market only allow the study of reduced field of view because of their size. Do you know if there are phantoms of sufficient size ? Which type of solution do you recommend for the filling ?
Thank you for your advice.
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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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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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Dan McGuan
Thu. 6 Oct.05,
20:35
[Reply (1 of 2) to:
'Machine Opening artifact'
started by: 'Neil Brice'
on Tue. 28 Sep.04]
Category:
Artifacts
|
| Machine Opening artifact |
Neil,
I think you're talking about the edges of the shimmed volume of the magnet, or the coil.
Magnets are shimmed to a specific volume in the field (every model magnet is different). When you attempt to scan an object that reaches the edge of this volume you will see distortion from imaging the unshimmed area of the magnet.
Also shimming large objects that exceed the range of the receiver portion of the coil will cause distortions.
Hopefully this answers your question?
Good Luck,
Dan McGuan
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