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| Result: Searchterm 'sequence'
found in 106 messages |
| Result Pages: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 [18] 19 20 21 22 |
More Results:  Database (378) News Service (28) Resources (10) |
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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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peter hobden
Wed. 14 Feb.07,
15:27
[Reply (1 of 2) to:
'MRI Marker'
started by: 'Tian Ming'
on Mon. 22 Jan.07]
Category:
Applications and Examinations
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| MRI Marker |
There is a company which make MRI skin markers but they are poor for fat-sat sequences.
I have emptied oil capsules of fish oil and instead added my own ingredients into them, according to the specific sequence I use.
Try:
*Pure Water
*V V Dilute MRI contrasts
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Tian Ming
Mon. 22 Jan.07,
10:23
[Start of:
'MRI Marker'
1 Reply]
Category:
Applications and Examinations
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| MRI Marker |
Are there any MRI markers that are visible on all sequences, small, flat, cheap and self-adhesive?
Vitamin E or fish oil capsules work mostly well, but the signal is suppressed on sequences with fat saturation.
To mark a small region they are too big and
dent the skin where fixed.
Thankful for every suggestion and friendly greetings to all.
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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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Renate Bloemer
Mon. 13 Nov.06,
19:46
[Reply (1 of 3) to:
'MRA'
started by: 'Marco Costa'
on Sun. 22 Oct.06]
Category:
Protocols
|
| MRA |
A test bolus helps to get the delay at which time the CE-MRA sequence has to be started. The sequence needed is a one-slice dynamic fast gradient echo sequence (if possible with fat suppression or subtraction) and a temporal resolution of 0.5 to 1.5 sec. This thick slice is placed over the vessel of interest and the dynamic is started simultaneous with a small (1-2ml) bolus of Gad.
In the follow up you can see at which time the bolus is visible. If it is not clear to differentiate, a ROI measurement will help. The starting time depends on the k-space filling. Around the peak of the highest intensity, the contrast information should be read out (with "centric" at the beginning of the sequence).
Centric k-space filling order means that the central lines of the k-space are filled in the first seconds after starting the scan. Depending on the equipment, there is more than one non-centric order, for example linear, where the central lines are filled in the middle of the scan time.
Hope this helps.
Renate Bloemer
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