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MRI Forum
'Gradient Echo Sequence'
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Result: Searchterm 'Gradient Echo Sequence' found in 3 messages
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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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Nancy Dudek

Fri. 26 Aug.05,
00:25

[Start of:
'3T imaging parameters'
2 Replies]


 
  Category: 
Sequences and Imaging Parameters

 
3T imaging parameters
Hi
Am looking for the ranges of acceptable TR and TE's for standard spin echo and gradient echo sequences on a 3T.
Does anyone know these or tell me where I can find this info?
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Schmidt Marga

Sat. 17 Apr.04,
20:41

[Reply (1 of 2) to:
'Moire fringing'
started by: 'Kelly Wimpey'
on Tue. 6 Apr.04]


 
  Category: 
Artifacts

 
Moire fringing
Moire fringes are typical for gradient echo sequences, especially balanced sequences like for example true fisp, bFFE. The reasons are interferences and field inhomogeneities. High order shimming (volume shimming), a more suitable coil, a smaller bandwidth, and scanning not in the edges of the magnetic field will avoid or reduce this artifact. Also parallel imaging techniques can have a positive influence. If this artifact appears, also by using other sequences, a new field adjustment can be necessary (service).
Hope this will help.
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