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MRI Forum
'Echo Time'
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Renate Semrau

Mon. 7 Mar.11,
09:11

[Reply (3 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
Slew rate, rise time and/or duty cycle are specific parameters to describe the performance of the gradient amplifier. Amplifiers with higher performance allow a faster slew rate (shorter rise time). Stronger gradients allow to reduce echo time, increase the bandwidth and/or use a smaller FOV by influencing the SNR. To use same parameters on magnets with different gradient performance may not be recommended, or you have to adjust all parameters to the level of your magnet with the poorest performance.
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Mel Chang

Thu. 21 Oct.10,
14:26

[Reply (1 of 2) to:
'cervicla axial image t2 and t2*'
started by: 'kim jk'
on Thu. 23 Sep.10]


 
  Category: 
Applications and Examinations

 
cervicla axial image t2 and t2*
T2* is fine to scan the intervertebral discs. T2 is the better choice to show small spinal cord lesions like MS plaques. The echo time of a T2* sequence may be not long enough to give a good differentiation between the pathology and surrounding tissue.rnDifferent 'Multi Echo Data Image Combination' (MEDIC) techniques have been developed to enhance contrast and pathology detection, if available on the scanner this type of sequence is maybe also a good choice, but due to longer scan times and artifact problems it is best for axial slices.rn
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Jacob Newton

Thu. 7 Oct.10,
14:22

[Reply (1 of 2) to:
'How does TE affect DWI acquisition?'
started by: 'danilo Scelfo'
on Wed. 29 Sep.10]


 
  Category: 
Sequences and Imaging Parameters

 
How does TE affect DWI acquisition?
I never tried to shorten only the echo time while keeping all other parameters the same, but I would expect a change in SNR and artifact appearance. I would use parallel imaging methods to get a shortest possible echo time. Parallel imaging provides DWI with shorter echo trains associated with further reduction of the echo and repetition times, which reduces susceptibility effects and also image blurring. Additionally, the shorter echo time may lead to changes in ADC measurement.
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Reader Mail

Tue. 6 Mar.07,
16:48

[Start of:
'fluid PD vs T2 weighting'
1 Reply]


 
  Category: 
Sequences and Imaging Parameters

 
fluid PD vs T2 weighting
Can anyone explain me, why - considering SE sequences with the same TR - fluid in a PD weighting (short TE) should have less signal than in a T2 weighting (long TE)? eg:
Fig 10, p 1397; radiographics resident tutorial: contrast mechanisms in spin echo MR imaging; Radiographics 1994; 14; pp 1389-1404

I would expect that the signal intensity of any tissue (regardless of it Proton density of T2-relaxation time) should decrease with increasing echo time.

Thank you
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Scott Lytle

Thu. 4 Jan.07,
11:52

[Reply (2 of 3) to:
'ETL for a STIR'
started by: 'Shaun Schofield'
on Wed. 29 Mar.06]


 
  Category: 
Sequences and Imaging Parameters

 
ETL for a STIR
It depends.

When Centric echo allocation is used you have higher SNR, a low TE, but more image blurring. Very similar to a PD. I prefer an echo train of less than 8 in this case.

When Sequential echo allocation is used you have lower SNR, a higher TE (I prefer less than a TE of 60), but significantly less image blurring. Very similar to a T2 or FLAIR. In this case your echo train length is governed by your TE and image blurring is not usually an issue. Depending on how short of an inter-echo time you can use, and by keeping an eye on the TE, the echo train can be as high as you want.

Hope this helps.
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