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| Result: Searchterm 'Echo'
found in 42 messages |
| Result Pages: 1 2 3 4 5 6 [7] 8 9 |
More Results:  Database (305) News Service (7) Resources (10) |
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Jenny Jordan
Sat. 17 Nov.07,
20:11
[Reply (2 of 4) to:
'Haste and Rare sequences'
started by: 'Elena sussi'
on Tue. 13 Nov.07]
 Category:
Sequences and Imaging Parameters
|
| Haste and Rare sequences |
Hi Elena,
you can find the different names for the same sequences and options used by manufacturers at: http://www.mr-tip.com/serv1.php?type=cam .
The manufacturers have in principle similar sequences with small differences. So, as you mentioned you can take "sequences as HASTE" or "sequences type RARE".
However, you can lead back these sequences also to the fundamental sequence type FSE ( fast spin echo: http://www.mr-tip.com/serv1.php?type=seq&sub=12 ). Fast sequences as HASTE ( http://www.mr-tip.com/serv1.php?type=db1&dbs=haste ) are especially useful in cases of movement caused by their single shot technique: http://www.mr-tip.com/serv1.php?type=db1&dbs=Single%20Shot%20Technique .
Hope this helps
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|  View the whole thread | | |
Reader Mail
Tue. 6 Mar.07,
22:48
[Start of:
'fluid PD vs T2 weighting'
1 Reply]
Category:
Sequences and Imaging Parameters
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| 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,
17:52
[Reply (2 of 3) to:
'ETL for a STIR'
started by: 'Shaun Schofield'
on Thu. 30 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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| | View the whole thread | | |
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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| | View the whole thread | | |
Jennifer Jackson
Fri. 21 Jul.06,
04:44
[Reply (1 of 2) to:
'Phase encoding'
started by: 'guillaume bierry'
on Fri. 7 Jul.06]
Category:
General
|
| Phase encoding |
Wow this is a long subject, First you have to under stand how the 3 main gradients are used. (slice select, Freq, then phase)
So you are use 1 of the gradients for your phase encoding. You need to fill the k-space which depends on you matrix. Lets assume you are using 256 (phase). In order to fill K-space you have to have 256 aquistions of the signal. Meaning for each picture (or slice) the signal must be acquire(sampled) 256 times each at a differnt amplitude to put it in a different Line of k-space.
Example- If you are performing a SE(spin echo) you have 1 TR period and 1 TE period (TE=is when the signal is sampled) so you will have to do the TR period 256 times to fill K-space with diffent amplitudes.
There is alot more that I left out. If this did not answer your question let me know
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