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| Result: Searchterm 'signal'
found in 52 messages |
| Result Pages: 1 2 3 4 5 [6] 7 8 9 10 11 |
More Results:  Database (369) News Service (50) Resources (8) |
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Steven Ford
Mon. 7 Mar.11,
15:24
[Reply (4 of 8) to:
'6-1.5T MAGNETS, DIFFERING GRADIENTS'
started by: 'Elise Gough'
on Wed. 23 Feb.11]
 Category:
Applications and Examinations
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| 6-1.5T MAGNETS, DIFFERING GRADIENTS |
If some of the system are signal starved, it's most likely not due to gradient field strength and speed, but it can be related to that. Like everything else in MRI, it's complex and interdependent.
You're best advised to talk with the apps specialist from the systems that are under-performing, and learn from them what the bandwidth is, and also check the shim. Is the fat suppression OK, but the signal weak, or is the suppression bad also? Do you get a graphic output of the linear (gradient)shim corrrection on the various systems?
It is well worth the money that they might charge, if it comes to that, in order to optimize the use of the systems and for your own education. If the apps person does not know why the other machine works so well, there should be someone higher up in the organization who can shed some light on your question.
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Elise Gough
Fri. 4 Mar.11,
13:56
[Reply (2 of 8) to:
'6-1.5T MAGNETS, DIFFERING GRADIENTS'
started by: 'Elise Gough'
on Wed. 23 Feb.11]
Category:
Applications and Examinations
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| 6-1.5T MAGNETS, DIFFERING GRADIENTS |
Thank you for your response. Our group is strict about FOV, thickness/gap parameters being the same across all magnets. One magnet has slew rate of 77, FRFSE T2, TE 85,TR 3500 Classic Fat supressed images which are pristine, vs magnets of 120 slew rate same parameters look signal starved. So gradient strength makes a speed difference, not an image quality difference?
Elise Gough RT(R)(CT)(MR)
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steven china
Fri. 24 Sep.10,
12:12
[Reply (3 of 4) to:
'coil configuration'
started by: 'Zhenghui Zhang'
on Thu. 24 Jun.04]
Category:
Coils
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| coil configuration |
hi buddy
in general,surface coils are designed for receive signals only and have no fuction of transmit
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| | View the whole thread | | |
Azza Ahmed
Thu. 8 Jul.10,
10:42
[Start of:
'exceeding slew rates'
0 Reply]
Category:
Sequences and Imaging Parameters
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| exceeding slew rates |
Can someone please let me know what happens to the MRI signal intensity if any of the gradient's slew rate was exceeded?
Azza AhmedrnPhD student
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Oliver Lyttelton
Mon. 1 Mar.10,
13:39
[Reply (8 of 12) to:
'90 excitation pulse vs 180 inversion pulse'
started by: 'Bjorn Redfors'
on Sat. 27 Jun.09]
Category:
Basics and Physics
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| 90 excitation pulse vs 180 inversion pulse |
Okay, so this thread is answering close to a question I had, which is how to conceptually understand what happens with alpha>90 degrees excitation pulses.
I can imagine spinning tops, precessing at the Larmor frequency, I can imagine that as you apply the excitation pulse which is always in the transverse plane to the main magnet, you start to pull the tops further away from the B0 axis and bring them into coherence so like lots of little lighthouses they are all bright/dark in phase with each other. I can imagine a 90 degree pulse bring the spins completely into the transverse plane. I can imagine them relaxing, dephasing quickly and then slowly reducing their angle of precession back up towards initial state close to direction B0.
But what I can't understand in my (rather newtonian) model, is what happens as you continue to excite beyond the 90 degree transverse plane. I sort of get that somehow the spins continue to rotate in some (weird) dimension, and that they have to come back through that (weird) dimension first before returning from 90 degrees back to the relaxed state. But what happens in "weird" dimension is beyond my conceptual model. Can someone extend my model for me, preferrably without signal equations?
tar muchly,
Oliver
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