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| Result: Searchterm 'Magnet'
found in 87 messages |
| Result Pages: 1 2 3 [4] 5 6 7 8 9 10 11 12 13 14 15 16 17 18 |
More Results:  Database (669) News Service (897) Resources (213) |
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Renate S.
Tue. 27 Feb.18,
16:31
[Reply (1 of 3) to:
'Damage from quench'
started by: 'Dan Russell'
on Fri. 9 Feb.18]
 Category:
Equipment
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| Damage from quench |
Accidental or spontaneous quenching may cause severe damage to the magnet and the surrounding (including coldhead). If the MRI quench pipe works as dedicated, the damage related to the coolant should be small. But in any case it is cost extensive and a decision to manual quench should only be made in extreme cases. If there is no potentially life threatening situation call the service engineer.
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mm jj
Thu. 31 Aug.17,
04:30
[Start of:
'flipping'
0 Reply]
Category:
General
|
| flipping |
hi
cam we flip net magnetisition vector more than 180? if so,what happens?
after flipping 360 degree,is there any relaxation?
360 pulse makes spins back to initial state?
thanks in advance.
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Math G
Fri. 30 Jun.17,
21:02
[Reply (10 of 12) to:
'90 excitation pulse vs 180 inversion pulse'
started by: 'Bjorn Redfors'
on Sat. 27 Jun.09]
Category:
Basics and Physics
|
| 90 excitation pulse vs 180 inversion pulse |
I will try an answer to this rather old tread, in case someone stumble upon this like me.
The phenomenon of "coherence" that produce transverse magnetization after a 90 RF pulse cannot be answered by classical mechanics, or any simple model that represents individual protons as precessing magnets in either the parallel/antiparallel direction with regards to the MRI magnetic field.
Rather, it is a phenomenon related to quantum mechanics and the effect of a RF field on a interacting group of particles with spins (not necessarily oriented as parallel/antiparallel, I might add, even under the effect of a magnetic field).
The simplest depiction, as I understand, would be to imagine a group of spins as literally rotating as a whole under the effect of the RF. After a certain time (corresponding to a 90 degree pulse), the net magnetization that was oriented parallel to the MRI magnetic field, is now oriented in the transverse plane, causing transverse magnetization and signal. If you further apply RF, the system will continue to rotate, shifting gradually toward an antiparralel orientation, losing transverse magnetization in the process.
Hope its clearer!
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Eduardo Mendes
Tue. 19 Jul.16,
12:59
[Start of:
'Need to quench a scanner now'
2 Replies]
Category:
General
|
| Need to quench a scanner now |
HellornrnI have on old Oxford 4.7 T scanner that has been working since 2011. Unfortunately these last few days we could not transfer He in. Although our He liquefier is completely full and the transfer line is connect to the magnet, no He is transferred. The transfer line has been made vacuo efficient two months ago and should be ok. rnrnIt seems that we need to quench the magnet. We don't have any external power supply to connect to the magnet and retrieve the current. rnrnWhat can we do? Is there any safety measures? Can we leave the magnet as it is? Should we evacuate the building? Should we isolate the area? rnrnThank you ever so much for your time and help. rnrnI have contacted Oxford several times but they didn't return my emails. rnrnMany thanksrnrnEdrnrn
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Marta Lancione
Thu. 5 May.16,
14:55
[Start of:
'Drawing MRI sequence'
0 Reply]
Category:
General
|
| Drawing MRI sequence |
Does anyone know of existing LaTeX macros or packages or any other software for drawing Magnetic Resonance Imaging pulse sequences?
I didn't find anything online. Thank you so much for your help!
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