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n p
Fri. 11 Sep.09,
11:50
[Reply (3 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 |
no hithesh n, that is a 180 rephasing pulse. thats not the question. the question is how is the net magnetization changed from the z plane to the -z plane without causing phase coherence, like the case of an inversion pulse. it is supposedly 2x as long or 2x as strong as the 90 degree pulse, but doesn't cause coherence. Why not is the question.
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hithesh n
Fri. 11 Sep.09,
08:33
[Reply (2 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 |
Hi Bjorn,
I might be able to explain this even though its too late.
Initially a 90 excitation pulse is applied, the Hydrogen protons precess in the XY plane. Now they are spinning in sync in the XY or transverse plane. This is where they emit the RF signal.
But pretty soon, the neighboring hydrogen protons go out of sync, ie one is going faster and the other is going slower. This is similar to runners running a race in a track, they all start at the same time(assume) but after a couple of secs, some run faster than the other. The faster ones are in the front and the slower ones are in the back.
How do you bring them back into sync?
This is where the 180 excitation comes into play.
Now you apply a 180 pulse, this is equivalent to making the runners run in opposite direction. Now suddenly, the slower runners are gonna be in the front and faster ones in the back. Eventually the faster ones catchup and all of them are gonna be in sync. They go out of sync again.
They go out of sync bcoz the magnetic field applied is not uniform and due to material (tissues, bones etc). Local variations in the field causes the protons to go out of sync.
The 180 brings them in to coherence, not instantly but they do catch up and become coherent.
The 90, brings them into coherence almost instantly.
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waseem zafar
Thu. 3 Sep.09,
11:09
[Start of:
'MRI TECHNOLOGIST'
0 Reply]
Category:
Jobs
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| MRI TECHNOLOGIST |
i am medical imaging technologist,i have passed BSc(HONS) Medical imaging technology in july 2007 from university of health sciences lahore.i have great experience of MRI(1.5T PHILIPS Magnetom,1.5T Siemens Avanto,Hitachi0.35T.ICAN PERFORM ALL TYPES OF SCANNING OF MRI INCLUDINGMRA,MRV,PERFUSION,DIFFUSION etc,
ihave also good experience of CT 64 SLICES TOSHIBA AQUILION,I CAN PERFORM ALL PERIPHERAL ANGIO,CARDIAC ANGIO,BIPHASIC AND OTHER CT PROCEDURES,I HAVE GREAT EXPERIENCE OF POSTPROCESSINF ON WORKSTATION OR VITREA,I CAN MAKE ALL 3D IMAGES ON VITREA.I AHVE EXPERINENCE OF NUCLEAR MEDICINE,AND FUJI CR SYSTEM,
I WANT TO WORK AT SAUDI ARABIA SO A I M LOOKING FOR THE JOB
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Christine Row
Tue. 1 Sep.09,
19:11
[Reply (1 of 4) to:
'Please recommend materials sensitive to T1-weighted MRI'
started by: 'Cindy Duan'
on Wed. 12 Aug.09]
Category:
Basics and Physics
|
| Please recommend materials sensitive to T1-weighted MRI |
Beside diluted contrast agents, you can use fat containing substances, for example fish-oil filled capsules.
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Bridget Galegher
Sun. 23 Aug.09,
19:51
[Reply (2 of 21) to:
'MRI registry equations'
started by: 'Donna Nusser'
on Tue. 18 Aug.09]
Category:
Basics and Physics
|
| MRI registry equations |
Take 1.006 - 1.000T or (1.0) this equals 0.006, or (6mT) then take 6 divided by 0.5 (which is your distance along the positive z-direction and this will give you the answer of 12. (Strength of the magnetic field divided ny the distance from the center of the magnet) My suggestion for you is get the new "MRI in Practice" not the green book but the new one with the multi-colors on the front of it (3rd edition) Explains everything and it is fun to read. I have to take mine too in September through ARRT. Just don't psyc yourself out.
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