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| Result: Searchterm 'Signa'
found in 78 messages |
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More Results:  Database (382) News Service (60) Resources (16) |
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Lyle Downing
Sat. 26 Sep.09,
20:27
[Reply (4 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 |
Perhaps this will help shed some light on this.
Keep in mind that before the initial 90 pulse all protons contributing to the MR signal are in a relaxed state completely in alignment with the static magnetic field. Flipping them 90 degrees into the transverse plane does align them up initially and yes they do relax at different rates as they give up their energy. The 180 pulse takes whatever state they are in at the time and flips them in order to not make them all 180, but to quickly get a cleaner non contaminated representation of the tissues in question. So for example after the initial 90 and after letting the protons relax for a bit you might see water at say 50 degrees and fat at say 70 degrees flipping them 180 keeps whatever energy state they are in the time.
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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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Daniel Robertson
Thu. 23 Jul.09,
04:54
[Start of:
'MRI Spinal Ligaments'
0 Reply]
Category:
Applications and Examinations
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| MRI Spinal Ligaments |
I am a graduate student conducting research on spinal ligament mechanics. I am looking for a good imaging sequence to determine the geometry of the supraspinous ligament. I am working with cadaver specimens so patient motion and scan time is of little relevance. I am just looking to get the highest resolution possible so that I can render a 3d volume of the supraspinous ligament. I am using a GE Signa HDx 3T. Thanks.
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palani arakkan
Wed. 1 Jul.09,
14:22
[Reply (9 of 26) to:
'MRI Technologists Jobs in Saudi Arabia'
started by: 'Mosta Mosta'
on Tue. 3 Mar.09]
Category:
Jobs
|
| MRI Technologists Jobs in Saudi Arabia |
Respected sir,
iam sam palani radiographer working in international hospital of bahrain. iam looking for the post of radiographer. handled 0.5 ge signa contour,siemens 1.5 symphony machines and experience in philips 1.5 tesla mri achieva assigned to do all kinds of special CE mr angiograms like renal,peripheral,upper limb angiogram and fetal,breast,mru,mrcp, ect
thank you your's faithfully
A.sam Palani
e.mail.sam_palanirs@yahoo.co.in
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werginn carvajal
Sat. 23 May.09,
21:42
[Reply (7 of 26) to:
'MRI Technologists Jobs in Saudi Arabia'
started by: 'Mosta Mosta'
on Tue. 3 Mar.09]
Category:
Jobs
|
| MRI Technologists Jobs in Saudi Arabia |
I have exp. 1.5 platform 5-LX Hispeed-LX Echospeed HDx 14 tesla SIGNA G.E and Philips 1.5 tesla INTERA and 3.0 tesla 0.2 0.3 tesla SIGNA Profile G.E open MRI Siemens 1.5 tesla SYMPHONY
wginncvjal@hotmail.com
305/984-2261
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