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| Result: Searchterm 'Proton'
found in 19 messages |
| Result Pages: 1 [2] 3 4 |
More Results:  Database (94) News Service (6) Resources (7) |
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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
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| 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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|  View the whole thread | | |
Maxima Watkins
Tue. 6 May.14,
19:38
[Reply (1 of 2) to:
'Patellofemoral syndrome by MRI'
started by: 'FRANCISCO MORALES'
on Tue. 8 Apr.14]
Category:
Applications and Examinations
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| Patellofemoral syndrome by MRI |
Hi, here is a helpful article: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2919651/ - we use proton density with fat saturation in three planes and a sagittal T1. The best protocol may be dependent on the MRI system and field strength.
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| | View the whole thread | | |
Steven Ford
Thu. 2 Dec.10,
15:18
[Reply (1 of 2) to:
'T1&T2 WAIGHTED MEANING ?'
started by: 'BINU VAEGHESE'
on Wed. 1 Dec.10]
Category:
Basics and Physics
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| T1&T2 WAIGHTED MEANING ? |
All MRI images have contrast (the bright and the dark) that is based on properties of the tissue that's being imaged. In MRI (unlike, for example, CT) those images are based on a combination of several physical properties. So to some extent ALL MRI images are based partly on property A, property B, etc.
The tissue properties that are referred to include proton density (how many hydrogen nuclei are in a given area), motion, and two other properties that are called T1 and T2. These are properties that can be seen onloy by using the MRI instrument, much as without a microscope one cannot see inside a cell.
A T1 weighted image is one in which the differences between T1 properties of the various tissues are the predominant reason why some parts of the image are bright and others are not as bright.
This is medically useful because, since T1 and T2 are distinct properties, diseased tissue may show up different than normal tissue on either the T1 weighted scan or the T2.
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| | View the whole thread | | |
George LoGuirato
Wed. 7 Apr.10,
13:28
[Reply (1 of 2) to:
'Proton Density Imaging'
started by: 'Jacquelyn Chiffons'
on Thu. 18 Mar.10]
Category:
Sequences and Imaging Parameters
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| Proton Density Imaging |
A Proton Density - like a T1 or T2 - is not considered anything; it is what you make it. Most all PD's are run as fast (turbo) spin echo, but many sites run a true spin echo PD on knees to evaluate the meniscus. (It's a long sequence.)
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| | View the whole thread | | |
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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