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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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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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James Shingola
Fri. 15 Jul.16,
19:22
[Start of:
'What does this mri report mean'
0 Reply]
Category:
General
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| What does this mri report mean |
Small developing vertical cleft along the radial side of the membranous TFC disc fibers, best seen on image 11 series 5. There is no evidence of contrast transit into the distal radioulnar joint. The remainder of the TFC disc is intact and grossly unremarkable.
Intact intrinsic ligaments. There is no widening of the intervals. There is no contrast in the midcarpal compartment.
Increased interstitial signal within the ECU tendon is likely due to tendinopathy and a developing longitudinal split. The remaining tendons are grossly unremarkable.
Normal caliber median and ulnar nerves.
Minimal generalized wrist osteoarthrosis with minimal to mild chondromalacia, small intraosseous cysts and minimal osteophytosis.
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Steven Ford
Thu. 17 Mar.16,
15:05
[Reply (1 of 2) to:
'Experiences with Artroscan C'
started by: 'Reader Mail'
on Fri. 3 Apr.15]
Category:
General
|
| Experiences with Artroscan C |
I know this is a really old question but I'm answering so that maybe others might learn.
The scanner you refer to is actually the E Scan (or possibly the E Scan XQ or the E Scan Opera) by Esaote.
You are correct, the flex coil for hips does not give good coverage or good signal. Most of our E Scan customers never use the coil.
A larger problem for hip studies is that the opening in the magnet and the FOV of the magnet severely limits the ability to scan patients of average and larger than average size.
the same can be said of doing shoulder exams on this scanner, in general the images are not met with happiness by the radiologists.
Steven Ford
Professional Imaging Services, Inc.
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John Smith
Wed. 11 Nov.15,
22:14
[Start of:
'Faster pulse sequences'
0 Reply]
Category:
General
|
| Faster pulse sequences |
Hi,
I have been learning about faster MRI sequences and have two questions
1) With "Fast (Turbo) gradient echo", in which we apply a spoiler gradient, do we not eventually end up with no longitudinal magnetization because TR is always shorter than T1? Hence shouldn't we eventually get no signal at all?
2) in SSFP (Steady-state free precession) we can apply an RF pulse of 90 degrees (in which T1>>T2) to get heart-blood contrast. How is this any different to a standard spin-echo sequence in terms of timing?
Thank you
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David Russell
Mon. 29 Jun.15,
15:31
[Start of:
'FLAIR'
0 Reply]
Category:
General
|
| FLAIR |
What are the causes of high FLAIR signal? Is there a list? Or is it just everything that is high on T2 and is not pure CSF fluid would be high.
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