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| Result: Searchterm 'Phase'
found in 33 messages |
| Result Pages: 1 2 [3] 4 5 6 7 |
More Results:  Database (285) News Service (25) Resources (11) |
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luna xu
Fri. 5 Jun.15,
14:22
[Start of:
'is this kind of zebra artifact?'
1 Reply]
 Category:
Artifacts
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| is this kind of zebra artifact? |
Always existed artifact made us crazy, is this a kind of zebra artifact or something? the line are in the phase encoding direction, really confusing.
 artifact
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shahrokh Rad
Sat. 4 Oct.14,
13:44
[Reply (9 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 |
All of the responds are misleading.
what is the correct answer??????
why does the 90 excitation pulse result in phase coherence while the 180 pulse won't.
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| | View the whole thread | | |
Steven Ford
Tue. 31 Jan.12,
08:19
[Reply (1 of 2) to:
'RF shimming'
started by: 'Reader Mail'
on Thu. 1 Oct.09]
Category:
Basics and Physics
|
| RF shimming |
For Magnetic fields, the overall field is adjusted to push it up a little bit in one spot and push it down a little bit in another area. The goal is to create a field that's perfectly homogenous.
The RF field created by the transmit coil likewise must be as homogenous as possible, so that the flip angle is constant throughout the imaging volume. In the past, designers have solved this problem by building coils such as the 'birdcage' style that would create a very even amount of energy inside. This is one reason why the transmit coils tend to be large.
With the advent of 3 Tesla and stronger magnets, the RF resonant frequency also rises. RF energy absorbed in the patient rises with the higher frequencies also, and another problem raises its head: it's a lot harder to make a very homogenous RF field. Even if you are scanning phantoms, the inside tends to be subject to different energy than the edges.
But in the human body, there are all sorts of irregular lumps and bumps that absorb RF differently, further complicating matters.
Now, on modern scanners it's possible to perform a magnetic field shim with the patient actually in the magnet in order to compensate for minute changes in the magnet from one exam to another. For super-high field magnets, an RF shim is also a handy thing to do.
If you have a Multi element RF transmit coil (regular phased array coils are just for receiving) you can run a program which selectively turns up the power in some elements so that the overall signal received is maximized. That's an RF shim.
Steven Ford
Professional Imaging Services, Inc.
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| | View the whole thread | | |
Katelin Lyons
Fri. 3 Jun.11,
11:55
[Reply (1 of 2) to:
'Dixon technique'
started by: 'Reader Mail'
on Wed. 1 Jun.11]
Category:
Sequences and Imaging Parameters
|
| Dixon technique |
Dixon technique uses alternative water/fat phase-encoding strategies. The technique is generalized to phase encoding of theta radians, and the signal-to-noise ratio (S/N) performance is evaluated.To get some more information regarding this please check out the following link : http://www.ncbi.nlm.nih.gov/pubmed/18777528
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| | View the whole thread | | |
Reader Mail
Wed. 1 Jun.11,
14:14
[Start of:
'Dixon technique'
1 Reply]
Category:
Sequences and Imaging Parameters
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| Dixon technique |
I have been searching the web for information regarding a "double-echo two-excitation pulse sequence encoding fat and water signals for a phase-sensitive three-point Dixon type analysis". Does anyone know what pulse sequence(s) this is referring to, or a publication that might be helpful???
Thanks
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