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| Result: Searchterm 'Flip Angle'
found in 4 messages |
| Result Pages: [1] |
More Results:  Database (37) |
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Kerstin Amort
Thu. 9 Aug.12,
09:47
[Start of:
'Flip angle'
0 Reply]
 Category:
Basics and Physics
|
| Flip angle |
A very basic question about flip angle:
How can I calculate the duration of the RF pulse when flip angle (90°) and radiofrequency (1 mT) are given?
Unfortunately I do not have an equation that fits perfectly...
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Gina Key
Sat. 27 Jan.24,
09:33
[Reply (1 of 2) to:
'IDEAL sequence help'
started by: 'gianluca turcatel'
on Mon. 10 Jan.22]
Category:
General
|
| IDEAL sequence help |
To calculate the Proton Density Fat Fraction (PDFF) from MRI images of the liver acquired using LMS IDEAL (Iterative Decomposition of Water and Fat with Echo Asymmetry and Least Squares Estimation) with optimized low flip angles, you'll typically have multiple image sets corresponding to different echoes. The fat and water signals are separated based on their chemical shift differences. Look for image sets labeled as Water, Fat, or PDFF (Proton Density Fat Fraction). Depending on the software or DICOM tags used, the images may be explicitly labeled, or you may need to review the sequence parameters to determine which set corresponds to fat or water.
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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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crystal f
Sun. 18 Oct.09,
21:34
[Start of:
'Math equation'
3 Replies]
Category:
Basics and Physics
|
| Math equation |
Can some one help me w/this question.
From the following parameters what will the scan time be, in minutes, to acquire data?
TR 2000msec FREQUENCY STEPS 256
TE 60msec NEX 2
T1 800msec FLIP ANGLE 90
pixel .95x.95mm PHASE STEPS 192
THANKS
mr registry review
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