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| Result: Searchterm 'Coil'
found in 50 messages |
| Result Pages: 1 2 3 4 5 [6] 7 8 9 10 |
More Results:  Database (193) News Service (27) Resources (17) |
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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
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| 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 | | |
Reader Mail
Thu. 20 Jan.11,
17:12
[Start of:
'Philips Pin Config - 4 channel'
0 Reply]
Category:
Devices, Scanner, Machines
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| Philips Pin Config - 4 channel |
Need the pin out configuration for 4 channel coil for Philips Intera and Achieva.
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| | Reply to this thread
(login or register first) | |
Don LaVille
Tue. 21 Dec.10,
20:57
[Reply (1 of 3) to:
'Muscle shading in 3T Images'
started by: 'Travis Conley'
on Thu. 21 Oct.10]
Category:
Applications and Examinations
|
| Muscle shading in 3T Images |
This artifact is known as the dielectric effect. It is a phenomena to all magnets. At 1.5T the dielectric effect is at 60cm so when we scan at a FOV of 40 or less we don't see it. At 3t the dielectric effect is reduced to 30cm so we now see it when using a FOV of 30 or more. There is no way to get rid of it that I know of and you will see an increase with patients with more magnetic suseptibility (ie. patients with ascities, and pregnant patient). You could try using Surface Coil Intensity Correction (SCIC) and it will help to even out the extreme dark and light in your image. Some vendors will suggest using a Fat Sat pad to help reduce this artifact. I have tried it with little success.
Looking at your image, it looks like you were scanning on a GE 3T HDX. I hope that the vendors will have a fix for this artifact soon. For right now though we are just dealing with it. I hope this helps.
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| | View the whole thread | | |
steven china
Fri. 24 Sep.10,
12:12
[Reply (3 of 4) to:
'coil configuration'
started by: 'Zhenghui Zhang'
on Thu. 24 Jun.04]
Category:
Coils
|
| coil configuration |
hi buddy
in general,surface coils are designed for receive signals only and have no fuction of transmit
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| | View the whole thread | | |
tang yu
Fri. 24 Sep.10,
10:55
[Reply (2 of 4) to:
'coil configuration'
started by: 'Zhenghui Zhang'
on Thu. 24 Jun.04]
Category:
Coils
|
| coil configuration |
body coil has a limited SNR, we never use BC as only received coil.
for siemens scanners. things will be easy.
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