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| Result: Searchterm 'Magnet'
found in 87 messages |
| Result Pages: 1 2 3 4 5 6 7 [8] 9 10 11 12 13 14 15 16 17 18 |
More Results:  Database (669) News Service (897) Resources (213) |
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Iosif Sogolov
Tue. 20 Mar.12,
17:16
[Reply (2 of 4) to:
'Who shims MRI systems in Uzbekistan'
started by: 'Reader Mail'
on Wed. 14 Mar.12]
 Category:
Equipment
|
| Who shims MRI systems in Uzbekistan |
Can shim the magnet. But how do you know you do need the shimming? I am in Germany.
mrirepairer@gmail.com
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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 | | |
Vandana Asaikar
Mon. 9 Jan.12,
23:37
[Reply (2 of 3) to:
'MR jobs'
started by: 'rajani subramanian'
on Thu. 30 Jun.05]
Category:
Jobs
|
| MR jobs |
Our facility in Scaramento is looking for an MRI tech with experience on a GE 1.5T magnet. Part time with possiblity for fulltime employment. We image a lot of kids. Must be ARMRIT certfied. Venipuncture and CPR
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| | View the whole thread | | |
Reader Mail
Wed. 24 Aug.11,
19:00
[Start of:
'Stent Safety and repeated MRI exposure'
1 Reply]
Category:
Safety
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| Stent Safety and repeated MRI exposure |
We have a anesthesia tech that has a stent in her aorta. The stent is safe at 1.5t. She at times needs to stay in the MRI room with a patient during the scan. She may do this several times a month. Is there any long term effect? Can the stent become magnetized over time? Cannot find any documented information.
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(login or register first) | |
Steven Ford
Tue. 7 Jun.11,
18:03
[Reply (2 of 3) to:
'LCD Display Monitors'
started by: 'robert popilock'
on Mon. 23 May.11]
Category:
Safety
|
| LCD Display Monitors |
I think that the question is, can you use a display near the magnet, inside the RF shielded room?
The short answer is, No, unless it's specifically marked MR-safe and/or included in equipment that's specificaly designed to be near the magnet, such as an injector.
The problem with using, for example, a monitor from Best Buy is that it will probably emit RF energy that will corrupt the very weak MRI signal recieved from the patient's body. Of course, there is also the question of anchoring the monitor to prevent it from being attracted into the magnet.
In general, an off the shelf monitor will not be affected by the magnet.
You can buy special RF shielded monitors, or enclosures.
If you were thinking about adding a patient DVD viewing capability, there are several other concerns to keep in mind. The signal feeding the monitor must be filtered where it enters the RF shield.
Steven Ford
Professional Imaging Services, Inc.
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