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| Result: Searchterm 'high field'
found in 11 messages |
| Result Pages: [1] 2 3 |
More Results:  Database (33) News Service (60) Resources (13) |
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Charlie McIntyre
Tue. 17 Apr.12,
16:28
[Start of:
'High Field Open MRI systems/Spatial Gradient limits'
0 Reply]
 Category:
Safety
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| High Field Open MRI systems/Spatial Gradient limits |
Anyone out there operating a Philips HFO or Hitachi Oasis? If so how is your facility handling the new FDA labeling of MR "conditional" limits of certain implants(stents, shunts, etc..) and the Higher Spatial Gradient Forces that these machines have? thanks.
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Gary Brown
Mon. 14 Jun.21,
15:20
[Start of:
'Stents'
0 Reply]
Category:
General
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| Stents |
Employer relates that any cardiac stent implanted after 2008 is safe on ANY MRI scanner within our system. This ranges from 0.3 Open scanners to 1.2 High field Open and 1.5 and 3T closed systems.
Contrarily, the manufacturer data on certain stents states 1.5 or 3 T ONLY, but we are urged to scan on an open if implanted after 2008. Does anyone have any type of testing documentation that this is safe? I'm not so much worried about the field strength as I am the magnetic field orientation as the defining safety issue.
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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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Adana Osco Barras
Tue. 3 Jan.12,
21:09
[Reply (1 of 2) to:
'Hyperintense blood vessels in SE'
started by: 'Peruvumba Jayakumar'
on Thu. 29 Dec.11]
Category:
Sequences and Imaging Parameters
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| Hyperintense blood vessels in SE |
Prolonged T1 relaxation times, decreased T1 tissue contrast, and increased susceptibility rnare typical effects at high field MRI.rnDue to the longer T1 times at 3T, the signal rnintensity inside the vessels is preserved even in smaller vessels. Try TR 700, TE 10.rnInversion recovery sequences are very well suited for optimal gray to white matter contrast, but enhancement after administration of gadolinium may not be visible.
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Reader Mail
Mon. 3 May.10,
14:09
[Start of:
'Philips Panorama 1.0T'
0 Reply]
Category:
Site Planning and Specifications
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| Philips Panorama 1.0T |
The hospital where I work is considering the purchase of a new MRI system. They are leaning towards a Philips Panorama 1.0T system. I have hard that there are cumbersome features with regard to the patient table, etc. I have also heard that Hitachi has a new high field open mri that is a better choice. Has anyone worked with either of these machines that can share some good advice with me please? I would appreicate it and thank you in advance.
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