|
Magnetic
Resonance -
Technology
Information
Portal |
Welcome to MRI Technology • |
|
|
 | Info
Sheets |
| | | | | | | | | | | | | | | | | | | | | | | | |
 | Out-
side |
| | | | |
|
| | | | | |
| Result: Searchterm 'Focus'
found in 6 messages |
| Result Pages: [1] 2 |
More Results:  Database (48) News Service (71) Resources (9) |
|
|
avinash poornan
Mon. 9 Feb.15,
00:45
[Start of:
'Self refocusing'
0 Reply]
 Category:
Basics and Physics
|
| Self refocusing |
How do you define a self refocusing pulse in NMR?
|
| |  Reply to this thread
(login or register first) | |
Reader Mail
Sun. 6 May.07,
17:28
[Start of:
'OVS & phase refocussing'
0 Reply]
Category:
Sequences and Imaging Parameters
|
| OVS & phase refocussing |
Why do we need to rephase spins in outer-volume regions after their excitation, still applying a crusher gradient afterward? Is this not too much work, rephasing and then dephasing them?
|
| | Reply to this thread
(login or register first) | | |
|
Clifford Thornton
Thu. 30 Jun.16,
17:48
[Start of:
'Max. SAR per second - Whole Body (Normal, 1st Controlled, 2nd Control)'
0 Reply]
Category:
Safety
|
| Max. SAR per second - Whole Body (Normal, 1st Controlled, 2nd Control) |
Hello fellow imaging technologists & professionals!
I'm involved in the development of a new type of cardiovascular medical device.
This device employs MRI technology/scans to power, guide, and control the medical devices and their active elements.
I conducted some research into the following question, "How much x-ray energy is allowed within a human every sec from a MRI machine?"
With regards to SAR rates, I understand that these are the upper-limits for the various settings for a full-body scan:
Normal setting: Whole body SAR - 2
1st Level Controlled: Whole body SAR - 4
2nd Level Controlled: Whole body SAR - >4
Would you agree with these calculations that I performed, and if not, why? And what would be a better way to calculate this?
For WHOLE BODY SAR:
-SO IF IN NORMAL MODE FOR MRI, THE MAX. ALLOWABLE SAR IS "2" OVER A 6 MIN. PERIOD, THEN
-6 MIN. = 360 SECONDS
-2 / 360 = 0.00555
FOR 1ST LEVEL CONTROLLED:
-SO IF IN 1ST LEVEL CONTROLLED FOR MRI, THE MAX. ALLOWABLE SAR IS "4" OVER A 6 MIN. PERIOD, THEN
-6 MIN. = 360 SECONDS
-4/ 360 = 0.01111
Other questions -- What is the difference between normal setting, 1st conrolled and 2nd controlled?
What is the clinical purpose of these various settings?
Any insights that you would be willing to share in regards to the above would be greatly appreciated!
I was trained and registred as a diagnostic echocardiographer, specializing in cardiovascular ultrasound, therefore I need help with MRI information/specifications. I am now focusing on the medical device field, but this technology/device happens to be highly dependent on MRI technology.
Any help from the group would be greatly appreciated!!
Thanks & regards,
Clifford Thornton
|
| | Reply to this thread
(login or register first) | |
Barry Ng
Wed. 10 Jul.13,
17:10
[Start of:
'Titanium & MRI Safety'
2 Replies]
Category:
Safety
|
| Titanium & MRI Safety |
I am trying to understand why titanium is considered "MRI Safe".
I see three potential problems when considering the MRI safety of a material:
1 - If it is a ferromagnetic material extreme damaging forces will be applied to the material if exposed to a very strong magnetic field. Titanium is not a magnetic material so I do not see this as a problem.
2 - When a relatively large flat conductor (e.g. a titanium plate) is exposed to a changing magnetic field (Faraday's law) eddy currents will be created internally as the result of induced voltages. These eddy currents can be very high and cause resistive heating ("I squared R losses"). I would think these eddy currents would have the potential to cause extreme heating of the titanium. I know from experience this does occur with steel and titanium has a conductivity about the same as steel. Titanium is not magnetic as is steel but induced voltages due not require a ferromagnetic material (.e.g. copper as used in real world generators, etc.).
3 - Induced voltages are created across the length of a conductor as the result of the conductor being exposed to a changing magnetic field ("genrator effect" - Faraday's Law). Again this effect does not require a magnetic material. So why, at best, does this effect not have the potential to be uncomfortable or even very painful to the MRI patient being exposed to a huge changing magnetic field?
Invariably the response to why titanium is safe focuses on the fact that it is not magnetic. I get the deer in the headlight look when I ask about eddy current heating and induced voltages.
Please help me understand why unduced eddy current heating and induce voltages are not a concern.
|
| | View the whole thread | Reply to this thread
(login or register first) | |
Mike ferty
Sat. 10 Apr.10,
17:39
[Start of:
'MRI terminology need clarification'
0 Reply]
Category:
Basics and Physics
|
| MRI terminology need clarification |
Hi,
This is a very wonderful site and I have learned alot from your definition database. I do have a question with some of the terminologies that I cannot find in your database, here are the ones:
What is:
Alpha pulse?
Inversion Pulse?
z-gradient pulse?
positive x-gradient pulse?
negative x-gradient pulse?
phase encoding pulse?
Refocusing gradient pulse?
Can you please help me know what there terms meant?
Many Thanks!
|
| | Reply to this thread
(login or register first) |
| |
| | Result Pages : [1] 2 | |
|
| |
 | Look
Ups |
| |
|
MR-TIP.com uses cookies! By browsing MR-TIP.com, you agree to our use of cookies. | | | [last update: 2024-02-26 03:41:00] |
|
|
bottom
top
