|
Magnetic
Resonance -
Technology
Information
Portal |
Welcome to MRI Technology • |
|
|
 | Info
Sheets |
| | | | | | | | | | | | | | | | | | | | | | | | |
 | Out-
side |
| | | | |
|
| | | | | |
| 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) |
|
|
Reader Mail
Tue. 8 Jun.10,
21:23
[Start of:
'Breast MRI selection-PLEASE HELP!'
1 Reply]
 Category:
Applications and Examinations
|
| Breast MRI selection-PLEASE HELP! |
Hi, i am new here..if this is in the wrong forum, PLEASE relocate, THANK YOU!!
I am not familiar with Breast MRIs and i need an advice on the most up todate Breast MRI as i may have b.cancer.
I have family history, maternal side and dense breast, thus the MRI.
I was offered 1) Siemens MAGNETOM Espree 1.5T
2) The Aurora® 1.5T Dedicated Breast MRI System with Bilateral 3-D SpiralRODEO™
3) Phyllips 3T Breast MRI
PLEASE, PLEASE HELP!!! Which one and WHY?
THANK YOU!!!
Eva.
|
|  View the whole thread | Reply to this thread
(login or register first) | |
Oliver Lyttelton
Mon. 1 Mar.10,
13:39
[Reply (8 of 12) to:
'90 excitation pulse vs 180 inversion pulse'
started by: 'Bjorn Redfors'
on Sat. 27 Jun.09]
Category:
Basics and Physics
|
| 90 excitation pulse vs 180 inversion pulse |
Okay, so this thread is answering close to a question I had, which is how to conceptually understand what happens with alpha>90 degrees excitation pulses.
I can imagine spinning tops, precessing at the Larmor frequency, I can imagine that as you apply the excitation pulse which is always in the transverse plane to the main magnet, you start to pull the tops further away from the B0 axis and bring them into coherence so like lots of little lighthouses they are all bright/dark in phase with each other. I can imagine a 90 degree pulse bring the spins completely into the transverse plane. I can imagine them relaxing, dephasing quickly and then slowly reducing their angle of precession back up towards initial state close to direction B0.
But what I can't understand in my (rather newtonian) model, is what happens as you continue to excite beyond the 90 degree transverse plane. I sort of get that somehow the spins continue to rotate in some (weird) dimension, and that they have to come back through that (weird) dimension first before returning from 90 degrees back to the relaxed state. But what happens in "weird" dimension is beyond my conceptual model. Can someone extend my model for me, preferrably without signal equations?
tar muchly,
Oliver
|
| | View the whole thread | | |
Iosif Sogolov
Sun. 3 Jan.10,
20:49
[Reply (7 of 12) to:
'90 excitation pulse vs 180 inversion pulse'
started by: 'Bjorn Redfors'
on Sat. 27 Jun.09]
Category:
Basics and Physics
|
| 90 excitation pulse vs 180 inversion pulse |
prior 90: spins precess around B0 uncoherently, there for the sum of their projections on TRANSVERSE plane is ZERO, they are "unfocused" in this plane. 90 and right after: all above mentioned spins are forced to rotate around B1, it should be stressed - in only one for ALL of them chosen direction of rotation (depends of B1 direction) to the TRANSVERSE plane, they all will come compact to this plane and now they do give here NET MAGNETIZATION, become "focused".
|
| | View the whole thread | | |
Lyle Downing
Sat. 26 Sep.09,
20:27
[Reply (4 of 12) to:
'90 excitation pulse vs 180 inversion pulse'
started by: 'Bjorn Redfors'
on Sat. 27 Jun.09]
Category:
Basics and Physics
|
| 90 excitation pulse vs 180 inversion pulse |
Perhaps this will help shed some light on this.
Keep in mind that before the initial 90 pulse all protons contributing to the MR signal are in a relaxed state completely in alignment with the static magnetic field. Flipping them 90 degrees into the transverse plane does align them up initially and yes they do relax at different rates as they give up their energy. The 180 pulse takes whatever state they are in at the time and flips them in order to not make them all 180, but to quickly get a cleaner non contaminated representation of the tissues in question. So for example after the initial 90 and after letting the protons relax for a bit you might see water at say 50 degrees and fat at say 70 degrees flipping them 180 keeps whatever energy state they are in the time.
|
| | View the whole thread | | |
n p
Fri. 11 Sep.09,
11:50
[Reply (3 of 12) to:
'90 excitation pulse vs 180 inversion pulse'
started by: 'Bjorn Redfors'
on Sat. 27 Jun.09]
Category:
Basics and Physics
|
| 90 excitation pulse vs 180 inversion pulse |
no hithesh n, that is a 180 rephasing pulse. thats not the question. the question is how is the net magnetization changed from the z plane to the -z plane without causing phase coherence, like the case of an inversion pulse. it is supposedly 2x as long or 2x as strong as the 90 degree pulse, but doesn't cause coherence. Why not is the question.
|
| | View the whole thread | |
| |
| | Result Pages : 1 2 3 4 5 6 7 8 9 10 [11] 12 13 14 15 16 17 18 | |
|
| |
 | 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
