|
Magnetic
Resonance -
Technology
Information
Portal |
Welcome to MRI Technology • |
|
|
 | Info
Sheets |
| | | | | | | | | | | | | | | | | | | | | | | | |
 | Out-
side |
| | | | |
|
| | | | | |
| Result: Searchterm 'hydrogen'
found in 2 messages |
| Result Pages: [1] |
More Results:  Database (22) News Service (4) Resources (2) |
|
|
Steven Ford
Thu. 2 Dec.10,
15:18
[Reply (1 of 2) to:
'T1&T2 WAIGHTED MEANING ?'
started by: 'BINU VAEGHESE'
on Wed. 1 Dec.10]
 Category:
Basics and Physics
|
| T1&T2 WAIGHTED MEANING ? |
All MRI images have contrast (the bright and the dark) that is based on properties of the tissue that's being imaged. In MRI (unlike, for example, CT) those images are based on a combination of several physical properties. So to some extent ALL MRI images are based partly on property A, property B, etc.
The tissue properties that are referred to include proton density (how many hydrogen nuclei are in a given area), motion, and two other properties that are called T1 and T2. These are properties that can be seen onloy by using the MRI instrument, much as without a microscope one cannot see inside a cell.
A T1 weighted image is one in which the differences between T1 properties of the various tissues are the predominant reason why some parts of the image are bright and others are not as bright.
This is medically useful because, since T1 and T2 are distinct properties, diseased tissue may show up different than normal tissue on either the T1 weighted scan or the T2.
|
|  View the whole thread | | |
hithesh n
Fri. 11 Sep.09,
08:33
[Reply (2 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 |
Hi Bjorn,
I might be able to explain this even though its too late.
Initially a 90 excitation pulse is applied, the Hydrogen protons precess in the XY plane. Now they are spinning in sync in the XY or transverse plane. This is where they emit the RF signal.
But pretty soon, the neighboring hydrogen protons go out of sync, ie one is going faster and the other is going slower. This is similar to runners running a race in a track, they all start at the same time(assume) but after a couple of secs, some run faster than the other. The faster ones are in the front and the slower ones are in the back.
How do you bring them back into sync?
This is where the 180 excitation comes into play.
Now you apply a 180 pulse, this is equivalent to making the runners run in opposite direction. Now suddenly, the slower runners are gonna be in the front and faster ones in the back. Eventually the faster ones catchup and all of them are gonna be in sync. They go out of sync again.
They go out of sync bcoz the magnetic field applied is not uniform and due to material (tissues, bones etc). Local variations in the field causes the protons to go out of sync.
The 180 brings them in to coherence, not instantly but they do catch up and become coherent.
The 90, brings them into coherence almost instantly.
|
| | View the whole thread | | |
| |
| | Result Pages : [1] | |
|
| |
 | 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
