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# 04 relajacion transversal

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• THIS IS THE
• Transverse relaxation is also called Spin-Spin relaxation. The speed of rotation is influenced by the neighbouring protons. Compare with walking in a shopping mall on a Saturday afternoon. While walking you have to change your speed and direction constantly to avoid collisions whith other shoppers. The only difference is that protons do collide.
• When we look at one single proton, we can see that it makes one 360 degree rotation in a certain time...
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• ... But in the same time the red proton has covered more than 360 degrees, and the blue proton less.
• After the next rotation these differences are bigger.
• ..and bigger
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• Back to the first rotation and look at the signals that belong to the protons..
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• Now we add the summed signal, and you can see that the signal is getting weaker the more the protons are pointing in different directions.
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• The signal shift relative to each other, cancelling each other out. This is called dephasing.
• The signal that is generated after the 90 degree pulse is called FID or T2*.
• And is different for the various tissues. The time untill 63% of the signal has ´´died´´ is called the T2 time.
• And is different for the various tissues. The time untill 63% of the signal has ´´died´´ is called the T2 time.
• At the dawn of MR this signal could not be measured, because the hardware did not allow the fast switching. So we had to find a trick to overcome this problem.
• For that we need the help of the transmit coil again.
• When we transmit a signal for so long time that the protons are flipped over 180 degrees, look what happens..
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• The slow protons will be overtaken by the faster ones, thus generating a new strong signal.
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• In other words. The signal is restored with the help of a 180 degree pulse, resulting in a strong echo.
• Thats why we call it a refocussing pulse.
• As you saw, after the rephasing of the protons they will dephase again. And again we can apply a 180 degree pulse in order to rephase them, resuting in new signal or echo...
• The curve that we can draw through the tops of the echos is called the T2-envelope.
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• ### 04 relajacion transversal

1. 1. PHYSICAL PRINCIPLES Signal Generation
2. 2. nuclei, protons and spins longitudinal relaxation T1 transverse relaxation T2 exitation and relaxation relation between T1 and T2 signal generation
3. 3. transverse relaxation T2 Spin - Spin relaxation signal generation
4. 4. X Y Z B o signal generation transverse relaxation T2
5. 5. X Z B o Y signal generation transverse relaxation T2
6. 6. X Y Z B o signal generation transverse relaxation T2
7. 7. X Y Z B o signal generation transverse relaxation T2
8. 8. X Y Z B o signal generation transverse relaxation T2
9. 9. X Y Z B o signal generation transverse relaxation T2
10. 10. X Y Z B o signal generation transverse relaxation T2
11. 11. X Y Z B o signal generation transverse relaxation T2
12. 12. X Y Z B o signal generation transverse relaxation T2
13. 13. X Y Z B o signal generation transverse relaxation T2
14. 14. X Y Z B o signal generation transverse relaxation T2
15. 15. X Y Z B o Signal signal generation transverse relaxation T2
16. 16. X Y Z B o Signal signal generation transverse relaxation T2
17. 17. X Y Z B o Signal signal generation transverse relaxation T2
18. 18. X Y Z B o Signal signal generation transverse relaxation T2
19. 19. X Y Z B o Signal dephasing signal generation transverse relaxation T2
20. 20. S time F ree I nduction D ecay signal FID T2 signal generation transverse relaxation T2
21. 21. T2 S T2 definition T2: the time that passes untill 63% of the original signal has been lost time 63 % signal generation transverse relaxation T2
22. 22. T2 S T2* time signal generation transverse relaxation T2* Due to magnetic inhomegeneities the transverse relaxation is lost faster !! T2 T2*
23. 23. X Y Z B o signal generation transverse relaxation T2
24. 24. X Y Z B o transmit coil radio frequency transmitter signal generation transverse relaxation T2
25. 25. X Y Z B o transmit coil radio frequency transmitter 180 º 180 º signal generation transverse relaxation T2
26. 26. X Y Z B o 180 º signal generation transverse relaxation T2
27. 27. X Y Z B o 180 º signal generation transverse relaxation T2
28. 28. X Y Z B o 180 º signal generation transverse relaxation T2
29. 29. X Y Z B o 180 º signal generation transverse relaxation T2
30. 30. X Y Z B o 180 º signal generation transverse relaxation T2
31. 31. X Y Z B o 180 º signal generation transverse relaxation T2
32. 32. X Y Z B o 180 º signal generation transverse relaxation T2
33. 33. X Y Z B o 180 º signal generation transverse relaxation T2
34. 34. X Y Z B o 180 º signal generation transverse relaxation T2
35. 35. X Y Z B o 180 º signal generation transverse relaxation T2
36. 36. 180 º refocusing pulse signal generation transverse relaxation T2
37. 37. refocusing pulse 180 º 180 º signal generation transverse relaxation T2
38. 38. T2 envelope signal generation transverse relaxation T2
39. 39. in conclusion: <ul><li>T 1 relates to magnetisation </li></ul><ul><li>T 2 relates to signal </li></ul>signal generation
40. 40. nuclei, protons and spins longitudinal relaxation T1 transverse relaxation T2 excitation and relaxation relation between T1 and T2 signal generation