01 physical principles signal generation

6,989 views

Published on

Published in: Education, Technology
3 Comments
0 Likes
Statistics
Notes
  • Be the first to like this

No Downloads
Views
Total views
6,989
On SlideShare
0
From Embeds
0
Number of Embeds
5,105
Actions
Shares
0
Downloads
120
Comments
3
Likes
0
Embeds 0
No embeds

No notes for slide
  • THIS IS THE
  • I will discuss these topics with you.
  • First...
  • The core of an atom is called the nucleus. The nucleus exists of neutrons and protons. Neutrons do not have an electrical charge, but protons do. Around this nucleus electrons are spinning. Electrons posses a negative electrical charge. In MRI we use the water atom as the source of our signals. First of all because it is the most abundant element in the Human Body, and, secondly, because it has only one electron around the nucleus. The more electrons around the nucleus, the more difficult it is to excite the nucleus or, in other words, the more the nucleus is ´´shielded´´.
  • The smallest part of the water atom is the proton The proton has a positive electrical charge....
  • ...and it rotates around it‘s own axis. electric charge and rotation generate magnetism. Compare with electromotor. Electricity and magnets generate rotation!
  • So we can state that protons behave like little magnets.
  • In the body there are many protons. When we put those protons in a magnetic field....
  • ...they will orient themselves into the direction of this magnetic field. When we look at the coordinate system to the right, we can say that the summed magnetisation is building up in the Z-direction.
  • ...
  • ...
  • However... If the protons are at a temperature close to the absolute 0 point, all protons will align.
  • But the reality is that we work at room temperature (or body temperature). In that case at a fieldstrenghth of 0.5 T only 5 protons per million will align. At 1.5 T, 15 protons will align. This explains why a higher fieldstrength has a better signal to noise ratio than a lower fieldstrength..
  • All these protons together can be represented as...
  • ..one big proton.
  • This rotation is called precession or Larmor frequency, after professor Larmor, who lived from....till..... and described...
  • This simple formula (don‘t worry, it‘s the only one I‘m showing) shows that the frequency of rotation of the protons depend on the fieldstrength we are working with. The higher the fieldstrength, the higher the frequency.
  • In this table the frequencies for the different elements are shown, relative to the applied fieldstrength. As you can see it‘s a linear function.
  • When we look at the relative sensitivity of the different elements, and take hydrogen as 100%, we can see that other elements are less sensitive to magnetisation. Another reason why we use the water atom as our source for imaging.
  • 01 physical principles signal generation

    1. 1. PHYSICAL PRINCIPLES Signal Generation
    2. 2. nuclei, protons and spins signal generation longitudinal relaxation T1 transverse relaxation T2 excitation and relaxation relation between T1 and T2
    3. 3. nuclei, protons and spins signal generation longitudinal relaxation T1 transverse relaxation T2 exitation and relaxation relation between T1 and T2
    4. 4. ATOM nucleus proton positive charge neutron no charge electron negative charge hydrogen atom proton signal generation nuclei, protons and spins
    5. 5. Proton signal generation nuclei, protons and spins
    6. 6. electric charge + rotation magnetism + signal generation nuclei, protons and spins
    7. 7. electric charge + rotation magnetism N S signal generation nuclei, protons and spins
    8. 8. X Y Z summed magnetization signal generation nuclei, protons and spins
    9. 9. X Y Z signal generation nuclei, protons and spins summed magnetization
    10. 10. X Y Z signal generation nuclei, protons and spins summed magnetization
    11. 11. X Y Z signal generation nuclei, protons and spins summed magnetization
    12. 12. o 0,01 Tesla 0 Kelvin = - 274 C o signal generation nuclei, protons and spins
    13. 13. signal generation nuclei, protons and spins 5 ppm 0,5 Tesla 1,5 Tesla 15 ppm 2,3 ppm 0,23 Tesla 20 Celsius o
    14. 14. B 0 signal generation nuclei, protons and spins
    15. 15. B 0 signal generation nuclei, protons and spins
    16. 16. B 0 signal generation nuclei, protons and spins
    17. 17. B 0 signal generation nuclei, protons and spins
    18. 18. B 0 signal generation nuclei, protons and spins
    19. 19. B 0 signal generation nuclei, protons and spins
    20. 20. B 0 signal generation nuclei, protons and spins
    21. 21. B 0 signal generation nuclei, protons and spins
    22. 22. B 0 signal generation nuclei, protons and spins
    23. 23. B 0 signal generation nuclei, protons and spins
    24. 24. B 0 signal generation nuclei, protons and spins
    25. 25. B 0 signal generation nuclei, protons and spins
    26. 26. B 0 signal generation nuclei, protons and spins
    27. 27. B 0 signal generation nuclei, protons and spins
    28. 28. B 0 signal generation nuclei, protons and spins
    29. 29. B 0 signal generation nuclei, protons and spins
    30. 30. B 0 signal generation nuclei, protons and spins
    31. 31. B 0 signal generation nuclei, protons and spins
    32. 32. B 0 signal generation nuclei, protons and spins
    33. 33. B 0 signal generation nuclei, protons and spins
    34. 34. B 0 signal generation nuclei, protons and spins
    35. 35. Precession Larmor frequency B 0 signal generation nuclei, protons and spins
    36. 36. f 0 =  x B 0 <ul><li>f = frequency </li></ul><ul><li>= constant of isotope </li></ul><ul><li>B = magnetic field </li></ul>B 0 signal generation nuclei, protons and spins
    37. 37. signal generation nuclei, protons and spins
    38. 38. signal generation nuclei, protons and spins
    39. 39. nuclei, protons and spins signal generation longitudinal relaxation T1 transverse relaxation T2 excitation and relaxation relation between T1 and T2

    ×