T he atomic magnetism

2. The atomic magnetism • Objectives • Atomic structure • Motion of the atomic particles • MRI Active elements • The selective element for MRI • Law of electromagnetism • Alignment • Precession • The precession frequency-larmor’s equation • Resonance • Radiofrequency energy • The Free induction decay • T1 recovery • T2 relaxation

3. TYPES OF ATOMIC MOTION • The electron orbits the nucleus • The electron spins on its own axis • ***The nucleus spins on its own axis***

4. Spinning proton produce magnetic moment

5. MAGNETIC MOMENT:

7. Hydrogen atom =Proton

8. Spinning of the Proton produce magmatic moment

10. LAW OF ELECTROMAGNETISM • A charged particle in motion will create a magnetic field • The positively charged, spinning hydrogen nucleus generates a magnetic field • WHY HYDROGEN? • Very abundant in the human body-H20 • Has a large magnetic moment

12. Spins in a magnetic field will be affected by the magnet field

13. Energy difference

14. When a body is placed into the bore of the scanner, the strong magnetic field will cause the individual hydrogen nuclei to either: A) ALIGN ANTI-PARALLEL TO THE MAIN MAGNETIC FIELD (B0) OR B) ALIGN PARALLEL TO THE MAIN MAGNETIC FIELD (B0) Anti-parallel high energy NMV B0 Parallel low energy

16. When a body is placed into the bore of the scanner, the strong magnetic field will cause the individual hydrogen nuclei to ALIGN PARALLEL TO THE MAIN MAGNETIC FIELD (B0) Anti-parallel high energy NMV B0 Parallel low energy

17. NET MAGNETIZATION VECTOR NMV • An excess of 2hydrogen nuclei will line up parallel to B0 and create the NMV of the patient Parallel low energy B0 NMV

18. Questions?

19. N N S S size direction The magnetic vector

21. PRECESSION Precessional path B0 Hydrogen nucleus

22. PRECESSION • The speed at which hydrogen precesses depends on the strength of B0 and is termed the • “precessional frequency” • The frequency is determined by the gyro magnetic ratio of atoms and the strength of the magnetic field. • The gyromagnetic ratio is different for each nucleus of different atoms.

23. The precessional frequency

24. 42.57 MHz/TeslaX1.5 Tesla=63.86MHz • 42.57 MHz/TeslaX1.0Tesla=42.57MHz • 42.57 MHz/TeslaX3 Tesla=127.71MHz • 42.57 Mhz/TeslaX7.0Tesla=?MHz

25. Influence of B0on the hydrogen • Due to the influence of B0, the hydrogen nucleus “wobbles” or precesses The precessional paths of the individual hydrogen nucleus’ is random, or “out of phase”

27. WE NEED THEM TO precesses“IN-PHASE” OR TORESONAT • RESONANCE • IN-PHASE RESONAT means to have the same speed

28. Resonance http://www.liveleak.com/view?i=ef6d79891a http://www.youtube.com/watch?v=WLVvnG__23s

29. WE can enforce protons to be “IN-PHASE” OR TO RESONATE… RESONANCE con’t

30. RESONANCE con’t

31. The energy, frequency and wavelength of the radiation which makes up the Electromagnetic Spectrum. The X- and gamma-ray window has been used for diagnostic and therapeutic medical applications . The NR window is used in Magnetic Resonance Imaging (MRI). Generated by Kieran Maher using Aldus Super Pain

32. RADIOFREQUENCYENERGY • WE Apply “pulses” of RF • RF pulse is applied by the RF coil so that: • B1_RF magnetic field is 90 to B0= maim magnetic field

33. Sending RF

34. What is the frequency of the radio waves we send to the protons to make them resonate or precesses in phase?

35. The precessional frequency

36. 42.57 MHz/TeslaX1.5 Tesla=63.86MHz • 42.57 MHz/TeslaX1.0Tesla=42.57MHz • 42.57 MHz/TeslaX3 Tesla=127.71MHz • 42.57 Mhz/TeslaX7.0Tesla=?MHz

37. DURING RESONANCE… 1) The hydrogen atoms begin to precess “in phase” 1) 2) The hydrogen atoms align with the RF’s magnetic field (B1) and they flip!! X direction Z direction RF B0 NMV flips! B0 NMV PULSE B1 B1

38. Degree of flip, Flip angle We decide the degree of flip from the Z direction into the X direction flip angle range from 1 to 180 degree depending on what we need

39. Changing names of directions X direction=Transvers direction X direction NMV flips! Z = Longitudinal direction B1 Z direction B0 NMV

41. MR signal Immediately after the flip of magnetic field from Longitudinal direction to the Transvers direction The Transverse magnetic field starts to lose its strength=relaxing= decay Relaxing of the transvers magnetic field results in releasing the energy as MRI signal

42. MR SIGNAL • Collected by a RF receive coil

43. Receiving coil

44. Free induction decay Free decaying of the transvers magnetic field results in inducing MRI signal This is called Free induction decay

45. T2 Spin-Spin relaxation Relaxing =decaying of the transvers magnetic field results in releasing the energy as MRI signal The time it takes 37% of the transvers magnetic field to relax is called T2

46. T1= Spin lattic recovery At the same time while The Transverse magnetic field starts to lose its strength=relaxing= decay The Longitudinal magnetic field starts to recover its strength=Recovery The time it takes 63% of the Longitudinal magnetic field recover is called T1

47. T2 and T1 times