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T he atomic magnetism

T he 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

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T he atomic magnetism

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  1. 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

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

  3. Spinning proton produce magnetic moment

  4. MAGNETIC MOMENT:

  5. Hydrogen atom =Proton

  6. Spinning of the Proton produce magmatic moment

  7. 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

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

  9. Energy difference

  10. 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

  11. 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

  12. 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

  13. Questions?

  14. N N S S size direction The magnetic vector

  15. PRECESSION Precessional path B0 Hydrogen nucleus

  16. 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.

  17. The precessional frequency

  18. 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

  19. 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”

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

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

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

  23. RESONANCE con’t

  24. 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

  25. 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

  26. Sending RF

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

  28. The precessional frequency

  29. 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

  30. 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

  31. 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

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

  33. 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

  34. MR SIGNAL • Collected by a RF receive coil

  35. Receiving coil

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

  37. 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

  38. 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

  39. T2 and T1 times

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