FSP Class-2-3 Magnet T1 T2 T2* IR FID

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flashsmilenet
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292378
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FSP Class-2-3 Magnet T1 T2 T2* IR FID
Updated:
2015-07-23 11:58:29
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FSP Class Magnet T1 T2 IR FID
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FSP Class
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FSP Class-2-3 Magnet T1 T2 T2* IR FID
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  1. MRI axis
    • Z - axial - longitudinal
    • X - sagittal
    • Y - coronal
    • X+Y - transverse
    • OBL - 2 simultaneously
  2. Larmor EQ
    • F = P = W= y B0
    •    F - frequency =
    •    P - precession = 42.6mhz/1T
    •    W0 - resonance frequency
    •    y - helium
    •    B0 - strength of the magnet
  3. NMR
    • Nuclear Magnetic Resonance (WRONG b/c no ionization)
    • NMV - Net Magnetic Vector - (RIGHT!)
  4. Nuclear spin
    ability of P to create (NMV = GMR) = AM + MM
  5. 3 necessaries for MRI:
    • 1) MR active nuclei - H1
    • 2) Static magnetic field - Main magnet - B0
    • 3) RF - Radiofrequency
  6. MR active nuclei
    • Proton (P) - subatomic nuclei
    • H1 - element
    •    - most abounded  
    •    - has property of spin - AM
    •    - MM of its own  
    • H1 is not only one:
    •    1) Phosphorus-31
    •    2) Fluorine-19
    •    3) Sodium-21
    •    4) Carbon-13
    •    5) Nitrogen-15
  7. What nuclei form MRI images
    - with odd atomic number
  8. W/o H1 how image looks like?
    grainy, not diagnostic
  9. Main Magnet
    - B0:
    - function:
    - criteria:
    - materials:
    • B0 - same value, never OFF
    • Function:
    •    1) Polarizes body tissue
    •    2) Possess strong attraction and deflection
    • Criteria:
    •    1) Stable
    •       - cryogenic materials (Helium, Nitrogen)
    •       - conductive under -469F, -269C, 4K
    •    2) Homogeneous - shim coils
    •       - active - always ON and has it's own power supply
    •       - passive - Sheets of iron cores stacked together
    •    3) Large - up to 3T
    • Materials:
    •    - Iron, Cobalt, Nickel
  10. Equilibrium
    • - body introduced to the magnet
    • - in a few sec magnet polarizes body
    • - week oriented parallel, strong - untiparallel
    • - NMV = Weak - Strong
    • - stronger magnet - stronger NMV - stronger signal and better image
  11. Magnetic susceptibilities
    • 1) Diamagnetic - weakly attracted (gold, silver)
    •       - no contribution to MRI
    • 2) Paramagnetic - slightly attracted (GPTA - Gadolinium Pentacetic Acid)
    •      - major contribution
    •      - very usefull
    • 3) Ferromagnetic - strongly attracted
    •      - catastrophic, deadly
    •      - depends on distance and orientation (position)
  12. Cryogenic materials
       - to maintain...
       - materials...
       - T
       - most modern...
    • - to maintain stability
    • - Helium, Nitrogen
    • - conductive under extremely low T
    •      -469F, -269C, 4K
    • - most modern MRI use Helium
  13. Resonance
    Exchange of energy between two systems at a specific frequency
  14. net magnetization
    • macroscopic magnetization
    • NM = Weak - Strong
    • has a longitudinal component (along the Z axis) aligned with B0
  15. B1
    • RF coils
    • second order of magnetism
    • detect and transmit MRI signal
  16. B0
    • Main magnet
    • static magnetic field - nonfluctuating
    • never OFF
    • cannot be adjusted
    • as ↥ B0 as T1 quicker
  17. Radiofrequency
    • - Criteria of magnetism
    • - Low level electromagnetic radiation
    • - Lowest energy wave in the electromagnetic spectrum (Radio wave)
    • - Applied to the human body by RF coils
    • - RF coils detect and transmit MRI signal
  18. Excitation
    • Radiofrequency applied by RF coils - B1 - second order of magnetism.
    • proton jumps from low to high energy state
    • from parallel to anti-parallel
    • gives magnitude (FOV) and direction (scanning plans)
  19. Longitudinal magnetization due to...
    ...a difference in the number of spins in parallel and anti-parallel state
  20. Transverse magnetization due to...
    ...spins getting more or less into phase
  21. Relaxation
    • radiofrequency OFF
    • P going back to equilibrium of net magnetization giving E to environment
    • electromagnetic energy is retransmitted (NMR signal)
  22. Longitudinal relaxation
       - corresponds to...
       - due to...
       - ?-? relaxation
       - % ?
    • corresponds to longitudinal magnetization recovery
    • due to energy exchange between the spins and surrounding lattice
    • spin-lattice relaxation
    • 63% of energy recovered - T1
  23. Transverse relaxation
       - corresponds to...  
       - result from...  
       - ?-? relaxation  
        - % ?
    • - corresponds to transverse magnetization decay
    • - results from spins getting out of phase
    • - spin-spin interaction
    • - 37% of energy left - T2
  24. T1 Conventional MRI scan (SE)
       - term
       - TR-TE
       - ... controls contrast
       - NMV in...
       - ?-?
       - energy...
       - ... time contrast
       - shows...
       - ... is bright
       - ... field strength
    • - longitudinal magnetization has returned to 63% of its final value
    • - TR­­↧ - TE↧
    • - TR primarily controls the contrast
    • - NMV in longitudinal (Z) direction
    • - spin-lattice relaxation
    • - energy given to surrounding tissue
    • - tissue-specific time constant
    • - shows anatomy (bone)
    • - fat is bright
    • - longer at higher field strengths
  25. T2 Conventional MRI scan (SE)
       - term
       - TR-TE
       - ... controls contrast
       - NMV in...
       - ?-?
       - energy...
       - ... time contrast
       - shows...
       - ... is bright
       - ... field strength
    • - transverse magnetization decay to 37% of its original value
    • - TR↥ - TE↥
    • - TE primarily controls the contrast
    • - NMV in transverse (X-Z) plane
    • - spin-spin interaction
    • - energy is exchanged to surrounding lattice
    • - tissue-specific time contrast and is always shorter than T1
    • - shows pathology (fluid)
    • - fluid is bright
    • - unrelated to field strength
  26. longitudinal magnetization has returned to 63% of its final value
    T1
  27. spin-spin interaction
    T2
  28. transverse magnetization left 37% of its original value
    T2
  29. spin-lattice relaxation
    T1
  30. shows pathology
    T2
  31. fluid is bright
    T2
  32. shows anatomy
    T1
  33. fat is bright
    T1
  34. longer at higher field strengths
    T1
  35. unrelated to field strength
    T2
  36. GPTA
    • Gadolinium Pent-acetic Acid
    • Paramagnetic - slightly attracted
    • major contribution, very usefull
    • Any spinal surgery must be done w gado. Must start immediately w 20 min to see diff b/w scar tissue and disk space.
    • QT - what enhances quicker? - scar tissue
  37. If BBB is disrupted - contrast will pass from what compartment to what
    From intravascular to interstitial
  38. BBB
    • Blood-Brain Barrier
    • dynamic interface that separates the brain from the circulatory system and protects the central nervous system from potentially harmful chemicals .
  39. FID
    • - Free Induction Decay
    • - Eddy Current
    • - occur before T1 and T2 (leakage current)
    • - caused by MF inhomogeneous
    • - decays along transverse plan
    • - when reach X-Y plan, becomes - T2*
    • - dephasing the P spin
    • - best for nerve roots
  40. T2*
    • product of FID
    • when FID reach X-Y plan, becomes - T2*
    • FID - Free Induction Decay
    • Eddy Current
    • occur before T1 and T2 (leakage current)
    • caused by MF inhomogeneous
    • dephasing the P spin
    • best for nerve roots
    • decays along transverse plan X-Y
  41. Best for nerve roots
    FID - Free Induction Decay - T2*
  42. Spin Echo Signal is...
    ... meaningful echo that contributes to the formation of an image
  43. Spin Echo PS
    • SE Pulse Sequence:
    •    - has 2 RF - starts w 90, ends w 180
    •    - FID - Free Induction Decay
    •    - TR - Time to repeat
    •    - TE - Time to echo
    •    - T1, T2, PD - SE
  44. TE
    • Time to echo
  45. TR
    • Time to repeat
  46. Brightest signal in MRI
    PD Conventional MRI scan
  47. PD Conventional MRI scan
    • PD - Proton Density
    • Brightest signal in MRI
    • Intermediate Pulse Sequence
    • TR↥ - TE↧
    • grayer in appearance
    • b/c 15% tissue differentiation
    • Pathology and anatomy
  48. TR primarily controls the contrast
    T1 (TR­­↧ - TE↧)
  49. TE primarily controls the contrast
    T2 (TR↥ - TE↥)
  50. Good for anatomy
    T1 (TR­­↧ - TE↧)
  51. Fat bright
    T1 (TR­­↧ - TE↧)
  52. Good for pathology
    T2 (TR↥ - TE↥)
  53. Fluid bright
    T2 (TR↥ - TE↥)
  54. Good for pathology and anatomy
    PD - Proton Density (TR↥ - TE↧)
  55. Grayer in apperance
    PD - Proton Density (TR↥ - TE↧)
  56. FSE Sequence
    • Fast Spin Echo
    • start w 90 followed by a train of 180
    • Difference - quicker scanning times
    • causes blurring as MRI is a tradeoff b/w parameteres
    • blurriness is solved by keeping ETL as low as possible
    • ETL - Echo Train Length - # of 180 pulses anfter the 90 pulse
    • FID - Free Induction Decay - T2*
    • SE - Spin Echo Signal
    • TE - Time to echo
    • TR - Time to repeat
  57. Intermediate Pulse Sequence
    • PD - Proton Density Contrast mechanism
    • TR↥ - TE↧
    • grayer in appearance
    • b/c 15% tissue differentiation
    • Pathology and anatomy
  58. IR Sequence
    • Inversion Recovery
    • start w 180 followed by 90
    • 180° RF inversion wave
    • 90° RF excitation wave
    • TI - Time to invert (delay between 180° and 90°)
    • TI controls contrast
    • Bone black - if white - pathology
  59. Good for all bone work
    STIR sequences
  60. Good for osteomyelitis
    STIR sequences
  61. STIR sequences
    • Short TAU IR
    • TAU - The interpulse times (time between the 90° and 180° pulse, and between the 180° pulse and the echo)
    • Good for:
    •      - osteomyelitis
    •      - all bone work
  62. Good for CSF flow
    FLAIR sequences
  63. Good for multiple sclerosis
    FLAIR sequences
  64. FLAIR sequences
    • Fluid Attenuated IR
    • Good for:
    •     - multiple sclerosis
    •     - whenever CSF flow
  65. T1 GRE
    • Grade and Echo
    • TR­­↧ - TE↧
    • Flip Ang ↥ <90o
    • the absence of a 180° RF rephasing pulse (GRE instead)
    • MRA - Angiography
    • Blood is bright
  66. How Pulse Sequence identified?
    By Flip angle
  67. T2 GRE
    • Grade and Echo
    • TR↥ - TE↥
    • Flip Ang ↧ <90o
    • the absence of a 180° RF rephasing pulse (GRE instead)
    • Blood imaging
  68. Gradient GRE echo
    • the flip angle usually below 90°
    • the absence of a 180° RF rephasing pulse (GRE instead)
  69. Motion artifact
    • - Ghosting
    • - phase encoding direction (mismapping the image

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