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
    • Image Upload 1
  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
    • AM - Angular Momentum
    • MM - Magnetic Moment
  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 (Angular Momentum)
    •    - MM (Magnetic Moment) 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. Main Magnet
    - B0:
    - function (2):
    - criteria (3):
    - 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
  9. 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
  10. 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)
  11. 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
  12. Resonance
    Exchange of energy between two systems at a specific frequency
  13. net magnetization
    • macroscopic magnetization
    • NM = Weak - Strong
    • has a longitudinal component (along the Z axis) aligned with B0
  14. B1
    • RF coils
    • second order of magnetism
    • detect and transmit MRI signal
  15. B0
    • Main magnet
    • static magnetic field - nonfluctuating
    • never OFF
    • cannot be adjusted
    • as ↥ B0 as T1 quicker
  16. 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
  17. 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)
  18. Longitudinal magnetization due to...
    ...a difference in the number of spins in parallel and anti-parallel state
  19. Transverse magnetization due to...
    ...spins getting more or less into phase
  20. Relaxation
    • radiofrequency OFF
    • P going back to equilibrium of net magnetization giving E to environment
    • electromagnetic energy is retransmitted (NMR signal)
  21. 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
  22. 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
  23. T1 Conventional MRI scan (SE)
       - term
       - TR-TE
       - what primarily controls the contrast?
       - NMV in what direction
       - ?-?
       - energy...
       - ... time contrast
       - shows...
       - what is bright
       - relation to field strength
    • - time to get to a point where 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 (other lattice)
    • - tissue-specific time constant
    • - shows anatomy (bone)
    • - fat is bright
    • - longer at higher field strengths
    • Image Upload 2
  24. T2 Conventional MRI scan (SE)
       - term
       - TR-TE
       - what primarily controls the contrast?
       - NMV in what direction
       - ?-?
       - energy is exchanged to...
       - ... time contrast
       - shows...
       - what is bright
       - relation to field strength
    • - time to get to a point where 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 other spin of the same lattice
    • - tissue-specific time contrast and is always shorter than T1
    • - shows pathology (fluid)
    • - fluid is bright
    • - unrelated to field strength
    • Image Upload 3
  25. Time to get to a point where longitudinal magnetization has returned to 63% of its final value
    T1
  26. spin-spin interaction
    T2
  27. Time to get to a point where transverse magnetization decay to 37% of its original value
    T2
  28. spin-lattice relaxation
    T1
  29. shows pathology
    T2
  30. fluid is bright
    T2
  31. shows anatomy
    T1
  32. fat is bright
    T1
  33. longer at higher field strengths
    T1
  34. unrelated to field strength
    T2
  35. 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
  36. If BBB is disrupted - contrast will pass from what compartment to what
    From intravascular to interstitial
  37. BBB
    • Blood-Brain Barrier
    • dynamic interface that separates the brain from the circulatory system and protects the central nervous system from potentially harmful chemicals .
  38. 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
    • Image Upload 4
    • Image Upload 5
  39. 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
    • Image Upload 6
  40. Best for nerve roots
    FID - Free Induction Decay - T2*
  41. 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
    • Image Upload 7
  42. TE
    • Time to echo
    • Image Upload 8
  43. TR
    • Time to repeat
    • Image Upload 9
  44. Brightest signal in MRI
    PD Conventional MRI scan
  45. 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
  46. TR primarily controls the contrast in...
    T1 (TR­­↧ - TE↧)
  47. TE primarily controls the contrast in...
    T2 (TR↥ - TE↥)
  48. Good for anatomy
    T1 (TR­­↧ - TE↧)
  49. Fat bright
    T1 (TR­­↧ - TE↧)
  50. Good for pathology
    T2 (TR↥ - TE↥)
  51. Fluid bright
    T2 (TR↥ - TE↥)
  52. Good for pathology and anatomy
    PD - Proton Density (TR↥ - TE↧)
  53. Grayer in apperance
    PD - Proton Density (TR↥ - TE↧)
  54. FSE Sequence
    • Image Upload 10
    • Fast Spin Echo
    • start w 90 followed by a train of 180
    • quicker scanning times
    • causes blurring as MRI is a trade-off b/w parameters
    • blurriness is solved by keeping ETL as low as possible
    • ETL - Echo Train Length - # of 180 pulses after the 90 pulse
  55. Image Upload 11
    • FID - Free Induction Decay - T2*
    • SE - Spin Echo Signal
    • TE - Time to echo
    • TR - Time to repeat
  56. Intermediate Pulse Sequence
    • PD - Proton Density Contrast mechanism
    • TR↥ - TE↧
    • grayer in appearance
    • b/c 15% tissue differentiation
    • Pathology and anatomy
  57. IR Sequence
    • Image Upload 12
    • 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
  58. Good for all bone work
    STIR sequences
  59. Good for osteomyelitis
    STIR sequences
  60. 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
    • Image Upload 13
  61. Good for CSF flow
    FLAIR sequences
  62. Good for multiple sclerosis
    FLAIR sequences
  63. FLAIR sequences
    • Fluid Attenuated IR
    • Good for:
    •     - multiple sclerosis
    •     - whenever CSF flow
    • Image Upload 14
  64. T1 GRE
    • T1 Grade and Echo
    • TR­­↧ - TE↧
    • Flip Ang ↥ <90o
    • the absence of a 180° RF rephasing pulse (GRE instead)
    • MRA - Angiography
    • Blood is bright
  65. How Pulse Sequence identified?
    By Flip angle
  66. T2 GRE
    • T2 Grade and Echo
    • TR↥ - TE↥
    • Flip Ang ↧ <90o
    • the absence of a 180° RF rephasing pulse (GRE instead)
    • Blood imaging
  67. Gradient GRE echo
    • Image Upload 15
    • the flip angle usually below 90°
    • the absence of a 180° RF rephasing pulse (GRE instead)
  68. Motion artifact
    • - Ghosting
    • - phase encoding direction (mismapping the image
  69. Diamagnetic
    • - weakly attracted (gold, silver)
    • - no contribution to MRI
  70. Paramagnetic
    • - slightly attracted
    • - major contribution
    • - major contribution
    • - GPTA - Gadolinium Pentacetic Acid)
  71. Ferromagnetic
    • - strongly attracted
    • - catastrophic, deadly
    • - depends on distance and orientation (position)
  72. Spin start w 90 followed by a train of 180
    Fast Spin Echo
  73. Spin with quicker scanning times
    Fast Spin Echo
  74. Why Fast Spin causes blurring?
    causes blurring as MRI is a trade-off b/w parameters
  75. How to solve blurriness in Fast Spin Echo?
    • - by keeping ETL as low as possible
    • - ETL - Echo Train Length - # of 180 pulses after the 90 pulse
  76. Spin start w 180 followed by 90
    Inversion Recovery
  77. What kind of wave is 180/90 in Inversion Recovery?
    • - 180° RF inversion wave
    • - 90° RF excitation wave
  78. What is Time to invert?
    - delay between 180° and 90° in Inversion Recovery
  79. What controls contrast in Inversion Recovery?
    TI - Time to invert (delay between 180° and 90°)
  80. In what spin if bone black - pathology?
    • Inversion Recovery
    • Bone black - if white - pathology
  81. In what spin the flip angle usually below 90° with the absence of a 180° RF rephasing pulse (GRE instead)
    Gradient GRE echo
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292378
Card Set
FSP Class-2-3 Magnet T1 T2 T2* IR FID
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FSP Class-2-3 Magnet T1 T2 T2* IR FID
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