Ch 1

  1. What is a mass number?
    Total number of nucleons in a nucleus
  2. Why is mass number important to MRI?
    Determines weather a nucleus has a net magnetic moment or not.
  3. What conditions are necessary for resonance?
    • Energy must be applied at the precessional frequency of the nucleus
    • And at right angles to the main field.
  4. What is phase?
    Position of the magnetic moment at any point in time
  5. What is frequency?
    • Number of revolutions per second
    • Or
    • The speed of the precession
  6. What is the most common atom in the body?
    Hydrogen
  7. Isotopes
    Atoms of elements with the same number of protons but different number of neutrons
  8. Ionization
    The process of knocking out electrons
  9. Angular moment
    Net spin of a nucleus because of an odd number of protons and neutrons
  10. MR Active Nuclei
    Nuclei with an odd mass number or atomic weight
  11. Law of electromagnetic induction (Faraday 1833)
    • Connection between electric and magnetic fields and motion.
    • A moving electric field produces a magnetic field and vise versa
  12. Magnetic Moment
    • Each nucleus in a magnetic field has vector properties
    • (Size and direction)
  13. MR active Nuclei (list)
    • Hydrogen
    • Carbon
    • Nitrogen
    • Oxygen
    • Fluorine
    • Sodium
  14. Mass number of hydrogen
    1 H
  15. Mass number of carbon
    13 C
  16. Mass number of nitrogen
    15 N
  17. Mass number of oxygen
    17 O
  18. Mass number of fluorine
    19 F
  19. Mass number of sodium
    23 NA
  20. Name the isotope of hydrogen
    Protium
  21. What is the most common MR active nucleus
    Protium (the isotope of hydrogen)
  22. Alignment
    When placed in a strong static external magnetic field, the magnetic moments of H1 Nuclei orientate with the magnetic field.
  23. Parallel Alignment
    Magnetic moments in the same direction as the main B0 field
  24. Spin up is also known as:
    Parallel Alignment
  25. Antiparallel Alignment
    Magnetic moments in the opposite direction to the main B0 field.
  26. Spin-down is also known as:
    Antiparallel Alignment
  27. Net magnetic vector
    After alignment there are alway more spin-ups than spin-down.
  28. Zeeman Interaction
    Protons of H1 couple with the external magnetic field B0 and cause a discreet number of energy states
  29. Low-energy Nuclei
    Not enough energy to oppose B0
  30. High-energy nuclei
    Enough energy to oppose B0
  31. What is B0
    The large magnetic field of an MRI scanner.
  32. How is B0 measured?
    Tesla (T)
  33. Avogadro's Law
    6 x 10 (to the 23rd power) molecules per gram of tissue, and the number of excess spins is in the order of 6 x 10(to the 17th power) per gram of tissue.
  34. Precession
    Secondary spin, causes magnetic moments to circle around B0
  35. Precessional Path
    Course magnetic moments take around B0
  36. Precessional Frequency
    The speed magnetic moments precess around B0
  37. Larmor Frequency
    Precessional Frequency. Is determined by the Larmor Equation
  38. Unit that precessional Frequency is measured
    Hertz (Hz)
  39. Gyromagnetic ratio
    Expresses the relationship between angular momentum and the magnetic moments of each MR active nucleus
  40. How is gyromagnetic ratio expressed
    MHz/T
  41. What is the gyromagnetic ratio for hydrogen
    42.58 MHz/T
  42. What is the Larmor Frequency of Hydrogen at 1.5T
    63.8646 MH/T
  43. Precessional Phase
    Position of magnetic moments on their precessional Path
  44. What is the unit of Phase?
    Radian
  45. Incoherent
    Out of phase
  46. Coherent
    In phase
  47. Resonance
    Occurs when an object is exposed to an oscillating perturbation that has a frequency close to its own.
  48. RF excitation pulse
    • Produced by a transmit coil.
    • How resonance is achieved.
  49. How is the RF excitation pulse different from B0
    • B1 (RF excitation) produces an oscillating magnetic field 90 degrees to B0.
    • Very weak.
  50. What axis is the transverse plane on?
    X - y axis
  51. Which axis is the longitudinal plane
    Z-axis
  52. Nutation
    The spiral motion cause by 2 precessional motions that happened simultaneously.
  53. Saturation
    When spins are unable to absorb more energy or to be stimulated and release more energy
  54. Electromotive force (emf)
    Energy available from a unit of charge traveling once around a loop
Author
adavis
ID
350868
Card Set
Ch 1
Description
MRI in practice ch 1
Updated