MRI Exam

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MRI Exam
2011-02-12 21:53:43

Exam 1
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  1. What are the two phenomenons that occur when protons are placed in Bo?
    align with Bo and precession
  2. What is precession?
    spinning or rotation around an external magnet and depends on type of nucleus and intensity of the magnet.
  3. Define equilibrium in relation to MRI.
    It is the highest state that net magnetization can have. It is when a patient is placed in a strong external magnet, the protons start aligning with Bo, more are aligning than not and start precessing out of phase.(they align with Bo because it is a lower energy state). the ones that align antiparallel are a higher energy state.
  4. What is the abbreviation used for equilibrium?
    Mo, Mxy=zero at equilibrium
  5. Why can M not be detected along the Bo?
    It is too weak and cannot electromagneticlly induce.
  6. what is an angle in which protons can be flipped/rotated from the z-axis because the RF is energized and as long as its energized will continue to rotate?
    flip angle
  7. What pulse is strong, but short?
    Hard pulse
  8. What is a weak, but long pulse?
    soft pulse
  9. What pulse has a rotation angle less than 90 degree?
    Alpha Pulse
  10. What is described as a when Mz is smaller than Mo and Mxy is no longer zero, it is at equilibrium?
    Partial saturation. (nuclear spin is partial saturated)
  11. A decrease in Mxy is called ____, whereas an increase in Mxy is called ____.
    transverse relaxation, longitudinal relaxation.
  12. What is symbolized by RFt and RFs?
    RFt is an RF pulse transmitted to a patient. RFS is a RF pulse that is received from the patient.
  13. What determines the amplitude of the FID?
    same parameters that influence Mo, the number of spins involved (proton density), Bo, and y.
  14. What is Hydrogen's gyromagnetic ratio?
    42.6 MHz/T
  15. What is hydrogen's frequency of precession in a 1.5 T magnet?
    63.9 MHz/T
  16. Ensemble of spins are hard to measure because signals represent each individual nucleus. Therefore the Net Magnetization is used, which is abbreviated by what letter?
  17. Net magnetization is the sum of the ___?
    individual nuclear magnetic moments
  18. List factors that are related to the amount of signal available for MRI.
    The temperature of the material under investigation, the strength of the external magnetic field, the gyromagnetic ratio and the number of nuclei available in the volum of interest.
  19. Explain why a signal can not be received from Mz.
    The net magnetization along the Z-axis, Mz, is invisible. From the quantum mechanical view, directly measuring this magnetization is impossible form the classical point of view, the magnetization is so small relative to Bo that it cannot be measured.
  20. What is the purpose of an RF in MRI?
    The us of RF pulses in MRI produces an XY component to the net magnetization. When the net magnetization vector is roated, the Mz shrinks and Mxy grows. The net magetization in the XY plane is the only magnetization that can be detected.
  21. Why are vector diagrams useful in MRI?
    They are important becasue they show us direction and magnitude and allow us to follow the net magnetization.
  22. What are electric currents measured in?
  23. What is the difference in A/C current and D/C current?
    In DC current the current is flowing in one direction. If the switch is open the current stops and when its closed it resumes going in the same direction again. In AC current if the switch is open current does not flow, but once its is closed it flows in one direction and then reverses to flow in the opp. direction.
  24. Household current is generated and transmitted as what type of phase?
    three phase
  25. The unit for electrical power is what?
  26. the smallest unit of charge is a____?
  27. Why is the proton used in MRI instead of an electron?
    Protons are used because they are in a fixed location in the nucleus and because tehy are larger than an electron.
  28. What are three means of electrification?
    contact, friction, induction
  29. Know the four principles of electrostatic laws
    • :)Chp. 2
    • unlike verses like charges
    • Coulomb's law
    • Charge Distribution
    • Charge Concentration
  30. What is the smallest region of magnetism?
    magnetic domain
  31. A magnet has two poles called what?
  32. The magnetic field leaves the ____ pole and enters the ____pole of the magnet.
    North, South
  33. The magnetic field lines are called what?
    magnetic lines of induction
  34. The father of MRI is who?
    Felix Bloch
  35. Despite controversy, who recevied the Nobel Peace Prize for developing MRI?
  36. What is the ability to image differences amoung low-contrast tissues?
    Contrast resolution
  37. What is the ability to identify an object as separate and distinct from one another?
    Spatial Resolution
  38. Lis the four advantages of MRI over all other imaging modalities.
    Contrast Resolution, Direct Mult. Planar Imaging, Spectroscopy, and No Ionizing radiation.
  39. What are the two essential characteristics of the MRI computer system?
    It has to be able to store a large amount of info. and it has to be fast.
  40. What is an atom and what part of the atome is used fror MRI imaging?
    Atoms ake up the body and include electrons, protons, and neutrons. Protons are used for MRI.
  41. State the correct abbreviations for the following:
    Static Magnetic Field
    Net Magnetization
    Net Magnetization along the Z axis
    Net Magnetization along the XY axis
    Net Magnetization at equilibrium
    • Bo
    • M
    • Mz
    • Mxy
    • Mo
  42. What is the interaction between the spinning mass of the gyroscope and the mass of the earth that is manifest through the gravitational field, or more simple term, wobble?
  43. What is the Larmor Equation and its parts?
    • f=yBo and it identifies the frequency of precession.
    • -f=precessional frequency
    • -y=gyromagnetic ratio
    • -Bo=Static Magnetic Field Strength
  44. What is a quantity that has magnitude and direction?
  45. What is when a patient is placed in the presence of a strong external magnetic field, some of the individual nuclear magnetic moment align with the external magnetic field?
    Net Magnetization
  46. What is a magnet when it has both a north and south pole present?
  47. Why is Hydrogen useful in MRI?
    because it is the most abundant in our body due to the majority of our body is made up of water.
  48. T/F Bo is measured in Tesla

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