MRI MIDTERM pt 2

  1. reducing the TR will increase the saturation and therefore will result in ____________ the SNR
    decrease
  2. TE is the time  _______



    B.
  3. For FSE imaging scan time for a 2D acquisition can be calculated as what formula:
    TR x Mx x NSA x /ETL
  4. for a 2D volume scan time can be calculated how
    TR x Mx x NSA x #of slices (partitions)
  5. For an EPI acquisiton scan time is calculated by
    TR x Mx x NSA
  6. TR is the time between successive 



    C.
  7. TR is generally chosen by the amount of _______ desired on the image 


    B.
  8. for T1 information in the brain at 1.5T TR times of ______ are usually desired
    400-500msec
  9. Pixel size is determined by _____ & ______
    FOV and MAtrix
  10. to determine the pixel size 



    A.
  11. For the area of the pixel 


    A.
  12. for the voxel volume 



    B.
  13. For an isotropic voxel
    one side should equal the other side and the slice thickness
  14. In most cases to demonstrate pathology, high contrast _)_______ are selected 



    D.
  15. the image contrast is determined by the pulse sequence selected and its associated extrinsic paramters (4 things)
    TR TE TI flip angle
  16. when the SNR is adequate the image quality is generally good however when SNR is bad 



    D.
  17. generally the resolution is determined by the 



    C.
  18. voxel size is determined by 



    D.
  19. during MR image acquisition unwanted signals is known as 



    A.
  20. the acronym snr refers to ratio
    signal to noise
  21. Noise is random and originated from multiples sources including 



    D.
  22. when metal is present within the body the magnetic field around such object is 



    B.
  23. one direction in k space represents phase information while other represents 



    C.
  24. high amplitude phase encoding steps (edge of k-space) are weighted more to



    D.
  25. Low amplitude phase encoding steps (center of k - space) are weighted more to ______



    C.
  26. as slice thickness is increased 



    D.
  27. the first gradient to be applied is the ______ gradient 



    A.
  28. in a spin echo sequence the frequency encoding gradient is applied during the
    production of echo
  29. In a spin echo sequence the phase encoding gradient is applied 



    D.
  30. With each repetition, the phase encoding gradient will be applied with a different



    D.
  31. spatial resloution maybe increased by acquiring a greater 



    A.
  32. Increasing the number of phase encoding steps causes the scan time to 



    B.
  33. the magnetic susceptiibility can be defined as the
    ability for material to become magnetized
  34. the nucleus of the hydrogen atom is
    one proton
  35. iron is an example of a ______ substance
    ferromagnetic
  36. a diamagnetic substances exhibit ______ when placed in an externally applied magnetic field 



    C.
  37. exposing magnetized tissue to an rf field at the Larmor frequency first causes the hydrogen spins to _________



    A.
  38. the combination of t2 spin spin, inhomogeneities and chemical shift result in a rapid loss of transverse magnetization known as __________



    C.
  39. the tz* image susceptibility artifacts are more prominent on 



    C.
  40. the longitudinal magnetization regrows along the z-axis as spins in the high energy state lose energy during a process known as ___



    A.
  41. what is the gyromagnetic ratio for hydrogen at 1.5 Tesla
    42.6
  42. a insulator can be characterized by which of the following:



    C. resistant to the flow of electrons
  43. magnets are said to have 



    C.
  44. gradient echo sequences are more sensitive to field inhomogeneities than spin echo based sequences because they lack



    A.
  45. a inversion recovery sequence with a short ti(STIR) can suppress signal from



    A.
  46. In a multi echo conventional spin echo sequence each of the echoes will have a different 




    B.
  47. the gradient that is on during the production of the echo is the 



    A.
  48. the condition that exists in a gradient echo sequence when the TR is shorter than the t2/t1 of the tissue is called
    steady state
  49. what give the most chemical shift artifact
    superconducting magnet
  50. chemical shift artifact can be characterized by a bright and dark band on opposite sides of certain anatomy. Which direction would we see this artifact on MRI images 



    D.
Author
MriSensei
ID
340097
Card Set
MRI MIDTERM pt 2
Description
mri
Updated