MRI MIDTERM

  1. within seconds of tissue being placed in a magnetic field the hydrogen protons will assume one of two possible spin states or energy levels 



    D.
  2. while in the magnetic field hydrogen protons wobble this wobbling is known as
    precession
  3. partial volume averaging is the result of large voxel imaging acquired 



    D.
  4. __________ is an example of a sampling artifact and occurs in both the phase and frequency direction where signal from outside the fov is superimposed 



    D.
  5. the 180 rf pulse that follows the initial 90 dg rf pulse in a spin echo sequence will produce an echo while correcting for 



    B.
  6. an inversion recovery sequence begins with ____
    180 deg rf pulse
  7. in a fast spin echo sequence the effective TE are the echos that are encoded 



    B.
  8. in a fast spin echo pulse sequence if the echo train length is increased by a factor of four:



    C.
  9. a leak in the RF shielding can result in extraneous signals entering the scan room and manifesting themselves as ________ artifactt on images
    zipper
  10. hydrogen in fat and hydrogen in water precess at different frequencies; this shift in resonant frequency is referred to as _______
    chemical shift
  11. Truncation and gibbs artifact can minimized by ______ encoding steps 



    D. increasing the frequency
  12. magnetic susceptibility artifact is proportional to _______ 



    D.
  13. magnetic susceptibility artifact appears as a ________ in the area of metal 



    C.
  14. if the slice thickness is increased from 3mm to 6mm the voxel colume will _______ and the SNR will increase by a factor of _________



    B.
  15. in a FSE acquisition the number of echoes produced in a single repitition is an operator selectable parameter known as the ____ (2 things)
    ETL and Turbo factor
  16. echoes generated following higher amplitude phase encoding gradients are encoded for the _______ lines of k-space and echoes generated following lower amplitude phase encoding gradients are encoded for the ____ lines of k-space
    outer/inner
  17. when a long effective TE is selected it can be used in combination with a ______ however, when a short TE is used it should be used with a _____ to minimze image blurring
    Long ETL/ short ETL
  18. motion artifacts occur along the _____ on MR images. For this reason the direction of ____ generally defaults along the short axis of the anatomy



    C.
  19. a 2d acquisition selectively excites a ____ of tissue while a 3d acquisition excites a ______



    A.
  20. A voxel that is isotropic is _____ in ______ dimensions and shaped like
    • equal 
    • all 
    • cube
  21. as the frequency matrix increases scan time 


    B.
  22. if a 256 frequency encoding is selected , the system will sample the echo ______ in the presence of the frequency encoding gradient
    256 times
  23. if a phase resolution of 256 is desired then the pulse sequence must be repeated a minimum of _____ and with each repetition the phase encoding gradient will be applies with a different amplitude/ polarity
    256
  24. increasing the matrix increases the number of phase and frequency steps and therefore 


    A.
  25. increasing the number of phase and/ or frequency encodings _______



    B.
  26. increasing the number of phase encoding (samplings)


    A.
  27. the slice thickness is determined by 


    C.
  28. in a 2d single slice selection scan time is determined by the ____ _____ ____
    tr x #of phase encodings x NSA
  29. Increasing the NSA by a factor of four increases sampling time ______ and increases snr about ______



    B.
  30. the FOV controls the _____ in 2 dimensions


    A.
  31. to reduce the FOV by 20% the voxel volume would decreases by
    40%
  32. the only way the spatial resolution can be increases is 



    C.
  33. Increasing the FOV _____



    D.
  34. the matrix is the ______ chosen to make the image 



    D.
  35. as the phase matrix increases scan time ____
    increases
  36. conventional SE sequences can acquire T2 or PD contrast with _________ selections 



    D.
  37. long tr sequences yield 



    C.
  38. In a gradient echo sequence ______ is manipulated to maintain image contrast
    flip angle
  39. As the flip angle is reduce ( assuming tr is constant) spins with longer t1 times exhibit greater longitudinal recovery and the image becomes 



    C.
  40. the flip angle that produces the maximum signal for a given tr is known as 



    C.
  41. Inversion recovery sequences were initially utilized to get images with very strong



    A.
  42. Inversion sequences begin with 180 rf pulse to invert longitudinal magnetization. After the inversion there is a operator specified delay time known as the ______.



    C.
  43. FLAIR sequences are useful for demonstrating 



    A.
  44. at 1.5 T STIR sequences generally use TI times of
    150ms
  45. At 1.5 T FLAIR sequences generally use TI times of
    2000ms
  46. Longer TE allows for _______ slices 



    C.
  47. using a short effective te places the echoes in the train in _______ of k space 



    D.
  48. FSE image blurring increases as the effective TE 



    C.
  49. In a spin echo sequence the time between the 90 rf pulse and 180 pulse is
    1/2 TE (TAU) time
  50. Presaturation pulses usually occur 
    prior to ______ pulse
    Prior to excitiation pulse
  51. An inversion recovery sequence, image contrast is controlled by:



    A.
  52. A narrow bandwidth 



    B.
  53. the best pulse sequence to minimize susceptibility artifact is 



    B.
  54. the effective te or target te is the echo that is encoded in the _____ most portion of k space 



    B.
  55. FSE images are obtained by filling ______ of k space at the same time in each TR period 



    A.
  56. Selecting a long te (80 msec or higher) will produce an image with
    more t2 contrast
  57. Using a long TR does not make image _____ it makes it less ______
    t2 weighted / t1 weighted
  58. If PD weighting is desired a short TE is selected (20ms or less) to reduce the ______ and a long TR is then selected (2000ms) to reduce ___________
    T2 weighting/ T1 weighting
  59. reducing the tr increases the _____ on the image



    A.
  60. as we increases TR scan time 


    C.
  61. As the tr increase the imaging time (within the sequence ) _____and therefore the number of slices allowed during the sequence _______
    increases/increases
Author
MriSensei
ID
340079
Card Set
MRI MIDTERM
Description
mri
Updated