MRI Image Basics

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Author:
hrmckensey1015
ID:
307881
Filename:
MRI Image Basics
Updated:
2015-09-18 20:15:54
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mri image basics scanning principles
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Scanning principles: MRI image basics
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  1. When does T1 relaxation occur?
    When nuclei give up their energy to the surrounding tissue
  2. What is T1 relaxation also known as?
    • Spin lattice relaxation
    • longitudinal relaxation
    • Z axis regrowth
  3. What is T1 relaxation time?
    Recovery of 63% longitudinal magnetization of a specific tissues original magnetization
  4. T2 relaxation time is defined as ______
    Time it takes for 63% of the transverse magnetization to decay
  5. Fat has _____T1 relaxation time
    short
  6. Fat has a _____T2 relaxation time
    short
  7. Water has a ____T1 relaxation time
    long
  8. Water has a _____ T2 relaxation time
    Long
  9. The Larmor frequency of hydrogen in water is ______ than hydrogen in fat
    higher
  10. To obtain ____signal , there must be a small component of magnetization in the transverse plane in the coil
    low
  11. To obtain ____ signal, there has to be a large component of magnetization in the transverse plane received in the coil
    High
  12. On T1 sequences fat has a ____ signal
    High (bright)
  13. On T1 sequences water has ___ signal
    low (dark)
  14. A T1 weighted image utilizes what kind of TR and TE?
    • Short TR
    • Short TE
  15. In T2 sequences Fat has ____ singal
    High (Dark)
  16. In T2 sequences water has _____signal
    High (Bright)
  17. T2 weighted images utilize what TR and TE?
    • Long TR
    • Long TE
  18. Long TR does what to T1 information
    Minimizes
  19. Long TE does what to T2 information
    Maximizes
  20. What controls T1 weighting/contrast in an image?
    TR
  21. What controls T2 weighting/contrast in an image?
    TE
  22. What Factors will Increasing the TR affect?
    • Improve SNR
    • Increase scan time
    • Reduce T1 weighting
    • Increase the available # of slices
  23. What factors will Decreasing TR affect?
    • Lower SNR
    • Reduce scan time
    • Increase T1 weighting
    • Reduce the available # of slices
  24. The _____ the TE the better the overall SNR
    shorter
  25. What happens to scan time if the TR is doubled?
    Scan time will double
  26. What factors will reduce scan time?
    • Reduce TR
    • Reduce NEX/NSA
    • Increase parallel imaging factor
    • Utilize RecFOV
    • Utilize Half-Fourier/halfscan
    • Coarse Matrix
  27. What factors does slice thickness directly affect?
    • SNR of the image
    • Image resolution
    • Anatomical coverage
  28. If NEX/NSA is reduced what happens to SNR?
    SNR is reduced
  29. What does NEX not have an effect on?
    pixel size
  30. What happens to pixel size when a higher phase matrix is used?
    • improved resolution¬†
    • decreased SNR
  31. What factors will increase SNR?
    • Increase NEX/NSA
    • Increasing FOV
    • Decreasing phase matrix
    • Increasing TR
    • Increasing slice thickness
    • Reducing bandwidth
    • Reducing ETL
  32. If you use longer ETL there is an increased chance of ______
    blurring in the image
  33. What formula is used to calculate the size of a pixel?
    FOV / matrix
  34. Reducing the FOV by a factor of 2 will reduce voxel volume by a factor of ____
    4
  35. Reducing FOV in half will reduce the ____ and ____ dimensions each by ___
    phase and frequency dimensions by 2
  36. Formula for scan time in spin echo
    TR x phase matrix x NEX
  37. Formula for Scan time in fast spin echo
    TR x phase matrix x NEX/ETL
  38. Formula fo scan time in gradient echo
    TR x Phase matrix x NEX
  39. Formula to determine pixel size
    Pixel size= FOV / Matrix
  40. Voxel size formula
    Voxel size=FOV/matrix + Slice thickness
  41. what is an Isotropic voxel
    equal measurements in all 3 dimensions
  42. Pixel area formula
    Phase x frequency
  43. Voxel volume formula
    Pixel area x slice thickness
  44. What is Kspace
    Storage location of MR signal data
  45. Each line of k space is defined by ______-
    phase encoding gradient
  46. What is located in the central lines of K space?
    Signal and contrast information
  47. What is located in the outer lines of K space?
    High resolution data
  48. Reducing the number of lines filled in K space will produce what in an image?
    Decreased spatial resolution
  49. _____slope creates more detail
    Steep
  50. What is the approximate ETL for T1 weighting?
    2-7
  51. What is the ETL for PD weighting?
    3-12
  52. What is the ETL for T2 weighting?
    10-40
  53. When you increase the ETL what happens to slices?
    It reduces the number of slices
  54. Echo Spacing is defined as _________
    The time between successive 180* echoes in a FSE pulse sequence
  55. What is a typical echo spacing for a FSE?
    5ms -20ms
  56. The echo of the ______ will have the most signal
    effective TE
  57. What type of contrast will there be more of with a longer ETL?
    T2 contrast
  58. How many rows of space are filled per TR period in a spin echo sequence?
    1
  59. How many rows of kspace are filled per TR in a FSE sequence?
    same as the ETL
  60. What is elliptic centric kspace filling?
    collecting the low frequency(high amplitude signal) data points in space at the start of the scan in a spiral fashion
  61. During dynamic enhanced imaging for vasculature, contrast is administered and space is filled with _______
    centric kspace filling
  62. Where is the maximum signal stored in kspace?
    Center
  63. What is half fourier aka?
    Zero fill
  64. What is half fourier?
    acquiring a bit more than half the phase dimension kspace samples then interpolating the data with zeroes for the remaining half
  65. What is partial or fractional echo?
    • Only half the views of space are filled in the frequency axis
    • An acceleration technique used to shorten TR and TE
  66. When increasing NEX/NSA, SNR increases by _______
    square root of the % increase
  67. What happens when FOV is decreased?
    • Decreased SNR
    • Increased spatial resolution

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