FSP Class-7 - K-space/Signal

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Author:
Anonymous
ID:
295201
Filename:
FSP Class-7 - K-space/Signal
Updated:
2015-02-07 23:13:16
Tags:
FSP Class space Signal
Folders:
Class-7
Description:
FSP Class-7 - K-space/Signal
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  1. Events after MRI signal
    • 1) Slice - every RF - slice
    • 2) Phase - dephase - rephase
    • 3) Frequency - reading the signal
    • 4) Fourier Transformer - from analog to digital and pixelized in a form of matrix
  2. Types of acquisition of a K-space
    • 1) Sequential - slower
    • 2) 2D - quicker
    • 3) 3D - entire space filled at once (one moment.  99% MRAs
  3. How K-space filled?
    • inside-out toward outer edge of phase encoding direction  
    • Inside - Brightness ↥ - Spatial Resolution ↧ - good for chest
    • Outside - Brightness ↧ - Spatial Resolution ↥
    • EFF TE -
  4. NEX
    Number of RF excitations performed on a particular slice.
  5. Half Fourier
    • Half Fourier = 0.5 NEX
    •   - half filled w echo, another half w interpoled "zeros"
  6. Rise Time
    It is time, the gradients takes to reach full potential
  7. Slew Rate
    distant strength the gradient extand
  8. Pre-Tuning
    - maintaining homogeneity to the region of the interest (optimize shim coils)
  9. In the matrix row corresponds to...
    ...Phase
  10. In the matrix column corresponds to...
    ... Frequency
  11. Matrix > 512 ...
    • good for Sp resolution
    • bad for signal (↧ SNR)
  12. Matrix < 256 ...
    • good for signal (↥ SNR)
    • bad for Sp resolution
  13. Voxel
    3D - H-W-D
  14. How many pixels in the matrix formula
    #Pix = FOV/M x #slices
  15. Pixel size formula
    Size pix = FOV/M
  16. Types of resolution
    • 1) Spatial resolution
    •   - ability to see differential b/w adjacent structures
    •   - the smallest object that can be produces as an image has the best Sp resolution
    • 2) Temp resolution - imaging of organs in motion
    •   - cine
    •   - heart - rapid motion
    • 3) Contrast resolution - signal difference b/w b/w adjacent structures
  17. Spatial resolution is ↥ when:
      - Mat size...
      - Slice thickness...
      - FOV...
    • - Mat size 
    • - Slice thickness
    • - FOV
  18. SNR - Contrast is ↥ when:
      - Mat size...
      - Slice thickness...
      - FOV...
    • - Mat size
    • - Slice thickness
    • - FOV
  19. SNR Contras ↥ when Matrix 256 or 192?
    Matrix 192
  20. SNR Contras ↥ when Slice thickness 5 or 3 mm?
    Slice thickness 5 mm?
  21. SNR Contras ↥ when FOV 24 or 10?
    FOV 24
  22. Spatial resolution is ↥ when Matrix 515 or 256?
    Matrix 515
  23. Spatial resolution is ↥ when Slice thickness 1 or 2 mm?
    Slice thickness 1 mm
  24. Spatial resolution is ↥ when FOV 10 or 12?
    FOV 10
  25. Main controlling factors?
    • Mat size
    • Slice thickness 
    • FOV
  26. NEX/NSA (explanation)
    • NEX - Number of Excitations (acquisitions)
    •    - Number of RF excitations performed on a particular slice.
    •    - Synonymous with NSA
    • NSA - Number of Signal Averages
    •    - Number of NMR signals average together to arrive at a final value for each signal location
  27. NEX/NSA controls...
    ... time of exam
  28. If NEX/NSA ↥ from 2 to 4. What amount of improvement in SNR?
    SNR to √2 = 1.41
  29. Bandwidth
    range of frequencies received and transmitted
  30. Bandwidth - SNR, CSA ?
    • A) SNR - CSA
    • B) SNR - CSA
  31. Classification of Gradients
    • Physical      Logical
    •    Gz            Axial
    •    Gx           Sagittal
    •    Gy           Coronal

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