FSP Class-7 - K-space - signal

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  1. Event that occurs after ANY MRI signal
    • 1) Slice
    • 2) Phase
    •     - Depahse
    •     - Rephase
    • 3) Frequency
    • Image Upload
  2. After each signal the Fourier Transformer...
    • 1) converts analog to digital
    • 2) pixilize in a form of matrix
  3. Image Upload
    • Sequential type of acquisition
    • slower
  4. Image Upload
    • 2D type of acquisition
    • quicker
  5. Entire space fills at once (one moment)
    3D type of acquisition
  6. Types of acquisition of a k-space
    • 1) Sequential - slower
    •  Image Upload
    • 2) 2D - quicker 
    • Image Upload
    • 3) 3D - entire space fills at once (one moment)
    •   - slab (пластина, большой кусок)
    •   - 99% MRAs
  7. ... holds row data
    K-space ...
  8. K-Space
    • - noise from GRE echo is placed in the k-Space
    • - k-space holds row data
  9. K-space Inside
    • - very brigth 
    • - ↥ contrast 
    • - ↧ resolution 
    • - used by (♢EFF TE - middle volume of the center of the case space) 
    • - good for chest
  10. K-space Outside
    best spatial resolution
  11. K-Space fills ...
    • ... inside-out
    • Inside -
    •   - very brigth
    •   - contrast
    •   - resolution
    •   - used by (♢EFF TE - middle volume of the center of the case space)
    •   - good for chest
    • Outside - best spatial resolution
  12. NEX is...
    • number of acquisitions
    • How many times each line of k-space data is acquired during the scan
  13. Image can be reconstructed using only one half of the k-space
    Half Fourier
  14. Image Upload
    • - Half Fourier
    • - 0.5 NEX
    • - image can be reconstructed using only one half of the k-space
    • - half w echos, another half w interpolated zeros
  15. Half Fourier
    • - 0.5 NEX
    • - image can be reconstructed using only one half of the k-space
    • - half w echos, another half w interpolated zeros
    • Image Upload
  16. Rise Time
    • - time the gradients takes to reach full potential
    • - occurs before gradient
  17. Pre-tuning
    • - maintaining homogeneity to the region of the interest optimize shim coils  - good for knee
    • - occurs before gradient
  18. Slew Rate
    • - distant strength the gradients extend
    • - occurs before gradient
  19. Before Gradients
    • 1) Rise Time
    •   - time the gradients takes to reach full potential
    • 2) Slew Rate
    •   - distant strength the gradients extend
    • 3) Pre-tuning
    •   - maintaining homogeneity to the region of the interest optimize shim coils
    •   - good for knee
  20. In matrix colums represent -
    frequency
  21. In matrix rows represent -
    phase
  22. Rows and columns of pixels
    matrix
  23. Matrix is...
    • ... rows and columns of pixels
    • Rows - phase
    • Columns - frequency
  24. Matrix size best for spatial resolution
    MS > 512
  25. Matrix size best for signal (↥SNR)
    MS < 256
  26. MS < 256
    best for signal (↥SNR)
  27. MS > 512
    - best for spatial resolution
  28. Matrix sizes
    • MS > 512 - best for spatial resolution
    • MS < 256 - best for signal (SNR)
  29. ↥ Matrix ... pixels
    ... smaller and more pixels
  30. Pixel
    2D
  31. Voxel
    3D (H, W, D)
  32. Pix Size Formula
    Pix Size = FOV/m
  33. # of pixels formula
    • #Pix = FOV/m x #slices
    • Pix Size = FOV/m
  34. Spatial resolution
    • - ability to differentiate b/w adjacent structures  
    • - how well we can see small structures apart
  35. Temp resolution
    • - imaging of organs in motion  
    • - rapid motion (heart)
  36. Contrast resolution
    • - signal difference b/w adjacent structures 
    • - differences in intensity in an image
  37. Types of resolutions
    • 1) Spatial
    •   - ability to differentiate b/w adjacent structures
    •   - how well we can see small structures apart
    • 2) Temp
    •   - imaging of organs in motion
    •   - rapid motion (heart)
    • 3) Contrast
    •   - signal difference b/w adjacent structures
    •   - differences in intensity in an image
  38. ↥ Matrix
    ↥ SP Resolution
  39. ↥ Slice Thk
    ↥ SNR/Contrast
  40. ↧ Slice Thk
    ↧ SP Resolution
  41. ↧ Matrix
    ↥ SNR/Contrast
  42. ↥ FOV
    ↥ SNR/Contrast
  43. ↧ FOV
    ↧ SP Resolution
  44. Main controlling factors:
    • ↧ Matrix -     ↥ SNR/Contrast
    • ↥ Matrix -     ↥ SP Resolution
    • ↥ Slice Thk - ↥ SNR/Contrast
    • ↧ Slice Thk - ↧ SP Resolution
    • ↥ FOV -        ↥ SNR/Contrast
    • ↧ FOV -        ↧ SP Resolution
  45. Matrix 256-192 - best for SNR/Contrast...
    ... 192
  46. Matrix 115-256 - best for SP Resolution...
    ... 515
  47. Slice Thk 5-3mm - best for SNR/Contrast...
    ...5mm
  48. Slice Thk 1-2mm - best for SP Resolution...
    ...1mm
  49. FOV 24-10 - best for SNR/Contrast...
    ... 24
  50. FOV 10-12 - best for SP Resolution...
    ... 10
  51. Signal comes form ...
    ... patient, RF coils and technical controllable factors
  52. Change NEX to 2NEX. What is the result on the SNR?
    If NEX is doubled, SNR get a √2 increase (1.41)
  53. TR is...
    • ... # of slices
    •   - ↥TR ⇒ ↥#slice - ↥time - ↧SAR
    •   - SAR - Specific Absorption Rate
  54. Range of frequencies received and transmitted
    BANDWIDTH (BW)
  55. BANDWIDTH (BW)
    • - range of frequencies received and transmitted
    •   - preselected band or range of frequencies which can govern both slice select and signal sampling
  56. Wide BW
    ↧Signal - ↧SNR - ↧CSA
  57. ↥Signal - ↥SNR - ↥CSA what BW?
    Narrow BW
  58. ↧Signal - ↧SNR - ↧CSA what BW?
    Wide BW
  59. Narrow BW
    ↥Signal - ↥SNR - ↥CSA
  60. Wide/Narrow BANDWIDTH
    • Narrow BW ⇒ ↥Signal - ↥SNR - ↥CSA
    • Wide BW ⇒ ↧Signal - ↧SNR - ↧CSA
    • Image Upload
  61. Classifications of gradients
    • Physical    Logical
    • Gz             Axial
    • Gx           Sagittal 
    • Gy            Coronal

    • Axial
    •  - slice
    •  - phase
    •  - frequency
    • Sagittal
    •  - specially encode the data
    • Coronal
Author:
flashsmilenet
ID:
295910
Card Set:
FSP Class-7 - K-space - signal
Updated:
2015-03-21 22:04:22
Tags:
FSP Class space signal
Folders:
FSP Class
Description:
FSP Class-7 - K-space - signal
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