FSP Class-7 - K-space - signal

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Author:
flashsmilenet
ID:
295910
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FSP Class-7 - K-space - signal
Updated:
2015-03-21 18:04:22
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FSP Class space signal
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FSP Class
Description:
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
  2. After each signal the Fourier Transformer...
    • 1) converts analog to digital
    • 2) pixilize in a form of matrix
    • Sequential type of acquisition
    • slower
    • 2D type of acquisition
    • quicker
  3. Entire space fills at once (one moment)
    3D type of acquisition
  4. Types of acquisition of a k-space
    • 1) Sequential - slower
    •  
    • 2) 2D - quicker 
    • 3) 3D - entire space fills at once (one moment)
    •   - slab (пластина, большой кусок)
    •   - 99% MRAs
  5. ... holds row data
    K-space ...
  6. K-Space
    • - noise from GRE echo is placed in the k-Space
    • - k-space holds row data
  7. K-space Inside
    • - very brigth 
    • - ↥ contrast 
    • - ↧ resolution 
    • - used by (♢EFF TE - middle volume of the center of the case space) 
    • - good for chest
  8. K-space Outside
    best spatial resolution
  9. 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
  10. NEX is...
    • number of acquisitions
    • How many times each line of k-space data is acquired during the scan
  11. Image can be reconstructed using only one half of the k-space
    Half Fourier
    • - 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
  12. 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
  13. Rise Time
    • - time the gradients takes to reach full potential
    • - occurs before gradient
  14. Pre-tuning
    • - maintaining homogeneity to the region of the interest optimize shim coils  - good for knee
    • - occurs before gradient
  15. Slew Rate
    • - distant strength the gradients extend
    • - occurs before gradient
  16. 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
  17. In matrix colums represent -
    frequency
  18. In matrix rows represent -
    phase
  19. Rows and columns of pixels
    matrix
  20. Matrix is...
    • ... rows and columns of pixels
    • Rows - phase
    • Columns - frequency
  21. Matrix size best for spatial resolution
    MS > 512
  22. Matrix size best for signal (↥SNR)
    MS < 256
  23. MS < 256
    best for signal (↥SNR)
  24. MS > 512
    - best for spatial resolution
  25. Matrix sizes
    • MS > 512 - best for spatial resolution
    • MS < 256 - best for signal (SNR)
  26. ↥ Matrix ... pixels
    ... smaller and more pixels
  27. Pixel
    2D
  28. Voxel
    3D (H, W, D)
  29. Pix Size Formula
    Pix Size = FOV/m
  30. # of pixels formula
    • #Pix = FOV/m x #slices
    • Pix Size = FOV/m
  31. Spatial resolution
    • - ability to differentiate b/w adjacent structures  
    • - how well we can see small structures apart
  32. Temp resolution
    • - imaging of organs in motion  
    • - rapid motion (heart)
  33. Contrast resolution
    • - signal difference b/w adjacent structures 
    • - differences in intensity in an image
  34. 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
  35. ↥ Matrix
    ↥ SP Resolution
  36. ↥ Slice Thk
    ↥ SNR/Contrast
  37. ↧ Slice Thk
    ↧ SP Resolution
  38. ↧ Matrix
    ↥ SNR/Contrast
  39. ↥ FOV
    ↥ SNR/Contrast
  40. ↧ FOV
    ↧ SP Resolution
  41. Main controlling factors:
    • ↧ Matrix -     ↥ SNR/Contrast
    • ↥ Matrix -     ↥ SP Resolution
    • ↥ Slice Thk - ↥ SNR/Contrast
    • ↧ Slice Thk - ↧ SP Resolution
    • ↥ FOV -        ↥ SNR/Contrast
    • ↧ FOV -        ↧ SP Resolution
  42. Matrix 256-192 - best for SNR/Contrast...
    ... 192
  43. Matrix 115-256 - best for SP Resolution...
    ... 515
  44. Slice Thk 5-3mm - best for SNR/Contrast...
    ...5mm
  45. Slice Thk 1-2mm - best for SP Resolution...
    ...1mm
  46. FOV 24-10 - best for SNR/Contrast...
    ... 24
  47. FOV 10-12 - best for SP Resolution...
    ... 10
  48. Signal comes form ...
    ... patient, RF coils and technical controllable factors
  49. Change NEX to 2NEX. What is the result on the SNR?
    If NEX is doubled, SNR get a √2 increase (1.41)
  50. TR is...
    • ... # of slices
    •   - ↥TR ⇒ ↥#slice - ↥time - ↧SAR
    •   - SAR - Specific Absorption Rate
  51. Range of frequencies received and transmitted
    BANDWIDTH (BW)
  52. BANDWIDTH (BW)
    • - range of frequencies received and transmitted
    •   - preselected band or range of frequencies which can govern both slice select and signal sampling
  53. Wide BW
    ↧Signal - ↧SNR - ↧CSA
  54. ↥Signal - ↥SNR - ↥CSA what BW?
    Narrow BW
  55. ↧Signal - ↧SNR - ↧CSA what BW?
    Wide BW
  56. Narrow BW
    ↥Signal - ↥SNR - ↥CSA
  57. Wide/Narrow BANDWIDTH
    • Narrow BW ⇒ ↥Signal - ↥SNR - ↥CSA
    • Wide BW ⇒ ↧Signal - ↧SNR - ↧CSA
  58. Classifications of gradients
    • Physical    Logical
    • Gz             Axial
    • Gx           Sagittal 
    • Gy            Coronal

    • Axial
    •  - slice
    •  - phase
    •  - frequency
    • Sagittal
    •  - specially encode the data
    • Coronal

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