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 Show Answers:

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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
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)
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