-
Event that occurs after ANY MRI signal
- 1) Slice
- 2) Phase
- - Depahse
- - Rephase
- 3) Frequency
-
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
-
Entire space fills at once (one moment)
3D type of acquisition
-
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
-
... holds row data
K-space ...
-
K-Space
- - noise from GRE echo is placed in the k-Space
- - k-space holds row data
-
K-space Inside
- - very brigth
- - ↥ contrast
- - ↧ resolution
- - used by (♢EFF TE - middle volume of the center of the case space)
- - good for chest
-
K-space Outside
best spatial resolution
-
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
-
NEX is...
- number of acquisitions
- How many times each line of k-space data is acquired during the scan
-
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
-
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
-
Rise Time
- - time the gradients takes to reach full potential
- - occurs before gradient
-
Pre-tuning
- - maintaining homogeneity to the region of the interest optimize shim coils - good for knee
- - occurs before gradient
-
Slew Rate
- - distant strength the gradients extend
- - occurs before gradient
-
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
-
In matrix colums represent -
frequency
-
In matrix rows represent -
phase
-
Rows and columns of pixels
matrix
-
Matrix is...
- ... rows and columns of pixels
- Rows - phase
- Columns - frequency
-
Matrix size best for spatial resolution
MS > 512
-
Matrix size best for signal (↥SNR)
MS < 256
-
MS < 256
best for signal (↥SNR)
-
MS > 512
- best for spatial resolution
-
Matrix sizes
- MS > 512 - best for spatial resolution
- MS < 256 - best for signal (↥SNR)
-
↥ Matrix ... pixels
... smaller and more pixels
-
-
-
Pix Size Formula
Pix Size = FOV/m
-
# of pixels formula
- #Pix = FOV/m x #slices
- Pix Size = FOV/m
-
Spatial resolution
- - ability to differentiate b/w adjacent structures
- - how well we can see small structures apart
-
Temp resolution
- - imaging of organs in motion
- - rapid motion (heart)
-
Contrast resolution
- - signal difference b/w adjacent structures
- - differences in intensity in an image
-
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
-
-
↥ Slice Thk
↥ SNR/Contrast
-
↧ Slice Thk
↧ SP Resolution
-
-
-
-
Main controlling factors:
- ↧ Matrix - ↥ SNR/Contrast
- ↥ Matrix - ↥ SP Resolution
- ↥ Slice Thk - ↥ SNR/Contrast
- ↧ Slice Thk - ↧ SP Resolution
- ↥ FOV - ↥ SNR/Contrast
- ↧ FOV - ↧ SP Resolution
-
Matrix 256-192 - best for SNR/Contrast...
... 192
-
Matrix 115-256 - best for SP Resolution...
... 515
-
Slice Thk 5-3mm - best for SNR/Contrast...
...5mm
-
Slice Thk 1-2mm - best for SP Resolution...
...1mm
-
FOV 24-10 - best for SNR/Contrast...
... 24
-
FOV 10-12 - best for SP Resolution...
... 10
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Signal comes form ...
... patient, RF coils and technical controllable factors
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Change NEX to 2NEX. What is the result on the SNR?
If NEX is doubled, SNR get a √2 increase (1.41)
-
TR is...
- ... # of slices
- - ↥TR ⇒ ↥#slice - ↥time - ↧SAR
- - SAR - Specific Absorption Rate
-
Range of frequencies received and transmitted
BANDWIDTH (BW)
-
BANDWIDTH (BW)
- - range of frequencies received and transmitted
- - preselected band or range of frequencies which can govern both slice select and signal sampling
-
Wide BW
↧Signal - ↧SNR - ↧CSA
-
↥Signal - ↥SNR - ↥CSA what BW?
Narrow BW
-
↧Signal - ↧SNR - ↧CSA what BW?
Wide BW
-
Narrow BW
↥Signal - ↥SNR - ↥CSA
-
Wide/Narrow BANDWIDTH
- Narrow BW ⇒ ↥Signal - ↥SNR - ↥CSA
- Wide BW ⇒ ↧Signal - ↧SNR - ↧CSA
-
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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