FSP Class7  Kspace/Signal
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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

Types of acquisition of a Kspace
 1) Sequential  slower
 2) 2D  quicker
 3) 3D  entire space filled at once (one moment. 99% MRAs

How Kspace filled?
 insideout toward outer edge of phase encoding direction
 Inside  Brightness ↥  Spatial Resolution ↧  good for chest
 Outside  Brightness ↧  Spatial Resolution ↥
 EFF TE 

NEX
Number of RF excitations performed on a particular slice.

Half Fourier
 Half Fourier = 0.5 NEX
  half filled w echo, another half w interpoled "zeros"

Rise Time
It is time, the gradients takes to reach full potential

Slew Rate
distant strength the gradient extand

PreTuning
 maintaining homogeneity to the region of the interest (optimize shim coils)

In the matrix row corresponds to...
...Phase

In the matrix column corresponds to...
... Frequency

Matrix > 512 ...
 good for Sp resolution
 bad for signal (↧ SNR)

Matrix < 256 ...
 good for signal (↥ SNR)
 bad for Sp resolution


How many pixels in the matrix formula
#Pix = ^{FOV}/_{M} x #slices

Pixel size formula
Size pix = ^{FOV}/_{M}

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

Spatial resolution is ↥ when:
 Mat size...
 Slice thickness...
 FOV...
  Mat size ↥
  Slice thickness ↧
  FOV ↧

SNR  Contrast is ↥ when:
 Mat size...
 Slice thickness...
 FOV...
  Mat size ↧
  Slice thickness ↥
  FOV ↥

SNR Contras ↥ when Matrix 256 or 192?
Matrix 192

SNR Contras ↥ when Slice thickness 5 or 3 mm?
Slice thickness 5 mm?

SNR Contras ↥ when FOV 24 or 10?
FOV 24

Spatial resolution is ↥ when Matrix 515 or 256?
Matrix 515

Spatial resolution is ↥ when Slice thickness 1 or 2 mm?
Slice thickness 1 mm

Spatial resolution is ↥ when FOV 10 or 12?
FOV 10

Main controlling factors?
 Mat size
 Slice thickness
 FOV

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

NEX/NSA controls...
... time of exam

If NEX/NSA ↥ from 2 to 4. What amount of improvement in SNR?
SNR ↥ to √2 = 1.41

Bandwidth
range of frequencies received and transmitted

Bandwidth  SNR, CSA ?
 A) ↥SNR  ↥CSA
 B) ↧SNR  ↧CSA

Classification of Gradients
 Physical Logical
 Gz Axial
 Gx Sagittal
 Gy Coronal