Chapter 6 K Space Flashcards
K space
stores data from spatial frequencies created from spatial encoding
- rectangular w/ 2 axes perpendicular
frequency axis
horizontal
- rows
phase axis
vertical
- columns
total number of K space areas
total number of selected slices
lowest numbers
near center
highest numbers
outer edges
upper portion lines
positive
lower portion lines
negative
lines filled with data determined by
polarity of phase encoding gradient
simplest method to fill K space
Cartesian
- filled linear (top to bottom)
frequency gradient is turned on
frequency echoes are digitized and data is acquired and located in K space
data arranged into
data points
number of data points determined by
frequency matrix
- process repeated for every slice
each gradient determines
how and when K space is filled
number of lines
number of phase matrix
number of data points
frequency matrix
each line filled
single TR period
wave form created by
plotting the change of phase of magnetic moments over time and distance
make data into format for FFT to create image of slices
- simplify the frequencies and amplitudes that are in the echo
- digitize the echo- Analog to digital conversion
analog
info about a variable illustrate in waveform
digital shows
info in binary numbers
analog digitization
takes place in the receiver coil or body of scanner
number of data points horizontally
frequency matrix
number of data points vertically
phase matrix
frequency matrix
long axis
phase matrix
short axis
two main components of pulse sequence
RF pulses and gradients
most optimum digital sampling frequency
Nyquist theorem
Nyquist frequency
highest frequency must be sampled twice as often to accurately represent
sampling window
how long the system has to acquire the data
- time the frequency encoding gradient is on
data points that are collected during sampling time
frequency matrix
digital sampling frequency and sampling window determine
how many data points can be collected (freq matrix)
altering the receive bandwidth or frequency matrix
sampling window is changed and it impacts the TE
Fast Fourier Transform
mathematical conversion of frequency/ time domain to frequency/ amplitude
