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21 Cards in this Set

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How does the MR computer determine where a signal is comming from
system can now locate an individual signal within the image by
measuring the number of times the magnetic moments cross the receiver
coil, (frequency) and their position around their precessional path (phase)
What is the phase axis of K space
Horizontal
What is the frequency axis of K space
vertical
What determines the number of lines that are filled during each TR interval
The number of lines of K space
that are filled, is determined by the number of different phase encoding
slopes that are applied
What happens to the amplitude of signal for a K space as the NEX increases
It will increase
NEX increases the amplitude of a frequency
same phase twice.
Which way is K space filled
from top to bottom
What fills the positve lines of K space
Positive gradient slopes fill lines in the positive half of K space,
and
negative gradients fill lines in the negative half. (TOP IS POSITIVE)
What does K space look like
How is K space filled
top to bottom
If there are 128 phase encoding gradients how many K spaces are positive and negative
64
What type of frequency is created by the phase encoding gradient
the frequency according to the change in phase. (pseudofrequency)
What happens to the if the amplitude of a frequency if the phase encoding gradient is steep.
high amplitude
shallow gradient?
large
Why do steep gradients produce small amplitude
Steep phase encoding slopes produce a large phase
shift along their axis. The resultant signal has a small amplitude
Are the amplitudes of the signal mapped in K space so the center is the highest amplitude (all protons in phase) and the left and right are rephasing and dephasing like the signal
yes
data collected after steep phase
encoding gradient slopes produces greater spatial resolution in the image
yes
The central lines of K space contain data with a low spatial resolution as
they are filled by shallow phase encoding gradient slopes
The central portion of K space contains data that has high signal
amplitude and low spatial resolution.
The outer portion of K space contains data that has high spatial
resolution and low signal amplitude
What determines how high up the phase encoding gradient is going to fill in K space
The steepness of the gradient used