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22 Cards in this Set

  • Front
  • Back
Why is how and when MR signals are mapped into K spaces important
How and when the MR signals are mapped into the k-space cause great differences in the spatial, temporal and contrast resolution of the resulting MR images
What does the location of the datas in K-space depend on
The location of the datas in k-space depends on the net strength and duration of the phase encoding gradient and frequency encoding gradient:
What does low amplitude or short duration gradient events encode
A low-amplitude or short-duration gradient event encodes low-spatial-frequency information
What does high amplitude or long duration gradient events encode
A high-amplitude or long-duration gradient event encodes high-spatial-frequency information
Where are the low spatial frequency informations maped
The low-spatial-frequency informations are mapped near the center of k-space and the
Where are high spatial frequency informations mapped
high-spatial-frequency informations are mapped to the periphery of k-space
Where is most MR image information located in K-space
Most MR image information (contrast and general shape) is contained in the center of k-space
What does the image information stored in the center of K-space look like
What information is stored in the center of K-space
Low-spatial-frequency data have the highest amplitude, giving the greatest changes in gray levels (contrast).
What does the high spatial frequency in the periphery do
They don't have effect on contrast or general shape but sharpens the image as they encode the edges (rapid changes of image signal as a function of position)
What happens to the image the farther from the center of K space the data is collected
Thus, the farther from the center of k-space the data are collected, the higher is the spatial-frequency information and the better the spatial resolution will be
What does the information at the periphery of K space look like
What does it look like if most of the data in the center K space is missing but the periphery is present
Can you use a line by line rectilinear trajectory to fill K-space
What does it look like if K-space is filled by a linear trajectory
What is filled first during linear trajectory filling of K-space
One line of k-space is fully acquired at each excitation, containing low and high-horizontal-spatial-frequency information (contrast and resolution in the horizontal direction).
What causes a change in the Y direction in the linear trajectory filling of K space
Between each repetition, there is a change in phase-encoding-gradient strength, corresponding to a change in ky-coordinate
Since linear trajectory move from top to bottom ( y direction) what is the sequence of information obtained
This allows filling of all the lines of k-space from top to botton, acquiring high-positive vertical-spatial-frequency information (resolution in the vertical direction) then low vertical-spatial-frequency information (contrast in the vertical direction) and then high-negative vertical-spatial-frequency information (resolution in the vertical direction again)
What is the appearance of the image as K space is createdd
During the filling of k-space, the resulting image is containing at the bigenning the edge information with low contrast, then the general shape and contrast with a blur in the vertical direction that will disappear as high-vertical-spatial-frequency information are completed
Where is the image about contrast and general shape located in K-space
the center
Where are the image edges located in K-space
the periphery
What improves the spatial resolution
data in the periphery of K space