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22 Cards in this Set
- Front
- Back
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Why is how and when MR signals are mapped into K spaces important
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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
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What does the location of the datas in K-space depend on
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The location of the datas in k-space depends on the net strength and duration of the phase encoding gradient and frequency encoding gradient:
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What does low amplitude or short duration gradient events encode
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A low-amplitude or short-duration gradient event encodes low-spatial-frequency information
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What does high amplitude or long duration gradient events encode
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A high-amplitude or long-duration gradient event encodes high-spatial-frequency information
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Where are the low spatial frequency informations maped
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The low-spatial-frequency informations are mapped near the center of k-space and the
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Where are high spatial frequency informations mapped
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high-spatial-frequency informations are mapped to the periphery of k-space
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Where is most MR image information located in K-space
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Most MR image information (contrast and general shape) is contained in the center of k-space
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What does the image information stored in the center of K-space look like
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What information is stored in the center of K-space
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Low-spatial-frequency data have the highest amplitude, giving the greatest changes in gray levels (contrast).
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What does the high spatial frequency in the periphery do
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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)
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What happens to the image the farther from the center of K space the data is collected
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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
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What does the information at the periphery of K space look like
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What does it look like if most of the data in the center K space is missing but the periphery is present
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Can you use a line by line rectilinear trajectory to fill K-space
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yes
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What does it look like if K-space is filled by a linear trajectory
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What is filled first during linear trajectory filling of K-space
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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).
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What causes a change in the Y direction in the linear trajectory filling of K space
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Between each repetition, there is a change in phase-encoding-gradient strength, corresponding to a change in ky-coordinate
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Since linear trajectory move from top to bottom ( y direction) what is the sequence of information obtained
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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)
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What is the appearance of the image as K space is createdd
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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
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Where is the image about contrast and general shape located in K-space
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the center
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Where are the image edges located in K-space
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the periphery
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What improves the spatial resolution
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data in the periphery of K space
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