Linear trajectory through k-space
The easier way to fill the k-space is to use a line-by-line rectilinear trajectory. 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). Between each repetition, there is a change in phase-encoding-gradient strength, corresponding to a change in ky-coordinate. 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).
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.