FIGURE 1.

Gradient timing errors cause radial projections to be shifted away from the center of k-space. (a) The total shift Δk_e can be expressed in terms of parallel (Δk_r) and perpendicular (Δk_p) components, or in terms of the shift in the k_x and k_y directions. (b) The magnitude k-space signal from a spherical phantom exhibits characteristic signal fluctuations from projection to projection due to golden angle sampling (top trace), which are also clearly visualized when the signal is reordered by projection angle (bottom trace). The miscentered sampling causes an error in the sampling location of the peak (brightest) k-space signal, which can be described as a constant offset in the direction parallel to the projection, the mean Δk_r, with an angle-dependent fluctuation.