Figure 10.

Examples of R = 4 GRAPPA kernel patterns for 3D imaging, where the black points are the source points and the gray points are the target points. The phase-encoding direction is up-down, the partition-encoding direction is left-right, and the frequency-encoding (or read) direction is into the plane of the page. a: The entire R = 4 acceleration is performed in the phase-encoding direction, which can lead to residual aliasing artifacts and high g-factor losses depending on the coil configuration. b: The acceleration has been split up such that the phase and partition-encoding directions each experience R = 2, leading to a total acceleration of R = 4. This type of acceleration can lead to an improved image quality compared to the pattern in (a). c: A CAIPIRINHA pattern, where the acceleration has been split up as in (b), but the acquired points are offset (the so-called R_phase = 2, R_partition = 2, delta = 1 pattern). Such a pattern causes the aliasing to be shifted and can lead to lower g-factors and more robust GRAPPA reconstructions than the patterns in either (a) or (b).