Figure 4.

Calibration-free parallel imaging reconstruction from partial k-space data does not impose smooth phase variation and does not recover both halves of k-space as seen in the k_y−k_z-plane for the first coil (a), which results in blurring in the image, shown reformatted in the xy-plane (b). Modifying calibration-free parallel imaging to separate real and imaginary parts also imposes smooth phase variation, which allows recovery of both halves of k-space (c), resulting in sharper images (d).