Figure 1
From: Single-shot frequency offset measurement with HASTE using the selective parity approach

Schematic showing how the odd- and even-parity echoes are bisected by the reference phase in a CP sequence for any arbitrary voxel. The assignment of OP/EP is arbitrary. The orientation of R is determined by the sensitivity profile of the receiver coil relative to the transmit field and will vary for any given voxel and receiver coil.