An illustrated comparison of processing methods for MR phase imaging and QSM: combining array coil signals and phase unwrapping

Phase imaging benefits from strong susceptibility effects at very high field and the high signal‐to‐noise ratio (SNR) afforded by multi‐channel coils. Combining the information from coils is not trivial, however, as the phase that originates in local field effects (the source of interesting contrast) is modified by the inhomogeneous sensitivity of each coil. This has historically been addressed by referencing individual coil sensitivities to that of a volume coil, but alternative approaches are required for ultra‐high field systems in which no such coil is available. An additional challenge in phase imaging is that the phase that develops up to the echo time is “wrapped” into a range of 2π radians. Phase wraps need to be removed in order to reveal the underlying phase distribution of interest.