Signal-to-noise in phase angle reconstruction: dynamic range extension using phase reference offsets.

The dynamic range of phase-reconstructed magnetic resonance images is compared to that of magnitude-reconstructed images. From analysis of propagation of errors, the phase angle noise is phase-independent and given in radians by sigma ([I])/[I], the noise-to-signal ratio of the corresponding magnitude-reconstructed image. As the phase can range from minus pi to pi, the phase angle dynamic range is 2 pi times that of the signal magnitude. These results agree with experiment, verifying that the noise in the two receiver channels is uncorrelated. An artifact-free technique is presented for correcting phase spillover, which further extends the phase angle dynamic range. The reconstruction-based reference phase is adjusted on a local basis so that the boundary of phase wraparound is reconstructed near the center of the [- pi, pi] interval. For a particular flow study, the phase signal-to-noise was extended over twofold by spillover correction, to a value 15 times that of the magnitude signal-to-noise.