Signal‐to‐noise in phase angle reconstruction: Dynamic range extension using phase reference offsets

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Abstract
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 σ (|I|)/|I|, the noise-to-signal ratio of the corresponding magnitude-reconstructed image. As the phase can range from minus π to π the phase angle dynamic range is 2π 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 [ − π, π] 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. © 1990 Academic Press, Inc.