ausblenden:
Schlagwörter:
flow MRI; real-time MRI; velocity-encoded MRI; phase-contrast MRI; phase unwrapping
Zusammenfassung:
Purpose: To develop and evaluate a practical phase unwrapping
method for real-time phase-contrast flow MRI using temporal
and spatial continuity.
Methods: Real-time phase-contrast MRI of through-plane flow
was performed using highly undersampled radial FLASH with
phase-sensitive reconstructions by regularized nonlinear inversion.
Experiments involved flow in a phantom and the human
aorta (10 healthy subjects) with and without phase wrapping
for velocity encodings of 100 cms1 and 200 cms1. Phase
unwrapping was performed for each individual cardiac cycle
and restricted to a region of interest automatically propagated
to all time frames. The algorithm exploited temporal continuity
in forward and backward direction for all pixels with a
“continuous” representation of blood throughout the entire cardiac
cycle (inner vessel lumen). Phase inconsistencies were
corrected by a comparison with values from direct spatial
neighbors. The latter approach was also applied to pixels
exhibiting a discontinuous signal intensity time course due to
movement-induced spatial displacements (peripheral vessel
zone).
Results: Phantom and human flow MRI data were successfully
unwrapped. When halving the velocity encoding, the
velocity-to-noise ratio (VNR) increased by a factor of two.
Conclusion: The proposed phase unwrapping method for
real-time flow MRI allows for measurements with reduced
velocity encoding and increased VNR.
