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Spatiotemporal phase unwrapping for real‐time phase‐contrast flow MRI
Author(s) -
Untenberger Markus,
Hüllebrand Markus,
Tautz Lennart,
Joseph Arun A.,
Voit Dirk,
Merboldt K. Dietmar,
Frahm Jens
Publication year - 2015
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.25471
Subject(s) - real time mri , imaging phantom , pixel , cardiac cycle , phase (matter) , temporal resolution , computer science , flow (mathematics) , phase unwrapping , contrast (vision) , artificial intelligence , computer vision , physics , optics , magnetic resonance imaging , radiology , mechanics , medicine , interferometry , quantum mechanics
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 cm·s −1 and 200 cm·s −1 . 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. Magn Reson Med 74:964–970, 2015. © 2014 Wiley Periodicals, Inc.