The purpose of this work is to develop a method for direct estimation of
the cardiac strain tensor by extending the harmonic phase reconstruction on
tagged magnetic resonance images to obtain more precise and robust measurements.
The extension relies on the reconstruction of the local phase of
the image by means of the windowed Fourier transform and the acquisition of
an overdetermined set of stripe orientations in order to avoid the phase interferences
from structures outside the myocardium and the instabilities arising
from the application of a gradient operator. Results have shown that increasing
the number of acquired orientations provides a signi cant improvement
in the reproducibility of the strain measurements and that the acquisition of
an extended set of orientations also improves the reproducibility when compared
with acquiring repeated samples from a smaller set of orientations.
Additionally, biases in local phase estimation when using the original harmonic
phase formulation are greatly diminished by the one here proposed.
The ideas here presented allow the design of new methods for motion sensitive
magnetic resonance imaging, which could simultaneously improve the
resolution, robustness and accuracy of motion estimates.
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