Two-dimensional multi-level strain estimation for discontinuous tissue

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Abstract
A large number of the strain estimation methods presented in the literature are based on the assumption of tissue continuity that establishes a continuous displacement field. However, in certain locations in the body such as the arteries in vivo scanning may produce displacement fields that are discontinuous between the two walls of the artery. Many of the displacement or strain estimators fail when the displacement fields are discontinuous. In this paper, we present a new 2D multi-level motion or displacement tracking method for accurate estimation of the strain in these situations. The final high-resolution displacement estimate is obtained using two processing steps. The first step involves an estimation of a coarse displacement estimate utilizing B-mode or envelope signals. To reduce computational time, the coarse displacement estimates are obtained starting from down-sampled B-mode pre- and post-compression image pairs using a pyramidal processing approach. The coarse displacement estimate obtained from the B-mode data is used to guide the final 2D cross-correlation computations on radio-frequency (RF) data. Results from finite element simulations and in vivo experimental data demonstrate the feasibility of this approach for imaging tissue with discontinuous displacement fields.