Two-dimensional multi-level strain estimation for discontinuous tissue

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.

Anthropomorphic Phantoms for Assessment of Strain Imaging Methods Involving Saline-Infused Sonohysterography

“…The mean CNR e value calculated from ten consecutive strain images produced using the 2-D block matching algorithm was 37.0 ± 4.49 dB, while the mean CNR e value from 34 consecutive strain images produced using the 2-D multilevel strain estimation technique was 29.0 ± 2.60 dB; thus the quality of the strain image produced using the 2-D block matching algorithm was slightly better given the higher CNR e . However, as shown previously by Shi and Varghese (2007), the 2-D multilevel strain estimation technique will be able to track the tissue motion better than the 2-D block matching method when the assumption of continuous tissue motion is violated (e.g., expansion about the inner cavity). Figure 13 was produced from RF data taken using the second uterine phantom and the Antares with the VF-X 9-4 probe operating at 9 MHz.…”

“…Offline analysis of the RF data acquired included up-sampling in the axial direction four times and in the lateral direction two times using the interp function in Matlab (MATHWORKS, Natick, MA). A 2-D crosscorrelation multi-level pyramid was used to track displacement (Shi & Varghese 2007), and a sliding linear regression window (given in Table 3) was used to estimate the axial strain from the displacement estimates (2-D multilevel strain estimation technique). Three sets of kernel lengths and widths are used in this algorithm to track the displacement from a coarse to fine search.…”

A PSF-Shape-Based Beamforming Strategy for Robust 2D Motion Estimation in Ultrafast Data

“…Such multi-scale methods are able to obtain accurate displacement estimates in highly discontinuous displacement fields [45,46]. Normalized 2D cross-correlation was used as the pattern matching function.…”

Electrode displacement strain imaging of thermally‐ablated liver tissue in an in vivo animal model

“…Pairs of these RF data frames were analyzed using a 2D multistep method for displacement estimation, followed by a linear least-squares strain computation algorithm. 27 Following electrode displacement-based strain imaging, the liver was excised and the ablation zone exposed for gross-pathology measurements by slicing along the ultrasound and elastographic imaging plane using a commercially available meat slicer.…”