Comb-Push Ultrasound Shear Elastography (CUSE): A Novel Method for Two-Dimensional Shear Elasticity Imaging of Soft Tissues

Abstract

Fast and accurate tissue elasticity imaging is essential in studying dynamic tissue mechanical properties. Various ultrasound shear elasticity imaging techniques have been developed in the last two decades. However, to reconstruct a full field-of-view 2D shear elasticity map, multiple data acquisitions are typically required. In this paper, a novel shear elasticity imaging technique, comb-push ultrasound shear elastography (CUSE), is introduced in which only one rapid data acquisition (less than 35 ms) is needed to reconstruct a full field-of-view 2D shear wave speed map (40 mm × 38 mm). Multiple unfocused ultrasound beams arranged in a comb pattern (comb-push) are used to generate shear waves. A directional filter is then applied upon the shear wave field to extract the left-to-right (LR) and right-to-left (RL) propagating shear waves. Local shear wave speed is recovered using a time-of-flight method based on both LR and RL waves. Finally a 2D shear wave speed map is reconstructed by combining the LR and RL speed maps. Smooth and accurate shear wave speed maps are reconstructed using the proposed CUSE method in two calibrated homogeneous phantoms with different moduli. Inclusion phantom experiments demonstrate that CUSE is capable of providing good contrast (contrast-to-noise-ratio ≥ 25 dB) between the inclusion and background without artifacts and is insensitive to inclusion positions. Safety measurements demonstrate that all regulated parameters of the ultrasound output level used in CUSE sequence are well below the FDA limits for diagnostic ultrasound.

Improved shear wave-front reconstruction method by aligning imaging beam angles with shear-wave polarization: Applied for shear compounding application

“…For shear wave motion estimation, 1-D normalized cross-correlation was performed, with kernel length of 2 mm (∼ 6λ) and step of 0.304 mm (∼ λ). To separate complex shear wave field into left and right travelling shear waves, directional filtering was performed [6]. For shear wave speed estimation, a 2-D shear wave speed estimation algorithm was applied with kernel size of 2.4 mm and patch size of 1.2 mm in the lateral and axial direction, as proposed by the [7].…”

“…For performance comparison, the background-to-inclusion ratio and contrast-to-noise ratio in dB were calculated for Young's modulus values, and a 5 x 5 mm rectangular region-of-interest (ROI) inside the inclusion, and two ROI surrounding the inclusion were used for these calculations. The following expression was used for CNR, where C I and C B are mean Young's modulus values in the inclusion and background, respectively; while σ B is standard deviation of the Young's modulus of the background [6] CNR = 20 log 10 |C…”

“…Two commercially available shear wave elastography techniques are supersonic shear-wave imaging (SSI) [5] and combpush ultrasound shear-wave elastography (CUSE) [6]. To enhance the stiffness estimation accuracy, the spatial shear compounding technique was proposed for both SSI and CUSE [5], [7].…”

“…To estimate the angled motion vector, there were various methods proposed in the research for both blood-flow and elastography applications. The strain elastography also share the similar challenge [10], and to overcome this limitation, U. Techavipoo, et al presented a method to measure both axial and lateral tissue motion by curve fitting angular displacements from multi-angle insonifications [6]. Another method proposed by the Tanter, et al used two differently angled insonifications from separate subapertures of the array, and estimated 2-D displacement tissue motion [9].…”

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“…GE has implemented the "comb push" technique [11], which (as illustrated in ▶ Fig. 4) pushes along a number of ARFI lines simultaneously.…”