Imaging and characterizing shear wave and shear modulus under orthogonal acoustic radiation force excitation using OCT Doppler variance method

Focused, impulsive, acoustic radiation force excitations can generate shear waves with microns of displacement in tissue. The speed of shear wave propagation is directly related to the tissue’s shear modulus, which can be correlated with tissue pathology to diagnose disease and to follow disease progression. Shear wave speed reconstruction has conventionally been measured over spatial domains that are spatially-offset from the region of excitation (ROE). While these methods are very robust in clinical studies characterizing large, homogeneous organs, their spatial resolution can be limited when generating quantitative images of shear elasticity. The ROETTP algorithm measures time-to-peak (TTP) displacements along the axis-of-symmetry in the ROE of an impulsive acoustic radiation force excitation. These TTP displacements are inversely proportional to shear stiffness and are dependent on the excitation-beam geometry. Lookup tables (LUTs) specific to an excitation/displacement tracking transducer configuration were generated from simulated data, and shear stiffnesses were estimated from experimental data as a function of depth using the LUTs. Quantitative ROETTP shear elasticity images of spherical inclusions in a calibrated tissue-mimicking phantom have been generated. Shear wave reflections and interference can lead to an underestimation of the absolute reconstructed shear modulus (20–25%), but the ratio of absolute shear stiffnesses is well-preserved (3.3 vs. 3.5).

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Dependence of shear wave spectral content on acoustic radiation force excitation duration and spatial beamwidth

2014 IEEE International Ultrasonics Symposium ◽

10.1109/ultsym.2014.0271 ◽

2014 ◽

Cited By ~ 20

Author(s):

Mark L. Palmeri ◽

Yufeng Deng ◽

Ned C. Rouze ◽

Kathryn R. Nightingale

Keyword(s):

Shear Wave ◽

Acoustic Radiation ◽

Radiation Force ◽

Acoustic Radiation Force ◽

Spectral Content ◽

Force Excitation

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Abstract 139: Future Clinical Tools: Carotid Plaque Characterization via Shear Wave Elastography - A Phantom Study

Stroke ◽

10.1161/str.46.suppl_1.139 ◽

2015 ◽

Vol 46 (suppl_1) ◽

Author(s):

Erik Widman ◽

Elira Maksuti ◽

Matthew Urban ◽

Kenneth Caidahl ◽

Matilda Larsson

Keyword(s):

Shear Modulus ◽

Mechanical Testing ◽

Shear Wave ◽

High Speed ◽

Acoustic Radiation ◽

Shear Wave Elastography ◽

Radiation Force ◽

Acoustic Radiation Force ◽

Good Agreement

Introduction: Shear Wave Elastography (SWE) is a recently developed noninvasive method for elastography assessment using ultrasound. The technique consists of sending an acoustic radiation force into the tissue that in turn generates an orthogonal low frequency propagating shear wave. The shear wave propagation speed, which is calculated from B-mode images, is correlated to the tissues mechanical properties. Currently, SWE is primarily used in breast and liver to detect tumors easily missed with normal B-mode ultrasound. SWE could potentially aid in the characterization of plaques in the carotid artery, which is critical for the prevention of ischemic stroke. Methods: Six polyvinyl alcohol (PVA) phantoms were created with soft and hard plaque mimicking inclusions. The plaques were excited with acoustic radiation force and the shear wave was measured using high speed B-mode imaging. The data was post-processed with a custom in-house algorithm fitting a model of a Lamb wave propagating through a plate to the shear wave dispersion curve, which allowed the shear modulus to be estimated. The results were validated by measuring the phantom plaque shear modulus with mechanical testing. Results: SWE measured a mean shear modulus of 6 ± 1 kPa and 106 ± 17 kPa versus 3 kPa and 95 kPa measured by mechanical testing in the soft and hard plaques respectively. The results show good agreement between the shear modulus measured with SWE and mechanical testing. In this study simplified homogenous phantom plaque models were examined in a static experimental setup with results validated by mechanical testing. Algorithm improvements for measurements in a dynamic environment are being developed for a future in vivo pilot study. Conclusion: The results show good agreement between the shear modulus measured with SWE and mechanical testing and indicate the possibility for an in vivo application.

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