Single Tracking Location Methods Suppress Speckle Noise in Shear Wave Velocity Estimation

Acoustic radiation force impulse (ARFI) imaging and shear wave elasticity imaging (SWEI) use the dynamic response of tissue to impulsive mechanical stimulus to characterize local elasticity. A variant of conventional, multiple track location SWEI (MTL-SWEI), denoted single track location SWEI (STL-SWEI) offers the promise of creating speckle-free shear wave images. This work compares the three imaging modalities using a high push and track beam density combined acquisition sequence to image stiff inclusions with diameters of 1.5 and 6 mm. STL-SWEI is shown to have significantly higher CNR than MTL-SWEI, allowing for operation at higher resolution. ARFI and STL-SWEI perform similarly in the 6 mm inclusions, but STL-SWEI images the 1.5 mm targets with the highest CNR and best resolution. The processing trade-offs between CNR and resolution for each modality are discussed.

Section: Single Track Location Sweimentioning

confidence: 99%

Micro-elasticity (μ-E): CNR and resolution of acoustic radiation force impulse imaging and single- and multiple track location shear wave elasticity imaging for visualizing small targets

Hollender

Rosenzweig

Nightingale

et al. 2014

“…We have previously demonstrated that estimation of shear wave velocity using singletracking-location methods exhibit significantly less variation in arrival time estimation [23,25]. In these methods multiple shear wave sources with known positions are employed, and tissue motion is tracked along a single Aline.…”

Section: Ieee Trans Ultrason Ferroelectr Freq Control Author Manuscrmentioning

confidence: 99%

“…In single-tracking-location techniques, like SMURF and STL-SWEI [20,21,25], tracking data from a single A-line is all that is required to estimate shear wave speed, because the spacing between shear wave peaks (SMURF) or the locations of the shear wave sources (STL-SWEI) is known. Speckle bias is suppressed in single tracking location (STL) methods, though tracking at multiple locations, as with parallel receive beamforming, can be useful as a means to suppress uncorrelated noise [23,27].…”

Section: Ii: Description Of Speckle Bias Of Shear Wave Arrival Time Ementioning

confidence: 99%

Shear wave arrival time estimates correlate with local speckle pattern

McAleavey

Langdon

Osapoetra

2014

We present simulation and phantom studies demonstrating a strong correlation between errors in shear wave arrival time estimates and the lateral position of the local speckle pattern in targets with fully developed speckle. We hypothesize that the observed arrival time variations are largely due to the underlying speckle pattern, and call the effect speckle bias. Arrival time estimation is a key step in quantitative shear wave elastography, performed by tracking tissue motion via cross correlation of RF ultrasound echoes or similar methods. Variations in scatterer strength and interference of echoes from scatterers within the tracking beam result in an echo that does not necessarily describe the average motion within the beam, but one favoring areas of constructive interference and strong scattering. A swept-receive image, formed by fixing the transmit beam and sweeping the receive aperture over the region of interest, is used to estimate the local speckle pattern. Metrics for the lateral position of the speckle are found to correlate strongly (r>0.7) with the estimated shear wave arrival times both in simulations and in phantoms. Lateral weighting of the swept-receive pattern improved the correlation between arrival time estimates and speckle position. The simulations indicate that high RF echo correlation does not equate to an accurate shear wave arrival time estimate -a high correlation coefficient indicates that motion is being tracked with high precision, but the location tracked is uncertain within the tracking beam width. The presence of a strong on-axis speckle is seen to imply high RF correlation and low bias. The converse does not appear to be true -highly correlated RF echoes can still produce biased arrival time estimates. The shear wave arrival time bias is relatively stable with variations in shear wave amplitude and sign (−20 μm to 20 μm simulated) compared to the variation with different speckle realizations obtained along a given tracking vector. We show that the arrival time bias is weakly dependent on shear wave amplitude compared to the variation with axial position/local speckle pattern. Apertures of f/3 to f/8 on transmit and f/2 and f/4 on receive were simulated. Arrival time error and correlation with speckle pattern are most strongly determined by the receive aperture.

“…ARF-based techniques include acoustic radiation force impulse (ARFI) imaging [1], shear-wave elasticity imaging (SWEI) [2], spatiallymodulated ultrasound radiation force (SMURF) [3], [4], and shear-wave dispersion ultrasound vibrometry (SDUV) [5]. Typically, these approaches displace tissue using long-duration excitation pulses and then measure the ARF-induced displacement between a pre-excitation pulse and tracking pulses acquired after the excitation.…”

Section: Introductionmentioning

confidence: 99%

“…Loupas's algorithmn [6]) tracking estimator to estimate ARF-induced displacements. However, thermal noise, shearing-induced decorrelation [7], [8], speckle-induced bias [3], [4], and finite tracking kernel-lengths, bandwidth, and sampling-rates [9] can limit the accuracy of the estimate.…”

Section: Introductionmentioning

confidence: 99%

Feasibility of using a generalized-Gaussian Markov random field prior for Bayesian speckle tracking of small displacements

Dumont

Palmeri

Eyerly

et al. 2014

Accurate displacement estimation can be a challenging task in acoustic radiation force elastography, where signal decorrelation can degrade the ability of a normalized cross-correlation (NCC) estimator to characterize the tissue response. In this work, we describe a Bayesian estimation scheme which models both signal decorrelation and thermal noise, and uses an edge-preserving, generalized Gaussian Markov random field prior. The performance of the estimator was evaluated in FEM simulations modeling the acoustic radiation force impulse response in a linearly-isotropic material. Bias, variance, and mean-square error were calculated over a range of estimator parameters, and compared to NCC. The results demonstrate that a significant reduction in mean-square error can be achieved with the proposed estimator. Finally, in vivo data of an radio-frequency ablation in a canine model are shown, demonstrating the in vivo feasibility of the proposed method.