Methods for robustin vivostrain estimation in the carotid artery

Abstract

A hierarchical block-matching motion tracking algorithm for strain imaging is presented. Displacements are estimated with improved robustness and precision by utilizing a Bayesian regularization algorithm and an unbiased subsample interpolation technique. A modified least-squares strain estimator is proposed to estimate strain images from a noisy displacement input while addressing the motion discontinuity at the wall-lumen boundary. Methods to track deformation over the cardiac cycle incorporate a dynamic frame skip criterion to process data frames with sufficient deformation to produce high signal-to-noise displacement and strain images. Algorithms to accumulate displacement and/or strain on particles in a region of interest over the cardiac cycle are described. New methods to visualize and characterize the deformation measured with the full 2D strain tensor are presented. Initial results from patients imaged prior to carotid endarterectomy suggest that strain imaging detects conditions that are traditionally considered high risk including soft plaque composition, unstable morphology, abnormal hemodynamics and shear of plaque against tethering tissue can be exacerbated by neoangiogenesis. For example, a maximum absolute principal strain exceeding 0.2 is observed near calcified regions adjacent to turbulent flow, protrusion of the plaque into the arterial lumen and regions of low echogenicity associated with soft plaques. Non-invasive carotid strain imaging is therefore a potentially useful tool for detecting unstable carotid plaque.

Motion artifact reduction in ultrasound based thermal strain imaging of atherosclerotic plaques using time-series analysis

“…Although a by-product of the time series analysis process, the mechanical strain is also useful to identify soft lipid pools. Due to the stiffness contrast with its surroundings, soft lipid pools can be identified with a high magnitude of mechanical strain – a fact that is used in ultrasound elasticity imaging (UEI) [32]–[34]. …”

“…Although noninvasive UEI can also detect large soft lipid pools in plaques [32]–[34], the results are sometimes difficult to interpret due to complex mechanical boundary conditions. US-TSI can provide complementary information to UEI, and the thermal strain image and elasticity image co-registered with US B-mode image can provide comprehensive information to assess the vulnerability of a plaque.…”

Multi-Plane Ultrafast Compound 3D Strain Imaging: Experimental Validation in a Carotid Bifurcation Phantom

“…Many arterial strain imaging techniques have already been developed and reported, like intravascular techniques [9], which use an US transducer on the tip of a catheter to image from within the lumen, and non-invasive techniques, which image from outside the body [10][11][12][13][14][15]. With these techniques, it has been shown that arterial strain distribution correlates with histological composition of plaques in pigs [16] and in humans [2,17].…”

A novel computerized tool to stratify risk in carotid atherosclerosis using kinematic features of the arterial wall

“…The role of kinematic features, which are estimated with motion analysis from B-mode US image sequences and represent dynamic phenomena and mechanical interactions occurring during the cardiac cycle (CC), remains unexplored, though. None of the related studies has considered kinematic features in CAD systems for CA, while only a few research groups have investigated potential motion-based risk markers [20], [21].…”