Principal Strain Vascular Elastography: Simulation and Preliminary Clinical Evaluation

Abstract

It is difficult to produce reliable polar strain elastograms (radial and circumferential) because the center of carotid artery is typically unknown. Principal strain imaging can overcome this limitation, but suboptimal lateral displacement estimates measured with conventional ultrasonic imaging methods make this an impractical approach for visualizing the mechanical properties within the carotid artery. We hypothesize that compounded plane wave imaging can minimize this problem. To corroborate this hypothesis, we performed (a) simulations with vessels of varying morphology and mechanical behavior (i.e., isotropic and transversely isotropic), and (b) a pilot study with 10 healthy volunteers. The accuracy of principal and polar strain (computed using knowledge of the precise vessel center) elastograms varied between 7–17%. In both types of elastograms, strain concentrated at the junction between the fibrous cap and the vessel wall, and the strain magnitude decreased with increasing fibrous cap thickness. Elastograms obtained from healthy volunteers were consistent with those obtained from transversely isotropic homogeneous vessels; they were spatially asymmetric–a trend that was common to both principal and polar strains. No significant differences were observed in the mean strain recovered from principal and polar strains (p > 0.05). This investigation demonstrates that principal strain elastograms measured with compounding plane wave imaging overcame problems incurred when polar strain elastograms are computed with imprecise estimates of the vessel center.

Lagrangian carotid strain imaging indices normalized to blood pressure for vulnerable plaque

“…Our group has reported on Lagrangian strain estimation on human subjects without the use of any simplifying assumptions such as the incompressibility constraint. Algorithms from other research groups include Eulerian strain, angular compounded Eulerian strain, Lagrangian strain estimated using the incompressibility assumption, or strain estimated from B‐mode cine‐loops . ARFI imaging displacements have also been used to characterize carotid plaques on five patients and 25 patients, respectively.…”

“…A criticism of our LCSI approach has been the lack of normalization of the respective maximum and peak‐to‐trough accumulated strain indices to the physiological stimuli, namely the underlying blood pressure. Blood pressure based normalization has been controversial as several investigators have reported that normalization is necessary and essential for reproducible carotid strain imaging . Our approach has always been that strain fluctuations provide sufficient information and normalization would just scale the strain indices and would not provide significant improvement.…”

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

“…More work has been published recently on the combination of ultrafast imaging and ST, for the assessment of blood velocity [28,29,38] and vessel wall strain [39][40][41][42]. Here, subsample resolution displacement estimates were obtained by performing 1D [28,29,38,43] or 2D [42] parabolic interpolation of the pattern matching function.…”

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

“…Principal strains based on the principles of continuum mechanics have the intrinsic characteristic of coordinate system independence and are therefore more suitable to report the full 3D strain distribution at the bifurcation. 2D principal strains were reported for vascular applications based on 2D strain tensor in previous studies [35,36]. In this paper we implemented the acquisition method of our previous simulation study in an experimental setup and extended the strain estimation algorithm to full 3D.…”