Influence of wall thickness and diameter on arterial shear wave elastography: a phantom and finite element study

Elira Maksuti,Franco Marinozzi,Matilda Larsson,Fabiano Bini,Giulia Blasi,Matthew W Urban,Stefano Fiorentini

doi:10.1088/1361-6560/aa591d

Abstract

Quantitative, non-invasive and local measurements of arterial mechanical properties could be highly beneficial for early diagnosis of cardiovascular disease and follow up of treatment. Arterial shear wave elastography (SWE) and wave velocity dispersion analysis have previously been applied to measure arterial stiffness. Arterial wall thickness (h) and inner diameter (D) vary with age and pathology and may influence the shear wave propagation. Nevertheless, the effect of arterial geometry in SWE has not yet been systematically investigated. In this study the influence of geometry on the estimated mechanical properties of plates (h = 0.5–3 mm) and hollow cylinders (h = 1, 2 and 3 mm, D = 6 mm) was assessed by experiments in phantoms and by finite element method simulations. In addition, simulations in hollow cylinders with wall thickness difficult to achieve in phantoms were performed (h = 0.5–1.3 mm, D = 5–8 mm). The phase velocity curves obtained from experiments and simulations were compared in the frequency range 200–1000 Hz and showed good agreement (R2 = 0.80 ± 0.07 for plates and R2 = 0.82 ± 0.04 for hollow cylinders). Wall thickness had a larger effect than diameter on the dispersion curves, which did not have major effects above 400 Hz. An underestimation of 0.1–0.2 mm in wall thickness introduces an error 4–9 kPa in hollow cylinders with shear modulus of 21–26 kPa. Therefore, wall thickness should correctly be measured in arterial SWE applications for accurate mechanical properties estimation.

Highlights

Changes in arterial mechanical properties strongly affect cardiovascular function and blood pressure levels (Hamilton et al 2007, Chirinos et al 2012, Palatini et al 2011)
The first part describes the experimental measurements on plate and hollow cylinder phantoms, the second part describes FEM simulations of equivalent phantoms as the ones used in the experiments, the third part describes the quanti tative comparison between experiments and simulations and the fourth part calculated the thickness-dependent error that can be generated in arterial shear wave elastography (SWE) applications
An example of the phase velocity map and the corresponding A(0) mode obtained with FEM and by SWE on a plate phantom can be seen in figure 7

Summary

Introduction

Changes in arterial mechanical properties strongly affect cardiovascular function and blood pressure levels (Hamilton et al 2007, Chirinos et al 2012, Palatini et al 2011). Current commercially-available methods aim at measuring global arterial stiffness by detecting the pulse wave velocity (PWV) between two arterial sites. This technique is at the moment the most simple and reproducible method (Laurent et al 2016), but suffers from several limitations. These are mostly due to the fact that PWV measurements are performed over a very long segment of the arterial tree, which can introduce large bias errors, up to 30%, because of inexact knowledge of the true length of the arterial segment (Nichols et al 2011, Davies et al 2012). Several research methods based on arterial motion tracking in ultrasound imaging have the potential to overcome these problems and measure arterial stiffness accurately and locally (Teixeira et al 2016)

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