In vivo repeatability of the pulse wave inverse problem in human carotid arteries

Abstract

Accurate arterial stiffness measurement would improve diagnosis and monitoring for many diseases. Atherosclerotic plaques and aneurysms are expected to involve focal changes in vessel wall properties; therefore, a method to image the stiffness variation would be a valuable clinical tool. The pulse wave inverse problem (PWIP) fits unknown parameters from a computational model of arterial pulse wave propagation to ultrasound-based measurements of vessel wall displacements by minimizing the difference between the model and measured displacements. The PWIP has been validated in phantoms, and this study presents the first in vivo demonstration. The common carotid arteries of five healthy volunteers were imaged five times in a single session with repositioning of the probe and subject between each scan. The 1D finite difference computational model used in the PWIP spanned from the start of the transducer to the carotid bifurcation, where a resistance outlet boundary condition was applied to approximately model the downstream reflection of the pulse wave. Unknown parameters that were estimated by the PWIP included a 10-segment linear piecewise compliance distribution and 16 discrete cosine transformation coefficients for each of the inlet boundary conditions. Input data was selected to include pulse waves resulting from the primary pulse and dicrotic notch. The recovered compliance maps indicate that the compliance increases close to the bifurcation, and the variability of the average pulse wave velocity estimated through the PWIP is on the order of 11%, which is similar to that of the conventional processing technique which tracks the wavefront arrival time (13%).

Effect of Local Neck Anatomy on Localized One-Dimensional Measurements of Arterial Stiffness: A Finite-Element Model Study

“…We hypothesize, that the stresses from the probe are more evenly distributed over the entire neck structure, and that the anatomical features have a more pronounced effect, affecting the behavior of the CCA cross section through the cardiac cycle (Table 3), with increasing background Young's modulus. However, the difference between the ground truth measurement and the 1D measurement remains limited (less than 0.4 m/s over all considered geometries), and is in the same order of magnitude as the measurement error of the 1D measurements in practice [37], as reflected in the mean bias and the limits of agreement (see Table 3), and the correlation between methods remains close to 1 for a background Young's modulus below 50 kPa.…”

“…We assumed measurement US probe direction to be perfectly through the center of the CCA. It has to be noted that in a real-life measurement, this is not always the case as partly reflected in a coefficient of variation of up to 20% for distensibility measurements [35][36][37]. However, we did not specifically include the potential effects of the variation in measurement positioning in this study.…”

Pulse Wave Imaging in Carotid Artery Stenosis Human Patients in Vivo

“…Thus, the choice of tracking feature may affect the PWV estimation in stenotic conditions. Ongoing work involves addressing this issue by estimating PWV with a sophisticated inverse problem solution -based method (Mcgarry et al, 2016;McGarry et al, 2017). Additionally, incorporating flow velocity Doppler measurements into our method will improve understanding of the complex pulse wave propagation and provide more robust arterial stiffness measurements.…”

An analytical model of full-field displacement and strain induced by amplitude-modulated focused ultrasound in harmonic motion imaging

“…Nonlinear inversion MR elastography fits unknown properties from a three-dimensional finite element model of harmonic motion for a heterogeneous viscoelastic (McGarry et al 2013) or poroelastic (McGarry et al 2015) material to the measured harmonic motion amplitudes. An inverse problem approach has also been demonstrated for ultrasound pulse wave imaging, where the unknown compliance distribution and inlet boundary conditions for the 1D pulse wave equations are fitted to spatiotemporal wall displacement measurements (Mcgarry et al 2016, McGarry et al 2017.…”