On the Feasibility of Quantifying Fibrous Cap Thickness With Acoustic Radiation Force Impulse (ARFI) Ultrasound

Abstract

Acute cerebrovascular accidents are associated with the rupture of vulnerable atherosclerotic plaques in the carotid arteries. Fibrous cap thickness has been shown to be an important predictor of plaque rupture, but has been challenging to measure accurately with clinical noninvasive imaging modalities. The goals of this investigation were first, to evaluate the feasibility of using transcutaneous acoustic radiation force impulse (ARFI) ultrasound to quantify fibrous cap thickness and second, to optimize both imaging and motion tracking parameters to support such measurements. Fibrous caps with varying thickness (0.1 – 1.0 mm) were simulated using a simple layered geometry, and their mechanical response to an impulse of radiation force was solved using finite element method (FEM) modeling. Ultrasound tracking of FEM displacements was performed in Field II utilizing three center frequencies (6, 9, and 12 MHz) and eight motion tracking kernel lengths (0.5λ – 4λ). Additionally, fibrous cap thickness in two carotid plaques imaged in vivo was measured with ARFI and compared to matched histology. The results of this study demonstrate that 1) tracking pulse frequencies around 12 MHz are necessary to resolve caps around 0.2 mm, 2) large motion-tracking kernel sizes introduce bias into thickness measurements and overestimate the true cap thickness, and 3) color saturation settings on ARFI peak displacement images can impact thickness measurement accuracy substantially.

Performance of acoustic radiation force impulse ultrasound imaging for carotid plaque characterization with histologic validation

“…higher than 0.5 mm) with a relatively significant predictive value. Finally, the overestimation bias across all three readers matched nearly identically to the mean positive bias predicted by finite element (FE) simulation in previous work (0.13 ± 0.05 mm) for the equivalent imaging parameters 24 . Given the considerably larger standard deviation on the reader’s measurements as compared to FE (±0.3 mm vs. ±0.05 mm), further investigation is needed to demonstrate the limits of ARFI FC thickness measurement, but nevertheless, the level of agreement between FE prediction and in vivo measurements was highly encouraging.…”

Multi-Focus Beamforming for Thermal Strain Imaging Using a Single Ultrasound Linear Array Transducer

“…There are currently research studies to utilize elastography and ARFI in characterizing plaques quantitatively in terms of elasticity modulus or shearwave speed (radially along the vessel cross section circumference as well as longitudinally along vessel length) or qualitatively based on the characteristic of plaques such as stiff/soft/stiff layers corresponding to vessel wall/lipid/calcified lesion respectively (Ramnarine 2014, Russell 2009). Recent in-vivo studies have shown compelling results of ARFI in characterizing fibrous cap thickness and mechanical properties of different layers in human carotid plaques (Czernuszewicz 2015, Czernuszewicz 2016). With diffused disease like fatty liver, there is a possibility for elastography to identify fatty liver using shearwave dispersion which can be quantified in terms of viscosity parameter.…”