Date Published: June 20, 2019
Publisher: Public Library of Science
Author(s): Viviana Mancini, Daniela Tommasin, Yanlu Li, Jonathan Reeves, Roel Baets, Steve Greenwald, Patrick Segers, Rudolf Kirchmair.
Early detection of asymptomatic carotid stenosis may help identifying individuals at risk of stroke. We explore a new method based on laser Doppler vibrometry (LDV) which could allow the non-contact detection of stenosis from neck skin vibrations due to stenosis-induced flow disturbances. Experimental fluid dynamical tests were performed with water on a severely stenosed patient-specific carotid bifurcation model. Measurements were taken under various physiological flow regimes both in a compliant and stiff-walled version of the model, at 1 to 4 diameters downstream from the stenosis. An inter-arterial pressure catheter was positioned as reference. Increasing flow led to corresponding increase in power spectral density (PSD) of pressure and LDV recordings in the 0–500 Hz range. The stiff model lead to higher PSD. PSD of the LDV signal was less dependent on the downstream measurement location than pressure. The strength of the association between PSD and flow level, model material and measuring location was highest in the 0–50 Hz range, however useful information was found up to 200 Hz. This proof-of-concept suggests that LDV has the potential to detect stenosis-induced disturbed flow. Further computational and clinical validation studies are ongoing to assess the sensitivity and specificity of the technique for clinical screening.
Stroke, a cardiovascular disease (CVD), is the second most common single cause of death in Europe . There are many underlying causes of stroke, but one of the most prominent is carotid stenosis , as the atherosclerotic plaque causing the narrowing might rupture and the thrombi would obstruct the blood flow in downstream vessels. Unfortunately, few patients with carotid stenosis present symptoms in the early stages of the disease. Moderate and severe asymptomatic stenosis affect 12.5% and 3.1% of the over 70 population, respectively [3,4]. However, asymptomatic stenosis is not commonly diagnosed unless associated with other CVDs  such as coronary stenosis and hypertension, or risk factors such as diabetes [6,7]. Thus, the possibility of assessing and stratifying the risk of future stroke in asymptomatic patients with carotid stenosis is limited .
In total, 564 data sets were recorded, with about 50% of the experiments performed under physiological flow conditions. An overview of how many experiments have been conducted under which condition is provided in Table 1. We provide the raw data in a public repository . The resulting Reynolds number (Re) of the ICA, based on the flow through it (QICA), its cross sectional area AICA = 8.74 mm2 at the bifurcation and on the kinematic viscosity of water of 1 . 10−6 m2/s, ranged from 198 to 5774.
In this hydraulic bench model study of a carotid artery, we have shown that post-stenotic flow instabilities induce vibrations that can be detected from surface measurements by means of laser Doppler vibrometry. Frequency domain analysis revealed that the relevant frequency band is 0–200 Hz, as little useful information was found at frequencies above 200 Hz. The sensitivity of the LDV measurement to changes in trans-stenotic flow level was found to be comparable to what can be achieved using an intra-arterial manometer. We consider the results of our study a proof-of-concept of the technique for carotid stenosis diagnosis by detecting neck skin vibrations.