Automated Spatial Mechanical Inhomogeneity Detection and Arterial Wall Characterization in Human Atherosclerotic Carotid Arteries In-Vivo

Abstract

Methods used in clinical practice to diagnose and monitor atherosclerosis present limitations. Imaging the mechanical properties of the arterial wall has demonstrated the potential to significantly improve atherosclerosis diagnosis and patient care. Pulse Wave Imaging (PWI)is a non-invasive, ultrasound-based technique, which provides information on arterial wall stiffness by imaging the pulse wave propagation along an arterial segment. The aims of the present study are to: 1)present a novel method that utilizes the PWI information to automatically and optimally divide the artery into the segments with most homogeneous mechanical properties and 2)Apply this method to characterize the mechanical properties of the arterial wall in atherosclerotic common carotid arteries in-vivo. A silicone phantom consisting of a soft and stiff segment along its longitudinal axis was scanned at the stiffness transition, and the compliance of both segments was estimated through static testing. The proposed algorithm was able to detect the soft-stiff segments interface with an error of 0.73 mm, and provided a good approximation of the compliance of both segments through the Bramwell-Hill equation (Soft segment: 7.95 ×10−9m2/Pa, Stiff segment 3.94×10−9m2/Pa), as compared to the static testing (Soft segment: 8.24 × 10−9m2/Pa, Stiff segment 3.86 × 10−9m2/Pa). Furthermore, the common carotid arteries of N=7 healthy subjects and N=12 carotid artery disease patients were scanned in-vivo. The number of most homogeneous segments in which the artery was divided was higher in the case of carotid artery disease patients (3.18±O.87)compared to healthy subjects (1.28±0.48), indicating increased wall inhomogeneity in atherosclerotic arteries. Finally, one patient underwent carotid endarterectomy and his plaque sample was retrieved. In this patient, a higher compliance value of the stenotic segment was estimated by the proposed algorithm, as compared with the adjacent arterial wall, and healthy carotid arteries. This was corroborated by histological staining of the plaque sample, which revealed the presence of a large necrotic core and a thrombus, characteristics associated with reduced plaque stiffness.