Improving ultrasonic imaging of the vascular wall and blood flow using a multiphysics simulation tool integrating fluid-structure interaction and ultrasound simulations

The currently applied ultrasonic blood flow and vessel wall imaging methods still demonstrate several limitations. To support the development of new vascular ultrasonic imaging modalities, we developed a simulation environment integrating ultrasound (US) and fluid-structure interaction (FSI) simulations, allowing construction of synthetic US-images based on physiologically realistic behavior of an artery. An in-house FSI-code was developed to strongly couple the flow solver Fluent and structural solver Abaqus; US-simulations were performed with Field II. A distensible tube, representing the common carotid artery was simulated. FSI and US-simulations were coupled by seeding scatterers in the fluid and structural domain and propagating them during the simulated scan procedure based on flow and structural displacement fields from FSI. Simulations yielded raw RF-data, which were further processed for arterial wall distension and shear rate imaging. Our simulations demonstrated that (i) the wall distension application is sensitive to measurement location (highest distension found when tracking the intima-lumen transition); (ii) strong reflections between tissue transitions can potentially cloud a correct measurement; (iii) maximum shear rate was underestimated during the complete cardiac cycle, with largest discrepancy during peak systole; (iv) due to difficulties measuring near-wall velocities with US, shear rate reached its maximal value at a distance from the wall. We conclude that our FSI-US simulation environment provides realistic RF-signals which can be processed into ultrasound-derived medical images and measurements.