A Technique to Track Scatterers for Continuous High-speed Plane-wave Ultrasound Simulations based on a Fluid Domain Model.

Ultrasound simulations of blood flow are useful to evaluate or optimize new transmit schemes, transducer geometries, or post processing methods such as vector flow. In cases of complex flow, a flow domain model (FDM) is often used to define the time history of the velocity field. Scatterers representing blood cells are seeded in the flow field and their positions are updated each time step after spatial and temporal interpolation of the FDM velocity field. At each time step, the scatterers are passed to an ultrasound simulator to generate synthetic ultrasound backscatter data. Here, a technique is described to continuously track, without temporal discontinuities, a stable concentration of scatterers representing complex flow with reverse, rotational, out-of-plane and/or helical features. The unique aspects of the tracking approach are 1) refresh zones at the input and output flow ports that randomly reseed scatterers each time step, 2) a stagnation threshold to remove low velocity orphaned scatterers near the boundary of the flow field, and 3) continuous tracking of particles in the full flow volume. The method can be adapted to any FDM, ultrasound simulator, transducer, or transmission scheme. To demonstrate the overall pipeline, we use the results of a prior fluid structure interaction (FSI) model of a mouse aorta to generate a continuous high-speed, plane-wave ultrasound simulation over 4 cardiac cycles with a 15-MHz linear array. The data were processed to produce vector flow to validate that the ultrasound vector-flow field was consistent with the FSI velocity field.