Multi-cpu calculation of pulsed wave phantom data for arteria femoralis

This example shows how to calculate RF signals from a pulsatile flow. Often this includes calculation of thousands of RF signals, which can take a very long time. This code splits the task into one job for each RF signal and the code can easily be run on several machines in parallel to speed up the execution. The scatterers positions and velocity are calculated and not stored to avoid excessive usage of disk storage. The approach also has the advantage that is can be restarted if a computer goes down. A file is stored for each RF signals before simulation and a failed simulation can be restarted by deleting the file and starting the simulation again.

The phantom is used for calculating RF data as measured from arteria femoralis in the upper leg. The scatterers are then propagated between pulses according to the Womersley model mentioned in Jensen (1996) thereby generating a three-dimensional, pulsed model of the flow in the femoral artery. Note, that all the scatterer position files are generated during the simulation to avoid generating massive amounts of data.

The scatterer position are used during the simulation for generating one RF signal for each pulse emission. These files can then be used for doing either spectral analysis as shown below or for estimating the profile in the artery.

The simulation is made so multiple workstations can work on the problem automatically at the same time, as long as they have access to the same directory. This is done by looking at which RF files that have been generated. The first one not simulated is reserved by the program by writing a dummy file, and then doing the simulation. Multiple workstations can then work simultaneously on the problem and generate a solution quickly.

The resulting spectogram for the simulation is:

Spectrogram from arteria femoralis.

The m-files can be found at:

The routine field.m should be written to initializes the field system, and to point to the directory holding the Field II code and m-files. This script must be made by the user running this script. The script sim_pulsed_flow_multi.m is then called. Here the field simulation is performed and the data is stored in RF-files; one for each RF-line done. The other scripts in the directory are used for defining the convex array transducer and for setting simulation parameters.

References:

Jørgen Arendt Jensen: "Estimation of Blood Velocities Using Ultrasound, A Signal Processing Approach", Cambridge University Press, 1996.