CFM image of vessel with parabolic flow.
The CFM phantom simulation is used for evaluating color flow imaging. It generates data for flow in vessels with properties like the carotid artery, The velocity profile is close to parabolic, which is a fairly good approximation during most of the cardiac cycle (Jensen, 1996) for a carotid artery. The phantom generates 10 files with positions of the scatterers at the corresponding time step. From file to file the scatterers are then propagated to the next position as a function of their velocity and the time between pulses. The ten files are then used for generating the RF lines for the different imaging directions and for ten different times. A linear scan of the phantom was made with a 192 element transducer using 64 active elements with a Hanning apodization in transmit and receive. The element height was 10 mm, the width was a wavelength and the kerf 0.05 mm. An F-number of 2 was used in receive. A single transmit focus was placed at 40 mm, and receive focusing was done at 2 mm intervals from 10 mm from the transducer surface. The resulting signals have then been used in a standard autocorrelation estimator with RF averaging (Jensen, 1996) for finding the velocity image.
The example was modified in October 2022 to update the m-files to have a single file with all parameters and the focusing was optimized to yield better results.
The resulting color flow image is shown below.
The m-files can be found at:
The routine field.m initializes the field system, and should be modified to point to the directory holding the Field II code and m-files. The routine make_sct.m is then called to make the file for the scatterers in the phantom. The script sim_flow.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 script sim_img.m is used for making the B-mode image as generated by tissue_pht.m. The images are then generated by the routines cfm_bmode.m and cfm_image.m. The routine define_parameters.m hold all the common parameters for the simulation and imaging.
Jørgen Arendt Jensen: "Estimation of Blood Velocities Using Ultrasound, A Signal Processing Approach", Cambridge University Press, 1996.