Calculation of synthetic color flow mapping image
The last phantom 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
5 mm, the width was a wavelength and the kerf 0.05 mm. The pulses where the
same as used for the point phantom mentioned above. A single transmit
focus was placed at 70 mm, and receive focusing was done at 20 mm
intervals from 30 mm from the transducer surface.
The resulting signals have then been used in a standard autocorrelation
estimator (Jensen, 1996) for finding the velocity image.
The resulting color flow image is shown below.
CFM image of vessel with parabolic flow.
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_flow.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.
Jørgen Arendt Jensen:
"Estimation of Blood Velocities Using Ultrasound, A Signal Processing Approach",
Cambridge University Press, 1996.