Calculation of the point spread function
The calculation of point spread functions is done by placing a point
in front of the transducer and then sweeping the beam over the point.
This gives the point spread function of the imaging system. This
example calculates the point spread function for a concave, round
transducer with a radius of 8 mm, a geometric focus at 80 mm and
a center frequency of 3 MHz.
The scanning with such a transducer is done by moving the transducer
relative to the tissue. Field II does not have the capability of
moving the aperture, so the point is moved instead. The point is
moved from -10 mm laterally in steps of 0.2 mm til +10 mm at a
distance of 30 mm to the aperture.
The envelope of the responses is then found and it
is log compressed to a dynamic range of 60 dB. A mesh plot
as the one shown below is then produced.
Point spread function for concave transducer in near field
The m-file for calculating the images 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
concave_logo.m is then called to calculate the point spread function
and make the plot.