Field Ⅱ超声成像代码，可以进行单个孔径成像和合成孔径成像、加权和不加权仿真。-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. Field II can make this calculation for a number of points simultaneously and thereby reveal the dynamic focusing properties of the imaging system. A point phantom has been made for this purpose. It consists of a number of point targets placed with a distance of 5 mm starting at 15 mm from the transducer surface