Parametric study of the peak negative acoustic pressure distribution within the image plane of a phased array transducer

A study is presented in which the influence of pulse and transducer characteristics on the distribution of the peak negative acoustic pressure within the image plane of a phased array transducer is shown. First, the influence of the center frequency, the bandwidth of the transmitted pulse, the position of the focus point, and the properties of the phased array are investigated by computer simulation. These simulations show that both the maximal amplitude and the homogeneity of the distribution of the peak negative pressure within a sector image depend on these parameters. Most remarkably, they show that the maximal peak pressure does not necessarily occur on the geometrical symmetry axis of the array transducer but can occur at the outermost lateral lines of a sector image. Second, this effect is demonstrated experimentally by hydrophone measurements of the sound field produced by a standard, clinically used, 2.5-MHz phased array transducer. The experimental results agree well with the theoretical model. The relevance of this study for contrast echography and the safety measurements of ultrasound is discussed.