Designing an array transducer for nonlinear imaging

In Nonlinear Imaging (NI), an ultrasound system utilizes overtone components in the echo signals to form an image. These overtone components are generated from either nonlinear propagation in human tissue in proportion to the square of amplitude of the fundamental components or nonlinear scattering of the pulse from microbubbles of a contrast agent. This requires that the array transducer used for the imaging have a broader bandwidth and a higher sensitivity. Here, with an example of a 3.5 MHz curved array, the authors discuss some general considerations in designing an array for NI as well as the conventional imaging. It shows that, to address the NI requirements adequately, one needs to evaluate bandwidth at large dB value. The authors' results also demonstrate that increase of bandwidth at larger dB value will make significant impact on its NI performance, e.g. improve its penetration, even though one can hardly distinguish the difference in conventional images.