A simulation study on the influence of dispersion on nonlinear wave propagation [in US contrast imaging]

Second harmonic imaging has become a standard technique to attempt to image the (myocardial) perfusion bed. For optimal image quality, the generation and detection of the energy in the harmonic frequency band has to be optimized. As in the clinical setting the incident and backscattered waves often have to travel through dispersive media (regions containing the agent), the aim of this study was to determine the influence of dispersion on nonlinear wave propagation by means of computer simulation. The simulations showed dispersion to elongate broadband waveforms making them chirp-like. It thus reduces the intrinsic axial resolution of the imaging system. However, it also results in a significant decrease in energy transfer to higher harmonics; more energy remains in the fundamental hand. This effect is shown to be independent of the phase of bandwidth of the pulse. Thus, highly dispersive contrast agents might offer a solution to excessive attenuation, a common problem in ultrasound contrast imaging.