From bench to bedside: Nonlinear bio-ultrasound

Abstract

In the early 1960s, David Blackstock developed the weak shock theory which characterized the development and evolution of harmonics in a finite-amplitude propagating plane wave. Later work developed an understanding of beam patterns of the fundamental and higher harmonics from piston radiators. All of these concepts were germane to the field of bio-ultrasound. However, nonlinear effects were largely unexploited in bio-ultrasound until the 1980s, when the role of finite-amplitude mechanisms was recognized as an enhancer of heating and lesion production in high intensity applications. Later, in the 1990s, the role and the advantage of higher harmonics in ultrasonic imaging were developed. In particular, the higher harmonics generated by nonlinear effects, especially in the presence of aberrating tissue, were shown to produce dramatic increases in the resolution and contrast of ultrasound images in cardiology and other applications. Today, every high-end medical ultrasound scanner has the capability of ‘‘harmonic imaging’’ for improved image quality in a number of applications. The physics and technology of this remarkable development will be reviewed, along with the important guiding role of David Blackstock and his collaborators, particularly at UT Austin and at U. Rochester.