Using nonlinear distortion to our benefit: Higher harmonic imaging of medical ultrasound

Acoustic wave propagation is inherently nonlinear. This causes a deformation of a propagating pressure pulse, and leads to higher harmonics of the emitted spectrum. Being avoided in the past, nowadays the second harmonic is used in diagnostic ultrasound to improve resolution and reduce artifacts. This paper shows how the improvements can be explained from the properties of the higher harmonics in a nonlinear ultrasound beam. Moreover, it is outlined how the idea of second harmonic imaging may be extended towards higher harmonic imaging. Finally, the paper presents the Iterative Nonlinear Contrast Source method, which is developed for the accurate computation of the higher harmonics in pulsed ultrasound beams.