Numerical Investigation of Superharmonic Imaging Using Chirp Excitation

At present, along with the fundamental method of ultrasound imaging, tissue harmonic imaging based on imprinting of the second harmonic component is established as the standard method of ultrasound imaging. Recently introduced superharmonic imaging (SHI) has an edge over this standard method and has improved spatial resolution. To explore further advancement in ultrasound imaging for enhanced resolution and penetration depth. SHI is the summation of higher harmonics generated due to nonlinear tissue propagation of ultrasound. Here, the addition of third, fourth and fifth harmonics has been done for the superharmonic field. The modeling of nonlinear wave propagation is done in frequency domain on the basis of the second order operator splitting approach. The higher harmonic components are picked up using the inverse filters. The standard evaluation parameters were significantly improved with linear frequency modulation (FM) chirp. The axial level was 2.8 times higher with linear FM chirp as compared to conventional short pulse. Minor benefits such as a 5% increase in beam width and suppression of side lobes were also recorded. This numerical investigation confirms that linear FM chirp in SHI provides better resolution and penetration depth. State of the art fundamental and second harmonic ultrasound imaging techniques were also improved with linear FM chirp as compared with conventional excitation. SHI is superior to the existing diagnostic ultrasound techniques.