Phase influence of a dual-frequency excitation pulse on the axial resolution of ultrasound images

Abstract

The propagation of acoustic waves is a nonlinear process. Nonlinear effects cause the distortion of an excitation signal and generate higher harmonics. These can be used for ultrasound image quality enhancement. Dual-frequency excitation combines the advantages of the high and low center frequencies. The aim is to investigate the influence of the phase relation between two frequency components of the transmission pulse on the axial resolution. Transmit signals with small variation, by stepwise changing the phase of the higher frequency component, are examined. The axial resolution is determined using phantom measurements and the resulting spectra are analysed. The evaluated frequency signals of the measurements leading to better axial resolution show higher harmonic content and broader bandwidth. This supports the assumption of nonlinear effects causing this difference in quality. To further investigate this assumption, acoustic and electrical measurements are performed. The acoustic signals in the frequency domain show the expected difference between better and worse axial measurements in harmonic levels, that can not be seen in the electrical pulse. This indicates a connection between the acoustic analysis of the transmission pulse and the resulting axial resolution. To quantify the results, correlations of spectra characteristics with their corresponding axial resolution are performed.

Date of Award	2025
Original language	English
Supervisor	Andreas Schrempf (Supervisor)