One-transmission harmonic imaging with high spatial resolutions using probe consisting of two piezoelectric layer elements.

Abstract

Purpose: Pulse inversion (PI) harmonic imaging has been commonly used because of its contrast and spatial resolution superior to conventional fundamental imaging. However, it requires two transmissions with opposite phases, which reduces the imaging frame rate by half. This study aimed to solve this problem METHOD: An ultrasonic array probe consisting of piezoelectric elements with two polarization-inverted layers, which requires only one transmission to extract the second harmonic components, was developed. Its characteristics, such as electric impedance and its phase, were predicted by solving piezoelectric as well as wave equations, and then compared with measurement. The acoustic pressures produced from the developed probe, when excited at the lower and higher resonant frequencies, were measured using a hydrophone. Finally, imaging of wires in water and phantoms containing wires and a cyst model were performed using the developed probe RESULT: The spatial resolution, especially in the axial direction, was significantly improved with the developed probe consisting of the two piezoelectric layer elements in comparison with the conventional second harmonic imaging (HI) using a band pass filter. It was almost comparable to that of conventional PI imaging despite only one transmission being required CONCLUSION: A probe consisting of two piezoelectric layer elements enabling one-transmission HI was developed. The spatial resolution obtained using the developed probe was slightly worse but almost comparable to that of conventional PI imaging even with only one transmission.