Development of transducer system for tissue harmonic imaging of long coded signal

Higher spatial resolution and higher signal-to-noise ratio (SNR) are important issues for the quality of the medical ultrasound image. The objective of this study is to develop a transducer system which can obtain the echo signals with high spatial resolution and high SNR using a pulse compression technique and tissue harmonic imaging. In previous study, we proposed inline transmitter/receiver system which has the potential to solve the problem. The system mainly consists of a PZN-PT, two PVDF films and polyethylene. If the PZN-PT transmits long coded signals in the system, both PVDF films directly receive the transmitted signals, while just one of them receives the echo signals from targets. Although the signal obtained by the PVDF film placed on the transmission side of the PZN-PT contains the second harmonic components generated by tissue propagation, the echo signals and the transmitted signal directly received from the PZN-PT are mixed. To separate those signals, by connecting electric wires of two PVDF films, two signals obtained by two PVDF films are subtracted and the only differential signal; i.e. the echo signals from the targets, are obtained. Although the inline transmitter/receiver system has been able to certify the usefulness, the system also has a problem that one of two transmitted signals is undesirable and should be decreased. For the solution of the problem, two types are proposed in this study; Type-1 reflects and absorbs undesirable transmitted signals, and Type-2 reflects desirable transmitted signals and echo signals from targets. The both systems mainly consist of a PZN-PT, two PVDF films, polyethylene and a reflector. In this study, we investigate the influence of the reflector with various distance between the transducer and the reflector using PZFlex which is a standard finite element method (FEM) simulator for ultrasound propagation. As a result, it is shown that there is an optimal distance, and we can extract the harmonic components from the echo signals if the PZN-PT receives the echo signals before finishing transmitting. Subsequently, the echo signals obtained by two proposed systems are described and finally the feasibility of the proposed system is shown.