Ultrasound imaging system using combinational coded excitation

Increasing penetration to a deep body is one of the most important targets for clinical ultrasound imaging. To this end, coded excitation technique is known as a fundamental solution to improve signal to noise ratio (SNR) without degradation of axial resolution. In order to improve the SNR, the coded excitation requires a longer pulse containing many wavelengths. However, a nonlinear characteristic of signal processing such as dynamic beam forming degrades the resolution. Decoding error tends to appear at different distances where focusing parameters vary at the long pulse decoded. At a previous symposium, our group proposed a new approach, sub-aperture decoding, to enhance performance of coded excitation, in which the combinational codes with multiple codes with relatively small size taps are transmitted and then received signals are decoded with these combinational codes. In other words, this approach´s transmission combines and compounds two or more codes of relatively small code length, and decoding processes divide into two or more decoding filters correspond to each code. In this report, we report more detailed simulation and preliminary experimental results for this approach of combinational coded excitation. Using this new coding approach, higher SNR without degrading lateral resolution is achieved. In the case of 3×5 codes, the combinational coding technique improves SNR up to 11.4 dB experimentally and this result is relatively coincidental with calculated value (11.5 dB).