Golay-encoded excitation for dual-frequency harmonic detection of ultrasonic contrast agents

Golay-encoded excitation in combination with the third harmonic (3f₀) transmit phasing is examined for both signal-to-noise ratio (SNR) and contrast-to-tissue ratio (CTR) improvements in harmonic imaging of contrast microbubbles. To produce the cancellation pair of tissue harmonic signal in 3f₀ transmit phasing, the phase of the bit waveform is properly designed for both the fundamental and the 3f₀ transmit signals to provide the Golay encoding of the received harmonic responses. Results indicate that the proposed Golay excitation can effectively suppress the tissue harmonic amplitude to increase CTR. Meanwhile, the SNR of the contrast harmonic signal also improves because of the elongated waveform of Golay excitation. Nevertheless, the generation of marked range side-lobes of the bubble region would degrade the achievable SNR improvement and the image contrast, especially when the bit of Golay excitation increases. The range side-lobes could result from the nonlinear resonance of the microbubbles that interferes with the phase modulation of the Golay encoding.