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Influences of bubble motion to second-harmonic inversion imaging

In ultrasound contrast harmonic imaging, the generated harmonics during wave propagation in tissues lead to a limited contrast-to-tissue ratio (CTR). Second-harmonic inversion (SHI), based on two 90° phase-shifted transmissions with the same frequencies and amplitudes, can effectively reduce the tissue-harmonic signals and improve CTR. However, the bubbles motion strongly influences the SHI effectiveness. Therefore, in-vitro experiments on circulating UCA were conducted to quantify the influence of moving bubbles to SHI technique, by regulating the pulse repetition frequency (PRF), in order to guarantee and to optimize the SHI technique. Experimental results show that when bubbles move in axial direction, the second-harmonic amplitudes exhibits an oscillating evolution with increasing bubbles motions. The maximum improvement reaches 12 dB when compared to SHI without bubbles motion. The influence of lateral bubbles motion is much less than the influence of axial bubbles motion.