High-frequency, plane-wave, multi-pulse acoustic contrast agent imaging at 16 MHz

Multi-pulse (MP) ultrasound contrast agent (UCA) imaging techniques take advantage of the nonlinear response of UCAs by transmitting 2 or more pulses of different phase or amplitude and combining them in such a way as to reduce the linear component of the backscatter (i.e, tissue) and emphasize the nonlinear components (i.e., UCA). The MP methods of pulse inversion (PI, +1 and -1 pair) and amplitude modulation (AM, +1 and +1/2 pair) were compared to standard multi-angle, high-speed plane-wave compound imaging for a flow of the UCA DEFINITY
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using a Verasonics Vantage 128 and an 18-MHz linear array. Transmissions were made at -10, 1 and 10 degrees. The PI and AM methods used a pulse pair at each angle and standard plane-wave imaging used a single transmission at each angle. DEFINITY
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was diluted in water to 2000:1 and then a circular flow was established through a 2-mm flow phantom in a tissue mimicking material. Beamformed data were processed to find the RMS values in the flow and depth matched background region in order to calculate a contrast-to-tissue ratio (CTR). MP methods resulted in a 5-10 dB improvement in CTR relative to standard multi-angle plane-wave imaging at 16 MHz.