Contrast-enhanced ultrasound imaging using capacitive micromachined ultrasonic transducers.

This article focuses on the feasibility and performance of capacitive micromachined ultrasonic transducers (CMUTs) for contrast-enhanced ultrasound (CEUS) imaging using a three-pulse amplitude modulation (AM) sequence. The study demonstrates theoretically and experimentally that the inherent nonlinear harmonic emissions of CMUTs, caused by their voltage-to-pressure conversion, do not impair the effectiveness of CEUS imaging when employing this three-pulse AM technique. Using a 4.8 MHz linear CMUT array and a comparable lead zirconate titanate (PZT) array, CEUS images of SonoVue microbubble contrast agents flowing through a 3D-printed hydrogel phantom showed significant contrast-to-tissue ratio (CTR) enhancements, with the CMUT achieving an average of 37.4 dB and the PZT 49.9 dB. Hydrophone measurements confirmed that the three-pulse AM sequence effectively cancels linear tissue signals despite the nonlinear emissions, leaving minimal residual power, and that the CMUT’s lower CTR compared to the PZT is primarily due to its lower signal-to-noise ratio rather than its nonlinear emission characteristics. The findings suggest that CMUTs, combined with the three-pulse AM sequence, hold promise for CEUS imaging, benefiting from their wide bandwidth, low emission pressure, and high receive sensitivity.