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Although high-frequency ultrasound imaging is gaining attention in various applications, hardly any ultrasound contrast agents (UCAs) dedicated to such frequencies (>15 MHz) are available for contrast-enhanced ultrasound (CEUS) imaging. Moreover, the composition of the limited commercially available UCAs for high-frequency CEUS (hfCEUS) is largely unknown, while shell properties have been shown to be an important factor for their performance. The aim of our study was to produce UCAs in-house for hfCEUS. Twelve different UCA formulations A-L were made by either sonication or mechanical agitation. The gas core consisted of C4F10 and the main coating lipid was either 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC; A-F formulation) or 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC; G-L formulation). Mechanical agitation resulted in UCAs with smaller microbubbles (number weighted mean diameter ~1 \mu \textm ) than sonication (number weighted mean diameter ~2 \mu \textm ). UCA formulations with similar size distributions but different main lipid components showed that the DPPC-based UCA formulations had higher nonlinear responses at both the fundamental and subharmonic frequencies in vitro for hfCEUS using the Vevo2100 high-frequency preclinical scanner (FUJIFILM VisualSonics, Inc.). In addition, UCA formulations F (DSPC-based) and L (DPPC-based) that were made by mechanical agitation performed similar in vitro to the commercially available Target-Ready MicroMarker (FUJIFILM VisualSonics, Inc.). UCA formulation F also performed similar to Target-Ready MicroMarker in vivo in pigs with similar mean contrast intensity within the kidney ( $n = 7$ ), but formulation L did not. This is likely due to the lower stability of formulation L in vivo. Our study shows that DSPC-based microbubbles produced by mechanical agitation resulted in small microbubbles with high nonlinear responses suitable for hfCEUS imaging. [ABSTRACT FROM AUTHOR]

In the above article , the authors regret that there was a mistake in calculating the mol% of the microbubble coating composition used. For all experiments, the unit in mg/mL was utilized and the conversion mistake only came when converting to mol% in order to define the ratio between the coating formulation components. The correct molecular weight of PEG-40 stearate is 2046.54 g/mol , , not 328.53 g/mol. On page 556, should read as shown here. [ABSTRACT FROM AUTHOR]