Exploring the Impact on Collapse and Ultrasound Backscattered Signal Intensity with Varying Ultrasound Power Incident on Gas Vesicle Used for Contrast Agent

Gas vesicles (GVs), gas-filled protein-encapsulated nanostructures, synthesized by microorganisms such as Halobacterium salinarum NRC-1 (HALO) and Anabaena flos aquae (ANA) have been reported as potential ultrasound contrast agents (UCA) due to their ability to mechanically vibrate with the same frequency, or harmonics, as the one from the incident ultrasound (US) wave. Despite GVs resonating in frequencies above 21 MHz, they collapse irreversibly when the US incident field pressure exceeds the vesicle collapse pressure. There are few reports on the relationship between the pressure of the acoustic wave incident in the GVs and the corresponding intensity of the backscattered wave signal from the GVs and, therefore, this study was designed to investigate how varying the relative incident US power, at 21MHz, reflects on the intensity of the US backscattered signal and the collapse of HALO and ANA GVs. The mean (±SD) of the grey level intensity for the ROIs, in maximum intensity pixel images, with GVs and PBS, were determined for transmitted acoustic relative power of 1, 5, 10, 20%. ANA-GVs presented a lower signal intensity, but greater resistance to the increase in relative US pressure. In conclusion, the best behavior was for the Halo-GVs at 5% power and at 21MHz frequency.