Acoustically Transparent Sample Containers for Quantitative Cavitation Imaging.

Passive Acoustic Mapping (PAM) is a powerful and widely used method of imaging cavitation activity. However, the presence of a container around a cavitating sample in experiments performed in vitro can introduce significant aberrations into recorded cavitation noise and resulting PAM images. These artefacts may lead to energy being incorrectly estimated or mapped to the wrong place, preventing accurate correlation between cavitation and bioeffects. In this work, we quantify these acoustic effects for six common types of sample container using an acoustic reciprocity experiment, then use the results to inform the design of a new container with improved acoustic transparency. Existing vessels were found to introduce up to 13 dB broadband insertion loss and change the location and spread of energy in PAM images by up to 1 mm and 25%, respectively. The new container caused up to 1.4 dB insertion loss (the lowest of any container tested) and introduced no significant phase aberration, source location error, or change in energy spread to the PAM images. Testing the new container with real cavitation noise produced very similar insertion loss figures of up to 1.6 dB. These results highlight deficiencies in existing sample containers for the purposes of quantifying cavitation activity with PAM, which is increasingly desired as cavitation matures as a therapy. The guidelines for acoustic transparency developed here may assist researchers in avoiding container aberrations and enable accurate measurement of cavitation energy in future studies.