Cavitation nucleation in medical ultrasound

In 1980, Ed Carstensen coauthored the first of several articles on the effects of ultrasound on drosophila [Child, et al., Ultrasound in Med. & Biol., 6, 127-130 (1980)]. As diagnostic ultrasound became an ever-increasing imaging modality, it was important to determine if there were any bioeffects of the relatively high pressure amplitudes, but relatively low time-averaged intensities, used in these systems. Ed and his colleagues discovered that drosophila larvae and eggs, had air channels within them and these channels acted as cavitation nuclei. When it was determined that there were few preexisting gas nuclei present in human tissue, it was assumed that diagnostic ultrasound devices were safe for human use. More recently, therapeutic ultrasound has gained considerable support from the clinical community, and High Intensity Focused Ultrasound (HIFU) systems have been approved for clinical use. Furthermore, ultrasound contrast agents—stabilized gas bubbles—are also in common use. Accordingly, cavitation can be very important in this application of medical ultrasound. Recently, we have examined the source of potential gas nuclei that may give rise to cavitation inception and will report on these studies along with a discussion of Ed’s earlier contributions.