MEASUREMENT OF COLLAPSE CAVITATION IN ULTRASOUND FIELDS

This note describes a method for the measurement of hydroxyl free radi cal concentration due to collapse acoustic cavitation in medical ultra sound fields using aqueous terephthalic acid (TA) solution. An enclose d cylindrical chamber with acoustically transparent membranes at eithe r end was used. Control of cavitation activity was achieved by seeding the solution with polystyrene microspheres to provide cavitation cent res. Insonation experiments using unseeded TA previously exposed to ai r gave very variable results, sometimes detecting cavitation activity and at other times detecting nothing, under the same exposure conditio ns. Introduction of polystyrene microsphere seeds into the TA enabled it to detect reproducibly levels of cavitation activity at least one o rder of magnitude higher that in unseeded solutions. An experiment usi ng the seeded TA in a standing wave ultrasound field, set up using a b rass reflecting plate, demonstrated that the presence of a standing wa ve inhibited the measured cavitation yield.