Effects of Dual Frequency Excitation on Cavitation of Microbubbles (2015)
Undergraduate: Alanna Smith
Faculty Advisor: Paul Dayton
Department: Applied Sciences
Background: Using focused ultrasound beams, diseased tissue can be ablated, and this process can be amplified with the use of microbubbles. At sufficiently high pressures, the microbubbles collapse in on themselves in a process known as cavitation. By using a dual frequency waveform, I hypothesize that effective cavitation will still occur with less energy, reducing surface heating and making high intensity focused ultrasound therapies safer.
Methods: Two transducers were submerged in water and aligned confocally onto a tube containing microbubbles flowing at a rate of 0.1mL/min. A 2.25 MHz transducer transmitted a pulse comprised of varying ratios of a 1.5MHz wave and a 3.0 MHz wave at pressures ranging from -0.75 MPa to -2.25 MPa. A 5 MHz transducer received the acoustic response. One hundred acoustic responses were collected for each waveform and each pressure.
Results: Acoustic responses from microbubbles were highest when the transmitted pulses were emitted at 10 Hz. The waveform with 80% 1.5MHz frequency wave and 20% 3.0 MHz frequency wave created the greatest cavitation.
Conclusions: Dual frequency pulses more efficiently cavitate microbubbles compared to single frequency pulses at the same pressure. The magnitude of cavitation is directly related to the pressure input. Cavitation is dependent on the pulse repetition frequency. In future experiments, the dual frequency acoustic pulses will be tested on ex vivo tissue.