Real-time Optical Imaging of Microbubble Destruction with an Acoustic Lens Attached Ultrasonic Diagnostic Probe in Microfluidic Capillary Models

In this work, an ultrasonic diagnostic system with an attachable acoustic lens was demonstrated for real-time optical imaging of ultrasound-mediated microbubble destruction in a microfluidic capillary model using an inverted microscope. Microbubble destruction under ultrasonic pressure was monitored via an EM-CCD camera with the frame rate of 70 fps. The acoustic field distribution of the transducer with the attachable acoustic lens was simulated via a finite element method (FEM) and measured by a hydrophone. The result of acoustic field distribution shows unfocused beam profiles with 50% decreased pressure of original focal area. With the unfocused beam, inertial cavitation of the microbubbles as a function of transducer input voltages of 30-60 Vpp was studied. In addition, the acoustic cavitation parameters such as frequency of 2 MHz, pulse length of 16 μs, and pulse repetition frequency (PRF) of 1 kHz were investigated under static and dynamic flow conditions in the microfluidic model. In our system, above 45 Vpp, the microbubbles were destroyed more than 50% within 20 seconds so that the threshold for the inertial cavitation was determined to be 45 Vpp in the channel without flow. In the microfluidic capillary model with fluidic flow, it is investigated that shape of microbubble mass continuously changed with acoustic pressure with 60 Vpp.