Photoacoustical evaluation of thermal response of microbubbles

Photoacoustic technique has emerged as a tool for the study of liquid, gel, suspension behaviour and has been recently employed in a number of new biomedical applications. A new photoacoustic sensor is presented, which was designed and realized to analysing photoacoustic signals from slotions filled with microbubbles, usually used as contrast agents in echotomography imaging. The device is a closed cell where photothermal expansion in acqueous solution samples causes the deflection of a thin membrane closing a short pipe 0.7 mm by radius. The overall set up acts as a Helmholtz resonator, where the solution in the pipe is the mass oscillating under the driving force produced by the alternating expansion of the solution in the cell body. Displacement of the smembrane was measured using a laser probe, whereas photoacoustic signal was generated by chopping a laser light beam impinging into the solutin through a glass window in the cell. The response of the cell filled with shelled microbubbles was investigated with respect to water behaviour, at the cell resonance frequency and for different temperatures.