Thermal behavior of ultrasound contrast agents for echographic imaging techniques through a photoacoustic technique

The ultrasound contrast agents used in echographic imaging techniques are essentially constituted by a suspension of microbubbles containing gas enclosed within an organic shell. In the present paper, the elastic characteristics of contrast agents have been studied, as they depend upon the temperature, using a photoacoustic technique. Central element of the experimental apparatus is a photoacoustic cell, where the ultrasound contrast agent is inserted and behaves as a Helmholtz resonator. A laser radiation modulated at frequencies in the range 100-1500 Hz, causes the solution volume containing the bubbles to vary; this causes thin membrane, which closes a small pipe inserted on the surface of the photoacoustic cell, to vibrate. The amplitude variations of the membrane, measured through a laser probe interferometer, vs. bubble concentration and temperature of the solution, allow one to investigate microbubbles thermal behavior.