Thermal dependence of ultrasound contrast agents scattering characteristics for echographic imaging techniques

Ultrasound contrast agents (UCA), used in echographic imaging techniques, may represent an interesting solution to the problem of realizing non-invasive thermometers, based on some thermal variations of their physical properties. UCA, indeed, are inserted into blood circulation and they reach the most important organs inside the human body; consequently, any thermometric property they share, it could be exploited for realizing a non-invasive thermometer. UCA essentially are a suspension of microbubbles, containing a gas enclosed within an organic shell. In the present paper, the acoustic scattering efficiency of such structures has been studied, as it depends upon the temperature, using a pulse-echo technique. This method is a commonly used and well-established experimental system for examining the acoustic behaviour of the UCA, around the resonance frequency. The experimental apparatus is composed of a test tube which contains the UCA solution and a spherical concave piezoelectric transducer that generates in a water cell ultrasound bursts focused on a plate mirror, that reflects the signal back to the transducer after passing twice through the test tube with the sample solution. Since the whole apparatus is immersed in a thermostatic bath, the spectrum of the received signal bears the frequency dependence from temperature of the scattering properties of the microbubble solution.