ULTRASOUND SCATTERING PROPERTIES OF ALBUNEX MICROSPHERES

Albunex is an ultrasound contrast agent used in echocardiography and i n other areas, it consists of microspheres of which more than 95% have a diameter in the range 1 - 10 mum. The scattering properties of this agent as functions of ultrasound frequency and microsphere diameter a nd concentration are investigated. A model of the Albunex microspheres has been previously described, considering the individual microsphere s as air bubbles surrounded by a thin elastic shell. In the present st udy this model is extended by including into it the internal friction in the shell when the microsphere vibrates. Acoustic scattering and tr ansmission are measured in the frequency range from 700 kHz to 12.5 MH z. The measured transmitted power is used to estimate the two paramete rs in the theoretical model: the shell elasticity parameter, S(p) and the shell friction, S(f). Introduction of the shell friction into the model improves the agreement between theory and measurements. For the scattered power, differences between measured and calculated values li e within 3 dB. It is concluded that for the frequencies 2.5 and 5 MHz, microspheres with a diameter between 5 and 12 mum are preferred as th ese deliver the most significant contribution to the total scattered p ower and cause relatively little attenuation.