Modeling frequency shifts and intensity variations from in-vivo Albunex microspheres

An acoustical model is proposed which enables one to estimate how back-scattered ultrasound intensity, mean frequency, and bandwidth depend on in-vivo contrast agent concentration and size distribution, on the depth of the scatterer the width of the blood volume containing microspheres in the ventricle, and the type of tissue between the scatterer and the transducer, and on ultrasound frequency and bandwidth of the emitted signal. An important result is that the frequency shifts and the intensity variations are caused both by the microspheres in the path between the transducer and the region of interest, and by the reflection properties of the contrast agent in the region of interest. The model enables one to explain and predict clinically observed intensity effects such as the shadow effect in the right ventricle, and the fact that received intensity increases with concentration up to a certain point where it falls off