An ultrasonic method for detection of fluid properties in the paranasal sinuses

We propose a method for detection of the degree of infection in the paranasal sinuses utilizing a previously published method whereby the viscosity in a sealed container may be measured using an ultrasound Doppler method. As ultrasound propagates in a liquid medium, due to attenuation, the resulting pressure gradient will cause the liquid to move in the propagation direction - the wellknown effect of acoustic streaming. The streaming velocity will, for a given acoustic output, be proportional to the viscosity of the fluid. In this study, we verify that acoustic streaming can be induced in an anthropomorphic sinus phantom cast from a human cranium. The sinus phantom was made from agar with added graphite providing sound attenuation prior to the sinus cavity corresponding to an in vivo situation. A number of water-glycerol solutions with scattering particles, were prepared to mimic a clinically interesting range of viscosities (7-47 mPas). Using a 4.2 MHz continuous wave Doppler probe, clearly detectable Doppler shifts in the range of 6.5 to 20 Hz were recorded. A linear relationship was found between the Doppler shifts and 1/viscosity (R²=0.94, corrected for the square-law dependence of sound speed variation due to varying glycerol concentration)