In vitro studies and safety assessment of Doppler ultrasound as a diagnostic tool in rhinosinusitis.

We have previously proposed the use of Doppler ultrasound to noninvasively stage a sinus infection. In this study, we first investigated the acoustic properties of nonpurulent and mucopurulent sinus secretions. The density, viscosity, speed of sound and attenuation of 18 samples of sinus fluid were examined. We then assessed the safety of the method by determining the temperature increase when ultrasound is transmitted through a bone sample of the same thickness as the anterior wall of the maxillary sinus. As a measure of the probability to generate acoustic streaming, we determined the ratio of sound attenuation over the viscosity of the sinus fluid and compared this with the value obtained from acoustic streaming measurements on a model system. The results indicated that detectable levels of acoustic streaming can be generated in serous sinus fluid, which has a low viscosity, but is very unlikely in mucopurulent secretions. The attenuation of the mucopurulent sinus fluid was 10 times higher than that of the serous cyst fluid, but the viscosity of the mucopurulent secretion was a thousand times higher than that of serous fluid. The safety experiments gave a temperature increase of the bone of <1.5°C at I(spta) of 640 mW/cm(2), below the temperature increase considered to be harmful by the World Federation for Ultrasound in Medicine and Biology.