Feasibility of measuring acoustic streaming for improved diagnosis of rhinosinusitis

No noninvasive methods exist currently with the capability of distinguishing between various stages of a sinus infection. We studied a method based on induced acoustic streaming in the accumulated fluid within the maxillary sinuses. The hypothesis was that acoustic streaming will not be induced at clinically acceptable intensity levels in infectious mucous fluid because of its high viscosity, whereas detected acoustic streaming is a strong indication that the sinus content is a noninfectious serous fluid. As a model, an anthropomorphic sinus phantom with bovine cortical bone to mimic the bone surrounding the maxillary sinus was constructed. Milk (1.5% fat content) was used as model fluid. From fluid and bone attenuation measurements, an ultrasound frequency of about 5 MHz was estimated to produce the highest acoustic streaming in the sinus phantom. Simulations of the acoustic streaming in a sealed cavity also showed that the width of the ultrasound beam should be about half the size of the cavity to optimize the streaming velocity. With a 4.9-MHz continuous-wave transducer operating at a spatial peak temporal average intensity of 640 mW/cm(2), an acoustic streaming velocity of 0.19 cm/s was generated and detected in the sinus phantom.