Emboli detection and discrimination using harmonics

The characterization of gaseous emboli is of high interest for clinical decision making after surgery. In this study, a new approach using the nonlinear behavior of gaseous emboli is presented. An in-vitro set-up was developed to generate air bubbles of uniform sizes, with diameter ranging from 19 μm to 200 μm to simulate gaseous emboli. These bubbles were characterized using low frequency transducers (130 kHz and 250 kHz) at moderate acoustic pressures (from 30 kPa to 55 kPa peak-to-peak). The use of a 130 kHz transducer together with a 250 kHz transducer allows the detection of a wide range of bubble sizes. Bubble diameters ranging from 19 μm to 30 μm and from 35 μm to 62 μm are leading to second harmonic emissions while larger bubbles responded only linearly. The production of a fourth or a fifth harmonic can be correlated to the presence of bubbles of resonance size. The theoretical model showed good agreement with experimental results