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 /spl mu/m to 200 /spl mu/m 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 /spl mu/m to 30 /spl mu/m and from 35 /spl mu/m to 62 /spl mu/m 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.