Subharmonic and ultraharmonic emissions for emboli detection and characterization

Emboli detection and characterization is of importance for different patients, such as those undergoing carotid or cardiac surgery. The emboli occur as particulate or gaseous matters. To select the appropriate treatment and reduce the risk of embolism, it is essential to first detect and then classify and, ultimately, size the emboli. We propose, in this study, an approach to characterize and size the emboli based on the nonlinear properties of the emboli. Gaseous emboli were produced by generating single and uniform air bubbles. These bubbles had diameters ranging from 40 μm to 120 μm. Acoustic measurements were carried out and special attention was devoted to the generation of subharmonic and first ultraharmonic components for gas bubbles of different sizes and at different acoustic pressures. For the scanning frequency and the applied acoustic pressures used in this study, only bubbles ranging from 58 μm up to 110 μm are capable of generating a subharmonic and an ultraharmonic frequency component. However, gas emboli outside this range behave differently. In conclusion, such an approach can be used to provide information needed to classify and size emboli.