SUPPRESSION OF PROPAGATING 2ND-HARMONIC IN ULTRASOUND CONTRAST IMAGING

Contrast agents, such as bubbles, are used in ultrasound to enhance ba ckscatter from blood. To increase contrast between these agents and ti ssue, nonlinear methods such as harmonic imaging can be used. Contrast is limited, however, by tissue second harmonic signals. We show that a major source of this signal is nonlinear propagation through tissue. In addition, we present methods to suppress this second harmonic gene ration. One simple approach is to decrease the f/number of the imaging system. Simulations show that doubling the size of the array, while k eeping total power output constant, decreases propagating second harmo nic generation. A second approach uses active noise cancellation to su ppress second harmonic generation. A specific method, the harmonic can cellation system (HCS), is developed and presented as an example. In s imulations, HCS decreased second harmonic generation by over 30 dB. Us ing such methods, contrast can be improved between tissue and bubbles in harmonic imaging.