Techniques To Improve Subharmonic Emission From Encapsulated Microbubbles.

Subharmonic contrast imaging promises to improve ultrasound imaging quality by taking advantage of increased contrast to tissue signal. However, acoustic pressures beyond the subharmonic generation threshold using common ultrasound pulses may induce significant contrast microbubble destruction. In this work, we propose two techniques to improve the subharmonic emission from encapsulated microbubbles, i.e. chirp excitation technique and dual-frequency excitation techniques. For the first technique, chirp signals with center frequency 5 MHz are employed to drive microbubbles in numerical simulation and experimental studies. For the second technique, both theoretical simulation and experimental verification are also presented. The simulation uses a modified mathematical model developed by Church and experimental work uses microbubbles sonicated by dual frequencies (2 MHz and 4 MHz) superimposed to simulate a truncated saw-tooth wave. [ABSTRACT FROM AUTHOR]