Ambient pressure dependence of the subharmonic signal from ultrasound contrast microbubbles

Ultrasound contrast agents (UCA) microbubbles have been well recognized as a potential noninvasive tool for blood pressure measurement. The effect of ambient pressure on UCA subharmonic optimal driving frequency (SODF), at which the subharmonic scattering signals were maximal, was investigated experimentally. For groups of microbubbles with 80.1%±1.6% in the diameter range of 1µm–2µm, the shift of the SODF (SSODF) was 0.6MHz between overpressures of 4mmHg and 100mmHg, which was approximately twice of the corresponding shift of the resonance frequency. The SSODF may be as a novel and sensitive index of the local blood pressure estimation based on UCA microbubbles.