Correlation analysis of received echoes from contrast agents in-vitro and in-vivo

Ultrasound contrast agents can be used to receive signals from vessels significantly smaller than the effective resolution of an ultrasound system. The signal from these microbubbles is coherent across pulses as long as the microbubble is intact, looking like a moving reflector that is more echogenic than blood cells and shifted in spectral mean. When the microbubble is destroyed, the received signal decorrelates between pulses. In-vitro optical and acoustical experiments observing single bubble echoes were conducted. Three mechanisms of destruction were observed optically: static diffusion, pressure-driven diffusion, and fragmentation. Fragmentation was often observed at pressures above 1.4 MPa, while static diffusion and acoustical diffusion were most frequently responsible for bubble destruction at low transmitted pressure. Correlation analysis between echoes received from the same bubble provided analytical evidence of bubble destruction; moreover, a detection scheme based on decorrelation was designed and tested.