A non-linear ultrasonic scattering approach for micro bubble concentration quantification

Ultrasonic imaging of microbubble contrast agents and their concentration quantification is an ongoing problem, complicated by the lack of accurate attenuation compensation (TGC) algorithms and by the complex behaviour of microbubbles. Indeed the ultrasound contrast agents behave non linearly in the power range for medical imaging, while the biological tissues behave mainly linearly. Such quantification is required to allow the physicians to estimate the local blood perfusion in the biological tissues. But the different imaging methods developed to distinguish the agent from the surrounding tissues do not give an accurate representation of local agent concentration, which therefore has to be qualitatively estimated by the physicians. In this paper, we expand an existing automatic attenuation compensation algorithm by introducing a nonlinear relationship between insonating power and scattering when medium acoustic pressure is used (0.33 MI - 0.52 MI at 3 MHz), and model amplitude modulation (AM). An acquisition system is set up to allow acquisitions of radio frequency data from Sonovue^reg suspension with a programmable ultrasound scanner and a sectorial probe. Results show that the behaviour of microbubble clouds with pressure and concentration follow the evolution expected from the assumptions formulated to be able to develop the model. In particular, the proposed equations for concentration estimation correctly predict the true concentration in the range [0-228] muL/L.