Experimental Method for Microbubbles Dynamics Monitoring and Radius Sizing

Abstract

Rationale and aim: Within the context of divers’ decompression illness prevention, ultrasonic detection and sizing of circulating microbubbles in blood is of great interest. In order to be representative of the divers gas tension level (supersaturation) and thus, to optimize decompression stages, the measurements (made in the right ventricle region) should be performed during a short period of time (ventricle filling <20ms), efficient to detect a broad range of bubbles’ radii population (radius from 20 to 200 _m) and harmless (Mechanical Index MI<0.3). Materials and methodsBased on a bi-frequency ultrasound excitation, the purpose of our method is to measure the relative and the absolute microbubble size variations. Because of our research interests, the experimental investigations were conducted on natural microbubbles, with radius ranging between 20 and 200μm, excited around their resonance frequencies by a low frequency transducer. Different types of excitation were tested (sweep, burst, pulse). A pair of high frequency transducers were arranged to focus at a common point. One of the transducers was used to transmit a 2ms duration high-frequency (1MHz) pulse while the other was used to passively receive backscattered signals. The scattered signal was acquired and visualized on a digital oscilloscope and transferred for offline calculations. Signal treatment were conducted in order to recover the amplitude and frequency modulations. ResultsUsing the same experimental setup, simple signal processing applied on both the amplitude and the frequency modulations leads to a double characterization of the microbubble dynamics. Moreover, under the assumption of small radial oscillations, the equilibrium radius of the microbubble can be accurately estimated.