Pulsed bi-frequency method for characterization of microbubbles in the context of decompression sickness

Abstract

International audienceDuring hyperbaric decompression, the absolute ambient pressure is reducing; microbubbles may be generated from pre-existing gas nuclei. An accurate monitoring of the size and of the density of the bubble population will provide a valuable means to understand the nucleation and growth processes in tissues. In this aim, an ultrasonic characterization method based on a dual frequency technique applied on a single bubble is tested. The method consists in sending two ultrasonic waves on a stationary bubble. One is a low frequency wave (30 kHz\leqflf\leq 60 kHz), which excites the bubble near its resonance frequency and the other is a high frequency (fhf=1MHz) wave that measures the changes in the acoustic cross-section induced by the low frequency activation. The resonance frequency, directly related to the radius, can be detected by looking at the spectrum. The development of an optimal sensor embedded on a diver leads to the use of a single transducer acting as an transmitter/receiver of pulsed waves. The straight forward outcome is a higher probability detection and a better radius estimation accuracy. Distinctions in the signal processing allows dedicated detection/sizing processes suitable either for bubbles circulating in the blood flow (larger bubble) or for stationary bubbles in tissues (several microns)