Multifrequency transducer for microemboli classification and sizing.

The classification of circulating microemboli as gaseous or particulate matter is essential to establish the relevance of the detected embolic signals. Until now, Doppler techniques have failed to determine unambiguously the nature of circulating microemboli. Recently, a new approach based on the analysis of radio frequency (RF) signal and using the nonlinear characteristics of gaseous bubbles to classify emboli was investigated. The main limitation of these studies was the requirement of two separate transducers for transmission and reception. This paper presents a multi-frequency transducer with two independent transmitting elements and a separate receiving part with a wide frequency band. The transmitting elements are positioned in a concentric design and cover a frequency band between 100 and 600 kHz. The receiving part consists of a polyvinylidene fluoride layer. The new transducer has been tested in vitro using gaseous emboli. It could correctly classify and size air emboli with diameters ranging from 10 microm to 105 microm.