A new multifrequency transducer for microemboli detection and classification

The classification of circulating microemboli as gaseous or particulate matter is essential to establish the relevance of detected embolic signals. Transcranial Doppler (TCD) technology has not yet fully succeeded in characterizing the composition of microemboli unambiguously. Recently, the authors proposed a new approach to detect, characterize and size gaseous emboli. The method is based on the nonlinear properties of gaseous bubbles. The application of this approach requires a dedicated transducer with the ability to transmit the adequate frequencies and simultaneously receive the high frequency scattered nonlinear components. The paper presents a multifrequency emboli transducer composed of two independent transmitting elements and a separate receiving part. The transmitting part can cover a frequency band between 100 kHz and 600 kHz. The reception of the signal is performed by a 110 /spl mu/m PVDF layer sensitive over a frequency band ranging from 50 kHz to 2 MHz. Experimental results show that a specific range of gaseous embolus size was detected by each transmitting element. Using the 130 kHz outer element in transmission, microemboli between 35 /spl mu/m and 105 /spl mu/m can be discriminated through their second harmonic or subharmonic emissions while gaseous microemboli between 10 /spl mu/m and 40 /spl mu/m were accurately classified using the 360 kHz inner element. The in vitro results demonstrate that nonlinear properties of microemboli combined with the new transducer offer a real opportunity to characterize and size microemboli.