PROCESSING DOPPLER ULTRASOUND SIGNALS FROM BLOOD-BORNE EMBOLI

Analysing Doppler ultrasound signals from blood-borne emboli has been hindered by two basic problems. Firstly, the ratio of the signal levels from blood and emboli is greater than the dynamic range of conventional Doppler instruments used to detect such emboli. This causes amplitude overload, which must be eliminated before accurate analysis of embolic data can be performed. Secondly, the temporal resolution of fast Fourier transforms (FFT) usually used to analyse Doppler signals, is insufficient to quantify accurately such short duration signals. This paper describes methods to overcome these two problems. The Doppler signal is recorded from close to the front-end of the velocimeter, and a Wigner distribution analyser is used to provide Doppler spectra with both high temporal and frequency resolution. The resulting sonographic display allows quantitative measurement of embolic events to be made.