Ultrasonic Blood Flow Spectral Analysis Using Coherent Optics

It has been shown that ultrasonic Doppler signals can be obtained easily and transcutaneously from many blood vessels in both normal and atherosclerotic subjects. The Doppler spectrum changes with time, giving rise toa distnbution of frequencies whose envelope has a waveform that is characteristic of the vessel site and closely folows the events of the cardiac cycle. This makes it very useful in diagnosing lesions of the arterial system. The paper presents a coherent optical technique for displaying and analyzing a blood-flow-generated ultrasonic Doppler spectrum. The system is highly cost-effective and produces spectrograms on-line. Other advantages include a large, continuously variable bandwidth, an instantaneous display of velocity profile, and simultaneous display of temporal spectra. The system makes use of the Fourier transformation property of converging lens and its use of processing time signals. The spectrum obtained from the brachial artery of a normal subject compares favorably with the spectrograms obtained using electronic spectrum analyzers.