Real-time DSP system for ultrasonic blood flow measurement

The application of advanced digital signal-processing techniques in a noninvasive ultrasonic Doppler flowmeter used to measure extracorporeal blood flow during open heart surgery is described. Although the use of ultrasonics to monitor blood flow is not in itself a novel concept, the application of advanced digital signal-processing techniques has resulted in a unique product for accurate and reliable blood-flow measurements. The continuous-wave ultrasonic flowmeter utilizes the Doppler principle of wave reflection. The reflected Doppler-shifted signal is composed of a mixture of different frequency components, each representative of a different cell velocity within the ultrasound beam´s path. Determining the blood-flow rate involves not only calculating the average frequency of the incoming signal, but also performing noise cancellation and zero-flow detection. The authors describe the underlying theory of the ultrasonic flowmeter, the digital signal-processing techniques used, and the practical application of software and electronics to implement the flowmeter as a product