The Physics of Doppler Ultrasound and its Measurement Instrumentation

Abstract

Doppler ultrasound, or the measurement of the frequency shift of an ultrasonic signal reflected from moving structures within the body, has been used to study and measure the hemodynamics of blood flow within the cardiac and vascular systems. The historical development of Doppler ultrasonic applications is detailed elsewhere in this book and will not be repeated here, rather, the basic principles of ultrasonic propagation within the body will be discussed. The relationship of ultrasonic propagation characteristics to the noninvasive measurement of blood flow will be investigated. Several types of Doppler measurement instrumentation have been developed in recent years. The basic similarities and differences between continuous wave (CW) Doppler, single gate pulse Doppler, and multigate pulse Doppler will be examined. Limitations of the various kinds of measurement instrumentation will be discussed as they relate to the accuracy and certainty of the measurement process. The effect of ultrasonic transducers and their associated beam patterns on the measurement process will be described. The application of advanced methods of analyzing the Doppler signal and extracting quantitative flow or velocity information through use of real time spectral analysis will be discussed.