The Doppler Signal: Where Does It Come From and What Does It Mean?

Doppler sonographic measurement of blood velocity and associated physiologic parameters is a powerful diagnostic technique. State-of-the-art instrumentation incorporates velocity measurement with two-dimensional imaging capability; it uses intensity and color coding to display complex physiologic and anatomic data to the observer in an easily understood format. Although the concepts underlying Doppler sonography are not complex, mastery of the technique requires extra training and commitment. The principal features and clinical practicalities associated with Doppler sonography are summarized in the following paragraphs. Continuous-wave Doppler is very sensitive to small vessels and has no upper velocity limit. In addition, the instrumentation is not complex and produces relatively low acoustic power. A significant drawback to continuous-wave Doppler is that there is no depth sensitivity, and thus complex structures or multiple vessels can give conflicting information. Pulsed Doppler (including duplex and ...