Doppler ultrasound techniques in medicine

Doppler ultrasound is a noninvasive technique which is widely used in medicine for the assessment of blood flow in intact vessels. The technique has improved much since Satomura first demonstrated the application of the Doppler effect to the measurement of blood flow velocity in 1959. However, rigorous analysis of their properties did not begin until the mid-1970s. Since then, Doppler assessment of blood flow has become routine in many diagnostic ultrasound exams. The analyses were motivated by a desire to extract specific physiologically relevant information with the devices. Measurements of interest included (1) flow rate, (2) velocity profiles, (3) coherent structures, (4) turbulent energy and turbulent spectra, (5) velocity gradients (shear rate), and (6) pressure drops. Inaccuracies in all of these measurements result from fundamental limitations in the Doppler ultrasound method itself. The instruments measure neither true flow nor point velocity. However, they provide a measure of the velocity distribution throughout the interrogated volume, and this unique aspect has suggested to researchers that the spectral content of the quadrature signals could be correlated to the severity of flow pathologies such as arterial stenosis and aneurism