Background
In clinical medicine, the main application of the Doppler effect is for evaluating blood flow and tissue movement. To this end, modern ultrasonography (US) equipment contains a Doppler component.
Historical Overview
The Doppler effect, which is defined as the observed changes in the frequency of transmitted waves when relative motion exists between the wave source and an observer, was discovered by Christian Andreas Doppler, an Austrian mathematician and physicist, in 1842.1 In 1845, Christoph Hendrik Diederik Buys Ballot, who was performing experiments to refute Doppler theory, ultimately confirmed it. French physicist, Armand hippolyte Louis Fizeau was the first to demonstrate that the Doppler effect also applies to light waves.2 Eventually, it was proven that the Doppler effect holds true for any electromagnetic (light, infrared, ultraviolet) and acoustic waves.2
The first medical applications of Doppler sonography were performed in the late 1950s. In Japan, Shigeo Satomura developed the first Doppler US device to measure blood flow and heart valve movements. In the United States, Robert Rushmer, a physician, and Dean Franklin, an engineer, reported blood flow assessment using the US Doppler frequency shift. The first pulsed-wave Doppler equipment was developed by Donald Baker, Dennis Watkins and John Reid in Seattle. This team also pioneered the development of duplex Doppler, which allowed evaluation of deep-lying circulation. The development of real-time, two-dimensional color Doppler US represented a major technological breakthrough; a prototype device incorporating this technology was first developed and used by a Japanese group in 1983.1
Description
The probe containing the Doppler transducer (5- to 12-MHz for extremities) is placed on the skin overlying the blood vessel of interest. The probe generates a US beam at the target; a portion of the beam is reflected back to a detector, which measures its perceived frequency. Basic Doppler principles are used to calculate the speed and direction of the target’s motion. This information is converted into three types of visual output. In color Doppler, normal blood flow is represented in homogenous color, and turbulent blood flow appears white at the source of pathology. In spectral Doppler, normal blood flow appears as sharp tracings that are close together, and when there is turbulence, the tracings are farther apart. In power Doppler, only the amplitude (not the direction) of the reflected signal is measured. Doppler US is frequently used by hand surgeons to assess blood flow, particularly around soft-tissue masses. Doppler US can establish whether there is blood flow to the mass itself or whether there are important vascular structures in close proximity.3 Doppler US also is used to distinguish between primary and secondary Raynaud’s phenomenon and to evaluate the response to treatment for the disorder.4
