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
