What is the principle of Doppler ultrasound based on?

The principle of Doppler ultrasound is fundamentally based on the change in frequency of sound waves as they reflect off moving objects. This phenomenon occurs due to the Doppler effect, which describes how the frequency of a wave changes for an observer moving relative to the source of the wave.

In the context of ultrasound, when sound waves are transmitted into the body and encounter moving structures, such as red blood cells, the frequency of the reflected waves is altered based on the velocity and direction of movement of those structures. If the object is moving toward the ultrasound transducer, the frequency of the reflected sound waves increases (a phenomenon known as a positive Doppler shift). Conversely, if the object is moving away, the frequency decreases (a negative Doppler shift).

This frequency change is critical for assessing blood flow, where it can be quantified to determine the speed and direction of blood flow within the circulatory system, making it an invaluable tool in medical diagnostics.

The other options do not accurately describe the principle of Doppler ultrasound. The change in temperature of surrounding tissues does not relate to the frequency shift fundamental to Doppler principles. Sound waves reflecting off stationary objects would not display any frequency changes, as there would be no relative motion; thus, it is not