What is the Doppler shift frequency proportional to?

The Doppler shift frequency is directly related to the velocity of the reflector, making this answer correct. In Doppler ultrasound, the frequency shift observed is a result of the motion of a reflecting object (such as blood cells). When the reflector moves towards the source of ultrasound, the frequency of the reflected sound waves increases, creating a positive shift. Conversely, when the reflector moves away, there is a negative shift in frequency. The amount of Doppler shift is proportional to the speed (or velocity) of that moving object, with higher velocities resulting in greater frequency changes.

Understanding the relationship between Doppler shift frequency and the velocity of the reflector is essential because this principle underpins many clinical applications of Doppler ultrasound, such as in assessing blood flow or heart function. The usefulness of the Doppler shift is most evident in evaluating the speed of blood flow, where accurate velocity measurements can provide vital diagnostic information.