What occurs when the frequency of the wave received is different from the transmitted wave due to relative motion?

The correct answer is the Doppler shift, which is a phenomenon that occurs when there is relative motion between a source of waves and an observer. In the context of ultrasound, when a wave is transmitted and reflects off a moving object, such as blood cells in a vessel, the frequency of the wave detected by the transducer may differ from the frequency of the wave that was originally transmitted. This change in frequency is utilized in Doppler ultrasound to assess blood flow, allowing for measurements of blood velocity and direction.

The Doppler shift helps in diagnosing and monitoring various vascular conditions by providing critical information about hemodynamics. The frequency change is proportional to the speed of the moving object, which allows practitioners to quantify the velocity of flowing blood.

Other terms, while relevant to aspects of ultrasound, do not describe this specific phenomenon. Waveform analysis pertains to the examination of the shapes of waves but does not directly involve the frequency shift. Echo time refers to the time taken for a transmitted sound wave to return to the transducer but is not related to changes in frequency. Frequency modulation describes a technique used to encode information onto a carrier wave and does not specifically connect with the effects of relative motion on wave frequencies in an ultrasound context.