What is the main principle behind Doppler ultrasound?

• A. Wave reflection
• B. Frequency change due to motion
• C. Wave absorption
• D. Image contrast

Answer: (B)

The main principle behind Doppler ultrasound is the frequency change due to motion. This phenomenon, known as the Doppler effect, occurs when a sound wave source moves relative to an observer. In the context of ultrasound, when sound waves are emitted towards a moving object, such as blood cells, the frequency of the waves changes based on whether the object is moving towards or away from the ultrasound source.

If the blood cells are moving towards the transducer, the frequency of the reflected sound waves increases, resulting in a higher pitch. Conversely, if the blood cells are moving away from the transducer, the frequency decreases, leading to a lower pitch. This frequency shift can be quantified and is used in medical diagnostics to assess blood flow and heart conditions. Hence, the ability to measure these changes in frequency is crucial for interpreting the movement and velocity of blood within the body, making it a fundamental aspect of Doppler ultrasound technology.