Doppler Effect and Sound Waves Quiz

Doppler Effect

• The Doppler effect is the change in frequency of a sound wave due to motion between the sound source and the receiver.
• Doppler shifts range from 20 Hz to 20 kHz, which are in the audible range.

Velocity and Doppler Shift

• Velocity is directly proportional to the Doppler shift.
• If the velocity doubles, the Doppler shift frequency also doubles.

Doppler Equations

• There are two types of Doppler shifts: one when the sound wave from the transducer strikes the blood in motion, and another when the reflected wave returns from the blood cells.
• The cosine of the angle is directly proportional to the Doppler shift.

Doppler Techniques

• Continuous wave (CW) Doppler does not provide range resolution.
• Pulsed wave Doppler provides range resolution.

Wall Filters

• If wall filters are set too high, lower velocity signals that produce low frequency shifts are eliminated, making it impossible to appreciate low velocities.
• Increasing the wall filter during Doppler sampling reduces the display of low frequency shifts.

Aliasing

• Aliasing can be beneficial in identifying the jet, as it makes the jet stand out against the normal flow.
• To eliminate the aliasing artifact, the transmit frequency should be lowered.

Direction of Blood Flow

• In non-directional power Doppler, direction cannot be determined.
• In color Doppler, the direction of blood flow can be determined.

True or False

• There is no Doppler shift at 90 degrees.
• Sound waves cannot exist in a vacuum.
• A shorter wavelength represents a higher frequency and occurs when relative motion is toward an observer.