Doppler Ultrasound Principles - Part 1

Explanation
When the source and receiver are approaching each other, there is a compression of the waves in front of the source, resulting in a decrease in wavelength and an increase in frequency. This causes a shift towards higher frequencies, known as a positive shift.

Explanation
When the source and receiver are moving away from each other, it causes an increase in the wavelength of the waves. This is known as a redshift and is associated with a decrease in frequency and energy. In terms of the Doppler effect, it is a negative shift because the observed frequency is lower than the emitted frequency. This negative shift indicates that the waves are stretched out and have a longer wavelength compared to when the source and receiver are at rest relative to each other.

Explanation
The given statement is true because the movement of red blood cells (RBCs) can cause a change in frequency. When RBCs move, they create disturbances in the surrounding fluid, which can be detected as changes in frequency. This phenomenon is utilized in various medical devices, such as Doppler ultrasound, where the movement of RBCs is measured by the change in frequency of reflected sound waves. Therefore, the statement is correct.

Explanation
When the frequency of a wave increases, the Doppler shift also increases. The Doppler shift refers to the change in frequency or wavelength of a wave as observed by an observer moving relative to the source of the wave. If the frequency of the wave increases, it means that the source is moving towards the observer, causing a higher frequency to be observed. Therefore, the correct answer is "increased".

Explanation
The velocity of the reflector is directly proportional to the Doppler shift. This means that as the velocity of the reflector increases, the Doppler shift also increases. The Doppler shift is a change in frequency that occurs when there is relative motion between the source of a wave and the observer. In the case of a reflector, the velocity of the reflector affects the change in frequency observed by the reflector. Therefore, the velocity of the reflector and the Doppler shift are directly related.

Explanation
The statement is true because the Doppler shift frequency is directly proportional to the velocity of flow. The Doppler effect occurs when there is relative motion between the source of waves (in this case, the flow) and the observer. When the source is moving towards the observer, the frequency of the waves appears higher, and when the source is moving away, the frequency appears lower. Therefore, as the velocity of flow increases, the Doppler shift frequency also increases.