Final answer:
The Doppler effect in ultrasound is used to delineate blood vessels by measuring the velocity of blood flow, which is particularly helpful in detecting occlusions and monitoring blood flow dynamics.
Step-by-step explanation:
The Doppler effect in ultrasound scanning is used primarily to delineate blood vessels. When utilized in Doppler-shifted ultrasound, this effect can monitor fetal heartbeat, measure blood flow velocity, and detect occlusions within the blood vessels. The Doppler effect takes advantage of the change in frequency of the sound waves due to the movement of the blood or the reflector (e.g., a fetal heart) relative to the ultrasound probe. The reflected sound waves from moving blood cells undergo a frequency shift that can be measured to assess the velocity of the blood flow. This is especially useful in situations where there is a constriction in a blood vessel. The reflected sound waves from blood cells moving through the constriction will exhibit a higher Doppler shift, indicating an increase in blood velocity at that point, as seen in Figure 17.49 where different velocities are color-coded.