Solved Examples of Ultrasound Doppler Effect Calculations

📚 Quick Study Guide

🔍 The Doppler effect is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. 🌡️ In the context of ultrasound, the Doppler effect is used to measure the velocity of blood flow. 💡 The formula for the Doppler frequency shift ($f_D$) is given by: $f_D = f_r - f_i = \frac{2v f_i cos(\theta)}{c}$, where $f_i$ is the incident frequency, $f_r$ is the received frequency, $v$ is the velocity of the blood, $\theta$ is the Doppler angle, and $c$ is the speed of sound in the medium. 📐 The Doppler angle ($\theta$) is the angle between the ultrasound beam and the direction of blood flow. ➕ A positive Doppler shift indicates that the blood is flowing towards the transducer. ➖ A negative Doppler shift indicates that the blood is flowing away from the transducer. 📏 Remember to keep units consistent! Velocity in m/s, frequency in Hz.

Practice Quiz

1. A 5 MHz ultrasound transducer is used to measure blood flow in an artery. The Doppler angle is 60 degrees, and the measured Doppler shift is 1 kHz. What is the velocity of the blood flow? (Assume the speed of sound in tissue is 1540 m/s)
   1. 0.154 m/s
   2. 0.308 m/s
   3. 0.4 m/s
   4. 0.2 m/s
2. An ultrasound machine emits a frequency of 7 MHz. If the blood is moving towards the transducer at a velocity of 0.25 m/s and the Doppler angle is 45 degrees, what is the Doppler frequency shift? (Assume the speed of sound in tissue is 1540 m/s)
   1. 1.27 kHz
   2. 2.54 kHz
   3. 3.81 kHz
   4. 5.08 kHz
3. If the Doppler angle increases, what happens to the measured Doppler shift frequency, assuming all other parameters remain constant?
   1. Increases
   2. Decreases
   3. Remains the same
   4. Becomes zero
4. What does a negative Doppler shift indicate?
   1. Blood flowing towards the transducer
   2. Blood flowing away from the transducer
   3. No blood flow
   4. Turbulent blood flow
5. An ultrasound probe emits a 3 MHz signal. The received frequency after interacting with moving blood cells is 3.002 MHz. The angle of incidence is 30 degrees. Calculate the velocity of the blood cells. (Assume the speed of sound in tissue is 1540 m/s)
   1. 0.26 m/s
   2. 0.52 m/s
   3. 1.04 m/s
   4. 0.13 m/s
6. The Doppler shift is 2 kHz, the incident frequency is 6 MHz, the velocity of blood flow is 0.3 m/s. Calculate the Doppler angle. (Assume the speed of sound in tissue is 1540 m/s)
   1. 30 degrees
   2. 45 degrees
   3. 60 degrees
   4. 90 degrees
7. Which of the following factors does NOT affect the Doppler frequency shift?
   1. Incident Frequency
   2. Velocity of Blood Flow
   3. Doppler Angle
   4. Transducer Size