12 Questions
What is the frequency range of audible sound for humans?
20 Hz to 20 kHz
What type of wave has particle motion perpendicular to the direction of wave propagation?
Transverse wave
What is the symbol for the speed of a wave?
c
What type of ultrasound is used to study blood flow dynamics?
Color Flow 3D Doppler
What is the term for the distance between two consecutive points of maximum compression or rarefaction in a longitudinal wave?
Wavelength
What is the term for waves with frequencies above the range of human hearing?
Ultrasonic
What is the main advantage of Continuous Wave Doppler?
It can measure high velocity flows in excess of 7m/sec
What is the optimal angle for Doppler measurements?
Parallel to the blood flow
What is the Doppler equation used to calculate?
The velocity of the target, such as blood cells
What is the effect of the Doppler principle when applied to vascular flow?
A higher frequency is received when blood cells are moving towards the probe
What is the limitation of Continuous Wave Doppler?
It lacks selectivity or depth discrimination
What is the main difference between the Doppler Effect in stars and the Doppler Effect in vascular flow?
The frequency shift is opposite in direction
Study Notes
Sound Frequency Spectrum
- The audible region of sound for humans lies between 20 Hz and 20 kHz.
- Infrasonic frequencies are below 20 Hz and can be generated by earthquakes, wind, airplanes, and rapidly moving objects.
- Ultrasonic frequencies are above 20 kHz and can be generated by high-frequency vibrations in crystals.
Waves
- Waves can be transverse or longitudinal.
- Transverse waves have particle motion perpendicular to wave propagation, examples include light and waves on water.
- Longitudinal waves have particle motion parallel to wave propagation, examples include sound waves.
Longitudinal Sound Waves
- Travel through solids, liquids, and gases.
- Particle motion is in the direction of wave propagation, producing areas of compression and rarefaction.
- Particles move backwards and forwards, transferring energy through the medium as they oscillate.
Properties of Waves
- Speed (c) is the speed of the wave moving through the medium, measured in m/s.
- Frequency (f) is the number of vibrations/oscillations per second, measured in Hz or MHz.
- Wavelength (λ) is the distance between one maximum or point of highest compression and the next, measured in meters.
Ultrasound
- Different modes of ultrasound include A mode (amplitude), B mode (brightness), M mode (motion), Doppler, Pulse Wave, Continuous Wave, Color Flow, and 3D Doppler.
- Doppler ultrasound is used to study blood flow dynamics and detect the direction and velocity of moving blood.
Doppler Effect
- Describes how the frequency of light emitted from stars changes depending on the relative motion of the observer and the wave source.
- Applies to Doppler ultrasound, where the frequency shift is used to measure blood flow velocity.
Doppler Equation
- Velocity (V) is given by V = cf d / 2f o cos θ.
- Where c is the speed of sound in tissue, f is the frequency shift, d is the frequency of emitted ultrasound, f o is the frequency of the original ultrasound, and θ is the angle between the ultrasound beam and the direction of target velocity.
Importance of Doppler Angulation
- Best Doppler measurements are made when the Doppler probe is aligned parallel to the blood flow.
- A divergence of up to 200 can be tolerated, resulting in an error of ≤6%.
Applications of Doppler
- Different modes of Doppler ultrasound can measure blood velocities.
- Continuous wave Doppler is used to measure high velocity flows (in excess of 7m/sec) and lacks selectivity or depth discrimination.
Quiz on sound frequencies, types of waves, and wave properties. Includes infrasound, ultrasound, transverse and longitudinal waves, and particle motion.
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