Basics of Sound Waves
What is ultrasound?
Sound waves with frequencies higher than 20,000 Hz, above the range of human hearing.
What is the frequency of a wave?
The number of cycles that occur in one second, measured in Hertz (Hz)
What is the average propagation speed of sound in soft tissue?
1540 m/s (or 1.54 mm/μs).
What is attenuation?
The reduction in amplitude, power, and intensity of the sound wave as it travels through a medium
What is the formula for intensity?
Intensity = Power / Area.
What type of waves are sound waves?
Mechanical, longitudinal waves.
Define period in ultrasound.
The time it takes for one cycle to occur, measured in seconds or microseconds.
How does propagation speed change in denser materials?
It increases in stiffer (less compressible) materials and decreases in more dense materials.
What is the relationship between frequency and attenuation?
Higher frequency results in greater attenuation.
What unit is used to measure intensity?
Watts per square centimeter (W/cm²).
What are the three acoustic variables?
Pressure, density, and distance (particle motion).
What is propagation speed?
The speed at which a sound wave travels through a medium, dependent on the medium's density and stiffness.
What happens to sound intensity as sound travels through tissue?
It decreases due to attenuation.
What is acoustic impedance?
A property of a medium that determines the amount of sound reflection at a boundary. It is the product of density and propagation speed.
How is power related to amplitude in ultrasound?
Power is proportional to the square of the amplitude.
What is the definition of wavelength?
The distance between two consecutive points of a wave, such as between two compressions.
What determines the propagation speed of sound in a medium?
The medium’s stiffness and density
Name one factor that contributes to the attenuation of sound waves.
Absorption, reflection, or scattering
What is scattering?
The redirection of sound waves in many directions after hitting small structures or rough surfaces
What happens to intensity when the area decreases?
Intensity increases if the power remains the same.
What does the amplitude of a wave represent?
The maximum variation of an acoustic variable from its normal value (how "strong" the wave is).
Which parameter is inversely related to frequency?
Wavelength (higher frequency means shorter wavelength).
What is refraction, and when does it occur?
Refraction is the change in direction of a wave as it passes from one medium to another at an angle. It occurs when there is a change in propagation speed between the two media.
What causes reflection in ultrasound?
Reflection occurs when there is a difference in acoustic impedance between two tissues.
Define spatial peak temporal average (SPTA) in ultrasound intensity.
The average intensity at the location where it is the greatest (spatial peak), averaged over the duration of the pulse (temporal average).