Module 1: Actions of Ultrasound with Tissue Flashcards
Define the term ultrasound
Any sound with a frequency above 20,000 hertz (Hz) which is a frequency above human hearing.
Describe how ultrasound travels through tissue
Compression
Regions of high pressure due to particles being close together
Describe how ultrasound travels through tissue
Rarefaction
Rarefactions are regions of low pressure due to particles being spread apart
Describe the properties of an ultrasound wave
Frequency
Number of vibration cycles that occur in 1 second
Represented = f
Describe the properties of an ultrasound wave
Period
Time it takes for each complete wave cycle
Time it takes for one wave length to occur
Represented = T
Describe the properties of an ultrasound wave
Wavelength
Distance between two points on a wave
Length of each complete wave cycle
Represented = lambda symbol (λ)
Describe the properties of an ultrasound wave
Velocity
Speed at which the sound waves propagate within tissue
Measured in meters per second (m/s)
Velocity is constant
Represented = c
Explain the relationship between speed of sound in tissue
Speed of sound in tissues vary from 1430 m/s to 1647 m/s.
Despite this variation, sonographers typically use an assumed speed of sound (1540 m/s) for image reconstruction.
Explain the relationship between speed of sound in wavelength
Explain the relationship between speed of sound in frequency
Discuss the various interactions of ultrasound with soft tissue
Attenuation
Amplitude and intensity of ultrasound waves decrease as they travel through tissue
Discuss the various interactions of ultrasound with soft tissue
Reflection
Return of the sound wave energy back to the transducer
Discuss the various interactions of ultrasound with soft tissue
Refraction
A change in direction of a wave due to a change in its speed, which occurs due to material differences.
Discuss the various interactions of ultrasound with soft tissue
Scattering
When particle smaller than a wavelength beam scattered in all directions
Discuss the various interactions of ultrasound with soft tissue
Absorption
Reduction in intensity of the sound waves as it passes through tissue
Discuss the various interactions of ultrasound with soft tissue
Divergence
The ultrasound beam spreads out, as it moves away from the transducer
Describe how ultrasound weakens as it travels through tissue
As sound waves travel through tissue, there is a progressive reduction in the intensity of the wave.
The waves are attenuated (weakened) as they travel through the body.
Explain the term refraction
A change in direction of a wave due to a change in its speed
Explain Snell’s Law
When light travels from one medium to another, it generally bends, or refracts.
The law of refraction gives us a way of predicting the amount of bend.
Explain the term acoustic impedance
Density of a medium through which the sound travels
Explain how the amount of energy reflected at an interface between two mediums is determined by their acoustic impedance
The greater the difference in acoustic impedance between the two mediums, the greater the reflection and the smaller the transmission
Explain why ultrasound is good at imaging different soft tissue interfaces but poor at imaging soft tissue/bone interface or soft tissue/air interface
Describe how echo ranging is performed and be able to use the echo ranging equation
A sound beam is transmitted into a medium and is reflected back from an object. The elapsed time between the transmitted pulse and the received echo is converted into the total distance traveled.
What is the echo ranging equation?
d = ct/2
d = distance (cm)
c = velocity of sound in soft tissue (m/s)
t = time (s)
What is power?
High-power applications of ultrasound often use frequencies between 20 kHz and a few hundred kHz.
Describe depth of penetration
A measure of how deep light can penetrate into a material.
Describe intensity
The rate at which energy passes through the unit area
Describe amplitude
Represents the strength (peak pressure)
Describe density
The ratio of nondense tissue to dense tissue
