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Ultrasound Physics and Instrumentation > Module 1: Actions of Ultrasound with Tissue > Flashcards

Module 1: Actions of Ultrasound with Tissue Flashcards

1
Q

Define the term ultrasound

A

Any sound with a frequency above 20,000 hertz (Hz) which is a frequency above human hearing.

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2
Q

Describe how ultrasound travels through tissue

Compression

A

Regions of high pressure due to particles being close together

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3
Q

Describe how ultrasound travels through tissue

Rarefaction

A

Rarefactions are regions of low pressure due to particles being spread apart

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4
Q

Describe the properties of an ultrasound wave

Frequency

A

Number of vibration cycles that occur in 1 second

Represented = f

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5
Q

Describe the properties of an ultrasound wave

Period

A

Time it takes for each complete wave cycle

Time it takes for one wave length to occur

Represented = T

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6
Q

Describe the properties of an ultrasound wave

Wavelength

A

Distance between two points on a wave

Length of each complete wave cycle

Represented = lambda symbol (λ)

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7
Q

Describe the properties of an ultrasound wave

Velocity

A

Speed at which the sound waves propagate within tissue

Measured in meters per second (m/s)

Velocity is constant

Represented = c

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8
Q

Explain the relationship between speed of sound in tissue

A

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.

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9
Q

Explain the relationship between speed of sound in wavelength

A
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10
Q

Explain the relationship between speed of sound in frequency

A
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11
Q

Discuss the various interactions of ultrasound with soft tissue

Attenuation

A

Amplitude and intensity of ultrasound waves decrease as they travel through tissue

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12
Q

Discuss the various interactions of ultrasound with soft tissue

Reflection

A

Return of the sound wave energy back to the transducer

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13
Q

Discuss the various interactions of ultrasound with soft tissue

Refraction

A

A change in direction of a wave due to a change in its speed, which occurs due to material differences.

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14
Q

Discuss the various interactions of ultrasound with soft tissue

Scattering

A

When particle smaller than a wavelength beam scattered in all directions

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15
Q

Discuss the various interactions of ultrasound with soft tissue

Absorption

A

Reduction in intensity of the sound waves as it passes through tissue

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16
Q

Discuss the various interactions of ultrasound with soft tissue

Divergence

A

The ultrasound beam spreads out, as it moves away from the transducer

17
Q

Describe how ultrasound weakens as it travels through tissue

A

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.

18
Q

Explain the term refraction

A

A change in direction of a wave due to a change in its speed

19
Q

Explain Snell’s Law

A

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.

20
Q

Explain the term acoustic impedance

A

Density of a medium through which the sound travels

21
Q

Explain how the amount of energy reflected at an interface between two mediums is determined by their acoustic impedance

A

The greater the difference in acoustic impedance between the two mediums, the greater the reflection and the smaller the transmission

22
Q

Explain why ultrasound is good at imaging different soft tissue interfaces but poor at imaging soft tissue/bone interface or soft tissue/air interface

A
23
Q

Describe how echo ranging is performed and be able to use the echo ranging equation

A

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.

24
Q

What is the echo ranging equation?

A

d = ct/2

d = distance (cm)
c = velocity of sound in soft tissue (m/s)
t = time (s)

25
Q

What is power?

A

High-power applications of ultrasound often use frequencies between 20 kHz and a few hundred kHz.

26
Q

Describe depth of penetration

A

A measure of how deep light can penetrate into a material.

27
Q

Describe intensity

A

The rate at which energy passes through the unit area

28
Q

Describe amplitude

A

Represents the strength (peak pressure)

29
Q

Describe density

A

The ratio of nondense tissue to dense tissue

Ultrasound Physics and Instrumentation (8 decks)

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