Ch. 6 Interaction of Sound and Media Flashcards by Destiny S

Sound waves weaken, or ______ as they travel through the body.

Sound waves weaken, or attenuate as they travel through the body.

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After a transducer receives a sound wave during reception, the sound wave is converted into electrical sound. The signal is sent to the ultrasound system where it is strengthened or _____________________.

After a transducer receives a sound wave during reception, the sound wave is converted into electrical sound. The signal is sent to the ultrasound system where it is strengthened or amplified

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Decibels are based on a mathematical construct called ______.

Decibels are based on a mathematical construct called logarithms

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A _________ is a number that represents the number of 10s that are multiplied to create the original number.

A log is a number that represents the number of 10s that are multiplied to create the original number.

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What is the log of 1,000?

We multiply 10 by itself 3 times to create the number 1,000 so the log of 1,000 is 3

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Decibel notation does not measure absolute numbers; rather decibels report ________________ changes.

Decibel notation does not measure absolute numbers; rather decibels report relative changes

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Positive decibels report signals that are ______ in strength or getting _______.

Positive decibels report signals that are increasing in strength or getting larger

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When a waves intensity doubles, the relative change is ______.

When a waves intensity doubles, the relative change is postive 3 decibels

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When intensity increases ten-fold, the relative change is ________.

When intensity increases ten-fold, the relative change is positive 10 decibels

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Negative decibels describe signals that are ______________ in strength, or getting ________________.

Negative decibels describe signals that are decreasing in strength, or getting smaller.

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When the intensity is reduced to 1/2 its original value, the relative change is _____________.

When the intensity is reduced to 1/2 its original value, the relative change is negative 3 decibels

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When the intensity is reduced to 1/10 its original value the relative change is ______.

When the intensity is reduced to 1/10 its original value the relative change is negative 10 decibels

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Every 3dB change means that the intensity will ____.

double

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Every 10dB change means that the intensity will _____.

increase ten times

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A reduction in the intensity of a sound beam to one-half of its original value is _____ dB.

-3dB

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A reduction in the intensity of a sound beam to one-quarter of its original value is _____ dB.

-6dB

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-10dB means that the intensity is reduced to __________ of its original value.

-10dB means that the intensity is reduced to one-tenth of its original value.

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If the final intensity of a sound beam is more than the initial intensity, then the gain in dB is ____. (+ or -)

Positive. The beams intensity is increasing.

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If the initial intensity of a sound beam is less than the final intensity, then the gain in dB is _____

Positive. The beams intensity is increasing.

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Attenuation is determined by TWO factors:

PATH LENGTH ( distance)
FREQUENCY ( penetration)

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Distance and attenuation are ______ related.

directly

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Frequency and attenuation are ______ related.

directly

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with longer distances and higher frequencies there is _____________ attenuation.

with longer distances and higher frequencies there is more attenuation

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with shorter distances and lower frequencies there is _____________ attenuation.

with shorter distances and lower frequencies there is less attenuation

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What three processes contribute to attenuation?

1. Reflection 2. Scattering 3. Absorption

As sound strikes a boundary, a portion of the wave's energy may be redirected, or _____ back to the sound source

reflected

What are the two forms of reflection?

1. Specular 2. Diffuse

When the boundary is smooth and the sound is reflected in only one direction in an organized manner. This is called?

*Specular Reflection* is when the boundary is smooth and the sound is reflected in only one direction in an organized manner

Most interfaces in the body are not smooth, but have irregularities. When a wave reflects off an irregular surface, it radiates in more than one direction. This is called?

*Diffuse Reflection or Backscatter* is when a wave reflects off an irregular surface, it radiates in more than one direction

_____________________ is the random redirection of sound in many directions.

*Scattering* is the random redirection of sound in many directions.

Higher frequency sound beams scatter _______________ (more or less) than lower frequency beams.

Scattering is ______ related to frequency.

directly

______________________________ is a special form of scattering that occurs when the structures dimensions are much smaller than the beams wavelength.

*Rayleigh Scattering* is a special form of scattering that occurs when the structures dimensions are much smaller than the beams wavelength.

In clinical imaging, the interaction of ultrasound and ________________________________ results in rayleigh scattering.

In clinical imaging, the interaction of ultrasound and *red blood cells* results in raylegh scattering.

Scattering is related to _________.

Frequency raised to the fourth power

When frequency doubles, Rayleigh Scattering is ________ times greater

When frequency doubles, Rayleigh Scattering is *16* times greater

organized sound back to the transducer is ____________________ reflection

organized sound back to the transducer is *Specular Reflection*

disorganized sound back to the transducer is _____________________ reflection

disorganized sound back to the transducer is *Diffuse Reflection or Backscatter*

organized sound in all directions is _______________________________

organized sound in all directions is *Rayleigh Scattering*

disorganized sound in all directions is ____________________________

disorganized sound in all directions is *Scattering*

_________________________ occurs when ultrasonic energy is converted into another energy form, such as heat.

*Absorption* occurs when ultrasonic energy is converted into another energy form, such as heat.

__________________________________ is the number of decibels of attenuation that occurs when sound travels one centimeter.

*Attenuation Coefficient* is the number of decibels of attenuation that occurs when sound travels one centimeter.

what are the units for attenuation coefficient?

dB/cm

Total Attenuation =

attenuation coefficient (dB/cm) x distance (cm)

In soft tissue the attenuation coefficient is _______________ the frequency.

In soft tissue the attenuation coefficient is *one-half* the frequency

attenuation coefficient formula:

frequency (MHz)/2

Attenuation for each: Water Blood, Urine, Biologic Fluids Fat Soft Tissue Muscle Bone & Lung Air

Water = extremely low Blood, Urine, Biologic Fluids = low Fat = low Soft Tissue = intermediate Muscle = higher Bone & Lung = even higher Air = extremely high

The ________________________________ is the distance sound travels in a tissue that reduces the intensity of sound to one-half its original value.

The *Half-Value Layer Thickness* is the distance sound travels in a tissue that reduces the intensity of sound to one-half its original value.

Half-Value Layer is also called: _______________________________, ______________________________, & _____________________________________.

Half Value Layer is also called: *penetration depth*, *depth of penetration*, *half-boundary layer*

A high frequency sound and media with a high attenuation rate will have a _____________ Half-Value

A high frequency sound and media with a high attenuation rate will have a *Thin* Half-Value

A low frequency sound and media with low attenuation rate will have a ___________ Half-Value

A low frequency sound and media with low attenuation rate will have a *Thick* Half-Value

The half-value layer thickness depends on two factors:

1. The medium 2. the frequency of sound

_____________________ is the acoustic resistance to sound traveling in a medium and is calculated by multiplying the density of a medium by the speed at which sound travels in the medium.

*Impedance* is the acoustic resistance to sound traveling in a medium and is calculated by multiplying the density of a medium by the speed at which sound travels in the medium

Impedance is reported in what units?

Rayls (Z)

Impedance is determined by

the medium, calculated not measured

Name three components of attenuation:

1. Absorption 2. Reflection 3. Scattering

As the path length increases, the attenuation of ultrasound in soft tissue _______.

increases

Attenuation in lung tissue is [less than, greater than, the same as] attenuation in soft tissue.

greater than

Attenuation in bone is _________ attenuation in soft tissue.

greater than

Attenuation in air is _______ attenuation in soft tissue.

greater than

What are the units of attenuation?

decibels (dB)

What are the units of the half-value layer thickness?

distance: centimeters

Impedance is associated with ____________________.

only the medium

Acoustic Impedance = ______________________ x __________________________

Acoustic Impedance = density (kg/m^3) multipled by propagation speed (m/s)

Impedance is important in ____ at boundaries.

reflections

_________________ incidence means that the incident sound beam strikes the boundary at exactly 90 degrees

*Normal Incidence* means that the incident sound beam strikes the boundary at exactly 90 degrees

Normal incidence is also called ____________________________, ________________________, _________________________, & _______________________________.

Normal Incidence is also called: - Perpendicular - Orthogonal - Right Angle - 90 degrees

_____________________ incidence occurs when the incident sound beam strikes the boundary at any angle other than 90 degrees

*Oblique Incidence* occurs when the incident sound beam strikes the boundary at any angle other than 90 degrees

Incident intensity = ____________________________ + ______________________________

Incident Intensity = reflected intensity + transmitted intensity

___________________________ is the intensity of the portion of the incident sound beam that, after striking a boundary, returns back where it came.

*Reflected Intensity* is the intensity of the portion of the incident sound beam that, after striking a boundary, returns back where it came.

_____________________________ is the intensity of the portion of the incident sound beam that, after striking a boundary, continues forward in the same general direction that it was traveling.

*Transmitted Intensity* is the intensity of the portion of the incident sound beam that after striking a boundary, continues forward in the same general direction that it was traveling.

The _______________________________________ is the percentage of the intensity that bounces back when a sound beam strikes the boundary between two media

The *Intensity Reflection Coefficient* (IRC) is the percentage of the intensity that bounces back when a sound beam strikes the boundary between two media

IRC formula

Intensity reflected divided by initial intensity

If the reflected and transmitted intensities are added, the result must be the?

The incident intensity

ITC formula

the transmitted intensity divided by incident intensity multiplied by 100 or 1 - intensity reflection coefficient

if IRC and ITC are added the result must equal?

100%

Sound is traveling from bone to soft tissue. The impedances of the media differ significantly, and 90% of the beam's intensity is reflected. What percentage of the intensity is transmitted?

100% of the energy must be counted for. If 90% is reflected, 10% must be transmitted.

When a sound beam strikes a tissue boundary at 90 degree angle, it is a ________________________ incidence

When a sound beam strikes a tissue boundary at a 90 degree angle, it is a *normal incidence*

reflection occurs only if the media on either side of the boundary have _______________________ impedances

reflection occurs only if the media on either side of the boundary have *different* impedances

With an oblique incidence, two physical priciples always apply to reflection:

1. conservation of energy 2. reflection angle = incident angle

_____________________ is a change in direction of wave propagation when traveling from one medium to another.

*Refraction* is a change in direction of wave propagation when traveling from one medium to another.

Refraction only occurs if two conditions are satisfied:

1. oblique incidence 2. different propagation speeds of the two media

C2 = C1

no refraction; transmission angle = incident angle

Which of the following terms does not belong with the others? A. orthogonal B. oblique C. normal D. perpendicular

B. Oblique means "other than 90 degrees" The other three terms all have the meaning of "equal to 90 degrees"

C2 > C1 =

transmission angle greater than incident angle

The ______________________________________ is the percentage of the intensity that continues to move forward when the beam reaches a boundary between two media.

The *Intensity Transmission Coefficient* is the percentage of the intensity that continues to move forward when the beam reaches a boundary between two media

C2 < C1 =

transmission angle less than incident angle