Edelman Ch 6 Interaction of Sound & Media Review

Every 3 dB change means that the intensity will

Double (Ch. 6, Question 1, pg. 78)

Every 10 dB change means that the intensity will

Increase ten times (Ch. 6, Question 2, pg. 78)

A reduction in the intensity of a sound beam to 1/2 of its original value is ____________dB .

-3 dB (Ch. 6, Question 3, pg. 78)

A reduction in the intensity of a sound beam to 1/4 of its original value is __________dB .

-6 dB (Ch. 6, Question 4, pg. 78)

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

1/10 (Ch. 6, Question 5, pg. 78)

dB is a mathematical representation with a ______________ scale.

A. logarithmic and relative

B. division and relative

C. longitudinal and relative

D. logarithmic and absolute

A. (Ch. 6, Question 6, pg. 77)

True or False We need one intensity to calculate decibels.

False (Ch. 6, Question 7, pg. 77)

A wave's intensity is 2 mW/cm². There is a change of +9 dB. What is the final intensity ?

A. 6 mW / cm³

B. 2 mW / cm²

C. 16 mW / cm²

D. 16 µW / cm²

C. 16 mW / cm²

(Ch. 6, Question 8, pg. 78)

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

Positive. The beam's intensity is increasing.

(Ch. 6, Question 9, pg. 77)

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

Positive. The beam's intensity is increasing.

(Ch. 6, Question 10, pg. 77)

Name the three components of attenuation.

absorption, reflection, scattering

(Ch. 6, Question 1, pg. 81)

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

increases

(Ch. 6, Question 2, pg. 80)

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

greater than

(Ch. 6, Question 3, pg. 86)

Attenuation in bone is ___________ in soft tissue .

greater than

(Ch. 6, Question 4, pg. 86)

Attenuation in air is ____________ attenuation in soft tissue .

greater than

(Ch. 6, Question 5, pg. 86)

What are the units of attenuation ?

Decibels ( dB )

(Ch. 6, Question 6, pg. 80)

True or False. In a given medium, attenuation is unrelated to the speed of sound.

True

(Ch. 6, Question 7, pg. 80)

What is the relationship between ultrasound frequency and the attenuation coefficient in soft tissue ?

In soft tissue , the attenuation coefficient in dB per centimeter is approximately one half of the ultrasonic frequency in MHz.

(Ch. 6, Question 8, pg. 85)

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

distance : centimeters

(Ch. 6, Question 9, pg. 87)

As frequency decreases , depth of penetration ______________.

increases

(Ch. 6, Question 10, pg. 80)

As path length increases , the half boundary layer _______________.

remains the same

(Ch. 6, Question 11, pg. 87)

Impedance is associated with ______________.

only the medium

(Ch. 6, Question 12, pg. 88)

As the path length increases , the attenuation coefficient of ultrasound in soft tissue [ decreases , remains the same , increases ] .

remains the same

(Ch. 6, Question 13, pg. 85)

Acoustic impedance =_____________ X ____________

density (kg/m³) x propagation speed (m/s)

(Ch. 6, Question 14, pg. 88)

Two media A and B have the same densities. The speed of sound in medium A is 10 % higher than in medium B. Which medium has the higher acoustic impedance?

Medium A's acoustic impedance is higher than medium B's. Recall that impedance equals speed multiplied by density. Since both media have identical densities and medium A's speed is 10 % higher, then medium A's impedance is 10 % higher.

(Ch. 6, Question 15, pg. 88)

Impedance is important in ____________ at boundaries.

reflections

(Ch. 6, Question 16, pg. 88)

Which is better to use while examining a carotid artery, a 7.5 or 3.0 MHz transducer?

The carotid artery is a superficial structure. A 7.5 MHz transducer is better because the higher frequency transducer produces the better image.

(Ch. 6, Question 17, pg. 80)

A pulse of ultrasound is propagating in soft tissue, such as liver. The pulse strikes a boundary with a different soft tissue at normal incidence. What portion of the intensity is reflected back toward the transducer? Why?

A very small percentage of sound, typically less than 1%, is reflected at a boundary between two soft tissues. The impedances of two soft tissues are similar, and the difference in impedance directly determines the intensity reflection coefficient. Very little reflection occurs when the impedances have similar, but not identical, values.

(Ch. 6, Question 1, pg. 88)

Sound is traveling in a medium and strikes a boundary with normal incidence. If 63% of the wave's intensity is reflected back toward the transducer, what percentage is transmitted ?

37 % of the intensity will be transmitted. 63 % + 37 % = 100 % .

(Ch. 6, Question 2, pg. 92)

A pulse of ultrasound is propagating in bone and strikes an interface with soft tissue at 90°. A giant reflection is created.

From these facts alone, what can be said about the impedance of bone?

What can be said about the impedance of soft tissue?

What can be said about the differences between the impedances of bone and soft tissue?

Nothing can be stated about the impedance of bone or soft tissue based on the information given. However, because a large reflection was created, the impedances of these two media must be dissimilar. Reflections with normal incidence are created based on the difference in the impedances, not on the actual values of the impedances.

(Ch. 6, Question 3, pg. 95)

Sound strikes a boundary between two media orthogonally. Although the media are very different, no reflection is created. How can this be?

With normal incidence, reflections occur only when the impedances of the two media at the interface are different. Two different media can have the same impedances, and when that happens, no reflection will be created.

(Ch. 6, Question 4, pg. 95)

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."

(Ch. 6, Question 5, pg. 91)

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?

If 90 % is reflected, 10 % must be transmitted.

(Ch. 6, Question 1, pg. 92)

Sound that is traveling in Jell-O passes through an interface at 90 degrees and continues to travel in whipped cream. The impedance of Jell-O and whipped cream are nearly identical. What percentage of the intensity is transmitted?

A. 2%

B. 25%

C. 78%

D. 99%

D. The best choice is 99%. If the impedances of Jell-O and whipped cream are nearly identical, only a very small percentage of the sound beam's intensity will reflect. The remainder will transmit .

(Ch. 6, Question 2, pg. 95)

A pulse of ultrasound liver. The pulse strikes a propagates in soft tissue, such as soft tissue-soft tissue interface with oblique incidence. Some of the sound energy is transmitted. To what extent is the transmitted beam refracted?

The transmitted beam undergoes little to no refraction. (Ch. 6, Question 1, pg. 101)

A sound pulse travels in Medium 1 and strikes an interface with another tissue, Medium 2, at 30°. The angle of transmission is 10°. From these facts alone, what can be said about

• the speed of sound in Medium 1?

• the speed of sound in Medium 2?

• the difference between the speeds of Media 1 and 2 ?

Given only this information, we can say nothing about the speed of sound in Medium 1 or Medium 2. However, because the beam refracted significantly (there was a 20° change in direction), the speeds of these two media are very different. Refraction depends on the difference in the speeds of sound in the two media, not the actual speeds.

(Ch. 6, Question 2, pg. 101)

A sound pulse travels in Medium 1 and strikes an interface with another tissue, Medium 2, at 30°. The angle of transmission is 10°. In which medium does sound travel slowest?

A. Medium 1

B. Medium 2

C. cannot be determined

B. Sound travels slowest in medium 2. When the angle of transmission is less than the angle of incidence, sound travels slower in the second medium.

(Ch. 6, Question 3, pg. 101)

A sound pulse travels in Medium 1 and strikes an interface with another tissue, Medium 2, at 30°. The angle of transmission is 10°. In which medium is the impedance higher?

A. Medium 1

B. Medium 2

C. cannot be determined

C. Refraction of sound at a boundary is unrelated to the impedances of the medium. Therefore, with the information provided, it cannot be determined which material has the greater impedance. Refraction is affected by the speed of sound in the media.

(Ch. 6, Question 4, pg. 101)

Sound travels in a medium and orthogonally strikes a boundary with a different medium. Although sound waves traveling in the media have vastly different speeds, there is no refraction. How can this be?

With normal incidence, refraction cannot occur . Refraction occurs only when there are different speeds and oblique incidence. Both conditions must be met.

(Ch. 6, Question 5, pg. 101)

A sound wave strikes a boundary with normal incidence. The impedances of the two media are identical. What percentage of the sound wave is refracted?

A. 100%

B. 75%

C. 0%

D. 25%

E. 90%

C. 0%

(Ch. 6, Question 6, pg. 103)

The impedance of Medium 1 is 8 rayls. The propagation speed is 1,450 m/s. The impedance of Medium 2 is 6 rayls and the speed is 1.855 km/s. A sound beam strikes the boundary between the media and is both partially transmitted and reflected. The angle of the incident beam is 30°. What is the reflection angle?

30°. Angle of reflection = angle of incidence

(Ch. 6, Question 7, pg. 100)

The logarithm of a numeral is defined as how many times _____ must be multiplied together to get that numeral.

A. 1

B. 2

C. 5

D. 10

D. 10

(Ch. 6, Question 184, pg. 76)

What is a decibel?

A. the absolute value of a number

B. a range of values

C. a relationship between two numbers

D. none of the above

C. a relationship between two numbers

(Ch. 6, Question 185, pg. 77)

Decibel notation is a _____ between two numbers.

A. difference

B. sum

C. product

D. ratio

D. ratio

(Ch. 6, Question 186, pg. 77)

Which of the following reports the relative strength of an ultrasound wave?

A. decibels

B. watts

C. W/cm²

D. pascals

A. decibels

(Ch. 6, Question 187, pg. 77)

The scale associated with decibel notation is __________.

A. linear

B. discrete

C. logarithmic

D. additive

C. logarithmic

(Ch. 6, Question 188, pg. 77)

What is the decibel representation when an acoustic signal is amplified?

A. positive

B. negative

C. equal to zero

A. positive

(Ch. 6, Question 189, pg. 77)

What is the decibel notation for an acoustic signal that is attenuated?

A. positive

B. negative

C. equal to zero

B. negative

(Ch. 6, Question 190, pg. 78)

The intensity of a signal declines from 1.5 mW/cm² to 0.75 mW/cm². How many decibels is this change in intensity?

A. 3 dB

B. 0.75 dB

C. -0.75 dB

D. -3 dB

D. -3dB

(Ch. 6, Question 191, pg. 78)

The power in a wave is increased to ten times its original value. How many decibels describe this change?

A. 3

B. 6

C. 10

D. 20

C. 10

(Ch. 6, Question 192, pg. 78)

How many decibels represent a 100-fold increase in the intensity of an acoustic pulse?

A. 10

B. 20

C. 100

D. 6

B. 20

(Ch. 6, Question 193, pg. 78)

This The intensity of an ultrasound wave is changed by -6 dB means that the current intensity is ___________ as much as its original level.

A. 1/10

B. 4X

C. 1/4

D. 1/6

C. 1/4

(Ch. 6, Question 194, pg. 78)

What units are used to describe attenuation?

A. watts

B. watts/cm²

C. macro

D. decibels

D. decibels

(Ch. 6, Question 195, pg. 80)

What does a 3 dB change in a value intensity mean?

A. the value has doubled

B. the value has tripled

C. the value has increased 30%

D. the value has increased ten times

A. the value has doubled

(Ch. 6, Question 196, pg. 78)

As sound propagates through a medium, the total power in the wave decreases. What is this entire process called?

A. absorption

B. scattering

C. attenuation

D. reflection

C. attenuation

(Ch. 6, Question 197, pg. 80)

Attenuation is determined by which of the following factors?

A. density and stiffness of the medium

B. frequency of sound and propagation speed

C. PRF of sound and path length

D. path length and frequency of sound

D. path length and frequency of sound

(Ch. 6, Question 198, pg. 80)

An acoustic wave is traveling through soft tissue. Its intensity undergoes six decibels of attenuation. How does the final intensity of the wave relate to the intensity of the wave when it started its journey?

A. it is now four times larger

B. it is now six times larger

C. it is now 1/4 as large

D. it is now 1/10 as large

C. it is now 1/4 as large

(Ch. 6, Question 199, pg. 78)

Which of the following is not one of the physical processes that contributes to attenuation of ultrasound waves passing through soft tissue?

A. reflection

B. redirection of sound in many directions

C. focusing

D. conversion of acoustic energy to heat

C. focusing

(Ch. 6, Question 200, pg. 81)

An acoustic pulse reflects from a very smooth boundary where the irregularities on the surface of the boundary are much smaller than the pulse's wavelength. What type of reflection is most likely to occur under these circumstances?

A. partial

B. Rayleigh

C. specular

D. total

C. specular

(Ch. 6, Question 201, pg. 81)

A sound wave reaches a rough or irregular border between two media. Under these explicit circumstances, which process is most likely to occur?

A. backscatter reflection

B. specular reflection

C. Rayleigh scattering

D. refraction

A. backscatter reflection

(Ch. 6, Question 202, pg. 82)

Which of the following is true of diffuse reflections?

A. they're created by smooth boundaries

B. they're created by large reflectors

C. sound reflects in many directions

D. they do not appear in soft tissue

C. sound reflects in many directions

(Ch. 6, Question 203, pg. 82)

What is the uniform dispersion of a sound wave in many different directions after striking a very small particle?

A. micro-scattering

B. backscattering

C. Rayleigh scattering

D. total absorption

C. Rayleigh scattering

(Ch. 6, Question 204, pg. 83)