ED Ch 6: Interaction of Sound and Media Review Questions

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 accounted for. If 90% is reflected, 10% must be transmitted. (ED Ch 6, Pg 98)

The attenuation of an acoustic wave traveling through bone is ____ its attenuation through soft tissue. A. greater than B. less than C. equal to

A. The attenuation of ultrasound in bone is greater than its attenuation in soft tissue. (ED Ch 6, Pg 466)

What is the decibel representation when an acoustic signal is amplified? A. positive B. negative C. equal to zero

A. positive (When a signal is amplified, its magnitude increases and becomes stronger. In decibel notation, an increase in signal strength is described with positive decibels.) (ED Ch 6, Pg 461)

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. Remember, refraction cannot occur with normal incidence. (ED Ch 6, Pg 105)

What type of incidence is there between Media 3 and4?

Oblique. (ED Ch 6, Pg 106)

a

What are the units of the intensity reflection coefficient? a. none b. W/cm2 c. Watts d. dB (ED Ch 6, Pg 468)

As frequency decreases, depth of penetration_______

increases (ED Ch 6, Pg 89)

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

-3 dB (ED Ch 6, Pg 79)

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

-6 dB (ED Ch 6, Pg 79)

A sound wave with an intensity of 50 W/cm2 strikes a boundary and is totally reflected. What is the reflected intensity? A. 50 w/cm2 B. 25 w/cm2 C. O w/cm2 D. 100% E. 0

A. Since the wave is totally reflected, intensity is 50 w/cm2. (ED Ch 6, Pg 94)

How many decibels represent a 100-fold increase in the intensity of an acoustic pulse? A. 10 B. 20 C. 100 D. 6

B. 100 (An increase of 100 times the intensity of a wave is equal to 20 dB. Each 10 dB indicates a tenfold increase. Therefore, 20 indicates (two 10 increases) means a pair of tenfold increases, 10 x 10 = 100.) (ED Ch 6, Pg 462)

What are the units of attenuation?

Decibels (dB) (ED Ch 6, Pg 89)

Every 3 dB change means that the intensity will?

Double (ED Ch 6, Pg 79)

We need one intensity to calculate decibels.

False (ED Ch 6, Pg 79)

Name the three components of attenuation.

absorption, reflection, and scattering (ED Ch 6, Pg 79)

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

distance: centimeters (ED Ch 6, Pg 89)

Attenuation in air is _______attenuation in soft tissue.

greater than (ED Ch 6, Pg 89)

Attenuation in bone is________ attenuation in soft tissue.

greater than (ED Ch 6, Pg 89)

Attenuation in lung tissue is [less than, 3. greater than, the same as] attenuation in soft tissue.

greater than (ED Ch 6, Pg 89)

increases]. Acoustic impedance =_______x_________

impedance density (kg/m) x propagation speed (m/s) (ED Ch 6, Pg 89)

Impedance is associated with

only the medium (ED Ch 6, Pg 89)

6. 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. logarithmic and relative (ED Ch 6, Pg 79)

What processes occur as the ultrasound passes through all media? What are the units of this process?

Attenuation (scattering, absorption, and reflection). Units: dB. (ED Ch 6, Pg 106)

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 (An increase of ten times the original power of a wave is reported as +10 dB.) (ED Ch 6, Pg 462)

To which of the following is Rayleigh scattering related? A. half of the wavelength B. square root of propagation speed C. frequency^4 D. PRF^2

C. The degree to which a wave exhibits Rayleigh scattering is related to frequency raised to the fourth power. That is, if the frequency is twice as high, Rayleigh scattering is increased 16-fold: 2^4 = 2 x 2 x 2 x 2 = 16. (ED Ch 6, Pg 465)

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 (The logarithm of a numeral is equal to the number of tens that are multiplied together to result in the number.) (ED Ch 6, Pg 106)

A sound wave with an intensity of 50 W/cm2 strikes a boundary and is totally reflected. What is the intensity reflection coefficient? A. 50 w/cm2 B. 25 w/cm2 C. O w/cm2 D. 100% E. O

D. Since the wave is totally reflected, the intensity reflection coefficient is 100%. (ED Ch 6, Pg 94)

What units are used to describe attenuation? A. watts B. watts/cm2 C. macro D. decibels

D. decibels (ED Ch 6, Pg 462)

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

One-tenth (ED Ch 6, Pg 79)

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. (ED Ch 6, Pg 79)

d

What results when the intensity transmission coefficient and the intensity reflection coefficient are added together? a. incident intensity coefficient b. acoustic impedance c. total intensity d. 1.0 (ED Ch 6, Pg 469)

c

Which of the following describes an angle with a measure of 123 degrees? a. orthogonal b. acute c. obtuse d. normal (ED Ch 6, Pg 467)

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

increases (ED Ch 6, Pg 89)

The impedance of Medium 1 is 8 rayls. 7. 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°. This question is quite simple. The angle of reflection equals the angle of incidence. (ED Ch 6, Pg 105)

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. Conservation of energy occurs at a boundary, and as a result, the sum of the reflected and transmitted intensities must equal 100%. 63% + 37% = 100%. (ED Ch 6, Pg 96)

c

A sound beam with an intensity of 45 W/cm2 strikes a boundary and 70% of the wave's intensity is reflected. How much is transmitted? a. 45 W/cm2 b. 25 W/cm2 c. 30% d. 100%

d

A sound wave strikes a boundary between two media at a 60 degree angle. This is called ___________ incidence. a. orthogonal b. angular c. obtuse d. oblique (ED Ch 6, Pg 467)

A pulse of ultrasound is propagating 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. (ED Ch 6, Pg 96)

a

A wave strikes an interface between two media and intensities are measured at the interface. What results when the reflected intensity is divided by the incident intensity? a. intensity reflection coefficient b. intensity transmission coefficient c. beam uniformity coefficient d. none of the above (ED Ch 6, Pg 468)

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. The smoothness or roughness of a boundary will help to determine what form of reflection takes place. Backscatter is likely to occur when the boundary has irregularities that are larger than the wavelength of the incident acoustic pulse. Diffuse reflection is another name for backscatter. (ED Ch 6, Pg 464)

Ultrasound waves traveling through lung tissue attenuate to a ____ extent than when traveling through soft tissue. A. greater B. lesser C. nearly equal

A. Ultrasound attenuates more when traveling through lung tissue than when traveling through soft tissue. (ED Ch 6, Pg 466)

Which of the following reports the relative strength of an ultrasound wave? A. decibels B. watts C. W/cm^2 D. pascals

A. decibels (The relative strength of a sound beam may be reported in decibels. The term "relative" indicates a comparison between two values, such as a beam has decreased in strength by 50%.) (ED Ch 6, Pg 460)

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 (A 3 decibel change in the intensity indicates that the value has doubled.) (ED Ch 6, Pg 462)

If the media are soft tissue, what is an estimate of the ultrasound frequency?

About 7 MHz; the attenuation coefficient multiplied by 2 approximates the frequency (3.5 x 2 = 7). (ED Ch 6, Pg 106)

d

An ultrasound wave strikes a boundary between two media. All intensities are measured directly at the boundary. What results when the transmitted is divided by the reflected intensity? a. intensity reflection coefficient b. intensity transmission coefficient c. beam uniformity coefficient d. none of the above (ED Ch 6, Pg 468)

b

An ultrasound wave strikes an interface between two media. All intensities are measured directly at the interface. What results when the transmitted intensity is divided by the incident intensity? a. intensity reflection coefficient b. intensity transmission coefficient c. beam uniformity coefficient d. none of the above (ED Ch 6, Pg 468)

Which two ATTRIBUTES help establish the acoustic impedance of a medium? a. density and temp b. density and stiffness c. stiffness and eslastance d. elasticity and compressability

B. Density and stiffness To calculate the acoustic impedance multiply the propagation speed of the medium by the density of the medium. A mediums propagation speed is determined by the density and the stiffness of the medium therefore the acoustic impedance is a property of both density and stiffness. (ED Ch 6, Pg 467)

Which of the following terms does not 5. 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 a meaning of "equal to 90 degrees" (ED Ch 6, Pg 96)

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. (ED Ch 6, Pg 104)

What is the amount of attenuation per centimeter that a sound wave undergoes called? A. beam uniformity coefficient B. AC C. attenuation D. DF

B. The AC reports a sound beam's decibels of attenuation per centimeter. This is a useful tool as its value remains constant, regardless of actual path length. (ED Ch 6, Pg 465)

As a pulse passes through soft tissue, a certain amount of acoustic energy remains in the tissue as heat. What is this constituent of attenuation called? A. scattering B. absorption C. refraction D. rarefaction

B. The conversion of acoustic energy into heat is called absorption. This process deposits a portion of energy from the beam into the soft tissues. (ED Ch 6, Pg 465)

Sound traveling through blood attenuates to a ____ extent than when traveling through soft tissue. A. greater B. lesser C. relatively equal

B. Ultrasound waves attenuate less when traveling through blood than when traveling through soft tissue. (ED Ch 6, Pg 466)

What is the decibel notation for an acoustic signal that is attenuated? A. positive B. negative C. equal to zero

B. negative (When a signal is attenuated, its magnitude decreases and it becomes weaker. In decibel notation, a decrease in signal strength is described with negative decibels.) (ED Ch 6, Pg 461)

To calculate the acoustic impedance of a medium, one should ____________ the ____________ by the _____________. a. /, ps, density b. *, density, ps c./, density, ps d. *,stiffness, density

B. to attain the value of acoustic impedance multiply the density of a medium by its prop speed. (ED Ch 6, Pg 467)

The incidence between the sound wave and the boundary between Media 1 and 2 is normal. What happens at the boundary between Media 1 and 2? Why?

Both reflection and transmission occur. There are normal incidence and different acoustic impedances. (ED Ch 6, Pg 106)

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. As a wave propagates through a medium, its power diminishes. This is attenuation. Choices A, B, and D are all components or contributors to attenuation. (ED Ch 6, Pg 463)

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. Diffuse reflections, also called backscatter, are dispersed in multiple directions. (ED Ch 6, Pg 464)

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 does not contribute to the attenuation process. In contrast, choices A, B, and D reduce the intensity of a wave as it propagates. (ED Ch 6, Pg 463)

What is the uniform dispersion of a sound wave in many different directions after striking a very small particle? A. microscattering B. backscattering C. Rayleigh scattering D. total absorption

C. Rayleigh scattering is the redirection of an acoustic wave in many different directions as a result of striking a small particle. When Rayleigh scattering occurs, the dimension of the reflecting particle is usually less than the wavelength of the ultrasound wave. The amount of Rayleigh scattering also depends on the frequency of the ultrasound. (ED Ch 6, Pg 464)

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. Reflections from a smooth boundary are specular. A mirror is a specular reflector. The waves strike this smooth boundary and reflect in an organized, systematic manner. A boundary is considered smooth when irregularities in its surface are smaller than the wavelength of the incident ultrasonic beam. (ED Ch 6, Pg 464)

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 media. cannot be determined which material has Therefore, with the information provided, it the greater impedance. Refraction is affected by the speed of sound in the media. (ED Ch 6, Pg 104)

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 on its journey? A. it is now 4x larger B. it is now 6x larger C. it is not 1/4 as large D. it is now 1/10 as large

C. When a wave undergoes 6 dB of attenuation, the intensity of the wave is decreased to 1/4 of its initial value. The term attenuation means "to weaken, or reduce." Attenuation always describes a reduction in the intensity of the wave. Six decibels of attenuation is made up of two groups of -3 dB. Each -3 dB indicates a halving of intensity. 1/2 multiplied by 1/2 means that only 1/4 of the original intensity remains. (ED Ch 6, Pg 463)

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 (A decibel represents a relationship between two numbers. A decibel is a relative measure of intensity or power. The term "relative" indicates that we are not dealing with an absolute power, but rather with how the power is related to a reference level.) (ED Ch 6, Pg 460)

The scale associated with decibel notation is ___? A. linear B. discrete C. logarithmic D. additive

C. logarithmic (ED Ch 6, Pg 461)

The intensity of an ultrasound wave is changes by -6 dB. This means that a current intensity is ___ as much as its original level. A. one-tenth B. four times C. one-forth D. one-sixth

C. one-forth (A change in intensity of -6 dB indicates that only one-forth of the initial intensity remains. The minus sign indicates a decrease in signal magnitude. Each -3 dB change means that one-half of the original intensity remains. Since there are two sets of -3 dB, one-half multiplied by one-half indicates that there is only one-forth remaining.) (ED Ch 6, Pg 462)

The intensity of a signal declines from 1.5 mW/cm^2 to 0.75 mW/cm^2. How many decibels is this change in intensity? A. 3 dB B. 0.75 dB C. -0.75 dB D. -3 dB

D. -3 dB (A decline in intensity to one-half of the original level is a change of -3 dB. When the new level is less than the reference level, the reported decibels must be negative. When the new intensity is greater than the reference level, the change in decibels is positive.) (ED Ch 6, Pg 461)

Which of the following is considered a Rayleigh scatterer? A. bone B. liver C. muscle D. blood cell

D. A blood cell is a Rayleigh scatterer. A red blood cell is smaller than the wavelength of the typical acoustic wave used in diagnostic imaging. When an acoustic wave strikes a blood cell, the energy within the pulse is scattered in many directions. (ED Ch 6, Pg 465)

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. The factors that determine the degree to which a sound beam weakens are: 1. the distance that the sound travels 2. the frequency of the sound (ED Ch 6, Pg 463)

Which of these lists indicates media with increasing attenuation of ultrasound? A. water, lung, soft tissue, bone, air B. lung, air, soft tissue, bone C. lung, fat muscle D. water, blood, fat, muscle, bone, air

D. This list orders tissues with increasing attenuation rates of ultrasound. (ED Ch 6, Pg 466)

Decibel notation is a ___ between two numbers. A. difference B. sum C. product D. ratio

D. ratio (Decibels are calculated by dividing the final strength of a signal by the starting strength. Thus, decibel notation is a ratio between two numbers.) (ED Ch 6, Pg 460)

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. (ED Ch 6, Pg 104)

What property has units of rayls? How is it determined?

Impedance is calculated, not measured. Impedance = density x speed. (ED Ch 6, Pg 106)

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. (ED Ch 6, Pg 89)

Every 10 dB change means that the intensity will

Increase ten times (ED Ch 6, Pg 79)

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. (ED Ch 6, Pg 89)

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. (ED Ch 6, Pg 96)

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. (ED Ch 6, Pg 79)

What happens at the boundary between Media 3 and 4? Why?

Reflection may occur, If transmission does occur, the sound beam will refract because there are different propagation speeds and oblique incidence. (ED Ch 6, Pg 106)

T/F: Attenuation and propagation speed are unrelated.

TRUE. Attenuation and propagation are entirely unrelated. Attenuation is the WEAKENING of a beam as it travels and has nothing to do with how FAST it travels. (ED Ch 6, Pg 466)

d

The angle between the direction of propagation and the boundary between two media is 90 degrees. What term describes the form of incidence of the wave? a. not normal b. direct c. oblique d. orthogonal (ED Ch 6, Pg 467)

What does the 3.5 dB/cm represent?

The attenuation coefficient of the sound in the media. (ED Ch 6, Pg 106)

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. We can use the higher frequency transducer in this example because the structure is superficial and attenuation is of little concern. (ED Ch 6, Pg 89)

What does the 100 mW/cm2 represent?

The incident intensity of the sound beam (ED Ch 6, Pg 105)

A pulse of ultrasound propagates in soft tissue, such as liver. The pulse strikes a 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. A transmitted beam is refracted propagation speeds are different. Because when the incidence is oblique and the the tissues on either side of the boundary are both "soft tissues," their speeds are nearly identical and little or no refraction occurs. (ED Ch 6, Pg 98)

A sound beam travels 9 cm in soft tissue. The AC is 3 dB/cm. What is the total attenuation that the beam experienced? A. 9 dB B. 3 dB C. 27 dB D. 18 dB

To calculate total attenuation, multiply path length by AC. In this example, the overall attenuation is 3 x 9 = 27 dB. (ED Ch 6, Pg 465)

The incidence between the sound wave and the boundary between Media 2 and 3 is normal. What happens at the boundary between Media 2 and 3? Why?

Transmission only. The impedances of the media are the same. (ED Ch 6, Pg 106)

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

True. Attenuation and propagation speed are unrelated. (ED Ch 6, Pg 89)

d

What are the units of the intensity transmission coefficient? a. watts/sq cm b. watts c. dB d. none of the above (ED Ch 6, Pg 468)

c

What is the maximum permissible value for both the intensity reflection coefficient and the intensity transmission coefficient ? a. 100 b. 1% c. 1 d. infinity (ED Ch 6, Pg 469)

d

What is the minimum permissible value for both the intensity reflection coefficient and the intensity transmission coefficient ? a. different from each other b. -1 c. 100% d. 0 (ED Ch 6, Pg 469)

d

What remains when the reflected intensity is subtracted from the incident intensity? a. 1.0 b. incident intensity c. transmitted intensity coefficient d. transmitted intensity (ED Ch 6, Pg 469)

b

Which of the following describes an angle with a measure of a 45 degrees? a. orthogonal b. acute c. obtuse d. normal (ED Ch 6, Pg 467)

c

Which term does NOT belong in the group below? a. orthogonal b. at right angles c. oblique d. 90 degrees e. normal f. perpendicular (ED Ch 6, Pg 467)

c

Which term has a meaning other than normal incidence? a. orthogonal incidence b. perpendicular incidence c. oblique incidence (ED Ch 6, Pg 467)

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. (ED Ch 6, Pg 96)

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. In this example, the incidence is normal-no refraction can occur. (ED Ch 6, Pg 105)

Acoustic impedance is a property of _____________ and has units of ______________. a. source of medium lmps b. medium, dB c. medium, rhayls d. medium ohms

c. Medium and rhayls Acoustic impedance is a property of the medium through which sound travels. It is UNEFFECTED BY SOUND SOURCE or characteristic of the wave itself Units of impedence are Rhayls (ED Ch 6, Pg 466)

Impedance is important in _____at boundaries.

reflections (ED Ch 6, Pg 89)

As path length increases, the half boundary layer

remains the same (ED Ch 6, Pg 89)

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

remains the same (ED Ch 6, Pg 89)