chapter 6

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 backscatter is likely to occur when the boundary has irregularities that are larger than the wavelength of the incident acoustic pulse.

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

a. greater than

ultrasound waves traveling through lung tissue attenuate to a ___ extent than when traveling through soft tissue. a. greater than b. less than c. nearly equal

a. greater than

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

a. intensity reflection coefficient

An acoustic wave is traveling from medium X into medium Z. medium Z has a propagation speed of 1,457 m/sec and an impedance of 1.44 MRayls. Medium Z has a propagation speed of 1,644 m/sec and an impedance of 1.26 MRayls. The angle of incidence is 32 angle. What is true of the angle of the transmitted wave. a. it is greater than 32 b. it is equal to 32 c. it is less than 32 d. cannot be determined

a. it is greater than 32 degrees

what are the units of the intensity reflection coefficient? a. none b. W/cm^2 c. watts d. dB

a. none the IRC is reported as a percentage and therefore is unitless

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 it becomes stronger. positive dB means "getting bigger"

An ultrasound wave strikes an interface between two media at a 90 degree angle. The propagation speeds of the media are identical. However, the densities of the media are different. which is true? a. reflection will definitely occur b. reflection will definitely not occur c. refraction may occur d. none of the above

a. reflection will definitely occur in this example, the densities of the media are different while their propagation speeds are the same. since impedance is propagation speed multiplied by density, it follows that the acoustic impedances of the media bordering the interface are indeed different. reflection will occur

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 10 times

a. the value has doubled

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 an increase of 100 times the intensity of a wave is equal to 20 dB.

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. absorption

which of the following describes an angle with a measure of 45 degrees? a. orthogonal b. acute c. obtuse d. normal

b. acute any angle that measures less than 90 degrees is an acute angle

what is the amount of attenuation per centimeter that a sound wave undergoes called? a. beam uniformity coefficient b. attenuation coefficient c. attenuation d. duty factor

b. attenuation coefficient the attenuation coefficient reports a sound beams decibels of attenuation per centimeter this is a useful tool as its value remains constant, regardless of the actual path length

Which two attributes help establish the acoustic impedance of a medium? a. density and temperature b. density and stiffness c. stiffness and elastance d. elasticity and compressibility

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.

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

b. intensity transmission coefficient

An acoustic wave is traveling from medium X to medium Z. Medium X has a propagation speed of 1,457 m/sec and an impedance of 1.44 MRayls. Medium Z's propagation speed is 1,644 m/s and its impedance is 1.26 MRayls. The angle of incidence is 32 degrees. What is true of the angle of reflection? A. it is greater than 32 degrees B. it is equal to 32 degrees C. it is less than 32 degrees D. cannot be determined

b. it is equal to 32 degrees

an acoustic wave in medium B is traveling toward medium A. The sound beam strikes the boundary at a 45 angle. The medium A and 1745 m/sec for medium B. What is true of the angle of transmission? a. it is greater than 45 degrees b. it is less than 45 degrees c. it is equal to 45 degrees d. cannot be determined

b. it is less than 45 degrees

an acoustic wave is in medium A and traveling toward medium B, the sound beam angle of transmission into medium B with relation to the boundary is 79 degrees. Sounds propagation speed is 1,547 m/sec in medium A, and 1,745 m/sec in medium B. if reflection and transmission both occur at the boundary what can be said of the reflection angle? a. it is greater than 79 b. is less than 79 c. is equal to 79 d. cannot be determined

b. it is less than 79 degrees

A wave of acoustic energy is leaving soft tissue and transmitting into fat. With an 86 degree incident angle. What is true of the angle of transmission? a. is equal to 86 degrees b. is less than 86 degrees c. it is ggreater than 86 degrees d. cannot be determined

b. it is less than 86 degrees

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

b. lesser

To calculate the acoustic impedance of a medium, one should ____ the ____ by the ____. A. divide, propagation speed, density B. multiply, density, propagation speed C. divide, density, propagation speed D. multiply, stiffness, density

b. multiply the density of a medium by its propagation speed

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. negative dB means "getting smaller"

what event does snells law govern? a. transmission b. refraction c. impedance

b. refraction

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

c. 1 the max percentage of the incident intensity that either reflects or transmits is 1.0 or 100%.

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

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

c. 27 dB to calculate total attenuation, multiply path length by attenuation coefficient 3 x 9 =27 dB

a sound beam with an intensity of 45 W/cm^2 strikes a boundary and 70% of the waves intensity is reflected. how much is transmitted? a. 45 W/cm^2 b. 25 W/cm^2 c. 30% d. 100%

c. 30% the law of conservation of energy states that the sum of the percentage of transmitted sound and the reflected sound equals 100%

what is the uniform dispersion of a sound wave in many direction after striking a very small particle? a. microscattering b. backscattering c. Rayleigh scattering d. total absorption

c. Rayleigh scattering it is the redirection of an acoustic wave in many different directions as a result of striking a small particle

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

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. as a wave propagate through a medium, its power diminishes. The rest are components of attenuation

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

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. frequency^4

if the __of two media are different and sound strikes a border between the media at 90 degree incidence, then reflection will occur. a. conductances b. densities c. impedances d. propagation speeds

c. impedances with normal incidence, as long as the impedances are dissimilar, reflection will always occur

the scale associated with decibel notation is ____. a. linear b. discrete c. logarithmic d. pascals

c. logarithmic

acoustic impedance is a property of the ____ and has units of ____. a. source and medium, lmps b. medium, dB c. medium, Rayls d. medium, Ohms

c. medium, Rayls

which term does not belong in the group below? a. orthogonal b. at right angles c. oblique d. 90 degrees e. normal f. perpendicular

c. oblique

Which term has a meaning other than normal incidence? A. orthogonal incidence B. perpendicular incidence C. oblique incidence

c. oblique incidence

which of the following describes an angle with a measure of 123 degrees? a. orthogonal b. acute c. obtuse d. normal

c. obtuse any angle that measures greater than 90 degrees is an obtuse angle

The intensity of an ultrasound wave is changed by -6 dB. This means that the current intensity is ____ as much as its original level. A. one-tenth B. four times C. one-fourth D. one-sixth

c. one-fourth since there are two sets of -3 dB, one half-multiplied by one-half indicates that there is only one-fourth remaining.

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.

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

d. 0 at one extreme it is possible to have total transmission and no reflection. (IRC = 0) at the other extreme, it is possible for total reflection to occur. no transmission would exist and the ITC = 0

what results when the intensity transmission coefficient and the intensity reflection coefficient are added together? a. indigent intensity coefficient b. acoustic impedance c. total intensity d. 1.0

d. 1.0 the sum of the IRC and the ITC equals one or 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

which value is closest to the impedance of soft tissue? a. 1.5 kiloRayls b. 2.5 deciRayls c. 19 megaRayls d. 2,000,000 Rayls

d. 2,000,000 Rayls the impedance of soft tissue is in the range of 1.5 to 2.5 millions Rayls

which of the following is considered a Rayleigh scattering? a. bone b. liver c. muscle d. blood cell

d. a blood cell is a Rayleigh scattering

sound propagates from one medium with a density of 1.16 kg/m^3. To a second medium with density of 1.02 kg/m^3. If the angle of transmission is 49 degrees what can be correctly stated about the angle of incidence. a. less than 49 b. equal to 49 c. greater than 49 d. cannot be determined

d. cannot be determined

what units are used to describe attenuation? a. watts b. watts/cm c. macro d. decibels

d. decibels

Two acoustic waves strike a boundary between two media. The waves are traveling in a direction 90 degrees to the boundary. Reflection of these waves depends on differences in the ___. a. frequencies of the two waves b. propagation speeds of the two media c. amplitudes of the two waves d. impedances of the two media

d. impedances of the two media with normal impedance, only one condition must be met for reflection to take place: the impedances of the media on either side of the boundary must be different

what are the units of the units of the intensity transmission coefficient? a. watts/square cm b. watts c. dB d. none of the above

d. none of the above the intensity transmission coefficient is defined as the percentage of an ultrasound beams intensity that is transmitted as the sound wave passes through a boundary between two media. the ITC is a percentage and is reported without units

An ultrasound wave strikes a boundary between two media. All intensities are measured directly at the boundary. What results when the transmitted intensity is divided by the reflected intensity? A. intensity reflection coefficient B. intensity transmission coefficient C. beam uniformity coefficient D. none of the above

d. none of the above when the transmitted intensity is divided by the reflected intensity, a number is obtained that has no special meaning in ultrasound physics and is not identified by a special name

an ultrasound wave approaches an interface between two media at a 90 degree angle. the propagation speed and the densities of the two media are difference. which is correct? a. reflection will definitely occur b. reflection will definitely not occur c. refraction may occur d. none of the above

d. none of the above the important fact is whether the impedances of the media are different, then reflection will occur. if the impedances are the same, then reflection will not occur. in this case, since we are unsure as to whether the impedances of the media are the same, we are unsure whether choices A or B are correct. choice C is incorrect because refraction will never occur when a sound wave strikes a boundary at a 90 degree angle.

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

d. oblique incidence is always present when the angle between the direction of a waves propagation and the boundary between two media is different than 90 degrees.

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

d. orthogonal incidence is attained when a sound wave strikes a boundary between media at exactly 90 degrees.

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 the factors that determine the degree to which a sound beam weakens are: 1. the distance that the sound travels, and 2. the frequency of the sound

decibel notation is a ____ between two numbers. a. difference b. sum c. product d. ratio

d. ratio

A sound pulse strikes a boundary between two media with normal incidence. The speed of sound in the two media are very different; however, the impedances of the media are identical. What will happen? a. a big echo will be produced b. a medium echo will results c. a small echo will result d. there will be no echo at all

d. there will be no echo at all in this example, the wave is normally incident but the media have identical impedances. under these circumstances, no reflection will occur and 100% of the sound will be transmitted

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

d. transmitted intensity the remainder of the energy continues to propagate and is called the transmitted intensity

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. water, blood, fat, muscle, bone, air

true or false? The period of a sound wave determined whether refraction will occur

false

true or false? Refraction always occurs at the interface between two media when the propagation speeds of the media are unequal

false

true or false? when reflections occurs with oblique incidence, the angle of reflection equals the angle of incidence. this is known as snells law.

false

which of the following best describes the process best described by snells law? a. reflection with normal incidence b. reflection with oblique incidence c. transmission with normal incidence d. transmission with oblique incidence

transmission with oblique incidence

true or false? refraction occurs at the border between two media if and only if there is oblique incidence of the wave at the boundary.

true

true or false? attenuation and propagation speed are unrelated.

true.

True or False? the proportion of the incident intensity that is reflected at a border between two media will increase as the impedances of the media become increasingly dissimilar.

true. as sound waves strike the border between two media, reflection occurs if their impedances are different. greater differences between the two impedances create stronger reflections

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 four times larger b. it is now six times larger c. it is now one-fourth as large d. it is now one-tenth as large

c. one-fourth as large when a wave undergoes 6 dB of attenuation, the intensity of the wave is decreased to one-fourth of its initial value.

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 diffuse reflections are also called backscatter and disperse in multiple directions.

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 reflections from a smooth boundary are specular.

What conditions are necessary for refraction to occur at a boundary between two media? a. unequal acoustic impedances and normal incidences at the boundary b. unequal densities of the media and normal incidence at the boundary c. dissimilar propagation speeds and oblique incidence at the boundary d. different elasticities of the media and oblique incidence

c.dissimilar propagation speeds and oblique incidence at the boundary