book study questions Test2 Flashcards by Heather Sholey

every 3dB change means that the intensity will:

double

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every 10dB change means that the intensity will:

increase 10 times

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

-3dB

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

-6dB

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

1/10

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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

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we need one intensity to calculate decibels

false

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a wave’s intensity is 2mW/cm²

there is a change of +9dB

what is the final intensity?

a. 6mW/cm³, b. 2mW/cm², c. 16mW/cm², d. 16µW/cm²

c. 16mW/cm²

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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 beam’s 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:(+or-)

positive-the beam’s intensity is increasing

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name the 3 components of attenuation

absorption

reflection

scattering

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as the path length increases, the attenuation of ultrasound in soft tissue:

increases

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attenuation in lung tissue is (less than, greater than, the same as) attenuation in soft tissue

greater than

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attenuation in bone is ____ attenuation in soft tissue

greater than

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attenuation in air is ____ attenuation in soft tissue

greater than

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what are the units of attenuation?

decibels (dB)

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

true-attenuation and propagation speed are unrelated

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

attenuation coefficient in dB per centimeter is approx 1/2 of the ultrasonic frequency in MHz

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

distance-centimeters

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as frequency decreases, depth of penetration:

increases

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as path length increases, the half boundary layer:

remains the same

impedance is associated with:

only the medium

as the path length increases, the attenuation coefficient of ultrasound in soft tissue (decreases, remains the same, increases)

remains the same

acoustic impedance=

_____x_____

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

two media A and B have the same densities the speed of sound in medium A is 10% higher than in medium B which has the higher acoustic impedance?

medium A's acoustic impedance is higher than medium B's recall that impedance = speed x density since both media have identical densities and medium A's speed is 10% higher, then medium A's impedance is 10% higher

impedance is important in ____ at boundaries

reflections

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

7.5MHz transducer higher frequency produces better image in a superficial structure

a sound wave with an intensity of 50W/cm² strikes a boundary and is totally reflected what is the intensity reflection coefficient? a. 50w/cm², b. 25w/cm², c. 0w/cm², d. 100%, e. 0

d. 100% coefficient is a percentage

a sound wave with an intensity of 50W/cm² strikes a boundary and is totally reflected what is the reflected intensity? a. 50w/cm², b. 25w/cm², c. 0w/cm², d. 100%, e. 0

a. 50w/cm²

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 is reflected at a boundary between two soft tissues, because the impedances of the two soft tissues are similar the difference in impedance directly determines the intensity reflection coefficient

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% conservation of energy occurs at a boundary everything must equal 100%

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

nothing can be said about the impedance of bone or soft tissue based on the info given because a large reflection was created, the impedances must be different reflections with normal incidence are created based on the difference in the impedances, not on the actual values of the impedances

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 if the two media have the same impedances, no reflection occurs

which of the following does not belong: a. orthogonal, b. oblique, c. normal, d. perpendicular

b. oblique all the others mean equal to 90°

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?

10% is transmitted

sound that is traveling in Jell-O passes through an interface at 90° 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. 99% best choice because the impedances are nearly identical only a small percentage would reflect

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?

transmitted beam undergoes little to no refraction transmitted beam is refracted when the incidence is oblique and the propagation speeds are different

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 info, nothing can be said about the speed of sound in medium 1 or 2 because the beam refracted significantly, the speeds of both media are different

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?

sound travels slowest in medium 2 sound travels slower in the second medium when the angle of transmission is less than the angle of incidence

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?

with the info provided, it cannot be determined which material has the greater impedance ## Footnote

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 only occurs when there are different speeds and oblique incident

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% refraction cannot occur with normal incidence

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° the angle of reflection = the angle of incidence

a sound wave is created by a transducer, reflects off an object, and returns to the transducer the depth of the reflector is 10cm in soft tissue what is the go-return time? a. 13µs, b. 1.3µs, c. 65µs, d. 130µs

d. time of flight = depth x 13µs 10cm x 13µs/cm = 130µs

a sound wave is created by a transducer, reflects off an object, and returns to the transducer the go-return time is 26µs what is the depth of the reflector? a. 1cm, b. 2cm, c. 3cm, d. 4cm

b. the reflector depth is 2cm 2cm x 13µs/cm = 26µs

a sound wave is created by a transducer, reflects off an object, and returns to the transducer the go-return time is 26µs what is the total distance that the pulse traveled? a. 1cm, b. 2cm, c. 3cm, d. 4cm

d. total distance traveled is twice the depth of the reflector

the maximum imaging depth (depth of view) during an ultrasound exam is 10cm the sonographer adjusts the imaging depth to 20cm what happens to pulse repetition period?

pulse repetition period is DIRECTLY related to imaging depth when imaging depth doubles, pulse repetition period doubles

the maximum imaging depth during an ultrasound exam is 10cm the sonographer adjusts the imaging depth to 20cm what happens to pulse repetition frequency?

pulse repetition frequency is INVERSELY related to imaging depth when imaging depth doubles, PRF is halved

the imaging depth during an ultrasound exam is 10cm the sonographer adjusts the imaging depth to 5cm what happens to pulse repetition period?

pulse repetition period is DIRECTLY related to imaging depth when the imaging depth is halved, PRP is halved

a sound wave is created by a transducer, reflects off an object, and returns to the transducer the imaging depth is 10cm in soft tissue what is the maximum pulse repetition frequency? a. 7,700, b. 7.7kHz, c. 3,500 Pa, d. 7,700µs

b. only one with correct units

a sound wave is created by a transducer, reflects off an object, and returns to the transducer the maximum imaging depth is 7.7cm what is PRF? a. 7,700Hz, b. 5,000kHz, c. 10,000Hz, d. 100µs

c. 77,000/7.7 = 10,000Hz

a sound wave is created by a tranducer, reflects off an object, and returns to the transducer the go-return time is 130µs what is the maximum PRF? a. 7,700Hz, b. 5,000kHz, c. 10cm, d. 100µs

a. 7,700Hz